Original Date: 07/14/1997
Revision Date: 01/18/2007
Best Practice : Heat Pipe Design
All electronic components, from microprocessors to high-end power converters, generate heat. Dissipation of this heat is necessary for optimum and reliable operation of electronic components. Many of today’s electronic devices require cooling beyond the capabilities of standard metallic heat sinks. Heat pipes offer a high efficiency, passive, compact heat transfer solution and are rapidly becoming a mainstream thermal management tool.
Heat pipes act as a passive heat transfer device for transferring heat from heat sources. Typically cylindrical in shape, heat pipes are sealed, evacuated vessels with a working fluid. The vessel’s walls are lined with a capillary structure (wick) which allows the working fluid to travel through it. This design enables heat pipes to operate with extremely high effective thermal conductance.
As a two-phase mechanism, heat pipes are able to operate against gravity and tolerate very low temperature drops. Heat is absorbed at the hot end (evaporator) where a portion of the working fluid is changed into a vapor and travels up the center of the pipe to the cool end (condenser). As it gives off latent heat, the vapor condenses into a liquid and travels back to the evaporator through the wick. This closed-loop, two-phase mechanism allows heat pipes to transfer heat at one hundred to several thousand times the capability of an equivalent-size piece of solid copper. The heat pipe’s construction and operation are illustrated in Figure 2-1.
Commercially available since the 1960s, heat pipes did not flourish in usage until the electronics industry started using them as reliable, cost-effective thermal management tools. The basic heat pipe design is well known and can be found in numerous technical publications. However, Thermacore improved upon this design through advanced development of envelope materials, working fluids, wicks, and processing techniques. As a result, Thermacore now excels in the electronics application of heat pipes, and has been recognized as a leader in heat pipe research and development through various avenues (e.g., Small Business Innovative Research grants; government and commercial contracts; heat pipe designs with the highest heat capacity).
Heat pipes contain no moving parts and have demonstrated long life and reliability. Thermacore maintains one of the world’s largest and longest life testing programs. Among those being tested are copper/water (envelope/fluid) heat pipes which have been continuously running for more than 15 years with negligible changes in performance. Copper/water heat pipes are able to tolerate storage temperatures between -65°C and 250°C, and can effectively operate between 10°C and 250°C. In volume, heat pipes are competitively priced with alternate cooling technologies.
Thermacore has become an innovative leader in heat pipe technology. Through its development of sintered powder metal wick technology, Thermacore provides its customers with a highly efficient and cost-effective tool for cooling critical electronic components.
Figure 2-1. Heat Pipe Operation
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