The heat transfer coefficient is used to describe convective heat transfer between a solid and a fluid, as in Equation (1). The heat transfer coefficient is a defined parameter, not a physical property like thermal conductivity, and different definitions are used for different situations. The preferred definition for use in the electronics-cooling situation is … [Read more...]
Estimating The Effect Of Flow Bypass On Parallel Plate-Fin Heat Sink Performance
In past issues of Electronics Cooling, methodologies were presented for estimating parallel plate-fin heat sink thermal resistance [1] and pressure drop [2]. The underlying assumption for both articles was that all the flow delivered by the fan is forced to go through the channels formed between the fins. As noted in the second article this is often not the case and much of the … [Read more...]
Air Cooled Compact Heat Exchanger Design For Electronics Cooling
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...]
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