Investigation on the effects of body force environment on flat heat pipes

This paper reports on the effects of body forces environment: gravitation, vibration, and acceleration forces using constant heat load on the thermal performance of a flat copper/water heat pipe. The effect of gravitation for ces is studied by testing the heat pipe in different positions: horizontal, vertical with a heat source upwards (antigravity position), and vertical w ith a heat source downward (thermosyphon position). Transient accelerations and vibrations are generated using centrifuge and shaking tables, respecti vely, in order to simulate vibration and acceleration forces corresponding to aircraft maneuvering in frequency, amplitude, duration, and direction. T he experimental results on the orientation effects show that the heat pipe is hardly affected by the gravitation forces and exhibits nearly the same t hermal performance whatever the tilt angle for input heat powers lower than 20 W. For input heat powers higher than 20 W, there is a slight heat pipe thermal performance dependency on gravitation. For the vibration tests the heat pipe is mounted on a tri-axis shaking table and it is subjected to sin usoidal excitation. The heat-pipe thermal performance is hardly affected by vibration whatever the mounting direction on the shaking table. An investi gation into the effects of transient acceleration forces with constant inpu t heat loads on the heat-pipe thermal performance has been conducted. Pooli ng of the excess working fluid plays a significant role in the heat transpo rt potential of the heat pipe subjected to accelerations. There is a decrea se in the heat-pipe thermal performance with increasing acceleration as a r esult of partial dryout of the evaporator and pooling in the condenser sect ion. Dryout, which is demonstrated as a result of increased acceleration, d epends on the input heat power and the acceleration type. However, under ce rtain acceleration tests the heat pipe successfully reprimed with a suppres sion of acceleration. In all cases the increase of the heat-pipe thermal re sistance does not exceed 70%. The maximum heat-pipe thermal resistance obta ined under 10-g acceleration level remains an acceptable value for the elec tronic package safety.