16th International Heat Pipe Conference (16th IHPC) Lyon, France, May 20-24, 2012 Experimental performance comparison of axially grooved heat pipes charged with acetone and ammonia Jorge Bertoldo Junior, Valeri V. Vlassov, Pedro Antônio Cândido, Gino Genaro Instituto Nacional de Pesquisas Espaciais – INPE, São José dos Campos – SP, Brasil. jorge.bertoldo@inpe.br Valery M. Kiseev Ural State University - USU Ekaterinburg, Russia ABSTRACT To validate proposed axially grooved heat pipe, designed to work with acetone, comparative characterization tests have been conducted for two heat pipes, having the same profile height of 19.1 mm, and length of 730 mm. First heat pipe is charged with acetone and has unique core however the second heat pipe, charged with ammonia, has two cores. Both heat pipes are directed to Space application and have profiles with similar flat interfaces to fit inserting in honeycomb satellite panels. Two different characterization tests were performed. First, an inclination test conducted by means of a motorized table; second, a dry-out test in horizontal position at different temperatures. The characteristic curves were obtained for both HP profiles under symmetrical heating/cooling KEY WORDS :heat pipe, thermal stabilization of satellite panels, HP performance test, ammonia, acetone. 1. INTRODUCTION Historically, when heat pipes (HPs) first were recognized in 1960's as promising devices for thermal control in space applications, aluminum HPs with different fluids began to be developed and tested. The fluids were mainly freons, ammonia, methanol, and propylene. Soon after the aluminum-ammonia HP demonstrated best heat transport capability, which allowed the producing of light HPs with very small diameter (about 10 - 20 mm); the technology was space-qualified and other technologies were restricted for special applications. Traditionally, aluminum-ammonia HPs are used in thermal control systems, because ammonia has appropriate temperature range and high Liquid Transport Factor. There are two main kinds of heat pipe aplications in satellites: (i) for tranferring heat to radiator over large distances from areas where are equipment with high heat dissipation or; (ii) for spreading heat over a structural panel to minimaze the thermal gradients over it and finally reduce the equipment temperature. In many cases where HPs are embedding in honeycomb panels, larger diameter tubes are quite desirable because they can provide higher area of thermal contact with the panel face- sheet and fits the panel thickness. In such applications the acetone heat pipes can comepetite with ammonia HPs; their lack of performance can be compensated by a particular design, as increasing the cross section area of the tube. Also, other criteria may be adopted on working fluid choice, in terms of vapor pressure, toxicity and dangerousness. As quoted by Nakamuro et al, 1984, amonnia heat pipe need to have a wall thickness high enough to endure the vapour pressure at temperature of ~120oC which is the imbedding process temperature to cure adhesive. Acetone heat pipe would not have this problem because the pressure inside the tube don’t offer explosion risks during imbedding process. Figure 1.a) Ammonia Heat Pipe Profile