Original Date: 07/14/1997
Revision Date: 01/18/2007
Best Practice : Heat Pipe Wick Structure
The heat pipe’s wick structure uses capillary pressure to pump the working fluid from the condenser to the evaporator. Typically, the restricting factor of heat pipe designs is the capillary limit, which is determined by the pumping capacity of the wick structure. The capillary limit is also a function of the heat pipe’s operating orientation and wick structure (e.g., groove, screen, cable/fiber, sintered powder metal). Pore radius and permeability are the two most important characteristics of a wick structure. Pore radius determines the pumping pressure that the wick can develop, while permeability determines the fractional losses of the working fluid as it flows through the wick.
It is important to select the proper wick structure based on the application. Thermacore has determined that sintered powder metal is the optimum wick structure for cooling electronic components in computer products (e.g., notebooks, laptops, desktops, high-end servers). Sintered powder metal wicks have small pore radii and relatively low permeability. The high capillary pumping pressure, achieved through a sintered powder metal wick, allows the heat pipe to operate in any orientation. Other wick structures do not work as well in non-horizontal orientations because they cannot lift the returning working fluid the length of the heat pipe against gravity.
By developing specialized equipment and processes, Thermacore can vary the physical properties of its sintered powder metal wicks, allowing the heat pipes to be custom designed to the customer’s application. In addition, the heat pipes can be bent to fit various heat sink shapes without any significant reduction in performance. Through its unique heat pipe technology, Thermacore has become a major supplier in the electronics industry.
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