Thermal behavior of axially grooved heat pipes aboard a rocket

The thermal and dynamic behaviors and the zero-g performance of axially grooved heat pipes aboard an S-520 sounding rocket were investigated. One heat pipe was made of aluminum and employed ammonia as the working fluid and the other heat pipe consisted of an aluminum alloy with freon 11 as the working fluid. N-eicosane was utilized as a phase change heat sink material for both cases. The heat pipes responded to several levels of varying acceleration such as large positive acceleration during the boosting period and a small negative acceleration immediately after the burnout caused by the aerodynamic drag on the rocket. The dynamic behavior of the working fluid resulted in responses such as dryout, recovery from the dryout with partial liquid blockage in the condenser section, and the resumption of normal heat pipe operation. It was found that the critical Bond number giving the threshold of the surface tension dominated condition over the body force was about 0.005.