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...]
Prediction of Thermal Contact Resistance
All engineering surfaces exhibit some level of microscopic roughness. The resistance to heat flow through a contact interface occurs because only a small portion (usually 1-2%) [1] of the nominal surface area is actually in contact. Heat may pass through the interface via three paths: conduction through the contact spots, conduction through the gas present in the gap between … [Read more...]
Cooling Technology Options, Part 2
(Editor's Note: Part 1 of this article appeared in the August 2003 issue of ElectronicsCooling. Illustration references in this part begin with Figure 5.) Cooling electronic systems is one of the major focal points of the design process and the key to a successful product launch. Many options to attain successful operation are available, ranging from passive cooling to … [Read more...]
Recognizing the Limits of Conventional Axial Hub-Motor AHS Devices
Conventional axial hub-motor AHS (Active Heatsink) devices (Figure 1) have reached their functional and cost limits and may not be improved significantly. These devices have a number of inherent, severe contradictions (design limitations) that determine the "evolutionary maturity" of this concept. Figure 1. Conventional axial hub-motor AHS. Let us look at different … [Read more...]
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