 I want to welcome you to today's celebration of faculty careers. And just to give you a little bit of background as to why we're doing these seminars, it's because the celebration of faculty careers was basically derived from two actions of the strategic plan within the College of Engineering. One was the faculty of 2020. And it focused on professional development at all stages and the alignment of criteria and processes for hiring and the promotion and tenure with the evolving scope of the college and leadership values. So there was a desire for review post-promotion to the rank of full professor that would feature the accomplishments, I should say, of faculty and provide an opportunity for a plan for the next phase of the faculty member's career. Basically, full professors at least seven years, not several years, but seven years, past promotion are basically asked to present a colloquia on their achievements and plans to their peers. And this is followed by a planning discussion with the dean and also the heads. This was piloted successfully in spring of 2013 with full implementation in the 2013-2014 academic year. So now I'd like to briefly introduce today's speaker. It is Professor Isam Moudawa. He joined Purdue University in 1984. And this was immediately after receiving his PhD in mechanical engineering with a minor in management from MIT. At Purdue, he founded the Boiler or the Boiling and Two-Face Flow Laboratory, BTPFL, and the Purdue University International Electronic Cooling Alliance, the PUIECA. He is also founder and president of Moudawa Thermosystems, Incorporated. He's a pretty busy person. This is a company that's based in the Purdue Research Park. And how many of you remember Paul Harvey? Do you remember Paul Harvey, the commentator? Following the expression from Paul Harvey, the rest of the story, I will ask Professor Moudawa to please share with us at this moment. Thank you. Thank you very much. I'd like to thank everybody for joining us today. My goal with this presentation is to make it as informative as possible. And at the very end, just share some of my personal experiences about my 32 years here at Purdue with some points of criticism, I guess, to the system that we have here. I think that's part of what we're doing with these colloquial. So I'm going to be talking about breakthroughs and two-phase theory and applications. I'm going to start by looking at the different applications where boiling heat transfer is very crucial today. You find that many of the advancements in all sorts of applications are becoming increasingly dependent on our ability to dissipate very large amount of heat from tiny little areas. This is far away from the conventional mode of dissipating heat using standard heat exchangers and air cooling. So as a designer, you're given the opportunity to look at the different cooling modes that are possible, natural convection using fans, for example, force convection. And you quickly find out that boiling is, in many cases, the only mode available to really tackle the heat dissipation from many of these applications. Now, how does that work? I'm showing it here with the A8. This is actually a demo that I show in class. You're seeing boiling on a wire. There is about a third of a millimeter in diameter. And this is really the mode that we're after. An abundance of bubbles formed at preferred nucleation sites along the surface. Bubbles growing and quickly being removed by buoyancy and replaced by liquid at very high frequency, which is really responsible for a lot of the high heat fluxes that we get in this regime. However, you have to be mindful of limitations, particularly critical heat flux, probably one of the most important parameters in these applications, where if you overdo it with respect to the amount of vapor being produced, you suddenly blanket the entire surface with vapor, preventing liquid from coming back and replacing the vapor that has been produced. What is the net effect? It's a large increase in surface temperature. It's a very dangerous phenomenon. So you have to keep your operating conditions a certain percentage below this critical heat flux. Now, in terms of the advantages of boiling, why boiling is so important? You could see them here with respect to a very simple application. This is an old device we had from IBM. We have a plot of heat flux versus temperature difference between the surface and the coolant. And the orange area that you see here is where you expect operation to take place. You want to dissipate heat fluxes up to 50 watts per square centimeters, but the device surface cannot exceed 85 degrees centigrade. And you could see with forced air convection, you're never going to be able to do it. With natural liquid convection, without phase change, again, you find that by the time you hit the 50 watts, you're going to reach 500 degrees. So if you are able to find a fluid with a boiling point, say, about 30 degrees below the maximum temperature, you see this large change in slope taking place right here. And what that does is allow you to maintain the surface temperature below 70 at the maximum flux, significantly less than the 525. Not only that, there is another advantage, and that is the slope itself. In many of these devices, you have fluctuations in power, and you're always concerned about the temperature changes that take place because that's going to delaminate, cause cracking, cause stresses. So with boiling, what you're doing is allowing those fluctuations to take place, corresponding to very small changes in surface temperature. These are the two main advantages with respect to boiling. Now, boiling configurations, there is a lot of versatility when you look at the different boiling configurations. We were fortunate back in 84 to have IBM and 3M support our experimental program related to high flux cooling. And by the way, a lot of the facilities that you're going to see here are custom crafted by students. They're not purchased. So a lot of the work involved detailed design, detailed instrumentation to bring it up to operational level. The simplest configuration is the thermo siphon that you see right here, where at that time the thought was to submerge all the electronics of a main frame in a pool of dielectric liquid. Heat is dissipated by forming bubbles, which rise by buoyancy. They're recondensed by a water cooled condenser. Within the system itself, there is no pump. It's passively driven, and that's a major advantage, obviously, from a cost and reliability standpoint. Now, when thermo siphons don't work, you start utilizing convection as a motor-enhanced heat transfer. And what you're doing here is supplying the fluid at a certain velocity parallel to the device surface to take advantage of motion. And the higher the velocity, the better the heat transfer, obviously. And one special case of force convection boiling is mini and microchannels. They are extremely popular right now in many, many industries. What they do is allow you to reduce the amount of coolant that is required, greatly increase the heat transfer coefficient, but they have their own limitations as well. I'm going to talk about that later on. We're talking here about for mini channels about 2 millimeters, microchannels typically anything less than half a millimeter in hydraulic diameter. And when that doesn't work effectively, you resort to jet impingement cooling where you are bombarding the surface with a liquid jet. And again, the higher the velocity, the better heat transfer you get. A competitor to jet impingement cooling is spray cooling, which is what you see here. What you're doing differently is breaking the liquid into tiny little droplets before they hit the surface. And what you're doing effectively is increasing the surface area to volume ratio of droplets, which is very advantageous for heat transfer. There are also specialized configurations for boiling, such as boiling in curved channels. Also, you can take advantage of curvature. Here you have a heated concave wall. And what you're doing is supplying the liquid with curvature, producing a centrifugal force, which would pull vapor inward and push liquid outward, which is exactly what you need to do. And with the higher centrifugal force, you get even better performance. Or you can do the same thing with rotation by spinning liquid at a certain rotational speed and achieving the same centrifugal effect. And what is nice about this is, again, there is no limit to how far you can enhance your heat transfer. If you rotate at 600 RPM versus 100, you're going to get much, much better heat transfer. So all of these were tested in our lab as means to enhance boiling heat transfer. Now, in terms of the specific applications, I'm just going to quickly go through those. We have looked into several applications we call the ultra-high flux applications. And here we're talking about 10,000 watts per square centimeters and above. These are typically encountered in fusion reactors, particle accelerators, MSD electrode walls. And we have developed a special high pressure facility here for this purpose. Takes us up to the critical point for water. And at the heart of the facility is the apparatus you see right here where you supply 700 amps up to 700 amps through a tiny little tube. That's where the flow is taking place. And you crank up the power until the tube burns. You get the critical heat flux phenomenon I talked about earlier. And this gave us a record, still a record, for critical heat flux into 27,000 watts per square centimeter. That's 270 light bulbs, by the way, if you want to get a feel for that with a dissipating heat out of an area have the size of a postage stand. Another area we have worked on particularly in the 90s was Avionics. This is the electronics for both commercial and military aircraft. And in most applications, what you're doing is cooling the electronic using the Avionics enclosure or Avionics box, a rectangular box like what you see here. And the circuit ports are slid into it. And air is used to cool it. Now, these modules, typically, they are standardized. They are about this size. You can put it in the palm of your hand. They dissipate only about 40 watts because of a lot of limitations in terms of flow rates and pressure drops, whatever. Now, with phase change, we quickly changed that. We did work in the 90s where we use microchannels and were able to boost that to 3 kilowatts and then was jet to pitchment to 12 kilowatt. And there are a lot of intricate features. There is a lot of design work more than heat transfer work within these modules. And you're talking about orders of magneton enhancement just by means of utilizing phase change. We also looked at curved channels in conjunction with rocket nozzles. We looked at turbine blade cooling also. And at Zucco Lab, we did recent work related to high Mach turbine engines. This is where you have compressors producing air at such a high temperature that they are no longer providing air that can be used for cooling in downstream parts of the engine. So the cooling air has to be cooled itself. And the way you do it is by using specialized heat exchangers that suck the heat out of the compressor air and send it to the fuel, the cold fuel that is available on the aircraft. And we developed a cooling module that you see right here, very compact cooling module where the fuel passes through the inside and air on the outside in cross flow. And you can package those modules in whatever configuration you want to get a three dimensional heat exchanger package. We also did a lot of work related to high power lasers, radar, microwave systems using phase change as well. At Zucco, we also did work related to hydrogen storage fuel cell systems. Here we're talking about storing hydrogen in high pressure metal hydride. You supply the hydrogen and store it by reaction with the high pressure metal hydride. The problem with this is that you produce enormous amount of heat over a very short period of time. And we developed three different heat exchanger designs for this purpose, highly optimized thermally. And here you have one of them. You can see the shape where the heat is optimized so that you fill the cavity with the hydride. And these are the cooling ports on the inside. And by the way, these are very unique types of heat exchanger because they are transient heat exchanger. They are operating over a few minutes. That's it. That's where you get this enormous heat dissipation. It's very different from conventional heat exchanger working on a steady state basis. And these are two different designs, other designs, coil type heat exchanger, and these disc-shaped micro-channel heat exchangers are stacked to store the hydride. Another area of interest has been hybrid vehicle power electronics. This is work we did actually at my company, not at Purdue, was NREL in Colorado. And again, the idea is to control the temperatures in these applications. And these are the variety of instruments. Actually, they were all built in the research park, and they make up the thermal lab right now at NREL. And by the way, the engineers who built this are all ME students, former ME students. Now, one important application I always like to highlight is materials processing. How boiling is also important in materials processing. I'm using aluminum as an example, but you can apply it for steel, for any other alloy. The idea here is summarized in this plot, where you take your metal alloy sample, preheat it to a temperature close to the melting point. And then what you want to do is quickly quench it down to room temperature. But ideally, freeze the microstructure that you had before so that you can reheat it in subsequent process in order to produce this behavior. You have hardening solutes dispersed evenly throughout the crystals. Now, that requires very careful manipulation of the quenching process and the aging process. If you don't do the quenching properly, it's going to be a total mess. It's a useless alloy. Now, I'm borrowing the same pictures from before to show you how in what we have here is temperature versus time, what happens as the quench proceeds. And what happens typically in most operations, I've actually designed a lot of aluminum plants, heat treating plants. And what you see in many cases is how they bring a lot of parts, different shapes and sizes, and throw them in a basket and put them in a bath. There is absolutely no control over the cooling process. You get distortions, cracking. And they live with that sometimes. Or they throw away the parts that are deformed more and they keep the good ones. And this is really the type of shape that you get. This is about two feet in length. And you can see an H shape completely distorted as a result of poor cooling. So what we're doing is replacing this, what we call bath quenching with far more effective spray quenching, not only to speed up the quenching process, but also to achieve control, as I'm going to show you. And we built a test bed for this purpose, where we have a furnace and we bring the part after being heat treated and quench it within this chamber that you see right here. And what we were able to do is combine our understanding of the quenching process with metallurgical transformation theory in order to optimize the impact of the quench on the material properties, namely hardness and strength of the part. So by this optimization process and changing spray boundary conditions all around the quench part, we are able to do two things. Achieve very high strength and very high hardness and also achieve uniform properties without distortion. And you can do that by prediction. You don't have to run experiments by trial in order to achieve this result. Ideally, and that's something I've been trying to promote and I'm talking to different people to do it, is to do all of this robotically by having robots lined up to quench the part from all directions based on predictions from a CAD system. Now, another area I want to talk about which is really the primary focus for us at the present time is flow boiling and conversation for future space missions. This is a NASA funded effort. And I just want to mention that in 2011, a report came out from the National Research Council on Future Space Exploration and presented to the Congress and with recommendation from a combination of national academies, science, engineering, et cetera, regarding space exploration, what fields of knowledge are needed to achieve the goals NASA has set forth. And when you look through the report, it's a very thick report, but section after section, you feel repeated mention of phase change as a primary area of research. Why? Because with phase change, you get better heat transfer. It was better heat transfer, you have smaller area devices, more compact, lightweight, which is ideal for space applications. And here are some examples where phase change becomes really important. High power, space mission, long duration space missions would require fishery actors. Recently, Project Prometheus talked about using also a reactor with liquid metal boiling and condensation. A more immediate application is thermal control systems, TCS, and we're really heavily involved in this. This is what is required to control temperature and humidity on board the space vehicle for the comfort of both electronics and crew. Very, very important. Another area is vapor compression heat pump for planetary bases. This year, there was an announcement from the government that NASA should refocus on planetary habitat, and temperature control is achieved at a level of about 40 kilowatts now with Martian habitat with systems like ones you see right here. So in our research, we looked at the various applications and we found that you're not just focusing on microgravity. We obviously know a lot about the 1G applications, Earth gravity, but there are a lot of gravitational fields in between that we have to understand. It's between zero and 1G. We have to understand that entire spectrum, 10G will be formality aircraft. That's a different application altogether. So around 2004, we did our first study related to microgravity phase change. We built a flight rig for flow boiling in microgravity. This was flown on a couple of occasions using K3-135 aircraft and NASA Glenn. And it produced, this is a plot NASA uses quite a bit from our data. It produces plot of critical heat flux as a function of fluid velocity and showed how at very low velocities, you've got to be really careful about the effect of reduced gravity on critical heat flux. You really compromise cooling tremendously compared to 1G. However, it also shows that at certain velocities, the inertia can completely overcome the down effects of microgravity. And this is very important because it tells you you would rather operate at this condition right here. You don't have to operate at much higher velocities because you're losing energy, okay, power dissipation here in the pumps. So this conversion value is extremely important. And nowadays, since 2012, we received a contract to develop the flow boiling and condensation experiment FBCE for the International Space Station. Two months ago, this was announced to be a very high priority project for NASA now. And we have literally over 50 scientists and engineers from NASA Glenn supporting this project. So it's growing and it keeps growing. And the idea behind it is to develop a very complicated flow loop loaded with instrumentation and high speed video to investigate both flow boiling and condensation using three test modules that you see right here. And we quickly developed a test rig, flight test rig for condensation because we had not done any work in this and nobody has done this type of work before. And this test rig, we build it here at Purdue, has two flow channels, as you see, it's loaded with instrumentation, pressure, temperature, high speed cameras everywhere, and it requires six operators dealing with various aspect of the experiment. And we flew that on couple of occasions using zero gravity aircraft. We had several students actually participate in this effort. And what we're at right now is really shifting attention to the integration into what's called the fluid integrated rack. This is a replica of the system available on the ISS. This is the largest syrup available to run fluid experiments. And we're trying to package all our hardware in an area in a space about one meter by one meter but maybe about less than one meter depth. Okay, all this instrumentation has to be converged. So we're due to transport the hardware for this application in two SpaceX flights, hopefully tentatively, this is what's scheduled right now because there's a lot of hardware involved over the next few years. Now, I wanna shift the attention to talk about predictive methods, talk about the theory a little bit. This is probably a very important chart in the sense that it summarizes what people have done over the years in regards to predictive methods in boiling and two phase flow. Now, ideally you wanna have convenient computational tools to do that, but you find that these are not very effective at the present, depending on the tool that you use, you get different results all the time. But it's very important because that's gonna be the next step in a lot of the predictive approaches that we're gonna use. Theoretical models, very few of those exist in the two phase literature. Next, semi-empirical models meaning models based on theory, on mechanism, but they lack closure and that's where you fit the model with empirical constants. The next step is universal correlations. These are correlations that are developed based on enormous databases for many fluids, many geometrical parameters, many operating conditions to give confidence in the predictions. Then you have not arranged experimental correlations. This is where if you look at the two phase literature, you find a vast majority of literature focused on this approach right here. Okay, and this is very dangerous because what you're doing is obtaining 10 data points for one fluid and one geometry and saying I've got a correlation to predict the flow. And I'm gonna show you why this is very dangerous in a minute. And then replication is used by some companies, just by testing a particular device at a particular condition. If it works, it works. We're happy with it. Now our approach is to use those first four. We have been using those three and now we're just beginning to converge on computational methods. Now, just to show you why it's very complicated to model two phase flow accurately. I picked the simplest geometry by far in two phase flow, which is slow boiling in a tube, circular tube. Now, to be able to predict heat transfer behavior in a situation like this, you have to know many different things. Heat transfer regimes, regime boundaries, pressure drop components, heat transfer coefficients, the limits of dry out, for example. Also, you have to appreciate the flow constraints. For example, you can have a lot of compressibility. You can have a lot of flashing due to latent heat effects. You can have two phase choking. You also have a lot of potential instabilities taking place in two phase systems. So you have to be mindful about those. And ultimately, you may hit critical heat flux and reach burnout before you know it. So you have to really be concerned about all these aspects simultaneously, which is why to do a good job with those predictions, you break it down very, very carefully and make sure that every component is handled properly. And these are some example of those. The most critical components are the ones where there is both vapor and liquid, obviously. And this is also important, because it explains why it's really vital to have what I call universal correlations. If you compare for one phase flow, a very simple correlation for heat transfer coefficient as a function of Reynolds and parental number, you find that you have three dimensionless parameters, two independent parameters, with fairly broad ranges for both. And this is a very powerful correlation and very easy to use. If you look at the counterpart, for example, a flow boiling critical heat flux in a pipe, you find that you have a dimensionless group that may be a function of as many as nine or 10 dimensionless groups. And each one of those is confined within limitations imposed by the experiments. And because these experiments are very expensive, it means those are all narrow ranges. So it's very, very difficult to achieve universal correlations. You have to be very patient. I worked very hard to get that kind of formulation. Now, we knew that for a long time and we tried to go in that direction. So back, that was in 1999, we were able to consolidate the water databases. This is for nuclear reactors. Went back and obtained literally every data point you can find anywhere. And it took us about five years of search with the library help to put it together and develop universal correlations, but they were still for water alone. And then we started doing it for mini and micro channels because that's a technology that is very important nowadays. And in the last three years, we developed a series of studies of truly universal heat transfer correlations for small channels, for heat transfer coefficients, for pressure drops, for condensation, for adiabatic flow, and for dry out. And you could see how we did that. It's large databases obtained for all the possible fluid we found in the literature, broad ranges of operating diameters and pressures up to close to the critical. And people have started using those correlations and they're extremely accurate because of the universal appeal. We also have been doing a lot of theoretical modeling in the form of proper use of conservation laws for two phase flow, such as year flow boiling, critical heat flux, theoretical model for critical heat flux, which as I said is the most critical point for boiling. And we are able finally to come out with very accurate predictions for, particularly for microgravity because we're very interested in this for the application of future space flights. Now, another application is condensation, which is flip side of boiling. Here what you're doing is rejecting the heat by condensing the vapor back to liquid. The liquid flows on the inside of a tube along the wall surrounding a vapor core, but the flow, even though it's separated, is very complicated. One of the complications is what happens at the interface. We found that there is significant dampening of turbulence taking place at the interface because of surface tension, which is something you don't encounter in other types of flows. So we had to model this effect very carefully. We also did LDV measurements of flow and turbulence within a liquid film. We did that extensively. Then we built several facilities related to condensation at different orientations relative to gravity. And the goal was to try to identify the flow mechanisms, particularly the waveness that takes place along the interface, which you see here changing drastically at Lorentz numbers versus high Reynolds numbers. We did the same for many channels and microchannels. And also we developed control volume models for condensation, which combines with the added diffusivity profile. I just mentioned we are finally able to make good predictions for condensation in microgravity. So NASA is actually using those right now for space applications. Now, we also did the same thing for falling films involving evaporation of liquid films. With specialized probes, there are capable to simultaneously measure film thickness, velocity of the waves, and temperature profile within a liquid film all at the same time. And also very recently, we started looking at what happens around wavy interfaces of liquid films, which is what's shown right here. And so looking also at research park activities, I was mentioned earlier, I wanted to mention this for you. What it is to start a company at the research park to me, it was very important because it's a unique opportunity to develop design products, actual products, something we cannot do at the university. And as I said earlier, all the present and former employees are Purdue grads because you need the, particularly Purdue ME students because you need that kind of expertise. And the mission statement is to provide solutions to temperature control and thermal management needs for which no commercial remedies are presently available in a nutshell. And we have received over the years aside from many industry contracts, six phase one and four phase two SBIR projects. I don't know if you know about phase one versus phase one is like they give you up to $150,000 to get started. Phase two, they give you a million dollars to go beyond and do the verification. And you can see here the variety of products produced and testing capabilities. And these are some examples of the different projects, CAD based predictive tools for two phase systems, grand mobile radio, thermal management, boosting the capability for that, Avionics and ultra high heat flux devices for extreme heat dissipation. Now, I'm almost done by the way. Teaching, I have just a few concluding slides here. Over the years, I taught these courses that you see here and the ones that are marked and read are the ones that I spend a lot of time on and a lot of energy over the years. A heat and mass transfer, the undergraduate 315, senior design and my two phase course, graduate course. Now, one of the things I always like to do is introduce lab experiments, introduce the lab to the classroom by running experiments in the classroom, particularly in this room by the way, for my ME506. I find it to be extremely useful, particularly for complicated phenomena where you can't just sketch it on a piece of paper, you have to run the experiment live. And it's been very rewarding to do so. If you look at our ME315 lab, we overhauled the lab so that now what we have is two different components, one of them is structured experiments to help the students appreciate fundamentals and also a design project where they build a device, instrument it, model it and show the performance and then compare it to predictions. And I should mention, by the way, that this format is very popular worldwide. We're constantly asked by other universities from the US and overseas how to duplicate this format. Now, fortunately, we have a huge investment in it, particularly in the form of a lot of TAs manning the effort. But we are very proud of this particular effort. Senior design, I've been involved in every stage of this course, starting with the mid-80s, where it was the worst course on earth. It was an utterly useless course, it's like homework assignments, we call them senior design, literally. So it changed over the years and in the late 90s, I decided to turn it to a prototyping course. And I called it the thermal design innovation initiative because I was demanding particularly thermal project for that purpose. The focus was on invention. The students had to use analysis everywhere. They can't just invent randomly, they had to really use their tools that they've learned in ME. And also the deliverables included oral presentations, reports, and a prototype, and they can't fail. I warned them, if you fail at the end, you're not gonna get a grade. I lied a little bit. Now, here's a point of criticism here. Despite persistent news about Purdue's emphasis on teaching, virtually no support was received for innovations in teaching, especially during this period. Now, Anil is sitting here, he should be happy because he came after 07. But this is true. It was an extremely, extremely frustrating period. And for example, ME315 lab, we passed through a period where volt meters were failing and we had no resources to repair them, literally. And I would go and argue about differential fees and other things, never got a penny. So what I did is I talked to Paul Zmola, he's somebody who donated money to us, and I told him to please dedicate the money that he has in mind that year to ME315 lab and he gave us $20,000 and we lived off that for four years, literally. And I was surprised that after the prototyping format for senior design were formally adopted, suddenly we didn't receive any funding for it, although everybody was using it, I don't know. And a few thoughts about research as well. One thing, collaboration. Something I want to mention. I've collaborated with a lot of people over the years and it's absolutely amazing how much you can do with collaborative work. Major breakthroughs are possible. For example, I talk about materials processing. When I started the work, I'm an expert in two-phase flow, I know nothing about metallurgical transformation theories. I work with a materials professor, which for him is a very easy topic. Just by combining it, we were able to do incredible things. And so virtually every one of these topics led to major breakthroughs. Recently, by the way, I got to emphasize Professor Scala was delighted about the collaboration because this is an area where we have very little expertise and he's really providing a lot of assistance in this area we're collaborating right now. Now, interestingly, these breakthroughs are not money related. In fact, there are some projects here involving a lot of money, but relatively minor yield. Okay, research trends and challenges. Again, this is highly controversial, I think. Increased university control over large research initiatives with decisions, highly influenced by politics and favoritism. Okay, we see a lot of announcement. Big centers, you know, whatever. I don't know who's running this, but you feel it's excluding rather than including in many situations. I've seen that firsthand. Suppression rejection of new initiatives for some faculty. I had two enormously large grants in the same year, 2013, where the attorneys said we're not gonna negotiate them, not even talk to the companies to try to make them happen. This is at the time when the university was spending over backwards to get other funds. So there is a lot of politics that I still don't understand. Awards and rewards at Purdue increasingly based on personal favors rather than scholarly performance. It's true. This has led to migration of many senior faculty to administrative positions away from teaching or research. That's a fact as well. I'm not talking about everybody, but I'm talking, there are certain factors leading to this. There is also something I'm very concerned about, which is the decline in the quality of research publications. With the focus on numbers rather than quality, in many cases, I'm seeing it more and more. Minimal faculty involvement in preparation of papers. I hear it from students as a matter of fact. Well, my advisor doesn't like to spend too much time looking at my papers before we send them. Papers with identical findings, presented in different journals, proliferation of new law quality journals seeking any articles, begging you for articles. I receive those every single day right now, announcement. Oh, we saw your article entitled whatever. Can you write another one without review? We're not gonna review it for you. Just send it to us for our journal. And also some relying on surrogates to write papers. The worst, this is something I had to deal with personally, conference papers hastily prepared by students over a weekend, literally, with no faculty oversight. I discovered that when I was working on a project and I asked the faculty member to remove my name from any paper submitted to a conference from that project. I didn't care and I don't wanna see my name attached to it, but it's a quality issue. And my wife got angry at me for doing this. This is the last slide. My favorite author. I don't know if you know it, George Orwell. And all whatever are equal, but some are more equal than others. I'm hoping when I retire, I forget that this happened, but that's the way I felt. Thank you. For questions. You mentioned several fluids such as water and R134, also JP8, but, and then you mentioned the importance of the critical point. Yes. Now, if you go past the critical point pressure-wise, so you go supercritical P, then you don't have a proper boiling, you have a pseudo-boiling. So there's no interface. Is that better for CHF or is that something you guys, people in this community avoid? Is it a structural problem for the heat exchangers to be designed with those pressures? Are those conditions that are probably worse for what you're trying to achieve or are they better? Any time you get close to the critical point, your CHF for all practical purposes is zero anyways. So as you're going up in pressure, it actually peaks, for example, for water, it peaks around 50 bars. It's low at one atmosphere, it peaks around 50 bars. Then when you hit the critical point, it's practically zero. So you are talking about the range nobody is interested in. If you look at the nuclear reactors, for example, you got 50 bar, 70 bar, because they want to take advantage of that sweet spot. And if you go on the other side, if you go supercritical, so you approach the critical. There is no indication that it is really advantageous from a critical heat flux standpoint. Having said that, not many people have done work in that area that is really conclusive. Yeah, what is the state of theory for, you know, you showed boiling starting all at walls. And, you know, if you have a homogeneous fluid that's above the boiling temperature, is there a theory for formation of bubbles in that? Or, you know, if you have a fluid where you have bubbles and the fluid temperature is below the condensation temperature, how long it takes those bubbles to collapse? Of course, there is a lot of work about related to bubble dynamics. It's all under the title of bubble growth theory. And it gives you diameters as a function of time. There are two regimes actually well identified. One of them is a dynamic regime. And another one is a thermal regime, okay, which is much slower. But the theory has been around for a while and there are publications in those areas available. Is that all connected with, you know, like theory of metastable equilibrium in these fluids? No, that's a totally different topic. Okay, what I'm talking about is the dynamics of bubble growth under low pressures versus high pressure. You may be talking about situations where you have like a mirror surface, mirror polished surface that doesn't promote boiling, yet you do finally end up with bubbles forming on the surface, okay? That is basically- That's preheated liquids and so cool. Absolutely, that's usually addressed from a thermodynamic standpoint rather than mechanistic heat transfer standpoint, a lot of the work that you see out there. But it has been addressed and you see it a lot in chemical engineering as a matter of fact, more than you see it here in mechanical engineering. So Issam, so after 32 years of research and teaching, so where do you wanna go from here and where do you want to be in 10, 20 years from now, scientifically and technically? Well, I'm gonna age here because I love research. I think research is extremely exciting and actually as I'm aging, I'm finding it more and more exciting. Believe it or not, I'm constantly asked to move somewhere else and serve in an administrative capacity and I'm consistently saying no because I don't see myself doing that kind of work at all, okay? And the fact that I'm doing my research along with the work I do in my company, which complements the things that I like to do, I'm very happy with that. You know, let me tell this to the younger faculty here. Recently, it was at a NASA event, there's a gentleman who's a fellow in a famous aerospace corporation. I don't wanna mention his name for a particular reason. Well-known for his patents, inventions in aerospace. He's a consultant for NASA forever. You know, anytime they have a review event for NASA related activities, they bring him on board and he just retired. So I asked him what he's gonna do. He wants to become a professor. He said, I'm not gonna sit home and my company doesn't allow me to continue after the age that I'm at. So he literally found a university that wanted to capitalize on his skills and he's gonna be a university professor until he hits whatever age, you know, 85, 90 and he's extremely delighted with that. So that should tell you, you're in an incredibly attractive career, okay? Unfortunately, it's plagued by politics but these things come and go with time. So the short answer, I really enjoy my teaching and I love my research and I love the work that I do at the research park. The only thing I don't have time for is my hobbies. I would rather do some oil painting but I don't have time for that. That'll hydride work you were doing and the heat transfer you're doing during that process. Is there a significant expansion of the metal as the hydride is formed? You absolutely have to account for that in the modeling and we discovered that from the experiments as a matter of fact. So absolutely that is very relevant to the design of the heat exchanger, okay? And to account for that, you have to accommodate some reduction in the performance of the heat exchanger. You can't fill it as much as you think you can because of that factor. Well, once again, if there are no further questions, I want to thank you for an excellent presentation. I was quite fascinated with all of the things that you're doing and I hope to perhaps collaborate with you in the future. And if you have other exciting things in the teaching domain and for classroom innovations, please contact my office because I would love to. Well, we're building one right now actually and when it's done, I'll probably show it to you. Okay, well, thank you. Thank you, let's give him. Thank you very much.