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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...]

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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