This time I found it difficult to find a suitable subject for my editorial. My original idea was to write about heat spreading, again. I found some interesting facts pointing at problems of interpretation for dual layers when using the often-used heat spreading equations while writing a white paper on basic thermal management for LED applications for this year’s APEX/IPC conference (devoted mainly to printed circuit boards). On second thought, I realized that the subject was far more suited for the Thermal Facts and Fairy Tales column, the problem being that I was on the verge of finishing a column on the subject of the danger of imposing a slope on certain Nu-correlation graphs, the one that features in this issue. I am afraid that you have to wait another half year on my comments on dual-layer heat spreading.
So, what to do, I wondered? It is the privilege of an editor writing an editorial to discuss any subject that comes to mind, as long as it is (remotely) linked to the theme of the journal. My Thermal Facts and Fairy Tales column is, as already indicated above, devoted again to the danger of using correlations for thermal management design purposes. I keep wondering why so many people stick to their use. In my opinion, the main reason is that correlations on the one hand fulfill the need to reduce the significant complexity of the real thermal world to something that is manageable, while on the other hand correlations seem to be based on science because so many handbooks devote so many chapters to their derivation and use in practice (“… for engineering convenience …”).
Fortunately, my feelings on the abuse of correlations are shared by two famous Stanford scholars: Bill Kays and Bob Moffat, who more or less gave up on dimensionless correlations about 40 years ago. Let me quote Bob Moffat: “The habit of assembling “dimensionless groups” and trusting the Buckingham Pi theorem was very important in the early years of the development of physics and engineering, but it has become so ingrained in our teaching that the dangers of blind obedience (the religious aspect) has been forgotten. When “irrelevant parameters” are included in the parameter list before the groups are formed, what comes out are correlations that have some elements that simply conceal the interactions among irrelevant parameters. Sometimes simpler is better.”
Moffat’s using the phrase “religious aspect” reminded me of the following. I once coined the abundant use of correlations “correligion,” not without a reason, because it has some similarity to certain aspects that all religions share. Holy books, priests and believers, preaching the pros but being blind to the cons. People who don’t share their beliefs are considered unreliable, at least. I realize that America is a very religious country, but I was really shocked by the following: the 2007 Gallup poll asked Americans whether they would vote for “a generally well-qualified” presidential candidate nominated by their party with each of the following characteristics: Jewish, Catholic, Mormon, an atheist, a woman, black, Hispanic, homosexual, 72 years of age, and someone married for the third time. The result? Atheists closed the row: 45%. A Mormon president would not raise objections by 72%.
What happened since the days of Jefferson and Adams, who wrote around 1800: “As the Government of the United States of America is not, by any sense, founded on the Christian religion; as it has in itself no character of enmity against the laws, religion, or tranquility, of Musselmen; and as the said States never have entered into any war or act of hostility against any Mehomitan nation, it is declared by the parties that no pretext arising from religious opinions shall ever produce an interruption of the harmony existing between the two countries.” This concerned a treaty with Tripoli, the capital of Libya! Indeed Mr. Dylan, times they are a-changin’.
What is the lesson to be learned, be it for the claims of any religion or the claims in heat transfer textbooks when we don’t talk fairy tales, but real life? As Timothy Leary once put it: “Think for yourself, Question authority”.