03. Electronics Packaging and Thermal Management

Copper-water heat pipes are popularly used for most of the electronic devices cooling systems. However, in the space applications, the environment temperature can be as low as -40 oC. Water may freeze and let the heat pipe not be able to operate normally at temperature below 0 oC. To resolve the problems for the application of copper-water heat pipe in satellite systems, grooved aluminum-ammonia heat pipes are considered as an appropriate candidate to replace the sintered copper-water heat pipes for space applications. However, since the capillary force of the grooved tube is very small, the heat transfer performance of grooved aluminum-ammonia heat pipes is significantly affected by the inclined angle of the heat pipe. This study conducted an experimental measurement of heat transfer performance of grooved aluminum-ammonia heat pipes at various negative inclined angle (i.e. evaporating section is higher than condensing section). It is aimed to provide further understanding of the heat transfer performance of grooved aluminum-ammonia heat pipes for space applications. The test results show that the thermal resistance of the heat pipe varied from 0.1 to 0.04 K/W with respect to heat rate from 10 to 190 W in horizontal position. The thermal resistance increased drastically with increasing heat pipe inclined angle,. While the inclined angle at -1.0o, the thermal resistance increased from 0.5 to 3.2 K/W at heat transfer rate from 4 to 24 W. The heat pipe completely dryout while heating rate higher than 24 W. It can be concluded that the capillary force provided by grooves is much lower than that of the sintered capillary structure. It is very sensitive for the heat pipe inclination to the heat pipe thermal resistance and maximum heat transfer rate.