Heat transfer characteristics of miniature heat pipes for cooling systems for electronics

Abstract

Decrease in mass and dimensional characteristics of semiconductor devices with simultaneous increase in allocated power dissipation creates conditions of heat-loaded operation of the most critical elements of radio-electronic equipment. Such growth of heat flows requires effective small-size systems for maintaining safe temperature conditions of electronic equipment and its reliable functioning. The use of miniature heat pipes (MHP) commensurate in size with the microchip crystals can significantly reduce their temperature level of operation. The paper presents the experimental results of investigation of thermal resistance and maximum heat fluxes of miniature heat pipes with diameters from 3 to 6 mm and lengths from 150 to 300 mm with metal-fiber capillary structure. The porosity of the capillary structure varied from 70% to 88%. Water and ethanol were used as coolants. The study was carried out at different orientations of MHPs in space: vertical by gravity forces, horizontal, and vertical against gravity forces (+90°, 0°, –90°). It is shown that the heat transfer characteristics of the MHPs are affected by both geometric and mode factors. It is determined that the minimum thermal resistance and maximum heat flux significantly depend on the diameter of the vapor channel, porosity of the capillary structure and thermal physical properties of the heat transfer medium. The data on the heat transfer intensity in the heating zone depending on the size of the vapor channel are given. It is shown that decreasing the diameter of the vapor space of MHPs worsens their heat transfer characteristics.