088 - Modeling fires of natural fuels with Eric Mueller

Transcript

WEBVTT 00:00:00.356 --> 00:00:00.956 <v Wojciech Węgrzyński>Hello, everybody. 00:00:01.016 --> 00:00:02.487 <v Wojciech Węgrzyński>Welcome to the Fire Science Show. 00:00:03.056 --> 00:00:07.977 <v Wojciech Węgrzyński>As this episode is published, it's most likely eighth February in the morning. 00:00:08.037 --> 00:00:13.426 <v Wojciech Węgrzyński>Got leaks in here, which means that's the last day for IAFSS paper submission. 00:00:13.817 --> 00:00:16.089 <v Wojciech Węgrzyński>IAFSS says is like Christmas for fire science. 00:00:16.089 --> 00:00:19.750 <v Wojciech Węgrzyński>And I am absolutely thrilled to see you all in Japan and see. 00:00:19.792 --> 00:00:25.253 <v Wojciech Węgrzyński>What newest achievements of fire science there are because that's, that's the fuel for my podcast. 00:00:25.507 --> 00:00:27.780 <v Wojciech Węgrzyński>And I hope your papers, went great.. 00:00:28.016 --> 00:00:30.957 <v Wojciech Węgrzyński>As I assume mine is still in production. 00:00:31.347 --> 00:00:35.606 <v Wojciech Węgrzyński>It ends up like this, every time I own every year, it's going to be a little better. 00:00:36.027 --> 00:00:50.796 <v Wojciech Węgrzyński>I bring IAFSS up, not just because it's a coincidentally the deadline for paper submissions, , But I think quite a nice thing happened last IFSS the one that was supposed to be at the Waterloo, but ended up in online space due to pandemic. 00:00:51.216 --> 00:00:53.587 <v Wojciech Węgrzyński>Um, maybe you recall if you've attended that. 00:00:53.676 --> 00:00:58.256 <v Wojciech Węgrzyński>Uh, there was this best theses awards and there was this guy from Edinburgh. 00:00:58.707 --> 00:01:05.727 <v Wojciech Węgrzyński>Uh, he gave like BBC style documentary about his research and everyone expected a PowerPoint. 00:01:05.727 --> 00:01:10.046 <v Wojciech Węgrzyński>And that was absolutely outstanding scientific communication. 00:01:10.406 --> 00:01:14.277 <v Wojciech Węgrzyński>And on top of that, he was presenting some really, really good science on. 00:01:14.727 --> 00:01:18.356 <v Wojciech Węgrzyński>Burning living material plants, vegetation. 00:01:18.519 --> 00:01:22.557 <v Wojciech Węgrzyński>In dead form But the material that comes from living plants. 00:01:23.126 --> 00:01:25.989 <v Wojciech Węgrzyński>And, uh, I enjoyed that talk a lot now. 00:01:26.469 --> 00:01:28.239 <v Wojciech Węgrzyński>Fast forward three years later. 00:01:28.629 --> 00:01:39.849 <v Wojciech Węgrzyński>I really need this knowledge because we working on green wall systems and suddenly we realized that burning plants is not exactly the same thing as burning timber or burning plastics. 00:01:40.090 --> 00:01:42.939 <v Wojciech Węgrzyński>We need to upgrade our knowledge and you know what? 00:01:42.939 --> 00:01:44.349 <v Wojciech Węgrzyński>I have a podcast and. 00:01:44.739 --> 00:01:48.730 <v Wojciech Węgrzyński>I am privileged to get, be the best people to learn from. 00:01:48.760 --> 00:01:50.500 <v Wojciech Węgrzyński>So I did reach out to him. 00:01:50.560 --> 00:01:52.180 <v Wojciech Węgrzyński>His name is Dr Eric Mueller. 00:01:52.420 --> 00:01:54.640 <v Wojciech Węgrzyński>He's working at NIST now. 00:01:55.150 --> 00:01:56.739 <v Wojciech Węgrzyński>And he's still researching. 00:01:57.073 --> 00:02:02.444 <v Wojciech Węgrzyński>Vegetation fires and living fuels and tries to update the ways, how we model them. 00:02:02.924 --> 00:02:05.563 <v Wojciech Węgrzyński>So I took all my tough questions. 00:02:05.653 --> 00:02:07.364 <v Wojciech Węgrzyński>I've asked them to him. 00:02:07.903 --> 00:02:09.883 <v Wojciech Węgrzyński>And here's the recording of that. 00:02:09.913 --> 00:02:13.484 <v Wojciech Węgrzyński>So, lets spin the intro and jump into the episode. 00:02:37.104 --> 00:02:39.834 <v Wojciech Węgrzyński>Before we start the episode, I would like to thank you once again. 00:02:39.834 --> 00:02:45.300 <v Wojciech Węgrzyński>OFR Consultants for sponsoring this podcast, It has been already a month and I'm really enjoying this collaboration. 00:02:45.300 --> 00:02:46.949 <v Wojciech Węgrzyński>It has brought a lot of good to the podcast. 00:02:47.526 --> 00:02:52.963 <v Wojciech Węgrzyński>OFR Consultants are a multi award winning independent consultancy dedicated to addressing fire safety challenges. 00:02:53.484 --> 00:02:56.473 <v Wojciech Węgrzyński>OFR is the UK is leading fire risk consultancy. 00:02:56.973 --> 00:03:06.152 <v Wojciech Węgrzyński>It's globally established team has developed a reputation for permanent fire engineering expertise with colleagues working across the world to help protect people, property and planets. 00:03:06.530 --> 00:03:10.280 <v Wojciech Węgrzyński>In the UK, that includes the redevelopment of the Printworks building in Canada water. 00:03:10.340 --> 00:03:17.479 <v Wojciech Węgrzyński>One of the tallest residential buildings in Birmingham, as well as historic structures, like the National Gallery, National History Museum. 00:03:17.840 --> 00:03:19.789 <v Wojciech Węgrzyński>And the National Portrait Gallery in London. 00:03:20.180 --> 00:03:29.782 <v Wojciech Węgrzyński>Internationally it's work ranges from Antarctic to Atacama desert in Chile, and the number of projects across Africa in 2023 of our will grow with seam. 00:03:29.872 --> 00:03:35.483 <v Wojciech Węgrzyński>And it's keen to hear from industry professionals who want to collaborate on the fire safety futures this year. 00:03:36.022 --> 00:03:39.022 <v Wojciech Węgrzyński>Get in touch at OFRconsultants.com. 00:03:39.366 --> 00:03:41.616 <v Wojciech Węgrzyński>And now back to the episode with Eric Mueller have fun. 00:03:42.133 --> 00:03:42.949 <v Wojciech Wegrzynski>Hello everybody. 00:03:42.949 --> 00:03:44.588 <v Wojciech Wegrzynski>Welcome to the Fire Science Show. 00:03:44.769 --> 00:03:45.949 <v Wojciech Wegrzynski>I'm today with Dr. 00:03:45.949 --> 00:03:47.308 <v Wojciech Wegrzynski>Eric Mueller from NIST. 00:03:47.308 --> 00:03:48.628 <v Wojciech Wegrzynski>Hey Eric, great to have you here. 00:03:48.804 --> 00:03:49.812 <v Eric Mueller>Hey, thanks for having me. 00:03:50.066 --> 00:04:03.653 <v Wojciech Wegrzynski>And we have a lot to talk about some stuff to differentiates, build environment and wildfire science in particular, I would love to talk about modeling, living fuels or just modeling vegetation in this podcast episode. 00:04:03.894 --> 00:04:12.320 <v Wojciech Wegrzynski>First, I, I would love to, to hear your professional story, how, how you ended into wildfires and, are you doing now at nist? 00:04:12.432 --> 00:04:19.326 <v Eric Mueller>I mean, I guess the, the story to go back is, uh, it starts in my undergraduate degree, which was, engineering physics, basically applied physics. 00:04:19.809 --> 00:04:26.778 <v Eric Mueller>I think it's a great degree to get some fundamentals, but probably more suited to graduate school than to going out and finding a job. 00:04:26.778 --> 00:04:31.858 <v Eric Mueller>You missed some of that practical education you might get in, you know, traditional mechanical engineering or something like that. 00:04:32.389 --> 00:04:34.778 <v Eric Mueller>Uh, and so I was looking at graduate programs. 00:04:35.048 --> 00:04:43.379 <v Eric Mueller>I was based in Boston trying to do material science and was looking at the website of WPI and their material science webpage was broken. 00:04:43.718 --> 00:04:47.939 <v Eric Mueller>And so I started clicking around and I discovered fire protection engineering that way. 00:04:48.238 --> 00:04:49.978 <v Eric Mueller>And I thought, oh, this sounds interesting. 00:04:50.119 --> 00:04:56.814 <v Eric Mueller>And then it just so happens to coincide with, professor Albert Simeoni when he was starting, his first round of being a professor there. 00:04:57.110 --> 00:04:57.831 <v Eric Mueller>at W P I. 00:04:57.831 --> 00:05:03.831 <v Eric Mueller>And so I went to meet with him to, you know, see about being a graduate student and he of course is an expert in wildfires. 00:05:03.831 --> 00:05:06.670 <v Eric Mueller>And that started kind of my interest, particularly in that space. 00:05:07.050 --> 00:05:11.031 <v Eric Mueller>And I've always had a love of, you know, the natural environment and being outdoors and everything. 00:05:11.040 --> 00:05:16.391 <v Eric Mueller>So the fact that I've been able to go do these big field experiments and be out in the woods and everything, I love that. 00:05:16.401 --> 00:05:18.500 <v Eric Mueller>So it kind of took off from there. 00:05:18.500 --> 00:05:22.901 <v Eric Mueller>And yeah, I ended up in Edinburgh following Albert Simi over to Edinburg to do my PhD. 00:05:23.404 --> 00:05:31.072 <v Eric Mueller>, stay there for postdoc and now have come back to the us to work at NS to kind of carry on this, uh, wildfire research and particularly around the modeling. 00:05:31.081 --> 00:05:34.769 <v Wojciech Wegrzynski>So, so it's, uh, applied physics turned into wildfire. 00:05:34.769 --> 00:05:37.050 <v Wojciech Wegrzynski>I, I guess that's, that's, that, that makes it even better. 00:05:37.050 --> 00:05:38.009 <v Wojciech Wegrzynski>That makes it even better. 00:05:38.536 --> 00:05:42.286 <v Wojciech Wegrzynski>so Eric, You have studied a lot of, a lot of fuels. 00:05:42.396 --> 00:05:45.706 <v Wojciech Wegrzynski>I I remember your paper from IAFSS. 00:05:45.725 --> 00:05:51.326 <v Wojciech Wegrzynski>Uh, we'll remember the, the brilliant presentation of that, uh, that will never be forgotten. 00:05:51.326 --> 00:05:54.848 <v Wojciech Wegrzynski>You've said the standard too high for the rest of us to compete. 00:05:54.848 --> 00:05:55.968 <v Wojciech Wegrzynski>Uh, thank you for that. 00:05:56.298 --> 00:05:57.728 <v Wojciech Wegrzynski>Uh, but it, it was really great if. 00:05:58.079 --> 00:06:05.636 <v Wojciech Wegrzynski>If you haven't seen that link in the show notes, so it is definitely worth, having the visual component to the great audio. 00:06:06.206 --> 00:06:08.036 <v Wojciech Wegrzynski>Uh, here we, we just have the audio. 00:06:08.305 --> 00:06:09.036 <v Wojciech Wegrzynski>I would love to. 00:06:09.672 --> 00:06:12.206 <v Wojciech Wegrzynski>Learn about, modeling vegetation. 00:06:12.206 --> 00:06:27.915 <v Wojciech Wegrzynski>So let's, uh, first try to, to make an introduction how modeling, uh, pine needles or, or a tree differentiates from modeling just, I don't know, solid piece of timber, which is also an organic material. 00:06:27.915 --> 00:06:31.475 <v Wojciech Wegrzynski>And I would assume many processes are similar in, in each other. 00:06:31.485 --> 00:06:33.235 <v Wojciech Wegrzynski>So, so what, what's the big deal? 00:06:33.235 --> 00:06:33.755 <v Wojciech Wegrzynski>What's the differe? 00:06:34.100 --> 00:06:34.790 <v Eric Mueller>Yeah, sure. 00:06:34.790 --> 00:06:42.670 <v Eric Mueller>I mean, I think that's a good context to start in because we might think of, uh, yeah, whether it's pine needles or even branches on a forest floor or something like that. 00:06:42.670 --> 00:06:43.951 <v Eric Mueller>Some dead material that's wood. 00:06:44.380 --> 00:06:48.492 <v Eric Mueller>Effectively from that, more material or, or fundamental chemical sense? 00:06:49.303 --> 00:07:01.158 <v Eric Mueller>Probably very physics going on in terms of looking at the, the ignition around a, you know, decomposition, the thermal decomposition, uh, how it's paralyzing and what sort of, gaseous species it's creating and, and how that's burning. 00:07:01.646 --> 00:07:06.877 <v Eric Mueller>Of course, that's, you know, I'm simplifying, there's some nuance there, but we can say, you know, if we look at timber in the built environment and. 00:07:07.401 --> 00:07:10.362 <v Eric Mueller>Timber on the forest floor, not terribly different. 00:07:10.692 --> 00:07:12.922 <v Eric Mueller>So where are the big differences coming from? 00:07:12.982 --> 00:07:20.721 <v Eric Mueller>And uh, I think it really comes down to, uh, a, the environmental conditions that these materials are gonna be exposed to. 00:07:20.812 --> 00:07:27.298 <v Eric Mueller>So, of course, uh, moisture is a huge thing, uh, the potential moisture content of, of these different fuels. 00:07:27.298 --> 00:07:34.922 <v Eric Mueller>And again, if we get to dead fuels, the range that they can have, uh, is dictated sort of by this fiber saturation point. 00:07:35.163 --> 00:07:38.786 <v Eric Mueller>Similar to what you would find with timber, uh, in the built environment. 00:07:39.036 --> 00:07:50.903 <v Eric Mueller>So you can get up to, you know, maybe 30, 40% moisture content, it's going to vary a lot more seasonally or as weather patterns, blow through a certain area, let's say, than what you would find in the built environment. 00:07:50.903 --> 00:07:57.543 <v Eric Mueller>So you really have to consider this whole spectrum of, you know, very, very low moisture content all the way up to 30, 40%. 00:07:57.954 --> 00:08:02.663 <v Eric Mueller>Uh, and then the other component of the environment, of course, is the wind that you. 00:08:02.793 --> 00:08:06.021 <v Eric Mueller>Typically have to deal with inside of, uh, of the built environment. 00:08:06.079 --> 00:08:12.358 <v Eric Mueller>but how that's going to affect, uh, certain processes that will, let's say, uh, alter the ignition behavior. 00:08:12.488 --> 00:08:21.141 <v Eric Mueller>So, whether that's driving convective, heating or cooling, or the mixture of gases or providing oxygen for, you know, oxidative processes like smoldering. 00:08:21.471 --> 00:08:24.221 <v Eric Mueller>So all of these things come into play when we think about the wind. 00:08:24.882 --> 00:08:28.605 <v Eric Mueller>And then beyond the environment, we also have the structure, of the fuel. 00:08:29.463 --> 00:08:44.264 <v Eric Mueller>if you think about just one log, maybe that's not so different from a slab of timber, but as we start to get finer fuels in, in these sort of fuel matrices or fuel layers, like pine needles, as you mentioned on the forest floor, uh, now we really have a problem of porous media and so. 00:08:44.802 --> 00:08:57.522 <v Eric Mueller>uh, we start to have to think about all of the, the complexities that come into understanding porous media, where we have this mixture of air and solid and, you know, the proportions matter, but also, uh, the sizes of, say, your elements. 00:08:57.522 --> 00:09:05.922 <v Eric Mueller>You could have two materials with the same overall porosity, but made of very thin pine needles or very thick sticks, like in a wood crip or something. 00:09:05.922 --> 00:09:11.442 <v Eric Mueller>And there's going to be, you know, different behaviors there because we have maybe thermally thick or thermally thin, we have. 00:09:11.956 --> 00:09:16.147 <v Eric Mueller>different, potential for convective heating or cooling, different reradiation. 00:09:16.147 --> 00:09:19.226 <v Eric Mueller>So there's a lot of complexity that comes into the mix. 00:09:19.226 --> 00:09:20.986 <v Eric Mueller>And we have this porosity introduced. 00:09:21.167 --> 00:09:34.234 <v Wojciech Wegrzynski>In, in your talk, you, you had this, example where you've walked with a cell or, or fin element and put it on a tree to illustrate what does it mean that there's a, there's a. 00:09:34.538 --> 00:09:35.708 <v Wojciech Wegrzynski>Fuel inside. 00:09:35.708 --> 00:09:58.946 <v Wojciech Wegrzynski>Uh, I'm actually gonna make it into the cover of the episode so everyone knows what we are talking about, . So if you went to this episode and seen the cover, you know exactly what I'm talking about and it, so that's a very, very good illustration on the issue with modeling that with competition free dynamic tools, with with volume of fin development methods because. 00:09:59.009 --> 00:09:59.975 <v Wojciech Wegrzynski>a, in a finished volume. 00:10:00.076 --> 00:10:03.456 <v Wojciech Wegrzynski>The, the assumption is that it's uniform in the, it is whole volume. 00:10:03.456 --> 00:10:09.895 <v Wojciech Wegrzynski>It's, it's just one block of matter that exists and is holy at the same state. 00:10:10.145 --> 00:10:15.535 <v Wojciech Wegrzynski>Whereas, uh, with this tiny needles, you, you have a set of really tiny elements. 00:10:15.535 --> 00:10:18.056 <v Wojciech Wegrzynski>It itch with its own physics insight. 00:10:18.125 --> 00:10:19.696 <v Wojciech Wegrzynski>That's control volume. 00:10:20.586 --> 00:10:35.395 <v Wojciech Wegrzynski>That essentially burned the, the, the gradients inside are enormous, but for the reasons of efficiency, computational efficiency, most likely we are unable to simulate them at this tiniest, tiniest scales. 00:10:35.846 --> 00:10:50.091 <v Wojciech Wegrzynski>So we have to assume something for, for the whole control volume and that that's, The really, really challenging part, how does one, uh, simulate stuff that's so tiny within quite large quantum volumes in a way that it makes sense? 00:10:50.721 --> 00:10:51.011 <v Eric Mueller>Y. 00:10:51.011 --> 00:10:51.251 <v Eric Mueller>Yeah. 00:10:51.251 --> 00:10:55.611 <v Eric Mueller>I mean, I think as you say, there's, there's two ways we can make these models more sophisticated, right? 00:10:55.611 --> 00:10:58.412 <v Eric Mueller>Because right now we have this very crude representation. 00:10:58.412 --> 00:11:04.971 <v Eric Mueller>We have a course model, and so theoretically we could go the direction of trying to resolve in a lot of detail. 00:11:05.308 --> 00:11:06.698 <v Eric Mueller>Uh, the actual structure. 00:11:06.698 --> 00:11:22.111 <v Eric Mueller>And, you know, maybe if you're looking at just a, a tiny piece of a bit of pine litter, you could actually simulate the flow through that whole matrix, but that's not really currently at least sustainable, uh, or achievable with the, you know, computational resources we have. 00:11:22.111 --> 00:11:30.672 <v Eric Mueller>So the other approach is with these assumptions, these approximations submodels, that allow us to describe the exchanges between phases. 00:11:31.211 --> 00:11:33.412 <v Eric Mueller>And I think we have a, a good starting. 00:11:34.182 --> 00:11:48.926 <v Eric Mueller>. But you know, if we wanna more models, more sophisticated, as I say, and go that approach, uh, we might need to refine these submodels and figure out how we can describe the fact that it isn't uniformly distributed, even though we're not fully representing what it looks like. 00:11:49.676 --> 00:11:59.527 <v Wojciech Wegrzynski>and when we are learning that when you are developing these, these models, With your experiments, you go all the way down to the scale of a single needle. 00:11:59.947 --> 00:12:02.246 <v Wojciech Wegrzynski>You, you take a a three branch. 00:12:02.336 --> 00:12:04.086 <v Wojciech Wegrzynski>Uh, how, how do you approach that? 00:12:04.277 --> 00:12:06.126 <v Wojciech Wegrzynski>I wonder like, how, how deep can you go? 00:12:06.126 --> 00:12:11.681 <v Wojciech Wegrzynski>Because in my eyes I see, like if I want to model a needle, I could make a CFD model of a needle. 00:12:11.681 --> 00:12:16.961 <v Wojciech Wegrzynski>But then a question is, should I model the boundary layer on the needle and go, you know, from one millimeter. 00:12:17.736 --> 00:12:25.846 <v Wojciech Wegrzynski>Fin elements to, uh, let's say one 40th of a millimeter element to really capture the, whole structure of the flow around the single needle. 00:12:26.057 --> 00:12:32.006 <v Wojciech Wegrzynski>So, so there really, you can really go far into, into making this, this very complicated. 00:12:32.006 --> 00:12:34.047 <v Wojciech Wegrzynski>I wonder how far have you went? 00:12:34.047 --> 00:12:35.541 <v Wojciech Wegrzynski>How, How far is sufficient? 00:12:35.912 --> 00:12:36.932 <v Eric Mueller>How far sufficient? 00:12:36.932 --> 00:12:37.611 <v Eric Mueller>That's a good question. 00:12:37.682 --> 00:12:41.331 <v Eric Mueller>I could tell you more easily how far I've gone, which I think is maybe bit too far. 00:12:41.511 --> 00:12:53.022 <v Eric Mueller>But, I mean the most that we, we did in detail when I was in Edinburgh is, uh, using X-ray ct micro CT to scan some samples that were of this kind of pine litter on the order of. 00:12:53.394 --> 00:12:58.573 <v Eric Mueller>let's say 10 centimeters in diameter of a cylindrical sample, you know, sort of a, a cone sized sample. 00:12:59.274 --> 00:13:07.897 <v Eric Mueller>And, uh, then you get this really, you know, micrometer resolution, uh, nice 3D image of all of your pine needles in space. 00:13:08.476 --> 00:13:13.136 <v Eric Mueller>And so you could mesh that up theoretically, I guess, and try to model it. 00:13:13.246 --> 00:13:19.616 <v Eric Mueller>I tried a little bit with, uh, with Latice, Boltzmann, uh, simulations, but it's well beyond anything I really understand. 00:13:19.626 --> 00:13:21.321 <v Eric Mueller>So , I kind of gave that up. 00:13:21.876 --> 00:13:24.596 <v Eric Mueller>I think that's an interesting scale to get to. 00:13:24.647 --> 00:13:34.636 <v Eric Mueller>Uh, if you do that kind of refined modeling to try to confirm some of the coarser approximations that we would make of, you know, what a bulk convective coefficient of this whole matrix. 00:13:34.636 --> 00:13:37.956 <v Eric Mueller>You know, we're not even talking about convection around a single cylinder. 00:13:38.447 --> 00:13:39.277 <v Eric Mueller>Uh, it's really. 00:13:39.777 --> 00:13:41.553 <v Eric Mueller>This whole matrix, effectively. 00:13:41.854 --> 00:13:56.524 <v Eric Mueller>And so, you know, you might be able to simulate something on that scale and try to confirm what you've shown experimentally, but getting into all of the combustion processes, trying to get the degradation of the fuel and the burning and everything at that scale, I think is a ways away. 00:13:57.269 --> 00:13:58.456 <v Wojciech Wegrzynski>you, you've mentioned convection. 00:13:58.456 --> 00:14:11.356 <v Wojciech Wegrzynski>And, in, in my giant ignorance of the subject of, of living fuels, I have been recently exposed to, to those, uh, types of problems while trying to, do some experiments with, uh, with greenwall facade systems. 00:14:11.657 --> 00:14:19.636 <v Wojciech Wegrzynski>And now we are, uh, oh boy, we're learning very quickly this difficult world of fire science and. 00:14:20.062 --> 00:14:25.432 <v Wojciech Wegrzynski>I've, I've learned the importance of convection in these type of, of of fuels. 00:14:25.432 --> 00:14:33.125 <v Wojciech Wegrzynski>I've learned that it's very difficult to ignite such fuels, uh, with, with just radiation because of their characteristics. 00:14:33.125 --> 00:14:33.806 <v Wojciech Wegrzynski>And I've learned that. 00:14:34.500 --> 00:14:38.120 <v Wojciech Wegrzynski>The convection in them is, is much more complicated in buildings. 00:14:38.410 --> 00:14:47.561 <v Wojciech Wegrzynski>We, I guess as a community chose to like, pretend it doesn't matter and we just assume one hit transfer coefficient that goes from Euro code and it's so convenient. 00:14:47.561 --> 00:14:48.961 <v Wojciech Wegrzynski>No one's trying to touch that. 00:14:49.571 --> 00:14:58.801 <v Wojciech Wegrzynski>Uh, however, at this, at this, uh, scale of fuels, it seems to be fundamentally important, uh, to understand the convective heat transfer. 00:14:58.850 --> 00:15:03.000 <v Wojciech Wegrzynski>So may, maybe you can enlighten me about the, the mode of heat transfer. 00:15:03.495 --> 00:15:10.385 <v Wojciech Wegrzynski>Again, if you, if you could compare that to how a piece of wood would be ignited by radiation and convection. 00:15:10.385 --> 00:15:13.025 <v Wojciech Wegrzynski>What role this, these modes played? 00:15:13.025 --> 00:15:14.505 <v Wojciech Wegrzynski>How will be splendid? 00:15:14.791 --> 00:15:16.041 <v Eric Mueller>Yeah, I mean, sure if. 00:15:16.336 --> 00:15:22.721 <v Eric Mueller>, down to just flame spread again in something like, uh, a layer of pine needles, uh, versus on a slab of wood. 00:15:22.721 --> 00:15:27.864 <v Eric Mueller>And as you say, it comes down to the scales we're dealing with and how that differs, uh, in those two cases. 00:15:27.864 --> 00:15:29.744 <v Eric Mueller>And you have these very fine particles. 00:15:29.923 --> 00:15:39.943 <v Eric Mueller>And as you start to reduce the sort of characteristic, Diameter of, of your pine needle or whatever it is, then you're getting into a regime where it can cool very effectively. 00:15:39.943 --> 00:15:44.943 <v Eric Mueller>You have, uh, potentially a very high convective heat transfer coefficient for these elements. 00:15:44.943 --> 00:15:56.086 <v Eric Mueller>And so, um, whether that's even just due to, natural convection or you have some entrainment, uh, due to the buoyancy of the fire itself, or, you know, in a wildfire you might have a considerable amount of wind anyways. 00:15:56.427 --> 00:16:00.821 <v Eric Mueller>And so, it's not, certainly not that there isn't radiation and that that isn't important. 00:16:01.546 --> 00:16:04.145 <v Eric Mueller>and it depends on, again, what the problem you're looking at is. 00:16:04.635 --> 00:16:12.125 <v Eric Mueller>Um, if that's flame spread in, in fine fuels versus, uh, the potential for ignition of the facade of a structure, let's say. 00:16:12.125 --> 00:16:23.386 <v Eric Mueller>Or, you know, we had some Prescribed fire experiments that we had done, uh, out in New Jersey in the us And we have a great video of, uh, auto ignition, of a tree trunk, uh, due to the radiation from this big flaming front. 00:16:23.596 --> 00:16:36.490 <v Eric Mueller>Um, so we see these processes, uh, we see radiation playing a big role in certain contexts, but when it comes down to the ability of these fine fuels to ignite, uh, they can just cool very, efficiently by convection when they're just being heated by radiation. 00:16:36.671 --> 00:16:47.081 <v Eric Mueller>But as soon as they become bathed in a flame or some hot gases from the plume, , then you've lost all of that, uh, convective cooling and potentially you have significant convective heating. 00:16:47.081 --> 00:17:03.667 <v Eric Mueller>And so even if it's just very intermittent or quick pulses, uh, you know, there's been a lot of, uh, great work from, uh, the US Forest Service out in Missoula looking at these, uh, sort of very high frequency, convective heating processes and how they really are important to driving, uh, flame spread in a lot of condit. 00:17:04.537 --> 00:17:29.326 <v Wojciech Wegrzynski>Uh, I, I find that fascinating because, because that's like the concept that, uh, it can so effectively cool by convection while being so vigorously heated by radiation, it, it's immense to the listeners, we're, we're talking about heat fluxes of let's say 30 kilowatt per square meter that still do not ignite the branch because it, it has capability to, to cool down. 00:17:29.767 --> 00:17:40.221 <v Wojciech Wegrzynski>That heat that that receives is, it's quite astonishing because I'm coming from a world where at 25 kilowatts per square meter, you have a flashover in your room and the game has ended. 00:17:40.221 --> 00:17:40.701 <v Wojciech Wegrzynski>Right? 00:17:41.151 --> 00:17:42.540 <v Wojciech Wegrzynski>So, so, so that's true. 00:17:42.540 --> 00:17:48.540 <v Wojciech Wegrzynski>But as soon as you start to, to, to compressing that, if you have a, a bat, that, that, that is not a. 00:17:49.205 --> 00:17:53.811 <v Wojciech Wegrzynski>Powerous medium that it loses the, the capability of, of convecting, cooling. 00:17:53.811 --> 00:18:00.852 <v Wojciech Wegrzynski>And then, then you have the, and is, is it the same for like plants with leaves or is it, is it something very specific to to 00:18:01.162 --> 00:18:11.638 <v Eric Mueller>I mean, I, I think there's been some good demonstrations, uh, again from Missoula just looking at, you know, clumps of excelsior, of shreds of wood, basically, and just compacting them in front of a radiant panel. 00:18:11.638 --> 00:18:16.999 <v Eric Mueller>And there is a point at which you can compress them enough that you've, uh, reduced that efficiency of cooling. 00:18:16.999 --> 00:18:19.838 <v Eric Mueller>And so, uh, you know, it comes back to this whole idea. 00:18:20.284 --> 00:18:25.141 <v Eric Mueller>Vegetative fuels and what are the structural, components that matter, the way that we describe the structure. 00:18:25.141 --> 00:18:32.181 <v Eric Mueller>And so it's the size of individual elements, but it's also the way that they come together potentially in different clumps and clusters. 00:18:32.181 --> 00:18:38.060 <v Eric Mueller>And so if you had a very dense, uh, vegetative canopy, then maybe that's not cooling, uh, as effectively. 00:18:38.382 --> 00:18:38.872 <v Wojciech Wegrzynski>Okay. 00:18:38.872 --> 00:18:39.832 <v Wojciech Wegrzynski>That's very interesting. 00:18:39.832 --> 00:18:45.832 <v Wojciech Wegrzynski>But now, as a modeler and, and how the hell do you do that in, in, in a control volume that's like 20 by 20 centimeters. 00:18:45.832 --> 00:18:47.670 <v Wojciech Wegrzynski>How, how do you adjust for that? 00:18:47.876 --> 00:18:48.366 <v Eric Mueller>Yeah. 00:18:48.366 --> 00:18:56.527 <v Eric Mueller>So that's the part where I think we, we needed to get more sophisticated with the way that we do things because right now, uh, you know, we conserve mass is, is our starting point. 00:18:56.527 --> 00:18:57.446 <v Eric Mueller>That's what we hope to do. 00:18:57.497 --> 00:19:07.406 <v Eric Mueller>So if you take the same control volume and increase its size and you still had the same, uh, cluster of vegetation in it, you are effectively changing its porosity. 00:19:07.656 --> 00:19:14.426 <v Eric Mueller>Uh, and so that's going to change the way that it, you know, interacts with the flow through drag and convection, the way that it attenuates radiation. 00:19:15.182 --> 00:19:22.933 <v Eric Mueller>. The hope or the way that it's working more or less right now is that we're not looking just one thing that's, uh, subgrid size. 00:19:22.933 --> 00:19:35.574 <v Eric Mueller>So that if you have a tree crown and you represent that with, thousands of grid cells, or you reduce that a little bit, then overall you're effectively still, conserving the same kind of, uh, properties and the way that it interacts with the flow around it. 00:19:35.574 --> 00:19:43.614 <v Eric Mueller>But yeah, as you start to push the bounds of that and you're resolving, trying to resolve, let's say a, an entire tree with one grid cell, then you're really violating. 00:19:43.614 --> 00:19:49.651 <v Eric Mueller>Some of these assumptions are really oversimplifying and so there might be ways that we need to look at, modifying the submodels. 00:19:49.651 --> 00:19:54.364 <v Eric Mueller>You know, there's ways when we look at, flame temperature, gas temperature is a classic one, you know, cfd right? 00:19:54.364 --> 00:20:03.284 <v Eric Mueller>Whereas you, uh, expand the grid sale size, you'll tend to under predict the temperatures because you're under resolving things like the flame, the actual flame sheet and things like that. 00:20:03.733 --> 00:20:10.923 <v Eric Mueller>Uh, and you know, there's ways to short sort of model probability, distributions of temperature to help improve your submodels. 00:20:10.923 --> 00:20:13.963 <v Eric Mueller>And so there's things that we can look at, uh, with vegetation in the same. 00:20:14.699 --> 00:20:28.326 <v Wojciech Wegrzynski>So basically what we need is a, is a bunch of submodels to resolve the drag ignition, the heat production within the control volume, and hopefully not violate the, the, the mass equation and, and accommodate for the, the fact that it's burning away. 00:20:28.740 --> 00:20:29.230 <v Eric Mueller>Yeah. 00:20:29.715 --> 00:20:30.205 <v Wojciech Wegrzynski>that, 00:20:30.550 --> 00:20:30.871 <v Eric Mueller>exactly. 00:20:30.871 --> 00:20:33.911 <v Eric Mueller>And, and we, that's how you know what we have now and the approach we take now. 00:20:33.911 --> 00:20:38.310 <v Eric Mueller>It's just how can we make that maybe less grid sensitive or less resolution sensitive. 00:20:38.467 --> 00:20:40.461 <v Wojciech Wegrzynski>well you were working at nso. 00:20:40.461 --> 00:20:45.294 <v Wojciech Wegrzynski>I guess you are familiar with this computer code fds and, I've seen in literature. 00:20:45.294 --> 00:21:06.371 <v Wojciech Wegrzynski>I think it's even in the, examples within fds, there's this bo by case, I think it's using some sort of lagrangian particles to simulate, the vegetation or, or fuels where I guess, uh, each branch of like pieces of vegetation are split into, into smaller lagrangian particles, which are then spread around within, uh, control volumes. 00:21:06.901 --> 00:21:09.250 <v Wojciech Wegrzynski>Um, any comments on, on that way of modeling? 00:21:09.766 --> 00:21:10.256 <v Eric Mueller>Yeah. 00:21:10.256 --> 00:21:18.471 <v Eric Mueller>I mean that is, Most of, or at least half of my day job, I guess, is working on, uh, fds and, uh, trying to improve the vegetation sub modeling there. 00:21:18.521 --> 00:21:26.459 <v Eric Mueller>So, the Lagrangian particle approach, I think it, it's helpful to consider it as like a numerical construct in a way. 00:21:26.459 --> 00:21:35.336 <v Eric Mueller>It's, for the most part, in terms of fds, it's just a handy way for us to add some, exchange terms, some source and sync. 00:21:36.131 --> 00:21:38.330 <v Eric Mueller>between the gas and solid phase within a grid cell. 00:21:38.540 --> 00:21:50.580 <v Eric Mueller>So there's no real point to have more than one particle within a grid cell because, you're just recalculating the same exchange, but you don't have any more information between two needles within one grid cell, right? 00:21:50.580 --> 00:21:53.540 <v Eric Mueller>Because it's the same average temperature, it's the same average flow field. 00:21:54.070 --> 00:21:56.901 <v Eric Mueller>So you know, the same integrated radiation intensity. 00:21:56.901 --> 00:21:58.300 <v Eric Mueller>All of these things are the same. 00:21:58.881 --> 00:21:59.300 <v Eric Mueller>You. 00:21:59.921 --> 00:22:06.721 <v Eric Mueller>calculating it twice, one for each needle, whereas you can calculate it once and just weight it by the number of needles that you have within a cell. 00:22:07.290 --> 00:22:14.320 <v Eric Mueller>So I think it's, yeah, a little bit confusing sometimes for people to look at this and it looks like, oh, it's a tree, and all of these particles are needles and everything. 00:22:14.320 --> 00:22:26.240 <v Eric Mueller>And in a way they are, they're representing them, but they're really just placeholders for more of a Eulerian approach where it's just the source and sync, uh, within particular grid cells, you know, representing that cell. 00:22:26.996 --> 00:22:27.675 <v Wojciech Wegrzynski>That's very interesting. 00:22:27.675 --> 00:22:28.945 <v Wojciech Wegrzynski>I, I didn't, know that. 00:22:29.439 --> 00:22:35.519 <v Wojciech Wegrzynski>so, so it's more like a clever representation of a fuel that's easier for the user to maybe defined. 00:22:35.519 --> 00:22:44.078 <v Wojciech Wegrzynski>But in the end, as soon as this Lagrangiajn particle within the control volume is transferred into the fuel, that's, that goes into reaction. 00:22:44.943 --> 00:22:53.693 <v Wojciech Wegrzynski>It essentially means it doesn't matter if it was 1 35 allian particles, it's, it's now just another burner that's emitting fuel into your control volume. 00:22:53.693 --> 00:22:57.334 <v Wojciech Wegrzynski>And at the scale of that control volume, you are burning it, right? 00:22:57.338 --> 00:22:57.759 <v Eric Mueller>Yep. 00:22:57.759 --> 00:23:02.398 <v Eric Mueller>Yeah, and everything's just waited to, again, conserve that mass that you have initially a vegetation. 00:23:02.564 --> 00:23:06.304 <v Wojciech Wegrzynski>And, and the same for the ignition conditions of that Lagrangian particle. 00:23:06.304 --> 00:23:09.824 <v Wojciech Wegrzynski>Like they're all solved at the level of that control volume. 00:23:09.993 --> 00:23:13.544 <v Wojciech Wegrzynski>So if I have seven in my control volume, they should technically. 00:23:14.067 --> 00:23:16.905 <v Wojciech Wegrzynski>Ignite at the same exact time and act like one. 00:23:17.291 --> 00:23:17.721 <v Eric Mueller>right? 00:23:17.721 --> 00:23:17.922 <v Eric Mueller>Yeah. 00:23:17.922 --> 00:23:21.848 <v Eric Mueller>There's no, there shouldn't be any temperature difference between these different, particles. 00:23:22.818 --> 00:23:23.239 <v Wojciech Wegrzynski>And. 00:23:23.378 --> 00:23:36.642 <v Eric Mueller>we could have them, you know, uh, Waited, let's say, based on some randomized position within the grid cell to get a temperature, that's, you know, if one pine needle is closer to one side of the grid cell and you have a higher temperature in the next cell, then you can wait the, 00:23:36.648 --> 00:23:37.048 <v Track 1>temperature 00:23:37.378 --> 00:23:39.769 <v Eric Mueller>of the particle or what it's exposed to. 00:23:39.769 --> 00:23:44.808 <v Eric Mueller>But for now, the approach is really just to, know, have them in the center of the sale effectively. 00:23:44.848 --> 00:23:49.439 <v Wojciech Wegrzynski>as you now expose yourself that you're working on this, I'm happy to ask you a hundred more questions. 00:23:50.872 --> 00:23:57.092 <v Wojciech Wegrzynski>and is the flow field in any way, uh, affected by the existence of vegetation in this control? 00:23:57.092 --> 00:24:00.061 <v Wojciech Wegrzynski>Volumes in terms of like the produce drag, 00:24:00.606 --> 00:24:09.574 <v Eric Mueller>So it's, uh, just a bulk, drag force term, uh, in the same way that you would have the convective term, uh, you know, applied to the entire gas volume that you have there. 00:24:09.574 --> 00:24:10.054 <v Eric Mueller>It's just. 00:24:10.548 --> 00:24:15.828 <v Eric Mueller>based on the density of vegetation you have and the geometry of the particles that you assume. 00:24:16.344 --> 00:24:26.943 <v Eric Mueller>. Then there's empirical correlations, and that's again, some space where we have a lot of work to do, I think, to try to improve the correlations that we rely upon now, or at least confirm their validity across. 00:24:27.094 --> 00:24:31.703 <v Eric Mueller>I mean, the wide range of plant types and geometry that you see out in nature. 00:24:32.094 --> 00:24:33.544 <v Eric Mueller>A bed of pine needles is one thing. 00:24:33.544 --> 00:24:43.304 <v Eric Mueller>And you know, if you look at the, the papers I've had, I've spent a lot of time looking at a bed of pine needles because it is easier to describe in a lot of ways than a lot of other vegetation. 00:24:43.304 --> 00:24:44.023 <v Eric Mueller>But even. 00:24:44.334 --> 00:24:51.141 <v Eric Mueller>We hope to apply this approach, know, to more complex plant types, shrubs, trees, and things that you would find in the wildland urban interface. 00:24:51.141 --> 00:24:54.344 <v Eric Mueller>Then we have to understand, uh, the validity of these submodels. 00:24:54.939 --> 00:25:07.784 <v Wojciech Wegrzynski>And to, to what extent it is important to include stuff like drag, in modeling the vegetation fuels, if I omitted it completely, am I introducing a huge error to my calculation, uh, of, of what importance is that factor? 00:25:08.067 --> 00:25:09.997 <v Eric Mueller>Yeah, I mean, that's a, a good question. 00:25:09.997 --> 00:25:13.317 <v Eric Mueller>A, a difficult one, but one we're trying to get a better handle on. 00:25:13.317 --> 00:25:21.106 <v Eric Mueller>Uh, actually we're putting together kind of a medium scale wind tunnel here at NIST and, know, do some more studies around plant drag, and especially when objects are burning and everything. 00:25:21.106 --> 00:25:27.013 <v Eric Mueller>But I, it certainly depends upon the type of vegetation and the density that you're looking at. 00:25:27.064 --> 00:25:28.334 <v Eric Mueller>So, uh, if you. 00:25:28.777 --> 00:25:31.547 <v Eric Mueller>A very low density forest canopy, let's say. 00:25:31.547 --> 00:25:47.084 <v Eric Mueller>Then maybe you're not introducing as much air, but if you look at like a, a dense conifer, you know, think of a Christmas tree or something like that, and you know, you impose some flow on it, you'll actually have very little flow penetrating all the way, through the tree and. 00:25:47.479 --> 00:25:54.078 <v Eric Mueller>the kinds of convection that you have on the, on the leeward side of the tree, for example, can be significantly affected by that drag. 00:25:54.078 --> 00:26:00.798 <v Eric Mueller>And then if you were to have another tree downstream of that, suddenly it's no longer exposed to this kind of ambient wind that you have. 00:26:00.798 --> 00:26:04.598 <v Eric Mueller>So yeah, I think you can introduce quite a bit of error if you just were to ignore the drag entirely. 00:26:04.604 --> 00:26:21.750 <v Wojciech Wegrzynski>a and once you advance from modeling a single plant to a whole forest canopy, I guess it becomes fundamental from the reasons you've just mentioned that y you then will have like the first layer that, is, burning, that's exposed to wind and the rest of the forest shielded from the wind, 00:26:22.715 --> 00:26:22.955 <v Eric Mueller>Yeah. 00:26:22.955 --> 00:26:29.355 <v Eric Mueller>I mean, these things, you should be able to kind of stack up the effects and you can see the attenuation of the flow into the, into the canopy. 00:26:30.334 --> 00:26:38.453 <v Eric Mueller>, it depends on the scale you're looking at, but you can get away with perhaps less, uh, description or detail in the description you have of the actual canopies. 00:26:38.453 --> 00:26:49.426 <v Eric Mueller>So you look at like, there's been a lot of work done around just flow profiles in forest canopies, as you can imagine for, you know, seed dispersion or, carbon exchanges and in forests and things like that, like this. 00:26:49.426 --> 00:26:52.951 <v Eric Mueller>And basically they just model the forest canopy as a. 00:26:53.941 --> 00:27:08.540 <v Eric Mueller>like a homogenous layer, and it will vary vertically to represent the canopy and maybe you have a sub canopy space, but you're not looking at treaty to tree gaps and things of that size because eventually deep within a forest, things typically are homogenous. 00:27:08.540 --> 00:27:11.020 <v Eric Mueller>Homogenous enough that you can get away with that representation, 00:27:11.431 --> 00:27:14.701 <v Wojciech Wegrzynski>Ma man, we went far away from boundary layer on a single needle 00:27:15.080 --> 00:27:15.641 <v Eric Mueller>right. 00:27:15.740 --> 00:27:17.221 <v Wojciech Wegrzynski>huge forest model as a sponge. 00:27:17.411 --> 00:27:21.780 <v Wojciech Wegrzynski>That's, that's, that's pretty interesting, uh, how far science can, can, can get you. 00:27:22.070 --> 00:27:26.368 <v Wojciech Wegrzynski>Um, if modeling drag would be important for the control volume. 00:27:26.368 --> 00:27:30.209 <v Wojciech Wegrzynski>What about the change of drag as the, as the vegetation burns out? 00:27:30.318 --> 00:27:32.209 <v Wojciech Wegrzynski>That's another interesting aspect. 00:27:32.209 --> 00:27:36.568 <v Wojciech Wegrzynski>Uh, what happens as, as it's changing because it's a very transient phenomenon. 00:27:36.568 --> 00:27:44.769 <v Wojciech Wegrzynski>It, it'll take not very long, uh, based on, uh, Maryland's, uh, Christmas tree burning tradition. 00:27:44.818 --> 00:27:48.021 <v Wojciech Wegrzynski>It doesn't take a long time to, to burn the, the pine tree. 00:27:48.097 --> 00:27:49.536 <v Wojciech Wegrzynski>So, so it's very transient. 00:27:50.266 --> 00:27:50.996 <v Eric Mueller>Yeah, sure. 00:27:50.996 --> 00:27:53.276 <v Eric Mueller>And, and the conditions under which it's burning, right? 00:27:53.276 --> 00:28:10.098 <v Eric Mueller>You think about, the production of, uh, firebrand and, you know, I know you've had talks with other guests about this kind of stuff, that's gonna change how much material you're, you're losing in a, a given instant because things will just be mechanically detaching and flying away, and so you're losing a lot of drag that way, potentially. 00:28:10.098 --> 00:28:16.973 <v Eric Mueller>And so capturing that is, difficult, let's say , but again, something that we're trying to get at more experimentally first, and. 00:28:17.653 --> 00:28:20.604 <v Eric Mueller>Uh, you know, build some more sophistication into the cell models we have. 00:28:20.894 --> 00:28:22.723 <v Eric Mueller>We can represent it if you want. 00:28:22.723 --> 00:28:30.844 <v Eric Mueller>Now, you know, effectively as mass goes away, then the drag coefficient has to, or the drag force, let's say, has to adapt to that. 00:28:30.844 --> 00:28:32.884 <v Eric Mueller>So it will effectively reduce its drag. 00:28:32.884 --> 00:28:38.124 <v Eric Mueller>And there's even ways to kind of hack in the detachment of particles and everything like that. 00:28:38.124 --> 00:28:41.203 <v Eric Mueller>But, you know, we prefer to be based on some better understanding of the. 00:28:41.929 --> 00:28:44.669 <v Wojciech Wegrzynski>Are you doing these measurements like wind tunnel burning trees, 00:28:44.903 --> 00:28:45.394 <v Eric Mueller>Yeah. 00:28:45.394 --> 00:28:45.634 <v Eric Mueller>Yep. 00:28:45.634 --> 00:28:47.394 <v Eric Mueller>Well, that's the, the plan moving forward, 00:28:48.044 --> 00:28:49.733 <v Wojciech Wegrzynski>That's, that's gonna be fun, man. 00:28:50.084 --> 00:28:51.054 <v Wojciech Wegrzynski>That's interesting. 00:28:51.544 --> 00:28:59.013 <v Wojciech Wegrzynski>Um, going back to the, uh, the smallest scale, so I understand and the image of, of how one model is, uh, fuel. 00:28:59.564 --> 00:29:09.903 <v Wojciech Wegrzynski>What, what about the, like the chemistry, the kinetic, uh, the pyrolysis, uh, evaporation of, of moisture content, uh, how do you introduce that and. 00:29:10.489 --> 00:29:12.259 <v Eric Mueller>Yeah, I mean that's a, that's a great question. 00:29:12.259 --> 00:29:15.739 <v Eric Mueller>And that's the, you know, a whole other side of the complexity, which I. 00:29:16.176 --> 00:29:19.207 <v Eric Mueller>we have a lot of questions to answer and I would say it's a big field. 00:29:19.207 --> 00:29:30.997 <v Eric Mueller>There's some excellent researchers looking at this kind of work, but it's also a field where we have some established techniques that we can apply from, you know, traditional, more traditional built environment, fire engineering, right? 00:29:30.997 --> 00:29:44.481 <v Eric Mueller>So the same kinds of apparatus you would use to get at some fundamental parameters of, you know, Heat of com of combustion or look at the specific heat and the different degradation peaks in a TGA or a dsc. 00:29:45.021 --> 00:29:49.682 <v Eric Mueller>And so, you know, we can apply all of these tools and come up with some different pyrolysis models. 00:29:50.501 --> 00:29:53.919 <v Eric Mueller>And again, there's a whole range of complexity there because there's. 00:29:54.566 --> 00:29:57.246 <v Eric Mueller>, really so many reactions occurring in pyrolysis. 00:29:57.246 --> 00:30:00.326 <v Eric Mueller>So do we treat that as just kind of one broad reaction? 00:30:00.326 --> 00:30:03.645 <v Eric Mueller>That's when we get to larger scales where people try to apply these models. 00:30:03.645 --> 00:30:14.951 <v Eric Mueller>That tends to be the approach because there's just so much going on that, it's hard to, to get into the details here and, and we're not even certain that the sensitivity around, some of these details is such that it warrant. 00:30:15.561 --> 00:30:18.321 <v Eric Mueller>13 step reaction, that's still kind of a, a big question, right? 00:30:18.321 --> 00:30:25.001 <v Eric Mueller>Is what level of detail do we need to go to, uh, in the sort of degradation kinetics, for example, or in the combustion chemistry. 00:30:25.278 --> 00:30:27.278 <v Eric Mueller>so I think it's just an iterative process, right? 00:30:27.278 --> 00:30:40.009 <v Eric Mueller>As we figure out more about the structure and how we can model at that scale, uh, we can then apply some of these more fundamental, kind of chemical models and look at the sensitivity between the two of them and advance from there. 00:30:40.133 --> 00:30:47.528 <v Wojciech Wegrzynski>When we are doing studies in, in the build environment, we, we have this, let's say, array of tools that are typically used from. 00:30:47.919 --> 00:31:10.558 <v Wojciech Wegrzynski>Cone calorimetry to, to identify the ignition and the fundamental aspects of combustion of elements through, let's say, single burning item, which is a test where you test a performance of an element of a building till like large scale furniture, Cal meters were, the whole things would be burned, uh, at, at once to, to identify large scale behavior. 00:31:10.796 --> 00:31:12.375 <v Wojciech Wegrzynski>what, what's, what's the. 00:31:12.486 --> 00:31:16.507 <v Wojciech Wegrzynski>Pathway in, in wildfire research for development of fuel models. 00:31:16.846 --> 00:31:19.987 <v Wojciech Wegrzynski>You use the same tools or how do you approach that? 00:31:20.172 --> 00:31:24.991 <v Eric Mueller>Yeah, I think a lot of the same tools are certainly, uh, useful and applicable. 00:31:25.189 --> 00:31:28.979 <v Eric Mueller>there's again, on the material side then certainly there's a lot to be learned. 00:31:29.788 --> 00:31:39.749 <v Eric Mueller>and on sort of the medium scale side, I would say sort of a furniture colorimeter, then I think, again, there's a lot that can be done to characterize the burning of individual items. 00:31:39.749 --> 00:31:47.429 <v Eric Mueller>And then, you know, you don't have to go to the full complexity of the sort of FDS CFD model we've been talking about, just because, you know, that's what I'm familiar with. 00:31:47.429 --> 00:31:56.596 <v Eric Mueller>But, example, in, again, in Missoula, in the Forest Service, I know they're working on sort of, you know, next generation operational fire spread models, and that's based on. 00:31:57.316 --> 00:32:03.236 <v Eric Mueller>Measurements of burning rates of, you know, different poorest structures at kind of that medium scale. 00:32:03.605 --> 00:32:07.435 <v Eric Mueller>So there's a lot that we can learn from these, you know, kind of engineering tests. 00:32:07.935 --> 00:32:18.711 <v Eric Mueller>The issue, or the, the caution I would give is, uh, kind of to the space in the middle of, let's say the cone scale, which again, I think there's a lot that we can learn, about flammability and things like that. 00:32:18.865 --> 00:32:20.486 <v Eric Mueller>particularly maybe in. 00:32:20.885 --> 00:32:25.144 <v Eric Mueller>Forest litter structures or you know, dead fuels like the pine needles we've been discussing. 00:32:25.364 --> 00:32:40.544 <v Eric Mueller>But the issue perhaps about applying some of that knowledge to the full range of complexity of structure we have is when you create this sample to put in the cone, how does that compare to the structure that you have in a real tree? 00:32:40.683 --> 00:32:45.743 <v Eric Mueller>You know, are you taking apart the needles and putting them in a basket or are you. 00:32:46.318 --> 00:32:55.038 <v Eric Mueller>putting a single branch and just kind of holding it in the cone and then is it really exposed to all the same heat flux and so can we apply the same methodology to understand the ignition of it? 00:32:55.038 --> 00:33:05.358 <v Eric Mueller>And so just the fact that we don't have these kind of nice plainer objects or nice, you know, geometric configurations that we have in construction materials, I think makes it. 00:33:06.165 --> 00:33:15.905 <v Eric Mueller>Not, uh, unuseful or unhelpful to apply these tools, but we just have to be cognizant of how we're applying the results that we get from 'em and how that compares to the real structure we find in a forest. 00:33:16.036 --> 00:33:20.095 <v Wojciech Wegrzynski>Yeah, that, that's what we've learned the hard way by trying to do the cone on, on the plants. 00:33:20.095 --> 00:33:27.575 <v Wojciech Wegrzynski>It, it just behaves a little, uh, a little different due to a lot of reasons that, that were already mentioned. 00:33:27.575 --> 00:33:36.117 <v Wojciech Wegrzynski>And I also know that in wildfire science, they're using this interesting, uh, holders that imitate the pity of the, of the fuel and load some air to go. 00:33:36.508 --> 00:33:37.577 <v Wojciech Wegrzynski>To go through that. 00:33:37.577 --> 00:33:52.704 <v Wojciech Wegrzynski>That's also very, an interesting concept, but also in, wildfire science, as you mentioned, the environmental conditions that are important from first the moisture content, but that I guess, that you could mimic with, with normal tools of build environment. 00:33:52.704 --> 00:33:59.505 <v Wojciech Wegrzynski>But the other, the, the wind is, is one thing that seems very fundamental and it is not very. 00:33:59.795 --> 00:34:00.529 <v Wojciech Wegrzynski>Important. 00:34:00.759 --> 00:34:02.769 <v Wojciech Wegrzynski>I mean, it is important in building fires. 00:34:02.769 --> 00:34:08.530 <v Wojciech Wegrzynski>Of course, that wind completely changes the, the, the compartment fire dynamics, and no one's questioning that. 00:34:08.530 --> 00:34:15.050 <v Wojciech Wegrzynski>But we just don't apply that during most of our, uh, object tests in, in, in for building environment. 00:34:15.219 --> 00:34:20.409 <v Wojciech Wegrzynski>Whereas in, in forest fire, it doesn't, it seems to not have, uh, much point to, to do. 00:34:20.875 --> 00:34:45.739 <v Wojciech Wegrzynski>No wind conditions because, uh, if wind is so, so impactful to the penetration of the fuel with the, the heat and, the ignition and everything, it, it seems, uh, paramount to have wind included in this large scale research that there's one complexity, but also the slope, as you mentioned this, the slope, uh, will also act, uh, because the way how the, the stuff will be ignited, that, that's well known. 00:34:45.739 --> 00:34:47.380 <v Wojciech Wegrzynski>That slopes are fundamental for that. 00:34:47.670 --> 00:34:56.099 <v Wojciech Wegrzynski>So, so I guess you also need a lot of outer research because I don't think you have a sloped full scale Winston yet to, to play with it. 00:34:56.230 --> 00:34:57.119 <v Eric Mueller>Yeah, not yet. 00:34:57.119 --> 00:34:57.840 <v Eric Mueller>That would be something. 00:34:57.840 --> 00:34:58.159 <v Eric Mueller>But 00:34:58.570 --> 00:34:59.090 <v Wojciech Wegrzynski>be something right. 00:34:59.280 --> 00:34:59.690 <v Eric Mueller>Yeah. 00:34:59.690 --> 00:35:04.489 <v Eric Mueller>I mean, at the end of the day, I think it's important to always try to connect to this larger scale. 00:35:05.085 --> 00:35:11.001 <v Eric Mueller>Understanding, and I've been fortunate in my own research to get to go out and do, you know, large scale tests in the forests. 00:35:11.001 --> 00:35:15.875 <v Eric Mueller>And I think you know yourself how challenging they can be, but how rewarding it can be as well. 00:35:15.875 --> 00:35:20.934 <v Eric Mueller>And you know, so we've had a lot of fun trying to pull these off, but they're good for what they're good for, right? 00:35:20.934 --> 00:35:34.369 <v Eric Mueller>You get, uh, you get conditions which are, let's say, more realistic, although in a wildfire, I'm not sure that we'll ever have a planned experiment that has the same, you know, intensity of Uncontained crown fire, let's say, but you're getting closer to, to real conditions. 00:35:34.802 --> 00:35:35.873 <v Eric Mueller>so that's, that's great. 00:35:35.873 --> 00:35:47.085 <v Eric Mueller>Your observations are becoming more relevant, but you're losing so much control, over the input variables and whether or not you can manipulate them in a way to get some findings that you can actually relate back to your models, let's say. 00:35:47.365 --> 00:35:48.445 <v Eric Mueller>So there's some difficulties. 00:35:49.300 --> 00:35:59.231 <v Wojciech Wegrzynski>I just had Rory in the podcast and he had this crazy idea of putting a, a piece of forest on a, on a scale and just measure the massless during this experince That that could, that that could actually work. 00:35:59.231 --> 00:35:59.951 <v Wojciech Wegrzynski>That could be funny. 00:36:00.347 --> 00:36:01.987 <v Wojciech Wegrzynski>please tell me more about the experiments. 00:36:01.987 --> 00:36:10.251 <v Wojciech Wegrzynski>I, I recall, uh, these, um, beautiful videos that you've shown from inside the forest fires in which you. 00:36:10.536 --> 00:36:19.476 <v Wojciech Wegrzynski>Not only observing the, the spread of a fire inside a forest, but also measuring the conditions, uh, at which this spread occurs. 00:36:19.826 --> 00:36:31.722 <v Wojciech Wegrzynski>Like what was learned from this experiment and how it relates, to these attempts to build, some sort of surrogate models that will help us understand the, the fires of of forests. 00:36:32.490 --> 00:36:39.610 <v Eric Mueller>probably what was learned, the most valuable finding was how difficult it is to do these experiments and, and how maybe we need to instrument them moving forward. 00:36:39.610 --> 00:36:43.170 <v Eric Mueller>And it is challenging because you have a field model, right? 00:36:43.170 --> 00:36:54.635 <v Eric Mueller>And so you want to, to have, let's say, field measurements of, temperature or, uh, Species concentration or heat fluxes, you wanna have point measurements all over the place and in the forest. 00:36:54.635 --> 00:37:04.635 <v Eric Mueller>It's just very difficult to get out there and, and lay out these instruments and have them operate successfully and even know exactly how the fire's going to spread once it's been ignited. 00:37:04.635 --> 00:37:06.755 <v Eric Mueller>And you know, the wind is just gonna do what it's gonna do. 00:37:07.295 --> 00:37:10.059 <v Eric Mueller>But I think the key was trying to. 00:37:10.655 --> 00:37:15.815 <v Eric Mueller>These larger scale observations, which are a little bit easier to make in, in such a big test. 00:37:15.905 --> 00:37:18.295 <v Eric Mueller>So just what is the spread rate of the fire? 00:37:18.295 --> 00:37:20.976 <v Eric Mueller>And you know, what maybe what does the fire contour look like? 00:37:21.306 --> 00:37:27.936 <v Eric Mueller>Uh, we had some nice remote sensing, some aerial imagery so we could look at, you know, the actual shape of the fire and the depth of the fire front and everything. 00:37:28.155 --> 00:37:29.135 <v Eric Mueller>And so these are nice. 00:37:29.467 --> 00:37:34.077 <v Eric Mueller>Kind of a macro scale comparisons that you can make if you then go do some modeling. 00:37:34.338 --> 00:37:46.038 <v Eric Mueller>But because our model is attempting to describe these things based on much more fundamental processes, we also want to have measurements of heat, fluxes of flow, really in and around the fire front. 00:37:46.038 --> 00:37:48.340 <v Eric Mueller>And so we tried to get at that, with these experiments. 00:37:48.340 --> 00:37:51.061 <v Eric Mueller>And yeah, it would be nice to do a lot more and get a 00:37:51.061 --> 00:37:51.141 <v Track 1>lot 00:37:51.141 --> 00:37:51.740 <v Eric Mueller>more measurements. 00:37:52.061 --> 00:37:54.840 <v Wojciech Wegrzynski>And, and how does a successful model look like? 00:37:54.840 --> 00:37:56.601 <v Wojciech Wegrzynski>Like what should it achieve? 00:37:57.210 --> 00:38:00.280 <v Wojciech Wegrzynski>Is it about predicting the, the spread rate? 00:38:00.451 --> 00:38:04.210 <v Wojciech Wegrzynski>Is it about predicting the size of the fire in terms of heat emitted? 00:38:04.740 --> 00:38:07.851 <v Wojciech Wegrzynski>Is it the model that predicts the amount of smoke produced? 00:38:07.880 --> 00:38:08.371 <v Wojciech Wegrzynski>I know. 00:38:08.371 --> 00:38:11.130 <v Wojciech Wegrzynski>Like how, how, when would you say that Okay. 00:38:11.130 --> 00:38:13.650 <v Wojciech Wegrzynski>My model is, is successful at, at, at doing. 00:38:14.181 --> 00:38:21.431 <v Eric Mueller>Yeah, I, I mean certainly it's application specific, but I think two big objectives are, are, as you mentioned, the spread rate is a big one. 00:38:21.715 --> 00:38:24.954 <v Eric Mueller>that tends to come more on the operational side of things. 00:38:24.954 --> 00:38:40.451 <v Eric Mueller>You know, if you're deploying firefighters to an actual fire and you wanna know where it's spreading and how quickly, and so, , it's still important for these detailed CFD models, but may, it may not even be the main parameter that you're interested in, in getting, is the spread rate, but I think it's important 00:38:40.635 --> 00:38:53.472 <v Wojciech Wegrzynski>But, uh, sorry, but the large scale of spread rate, like within the forest, how many meters per minute or whatever the, the, the unit is on a large scale, not necessarily just on a pine needle, how quickly a, a pine needle burns out, right? 00:38:53.762 --> 00:38:55.193 <v Wojciech Wegrzynski>So, so that, that spread rate, 00:38:55.297 --> 00:38:57.387 <v Eric Mueller>Yeah, yeah, and and certainly you want to try to. 00:38:58.188 --> 00:39:00.748 <v Eric Mueller>to get that spread rate, to be able to predict that accurately. 00:39:01.288 --> 00:39:04.628 <v Eric Mueller>But there's also a lot of complexity going on in the model. 00:39:04.628 --> 00:39:13.708 <v Eric Mueller>And so I think it's very easy in a way to achieve that spread rate, uh, for the wrong reasons or with the, you know, errors canceling out incorrect submodels. 00:39:13.847 --> 00:39:23.807 <v Eric Mueller>And so then I think the next step is if you're able to characterize it, which is difficult in the field, but getting that heat release rate or getting some metric of the energy release or the burning rate. 00:39:24.018 --> 00:39:25.248 <v Eric Mueller>So when we do this in the. 00:39:25.972 --> 00:39:40.103 <v Eric Mueller>. The other thing is, you know, if you put it on a load cell or whatever, or as Rory said, maybe you could put a forest on a load cell and you can get that burning rate, then that gives you a little bit more confidence that the spread rate you're getting is because you have at least the right energy release from the fire. 00:39:40.512 --> 00:39:46.422 <v Eric Mueller>Uh, and then of course, you can get into more details about are you getting the heat fluxes right, that are driving the spread rate and all of this. 00:39:47.016 --> 00:39:49.335 <v Eric Mueller>, you know, for the end goals, for the objectives we want to achieve. 00:39:49.565 --> 00:39:57.175 <v Eric Mueller>I think being able to supply that information about spread rate and about energy release, because then you can say something about the buoyancy and. 00:39:57.320 --> 00:40:15.519 <v Eric Mueller>predicting the smoke products somehow accurately from a combustion model would be nice, but we can at least approximate what they'll be from certain materials and then supply this energy release and an emissions factor to some larger scale model, let's say, and they can look at, you know, long range transport of the smoke. 00:40:15.519 --> 00:40:17.559 <v Eric Mueller>So I think being able to get that heat release. 00:40:18.429 --> 00:40:20.369 <v Wojciech Wegrzynski>And what's the end use of that? 00:40:20.380 --> 00:40:21.876 <v Wojciech Wegrzynski>Is pre partners? 00:40:21.876 --> 00:40:23.876 <v Wojciech Wegrzynski>Is it, uh, response. 00:40:24.327 --> 00:40:29.277 <v Eric Mueller>Uh, I mean for a, a very detailed kind of CFD model, I would say not for response. 00:40:29.277 --> 00:40:29.518 <v Eric Mueller>Yeah. 00:40:29.518 --> 00:40:31.358 <v Eric Mueller>Much more so for preparedness. 00:40:31.639 --> 00:40:44.480 <v Eric Mueller>We're trying to work a bit more with nist, with some fire managers and look at, uh, prescribed fires and help them when they go and plan how they're going to conduct a prescribed fire, where they're going to light the forest and what ignition pattern they're going to use. 00:40:45.050 --> 00:40:46.559 <v Eric Mueller>Um, those are the kinds of things that you have. 00:40:46.715 --> 00:40:49.355 <v Eric Mueller>Potentially a lot more time to study ahead of time. 00:40:49.355 --> 00:40:52.114 <v Eric Mueller>And you have these kind of idealized design scenarios. 00:40:52.114 --> 00:40:53.835 <v Eric Mueller>You know, what if I do this, what if I do this? 00:40:53.974 --> 00:41:02.074 <v Eric Mueller>And so you have the opportunity to actually run, you know, a more detailed model and you might need some more detail in your model to be able to understand. 00:41:03.025 --> 00:41:08.224 <v Eric Mueller>the interactions say of two fire lines, if you have two simultaneous ignitions, how do those come together? 00:41:08.594 --> 00:41:15.664 <v Eric Mueller>If you don't have enough detail on the interaction between the atmosphere and the buoyancy and the plume, then you're not gonna capture that. 00:41:15.715 --> 00:41:23.065 <v Eric Mueller>So we're trying to find some middle ground of, you know, capturing enough physics to give the sorts of answers that fire managers are looking for. 00:41:23.065 --> 00:41:27.221 <v Eric Mueller>But, you know, not requiring a research level project every time you want to get. 00:41:27.730 --> 00:41:29.219 <v Wojciech Wegrzynski>As a smoke control engineer. 00:41:29.219 --> 00:41:38.260 <v Wojciech Wegrzynski>I must ask you about, about smoker and we, we've just kept talking about, about fire and to what extent you are capable of, of modeling the the smoke. 00:41:38.389 --> 00:41:47.650 <v Wojciech Wegrzynski>Production in, in such fires and to what extent you're able to scale from your bench research to to, to drill fire forest fires. 00:41:47.873 --> 00:41:50.655 <v Eric Mueller>it's quite crude right now, or at least what's been done. 00:41:50.965 --> 00:41:54.860 <v Eric Mueller>I think the capability is there to improve this, so you can. 00:41:55.835 --> 00:42:00.780 <v Eric Mueller>Actually look at or try to solve for the conditions that you would have, in different parts of the fire. 00:42:00.780 --> 00:42:02.980 <v Eric Mueller>You can get some very deep flame fronts, let's say. 00:42:02.980 --> 00:42:11.539 <v Eric Mueller>And so you can have very different oxygen conditions and, uh, you can have a certain amount of fuel that's consumed in smoldering behind the flame front and so on. 00:42:11.539 --> 00:42:17.485 <v Eric Mueller>And so you know, some rough emissions factors that you can look at now that maybe will help you understand. 00:42:17.889 --> 00:42:22.610 <v Eric Mueller>how much, uh, of a certain product you're producing, uh, you know, under this condition or that condition. 00:42:22.610 --> 00:42:35.565 <v Eric Mueller>But if we can provide some greater detail, in terms of what is the actual oxygen concentration deep within this volume front, and for how long are the fuels exposed to that and under what heating conditions, then we can provide, uh, some more detail. 00:42:35.565 --> 00:42:39.846 <v Eric Mueller>But then we have to connect that back to the detailed chemistry, which for now we've. 00:42:40.315 --> 00:42:43.175 <v Eric Mueller>Put to the side just to, you know, focus on the flame spread. 00:42:43.175 --> 00:42:48.733 <v Eric Mueller>So I think it's a long term objective, but we still have some work to there to get a better prediction of actually what is produced. 00:42:49.353 --> 00:43:16.126 <v Wojciech Wegrzynski>That's a really interesting world of, of fire science, like one hand, you know, all these complexities that are related To the tiny scale of the parts of your fuel on the other end, the necessity to, to have a bulk representation of that to to make it useful, quick, reliable, robust, especially when you encounter like predictive modeling and you would like to give real time. 00:43:17.016 --> 00:43:18.775 <v Wojciech Wegrzynski>considerations to the firefighters on the front. 00:43:18.775 --> 00:43:24.775 <v Wojciech Wegrzynski>You cannot tell them, okay, now give me three weeks because my CFD must calculate it must be must be it. 00:43:24.775 --> 00:43:25.815 <v Wojciech Wegrzynski>It kills the the point. 00:43:25.826 --> 00:43:31.655 <v Wojciech Wegrzynski>Uh, so a very interesting set of challenges, uh, to overcome as we are. 00:43:31.675 --> 00:43:35.913 <v Wojciech Wegrzynski>Transition into more, let's say, sustainable, uh, world. 00:43:35.913 --> 00:43:40.179 <v Wojciech Wegrzynski>Or maybe we are just, more considerable about sustainability in the build environment. 00:43:40.769 --> 00:43:55.260 <v Wojciech Wegrzynski>I know from my own example that, uh, implementations of technologies including, uh, living, uh, walls, like greenwall systems, green roof systems, there's a huge rise of that, uh, amount of solutions. 00:43:55.985 --> 00:44:00.414 <v Wojciech Wegrzynski>Also with, uh, increasing, care about, wildfire Urban interface. 00:44:00.824 --> 00:44:12.413 <v Wojciech Wegrzynski>Uh, Areas more and more fire engineers are involved in some sort of design or, considerations related to the, the threats typical for, for such, uh, aures. 00:44:12.702 --> 00:44:37.206 <v Wojciech Wegrzynski>My prediction is that more and more fire engineers will have to deal With, uh, vegetation or living fuels, you who has crossed that path, uh, uh, what would be your advice for the fire engineer who's, uh, suddenly exposed to, to having to deal with, with life or, or vegetation, uh, fuel in, in their professional career for the first time? 00:44:38.110 --> 00:44:38.960 <v Eric Mueller>Good question. 00:44:39.385 --> 00:44:41.576 <v Eric Mueller>Uh, I mean, I think I would try to. 00:44:41.911 --> 00:44:52.231 <v Eric Mueller>, look at what's been done, perhaps more in the wild and urban interface context because it's at least a bit more mature of a field in some ways, perhaps than living walls, let's say. 00:44:52.405 --> 00:44:57.994 <v Eric Mueller>and there you can at least get some sense of, uh, what we understand about say vegetation flammability. 00:44:57.994 --> 00:45:00.835 <v Eric Mueller>And, you know, there's some good work going on to understand. 00:45:01.085 --> 00:45:11.166 <v Eric Mueller>rather than telling people we can't have any plants around their house in the weld and urban interface, maybe plants of this species will be more appropriate, less flammable than plants of another species. 00:45:11.226 --> 00:45:17.900 <v Eric Mueller>And so, trying to understand what are the kind of broad parameters that describe that plant that make it less flammable. 00:45:18.418 --> 00:45:20.277 <v Eric Mueller>that's perhaps a good starting place. 00:45:20.579 --> 00:45:23.519 <v Eric Mueller>and then, yeah, I think you just have to try. 00:45:24.003 --> 00:45:29.152 <v Eric Mueller>Be aware of the complexities that make these materials different from what you're used to encountering. 00:45:29.202 --> 00:45:31.512 <v Eric Mueller>So, you know, getting back to the porosity. 00:45:31.512 --> 00:45:37.833 <v Eric Mueller>And then unfortunately with living fuels like a green wall, it gets even more complex than kind of the dead fuels. 00:45:37.833 --> 00:45:38.592 <v Eric Mueller>We've talked a lot about. 00:45:39.322 --> 00:45:50.432 <v Eric Mueller>So far, , and there's, there's a lot that's just not known yet, I think, or, you know, we have a broad understanding of, of the complexity that's there, but maybe not a good description of the physics behind it. 00:45:50.733 --> 00:45:56.393 <v Eric Mueller>You know, we have observations of, uh, live fuels burning still with a lot of moisture. 00:45:56.393 --> 00:46:02.992 <v Eric Mueller>Content are still releasing a lot of moisture, which is not the way that we describe how dead fuels burn, at least in our models. 00:46:03.503 --> 00:46:03.853 <v Eric Mueller>we. 00:46:04.603 --> 00:46:12.402 <v Eric Mueller>, there's some studies showing that, uh, def flammability of live fuels can actually increase with moisture content over certain ranges. 00:46:12.402 --> 00:46:24.594 <v Eric Mueller>And so yeah, there's a lot of complexity there, which is a little bit outside of my wheelhouse, but, uh, I think we just have to be careful moving into the space to be aware of how different it can be from the materials that you're probably used to working with. 00:46:24.992 --> 00:46:29.440 <v Wojciech Wegrzynski>two things I've learned working with these green wall systems and, uh, vegetation fuels. 00:46:29.440 --> 00:46:38.480 <v Wojciech Wegrzynski>One thing is that the fact that at the beginning of your fire, the, the plants were very moist, does not guarantee you that they will not dry out during the fire. 00:46:38.480 --> 00:46:41.280 <v Wojciech Wegrzynski>And fires seem to be pretty decent that drying out. 00:46:41.289 --> 00:46:42.369 <v Wojciech Wegrzynski>Uh, Plan. 00:46:42.380 --> 00:46:46.170 <v Wojciech Wegrzynski>So if it goes for long enough, it's gonna be dry enough to ignite that. 00:46:46.170 --> 00:46:50.010 <v Wojciech Wegrzynski>That's one thing that we've learned and, and quite interesting, uh, to, to observe. 00:46:50.269 --> 00:46:53.739 <v Wojciech Wegrzynski>The second thing is, Ivy, the, the ivy plant. 00:46:53.789 --> 00:46:54.900 <v Wojciech Wegrzynski>It, it's ridiculous. 00:46:54.900 --> 00:46:56.460 <v Wojciech Wegrzynski>We cannot dry the damn thing. 00:46:56.590 --> 00:46:59.900 <v Wojciech Wegrzynski>It just refuses to drop its moisture content. 00:47:00.289 --> 00:47:01.699 <v Wojciech Wegrzynski>That's an amazing plant. 00:47:01.699 --> 00:47:06.539 <v Wojciech Wegrzynski>I, I was astonished like seeing other plants around on the wall being like dry. 00:47:06.800 --> 00:47:09.219 <v Wojciech Wegrzynski>You could crack them in your fingers and it's. 00:47:09.784 --> 00:47:12.114 <v Wojciech Wegrzynski>Damn thing refuses to die. 00:47:12.114 --> 00:47:13.155 <v Wojciech Wegrzynski>It's so resilient. 00:47:13.324 --> 00:47:15.235 <v Wojciech Wegrzynski>It, it's fascinating to observe that. 00:47:15.635 --> 00:47:17.474 <v Wojciech Wegrzynski>Probably more fascinating for us than for the Ivy. 00:47:17.534 --> 00:47:25.474 <v Wojciech Wegrzynski>But, uh, but, uh, yeah, it's, it's, it's, it's, it's, certainly an interesting world that, uh, I was maybe not very ready, uh, for 00:47:25.590 --> 00:47:36.710 <v Eric Mueller>Yeah, and I think like that's where a lot of this complexity comes in then with the live plants is it's no longer just wood, let's say chopped up and rearranged into different interesting structures and, and now the actual. 00:47:37.126 --> 00:47:50.090 <v Eric Mueller>Plant physiology and morphology comes into play and does it have something like a waxy layer, like, know, certain plants have to really encapsulate that moisture and then that can affect how it actually then releases the moisture when exposed to a high heat flux. 00:47:50.090 --> 00:47:53.679 <v Eric Mueller>And so things get fastly more complicated pretty quickly. 00:47:54.677 --> 00:48:05.025 <v Wojciech Wegrzynski>and we didn't, didn't even go into like fire brands production and, what happens in, in, in, in the complex fields where you mix different sorts of like, Plants. 00:48:05.025 --> 00:48:07.706 <v Wojciech Wegrzynski>You have bush layer, you have crown layer. 00:48:08.005 --> 00:48:11.780 <v Wojciech Wegrzynski>The, Interplay between the, the, the scales of the first fire. 00:48:11.911 --> 00:48:14.661 <v Wojciech Wegrzynski>So there is so much more to unravel here. 00:48:15.090 --> 00:48:18.740 <v Wojciech Wegrzynski>Eric, thank you very much for this in insightful talk. 00:48:18.771 --> 00:48:31.661 <v Wojciech Wegrzynski>I think for anyone who would have to deal with, vegetation fires or living fuels, I think it was very interesting to learn about some sort of complexities that, uh, I don't think I would cons. 00:48:31.661 --> 00:48:35.101 <v Wojciech Wegrzynski>I know I did not consider when dealing with my building fires. 00:48:35.456 --> 00:48:42.043 <v Wojciech Wegrzynski>I've just learned them really recently exposed to this, uh, new, fascinating, and, and difficult world. 00:48:42.510 --> 00:48:43.510 <v Wojciech Wegrzynski>thank you so much. 00:48:43.530 --> 00:48:48.949 <v Wojciech Wegrzynski>I'm gonna link, uh, your IAFSS paper and, uh, and the video. 00:48:49.519 --> 00:48:53.625 <v Wojciech Wegrzynski>It was the award for, for the best thesis, uh, by the F Ss. 00:48:53.625 --> 00:48:54.905 <v Wojciech Wegrzynski>So congratulations on that. 00:48:54.905 --> 00:48:57.625 <v Wojciech Wegrzynski>That's, uh, that's actually quite a big achievement. 00:48:57.625 --> 00:49:01.864 <v Wojciech Wegrzynski>So that's a, that's a statement to the quality of the work that you, you have been doing. 00:49:02.420 --> 00:49:10.867 <v Wojciech Wegrzynski>If someone would like to, to take a next step and just go, go and read something immediately, what would be the first thing that comes to your mind? 00:49:10.867 --> 00:49:14.387 <v Wojciech Wegrzynski>Someone should go and, and see, uh, after this. 00:49:14.978 --> 00:49:16.987 <v Eric Mueller>well, actually, I was just looking at. 00:49:17.481 --> 00:49:27.934 <v Eric Mueller>Wildland Fire Behavior is a textbook, uh, that came out not so long ago from Missoula, from the US Forest Service, uh, mark Finney, Sarah McAllister, Tobin Grump Trump, and Jason Forer. 00:49:28.355 --> 00:49:42.481 <v Eric Mueller>And if you're interested in kind getting into the space of these different fuels and understanding what's important, I think that's a really nice textbook that kind of gives an overview, uh, of a lot of the topics that we've been covering and probably in much , greater detail or 00:49:43.101 --> 00:49:48.411 <v Wojciech Wegrzynski>Ah, you cannot fit much into one hour podcast episode, but it's a good starting point for everyone. 00:49:48.561 --> 00:49:57.880 <v Wojciech Wegrzynski>I'll link to that, book, and maybe you'll find, we'll find together some more resources to sharing the show notes, so, so people know where to, where to go to. 00:49:58.536 --> 00:49:58.956 <v Eric Mueller>Yep. 00:49:59.360 --> 00:50:06.130 <v Wojciech Wegrzynski>Eric, thank you very much for coming all the best in your developments of surrogate fuel models for fds. 00:50:06.130 --> 00:50:10.610 <v Wojciech Wegrzynski>I, I actually, I, I would love to have a really good fuel model within fds. 00:50:10.610 --> 00:50:13.731 <v Wojciech Wegrzynski>I, I, I think the whole community would, uh, benefit from that. 00:50:13.731 --> 00:50:18.204 <v Wojciech Wegrzynski>So I'm looking forward to your achievements at NIST all the best, and, and thank you 00:50:18.324 --> 00:50:18.864 <v Eric Mueller>All right. 00:50:18.864 --> 00:50:19.224 <v Eric Mueller>Thanks. 00:50:19.224 --> 00:50:20.664 <v Eric Mueller>Thanks so much for having me. 00:50:20.945 --> 00:50:21.715 <v Wojciech Wegrzynski>Cheers, man. 00:50:22.666 --> 00:50:23.237 <v Wojciech Węgrzyński>And that's it. 00:50:23.327 --> 00:50:24.407 <v Wojciech Węgrzyński>I told you was going to be good. 00:50:24.436 --> 00:50:33.527 <v Wojciech Węgrzyński>And I got access to all my questions, which makes me very happy and actually helped us proceed with our research for which I'm very thankful to Eric. 00:50:34.007 --> 00:50:36.527 <v Wojciech Węgrzyński>After finalizing the recording. 00:50:36.626 --> 00:50:43.077 <v Wojciech Węgrzyński>, Eric contacted me as he was reflecting on our discussion, uh, related to the grid size and porous media. 00:50:43.106 --> 00:50:44.367 <v Wojciech Węgrzyński>You know, the one that's on the. 00:50:44.489 --> 00:50:45.949 <v Wojciech Węgrzyński>Cover of the podcast all then. 00:50:45.978 --> 00:50:50.599 <v Wojciech Węgrzyński>And he said that that there's one more concept that, that needs to be clarified. 00:50:50.777 --> 00:50:58.036 <v Wojciech Węgrzyński>So if all vegetation that is contained within a numerical cell and it is increased in size. 00:50:58.302 --> 00:51:03.222 <v Wojciech Węgrzyński>In fact, the porosity must go up because we need to conserve mass in that cell. 00:51:03.351 --> 00:51:06.581 <v Wojciech Węgrzyński>But if instead we, we split the cell in half,. 00:51:06.862 --> 00:51:09.771 <v Wojciech Węgrzyński>We would have half the volume and health mass in each cell. 00:51:09.981 --> 00:51:11.782 <v Wojciech Węgrzyński>So porosity would not be changed. 00:51:12.172 --> 00:51:24.021 <v Wojciech Węgrzyński>So when we have many cells across a piece of vegetation, generally we can make small, moderate adjustments to their size and conserve porosity, which from Eric's point is, is. 00:51:24.442 --> 00:51:24.981 <v Wojciech Węgrzyński>Variable. 00:51:25.431 --> 00:51:30.621 <v Wojciech Węgrzyński>So in the end, the grid sensitivity, maybe we have little overstated. 00:51:30.831 --> 00:51:35.844 <v Wojciech Węgrzyński>That and, It can be used to play with the models and conserving the things that matter. 00:51:36.175 --> 00:51:38.184 <v Wojciech Węgrzyński>So that's additional clarification. 00:51:38.545 --> 00:51:42.114 <v Wojciech Węgrzyński>From Eric, I think an important one and I hope useful one. 00:51:42.684 --> 00:51:45.025 <v Wojciech Węgrzyński>Um, back to the episode itself. 00:51:45.054 --> 00:51:47.905 <v Wojciech Węgrzyński>I hope you got something interesting from it. 00:51:47.905 --> 00:51:50.034 <v Wojciech Węgrzyński>I was absolutely shocked to learn. 00:51:50.394 --> 00:51:51.324 <v Wojciech Węgrzyński>Well, maybe not shocked. 00:51:51.324 --> 00:51:53.094 <v Wojciech Węgrzyński>I was surprised by my ignorance. 00:51:53.454 --> 00:51:53.815 <v Wojciech Węgrzyński>The hats. 00:51:54.144 --> 00:51:59.695 <v Wojciech Węgrzyński>Uh, the convective cooling makes such a big difference in living fuel fires. 00:51:59.695 --> 00:52:01.644 <v Wojciech Węgrzyński>And I mean, they tell you that. 00:52:01.885 --> 00:52:12.144 <v Wojciech Węgrzyński>The you take it as granted, but only when you see this samples not igniting from really large heat fluxes imposed on them. 00:52:12.144 --> 00:52:13.614 <v Wojciech Węgrzyński>You start to realize, wow, this, this. 00:52:13.644 --> 00:52:14.605 <v Wojciech Węgrzyński>This is really. 00:52:14.742 --> 00:52:19.302 <v Wojciech Węgrzyński>Impactful on the fire behavioral of the, of the whole system. 00:52:19.811 --> 00:52:22.512 <v Wojciech Węgrzyński>So definitely a biggest learning for me. 00:52:22.992 --> 00:52:25.692 <v Wojciech Węgrzyński>And I hope you also got some learnings in here. 00:52:26.202 --> 00:52:26.711 <v Wojciech Węgrzyński>No. 00:52:26.932 --> 00:52:28.972 <v Wojciech Węgrzyński>That'll be it for today's episode. 00:52:28.972 --> 00:52:31.643 <v Wojciech Węgrzyński>I guess I should go back to my IAFSS submission. 00:52:31.672 --> 00:52:36.833 <v Wojciech Węgrzyński>Now, after this episode, I'm even more pumped up to get a good IAFSS is paper. 00:52:36.893 --> 00:52:38.693 <v Wojciech Węgrzyński>This conferences are just amazing. 00:52:38.693 --> 00:52:41.032 <v Wojciech Węgrzyński>And yeah, that's the home for fire science. 00:52:41.032 --> 00:52:42.862 <v Wojciech Węgrzyński>So I guess that's a good place for me to be. 00:52:43.005 --> 00:52:44.286 <v Wojciech Węgrzyński>So thanks once again. 00:52:44.376 --> 00:52:48.365 <v Wojciech Węgrzyński>See you here next Wednesday and hopefully see you in Japan. 00:52:48.365 --> 00:52:49.596 <v Wojciech Węgrzyński>Tsukuba in October. 00:52:49.626 --> 00:52:50.436 <v Wojciech Węgrzyński>It's going to be great. 00:52:50.576 --> 00:52:50.905 <v Wojciech Węgrzyński>Cheers. 00:52:50.936 --> 00:52:51.295 <v Wojciech Węgrzyński>Bye.

088 - Modeling fires of natural fuels with Eric Mueller

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