{"id":355,"date":"2012-09-01T13:55:33","date_gmt":"2012-09-01T18:55:33","guid":{"rendered":"http:\/\/tonykordyban.com\/?page_id=355"},"modified":"2014-04-13T20:26:34","modified_gmt":"2014-04-14T01:26:34","slug":"everything-you-know-is-wrong-march-2002","status":"publish","type":"page","link":"http:\/\/tonykordyban.com\/?page_id=355","title":{"rendered":"Everything You Know Is Wrong March 2002"},"content":{"rendered":"

Answers to those Doggone Thermal Design Questions<\/strong><\/p>\n

By Tony Kordyban<\/strong><\/p>\n

Copyright by Tony Kordyban 2002<\/p>\n

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Dear Thermal Guru,<\/em><\/p>\n

Your no-nonsense writing about cooling electronics has finally convinced me (and more to the point, my boss) that we need some CFD software.\u00a0 I have looked at the web sites and the sales brochures and even some demos of all the vendors for electronics cooling CFD tools.\u00a0 Each one has a good story to tell about why theirs is the one to buy.\u00a0 I think I can trust you to cut through the hype and give us the straight dope — which CFD package is the best?<\/em><\/p>\n

Bubbles from Townsville<\/em><\/p>\n

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Dear Bubbles,<\/p>\n

You trust me to cut through the hype after you’ve seen the way I shamelessly promote my book in this forum?\u00a0 I’ll give you an honest answer, but just remember, what you’ve asked me for is my opinion, which is a lot different from asking me for the truth.<\/p>\n

For the benefit of those who haven’t had the pleasure of seeing all the lovely color brochures that you have, I’ll explain what CFD is.\u00a0 Computational Fluid Dynamics.\u00a0 That’s what the letters stand for, but that doesn’t give you much of an idea why it might be useful for predicting electronic component temperatures.\u00a0 CFD is the technology behind computer codes that solve fluid flow problems.\u00a0 You specify a flow geometry and some boundary conditions, and the code will solve for the fluid pressure, velocity, and temperature at every point in the domain.\u00a0 CFD was originally developed to solve general purpose, high-budget flow problems, ranging from flow around an airplane wing to blood pumping through an artificial heart.<\/p>\n

Most electronic assemblies use some kind of fluid (like air) to get the heat out.\u00a0 A CFD tool can predict that flow through an electronic assembly, which is where its usefulness to us comes in.\u00a0 The same code can calculate temperatures for the solid parts of the domain (that is, the components and circuit boards) by treating them as fluid that moves very, very, very slowly.\u00a0 General purpose CFD\u00a0 tools can be used to analyze electronics, but they are very big, very expensive, and have lots of features that don’t apply to air flow through electronics, but still require you to know how to turn them off.\u00a0 Some would say that the Electronics Cooling CFD packages are “stripped down” versions of the general purpose tools.\u00a0 I agree, in the sense that a finely tailored suit of clothes can be considered a “stripped down” version of a circus tent.\u00a0 It has had a lot removed to make it fit a lot better.\u00a0 Packages like FLOTHERM, Icepak, and Coolit won’t help you design the next Space Shuttle, but they might help you design the next computer that goes into it.<\/p>\n

I also want to distinguish CFD tools from other computer tools that deal with heat transfer in electronic assemblies, but are not based on CFD technology.\u00a0 There are finite element programs that are very good at solving solid conduction problems, in addition to stress and vibration\u00a0 but don’t deal directly with the fluid flow.\u00a0 There are resistance network solvers, like MacroFlow, which are excellent at solving flow problems that can be defined as a network of simple resistances, like a bunch of different pipes or ducts connected together.\u00a0 You didn’t ask me about those, so I won’t say much about them, except that they aren’t really competitors of CFD.\u00a0 They solve specific types of problems better, or at least faster, than CFD, but they can’t really solve the fluid flow problems that CFD is best at.\u00a0 You may want to have all three types of tools if you are really serious about thermal analysis.<\/p>\n

So back to your original question.\u00a0 Which one is the best?\u00a0 The honest answer is:\u00a0 I can’t tell you.\u00a0 There are three reasons, ranging in nature from corporate regulations to epistemology:<\/p>\n

1.\u00a0 My employer expressly forbids me (and all their other employees) from saying good or bad things about the products of other companies.\u00a0 They hate getting sued, and I hate getting fired.<\/p>\n

2.\u00a0 I don’t actually know which one is the best, because I haven’t tried all of them.\u00a0 I have used one for many years, and I played with one for a couple of months on a demo basis.\u00a0 Even if I had an opinion (which Reason 1 forbids me from having), it would not be an informed one.<\/p>\n

3.\u00a0 I think the question may be practically impossible to answer, not just for me, but for anybody.<\/p>\n

You are asking me a question very similar to, “Who is the best spouse for me?”\u00a0 Because taking on a CFD tool is very much like getting married.\u00a0 The problem is two-fold:\u00a0 such a judgment would be very personal, plus it takes a long time to form one.\u00a0 It will take years for you to really get to know each other, what you each bring to the relationship.\u00a0 Who will know your potential spouse well enough to give you an informed opinion, without being married to that person?\u00a0 He or she couldn’t be married to ALL your potential spouses at the same time, either.\u00a0 And by the time you may find out that you don’t have a good match, years will have passed, and your needs will have changed, and the CFD tool that might have been best for you at the beginning, may not be best for you anymore.\u00a0 The truth is that there are many people who would make an excellent spouse for you.\u00a0 But you will never find out which one would have been the best, because you don’t get several lifetimes to try them all out and compare them one against the other.<\/p>\n

Another similarity is that even the best spouse will cause you lots of aggravation at time, along with the many benefits and joys.<\/p>\n

The brochures won’t tell you this.\u00a0 But it take time, lots of practice with a CFD tool, solving real problems day after day, before you learn how to get good, reliable results from it.\u00a0 Thermal modeling is an art, as well as a science.\u00a0 Give the same problem to ten engineers, and they will come up with ten unique ways to solve it using the same CFD tool.\u00a0 And the results they get may vary quite a bit.\u00a0 Some vendors make claims that their package is easiest to learn, generates grid the fastest, or has the fanciest way of displaying results.\u00a0 It doesn’t matter whether you can learn the user interface in three hours, three days or three weeks.\u00a0 You won’t know whether you have a good engineering tool for at least a year after you buy it.\u00a0 And if you are only using it a few hours a week, you may never learn all the things it can and can’t do.<\/p>\n

So unless someone has used each of the CFD packages for a minimum of a year apiece, on a daily basis to solve real electronics cooling problems, I wouldn’t trust him to give you a realistic answer about which one is the best.\u00a0 And if that person exists, his knowledge of at least one tool is already a few years out of date.\u00a0 Presumably the software has been revised over time, maybe for the better.\u00a0 That’s why I think there is no real way to get an answer to your question.\u00a0 Nobody knows the answer.\u00a0 Perhaps nobody can know.<\/p>\n

I suppose you ask the question because you don’t want to buy an expensive one-year license and then find you bought a lemon — a horrible piece of software that just doesn’t work.\u00a0 Based on what I have seen of all the packages, they are ALL horrible, but they all work.\u00a0 CFD is not a simple subject.\u00a0 I am amazed that they work at all, let alone as well as they do.\u00a0 So no matter which one you buy, there will be bugs, there will be incomprehensible menus, there will be gridding headaches, and there will be convergence problems.\u00a0 That is the nature of CFD.\u00a0 But they are all capable of solving a good portion of electronics cooling problems, with reasonable accuracy, if you stick with them.\u00a0 I don’t think they could stay in business if the software just plain didn’t work.<\/p>\n

So I think you will have to decide which CFD package to get based on something else besides which one is “the best”.\u00a0\u00a0 Will you get good technical support?\u00a0 I promise that no matter which one you buy, you will be on the phone with their support people a lot.\u00a0 Maybe you need the absolute lowest price, or you won’t be able to get any CFD at all.\u00a0 Cheap CFD is better than none.\u00a0 Do you also do the mechanical design?\u00a0 Maybe an interface to your mechanical CAD is important (my opinion is that it usually isn’t, but that’s just me.)\u00a0 Is the vendor financially committed to the product?\u00a0 It would be frustrating if after you get really good with it in three years, the product is discontinued and you have to switch to another one.\u00a0 Did the sales rep give you a cool T-shirt, coffee mug, or flashlight?\u00a0 One or another of these things not embedded in the software itself will matter to you.\u00a0 You might as well base your choice on them as on somebody’s partially informed opinion.<\/p>\n

So, just as in choosing your spouse, try to get to know as much as you can before the wedding, don’t worry about getting the absolute best, and pick someone that is at least “good enough” before you make your commitment.\u00a0 Isn’t that what most of the decisions in engineering, and in life, are like?
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\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014<\/strong><\/p>\n

Hi Tony,<\/em><\/p>\n

Honest?\u00a0 Boy, you sure weaseled out of that CFD question.\u00a0 Here’s something simpler.\u00a0 What type of thermocouple wire is the best in electronics cooling testing?<\/em><\/p>\n

Mike and the Bots, S.O.L.<\/em><\/p>\n

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Dear Mike,<\/p>\n

That one is a little easier.\u00a0 My employer won’t come down on me, I hope, for giving out this preference.<\/p>\n

The answer is Type J.\u00a0 My thermocouple meter is calibrated for Type J wire.\u00a0 I find that the measurements are somewhat less accurate if I use the other types of wire.\u00a0 Of course, the closer the object you want to measure is to room temperature, the more accurate they all become.<\/p>\n

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\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014<\/strong><\/p>\n

Isn\u2019t Everything He Knows Wrong, Too?<\/strong><\/p>\n

The straight dope on Tony Kordyban<\/em><\/strong><\/p>\n

Tony Kordyban has been an engineer in the field of electronics cooling for different telecom and power supply companies (who can keep track when they change names so frequently?) for the last twenty years.\u00a0 Maybe that doesn\u2019t make him an expert in heat transfer theory, but it has certainly gained him a lot of experience in the ways NOT to\u00a0cool electronics.\u00a0 He does have some book-learnin\u2019, with a BS in Mechanical Engineering from the University of Detroit (motto:Detroit\u2014 no place for wimps) and a Masters in Mechanical Engineering from Stanford (motto: shouldn\u2019t Nobels count more than Rose Bowls?)<\/p>\n

\"\"<\/a>In those twenty years Tony has come to the conclusion that a lot of the common practices of electronics cooling are full of baloney.\u00a0 He has run into so much nonsense in the field that he has found it easier to just assume \u201ceverything you know is wrong\u201d (from the comedy album by Firesign Theatre), and to question everything against the basic principles of heat transfer theory.<\/p>\n

Tony has been collecting case studies of the wrong way to cool electronics, using them to educate the cooling masses, applying humor as the sugar to help the medicine go down.\u00a0 These have been published recently by the ASME Press in a book called, \u201cHot Air Rises and Heat Sinks:\u00a0 Everything You Know About Cooling Electronics Is Wrong.\u201d\u00a0 It is available direct from ASME Press at 1-800-843-2763 or at their web site at\u00a0http:\/\/www.asme.org\/pubs\/asmepress<\/a>,\u00a0\u00a0<\/em><\/strong>Order Number 800741.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Answers to those Doggone Thermal Design Questions By Tony Kordyban Copyright by Tony Kordyban 2002   Dear Thermal Guru, Your no-nonsense writing about cooling electronics has finally convinced me (and more to the point, my boss) that we need some CFD software.\u00a0 I have looked at the web sites and the sales brochures and even […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-355","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"http:\/\/tonykordyban.com\/index.php?rest_route=\/wp\/v2\/pages\/355","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/tonykordyban.com\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"http:\/\/tonykordyban.com\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"http:\/\/tonykordyban.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/tonykordyban.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=355"}],"version-history":[{"count":3,"href":"http:\/\/tonykordyban.com\/index.php?rest_route=\/wp\/v2\/pages\/355\/revisions"}],"predecessor-version":[{"id":357,"href":"http:\/\/tonykordyban.com\/index.php?rest_route=\/wp\/v2\/pages\/355\/revisions\/357"}],"wp:attachment":[{"href":"http:\/\/tonykordyban.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=355"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}