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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...]

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...]

Hot Spots in Data Centers

 

Heat loads of data processing equipment continue to increase at a rapid rate. This increasing heat load has been documented by a Thermal Management Consortium of 17 companies [1] as shown in Figure 1. Also shown in this figure are measured heat fluxes (based on product footprint) of some recent product announcements. The most recent shows a rack dissipating 28,500 watts, … [Read more...]

E missivity in Practical Temperature Measurements

 

When making temperature measurements with infrared cameras and point detectors, we are always facing the question of the emissivity of our sample. In practice we would like to have a single number set in the IR device. To approach the question, let's first recall some fundamental definitions. Planck's radiation law gives the energy density emitted by a blackbody as a function … [Read more...]

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