The Effects of Transverse Acceleration-Induced Body Forces on the Capillary Limit of Helically Grooved Heat Pipes

Abstract

A helically grooved copper heat pipe with ethanol as the working fluid has been fabricated and tested on a centrifuge table. The heat pipe was bent to match the radius of curvature of the table so that uniform transverse (perpendicular to the axis of the heat pipe) body force fields could be applied along the entire length of the pipe. By varying the heat input (Qin = 25 to 250 W) and centrifuge table velocity (radial acceleration |a⃗r| = 0 to 10g), information on dry out phenomena, circumferential temperature uniformity, heat lost to the environment, thermal resistance, and the capillary limit to heat transport was obtained. Due to the geometry of the helical grooves, the capillary limit increased by a factor of five when the radial acceleration increased from |a⃗r| = 0 to 6.0g. This important result was verified by a mathematical model of the heat pipe system, wherein the capillary limit to heat transport of each groove was calculated in terms of centrifuge table angular velocity, the geometry of the heat pipe and the grooves (including helix pitch), and temperature-dependent working fluid properties. In addition, a qualitative study was executed with a copper-ethanol heat pipe with straight axial grooves. This experimental study showed that the performance of the heat pipe with straight grooves was not improved when the radial acceleration was increased from |a⃗r| = 0 to 10.0g.