Introduction This article will discuss air-cooled compact heat exchanger design using published data. Kays & London's Compact Heat Exchangers [1] contains measured heat transfer and pressure drop data on a variety of circular and rectangular passages including circular tubes, tube banks, straight fins, louvered fins, strip or lanced offset fins, wavy fins and pin fins. … [Read more...]
Thermal Interface Materials
It doesn't take long for an electronics assembler to realize that a thermal interface material (TIM) is essential when two or more solid surfaces are in the heat path. Standard machined surfaces are rough and wavy, leading to relatively few actual contact points between surfaces. The insulating air gaps created by multiple voids of "contacting" hard surfaces are simply too … [Read more...]
The Thermal Conductivity of Moist Air
In the Tech Data series on thermal conductivity, gases - especially air - have been the subject of a few contributions. So far, the influence of two important parameters has been covered: temperature and pressure. However, people regularly ask: "What exactly is the influence of humidity?" And my standard answer has always been: "Nothing to worry about." Some time ago, one of … [Read more...]
The 45° Heat Spreading Angle – An Urban Legend?
Ever hear about the 45° heat spreading angle? Most of us have. However, no one I've talked to seems to know where it came from. Is it an urban legend, such as alligators in the sewers of Manhattan, or is it an eternal truth deposited into the collective subconscious of the thermal engineering community? However fascinating it might be to explore the historical origins of this … [Read more...]
Problems with Thermal Interface Material Measurements: Suggestions for Improvement
Preface Increasingly it is apparent that measuring the thermal properties of Thermal Interface Materials (TIMs) causes much irritation for vendors and users alike. This article focuses on various measurement and standardization aspects and offers a strategy to overcome the problems. It is essentially an abbreviated version of a paper presented at SEMITHERM '03 … [Read more...]
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