—- Transcript ———————-
Audio File: 2014 Feb 12 – Cooling Electronic Enclosures.mp3
Audio Length: 14:12 minutes
Hello. My name is Montie Roland. I’m with Montie Design in Morrisville, North Carolina.
And today, I’d like to spend a few minutes talking about how to develop a strategy for cooling your electronics enclosure.
One of the products that we do a lot of design for is the electronics industry, but in a bunch of different facets. Because when you say electronic enclosure, that could be anything from a computer or related; it could personal electronics; it could be lab equipment; it could even be machinery or process. So, there’s electronic enclosures that go in a variety of locations, from factories to vehicles to aircraft to your pocket. And so it’s important to consider how you’re going to keep that device cool.
Over the past twenty years, we’ve grown to expect more and more from our boxes filled with electronics. And part of that’s because of our capacity to do more with those boxes has gone up dramatically. A good example would be, you know, in the nineties, phones were just that. Cell phones were phones. Before that, they were car phones, because they were physically mounted in your car. If you were born after 1980, you’ve probably never seen a car phone. Back then, car phones were expensive; they were expensive per minute; and they were boxes mounted in your car. Think it more as a radio with an operator. And then what happened was is we got bag phones. And bag phones were . . . well, they were about the size of a laptop, but about double the thickness or triple the thickness. So, you opened the bag, you pull the handset out, you dial. Those were big; they were clunky; all analog. And pretty soon we had handsets that didn’t need a bag. And then pretty soon we had smartphones. My wife will be the first one to tell you that I probably pay way too much attention to my smartphone and keep way on track of things. And the guys who’ve gone camping with me; I had a threat that my nice, new iPhone might meet a horrible death on Troublesome Gap if I didn’t put it in the truck and lock the truck.
So, having said that, we rely on these boxes to do a lot of stuff for us. But, as we rely on them to do more and more, we’re packaging more and more electronics in there and we’re getting them hotter and hotter. So, one of the things that’s a common application for Montie Design, as we design products for clients, is to come up with a strategy for cooling that box. Now, we see a variety of cooling needs. There are some enclosures that we just need to do some very basic things and manage the thermal load in a simple way. You know, we tie PCBs to the outer enclosure; use thermal materials. Then we have other enclosures where we have to vent those somehow. And then we have other ones where either it takes a lot of airflow to cool; or, it takes a lot of analysis to make sure that we can cool the box within whatever limitations we have. Maybe it’s a handheld device but there’s a lot of power coming out of it. So we’ve got to get that power out to the atmosphere, or that thermal energy out; keep the box cool but we also don’t want to burn somebody’s hand, or make it uncomfortable to use.
So, we’ve had a lot of cases like that, so we’ve had a good bit of experience in how to meet these thermal requirements and how to keep the electronics cool so they function efficiently – and function. And there’s a couple ways to go after that. One thing you can do is once we have a computer model, we can do what’s called CFD analysis – Computational Fluid Dynamics. And with that, we actually model the heat transfer in conduction; so, from one part to another, or through a part, that, across a joint – either, maybe its bolted; maybe there’s a thermal material like a gap pad or a cell pad; or, from the part to the air via convection; or forced convection where there’s a fan or some other driver that’s causing airflow across that face. So, CFD is great because we can actually tell you down to the chip level how hot or what the temperature is of every component in there. Now, we can also look at what are the effects of airflow; run analysis to figure out how much airflow we need; you know, model the effect of the fan; model the other effects; and give you really, really great results. The downside of CFD is that where . . . of course, we have to have a computer model to start with, but they’re fairly simple for CFD. So you can do that very early on in the design process. The downside is it’s an expensive process to set up. Now, if you’re designing a product that going to be mass-produced or a very high value product, or just a high value product, the cost of the CFD may be very palatable. If you’re designing a product that is lower volume or has extremely tight financial constraints, then that may or may not fit in there. It just depends. We can take a look at that and give you an estimate. And there’s some things that are easier to predict than others. Like, for example, we use CFD very effectively to model LED lights. In that case, you’ve got a small amount of elements; often, you’ve got a heat sink; not a lot of modeling we have to do between the chip and heat sink; usually it’s a short path. Not a lot of components and that helps. And so then we’ve managed to very cost effectively do it for that type of application. So it really depends on your application if it’s cost effective.
Now, the other option is to build your product, and then after you’ve built it, instrument it and see what the results are. For some projects, that’s a good idea. If you have a product where there’s not a lot of thermal energy – you’re not trying to dump a lot of heat into the environment – then, maybe it’s okay just to go ahead and build it. Especially if you have historical data and you’re not making a huge change from the previous product. So, in that case, it may be good to build it and then make some tweaks afterwards to the design to solve the problem. There are cases where you’re not sure. You think you may be okay, but you’re not sure. In that case we can run a CFD, or we can build a mock-up. And there’s cases where you know you have thermal problems. So, in that case, a lot of times we’ll end up doing a CFD and a mock-up. When you think about a mock-up, first thing to remember is that when it comes to thermal management, there are a lot of things that aren’t as critical for the thermal performance as they are for functional or esthetic reasons. And this applies to building a CAD model to do a CFD analysis on or a thermal analysis on, or it applies to your mock-up. So, there’s an appropriate level of detail in your mock-up so that you’re keeping the mock-up simple but you’re getting relevant data on what you’re thermal performance is. You know, how hot everything is getting. And so, generally, the rule of thumb is that you want to have much less detail in your mock-up than you have in your final product. And this is good because if you’re building a mock-up just for thermal testing, you want to keep the cost low, and a lot of times the best way to keep the cost low is to pull out features that you don’t need. So, you’ve dumbed down your prototype. Now, obviously, if you have production parts already then you should go ahead and use those. But if you don’t, a lot of times we’ll build a box, maybe out of Lexan™ or wood (and I’ll get back to the Lexan™ for a second when it’s important). And then you got this clear box. And now we can put fans or we can put chips; we can put heat sources in there, and then turn around and start measuring the performance of this, both from a thermal standpoint and from an airflow standpoint. For a lot of products nowadays, the airflow has become very important because you can’t cool it from natural convection alone. And this is one of the reasons that a lot of these enclosures end up being Lexan™ or some other Plexiglas or some other clear plastic. Because then we can introduce smoke and visually see what the airflow patterns are. This is especially helpful if you’ve done a CFD analysis, and you can compare the predicted airflow from the CFD analysis on the computer to what you’re actually seeing with your eyes based on the mock-up. Then you can correlate that to the computer analysis. And the beauty there is that now if we make a change to our computer model, we can rerun the analysis and see what the impact is without having to build another prototype; especially where you’re making an incremental change. And after we’ve taken and confirmed that our model’s correct, then you’ve got a lot of confidence that your CFD model matches the reality. Then it’s very . . . well, I won’t say very quick, but it’s very possible to start making changes in the computer model, rerun the analysis, and see what the result is.
I know I’m kind of hitting a lot at once here. But these two different tools – one is your physical mock-up; and the other is your computer model using CFD tools – are a great way to determine how your product’s going to perform. The challenge is to right-size your effort based on the need. And sometimes there’s an experience factor. Sometimes there’s a historical data factor that can be brought into effect. There again, if you’ve built similar products, you know what the thermal performance is, hopefully. We can use that data to determine how exhaustive an analysis we need to do. Sometimes we need to do a very exhaustive analysis; and other times, let’s put a fan and a heater in a box and see how warm it gets. And that’s a matter of just right-sizing. That’s something we can definitely help you with or happy to help you with. We offer that as part of our project services to do that analysis.
I hope this has been helpful today, talking about the different ways you can plan for your thermal analysis as part of your design project. If you have any questions, please don’t hesitate to give me a call – Montie Roland. 1-919-481-1845, or 1-800-722-7987. 800-722-7987. Email me – Montie (M-O-N-T-I-E ) @ Montie(M-O-N-T-I-E ) dot com. Or, visit the website – www.montie.com. Your comments, suggestions or questions or project opportunities for us are always welcome. We’d love to help you out with your next project. Or, maybe it’s just a lunchtime discussion on one of these topics. Have a great day. Montie Roland, president of Montie Designs, signing off.