Analysis of Loop Heat Pipe Operation with Radiators of Different Orientation 2002-01-2504

A performance analysis model is presented to investigate operability of a loop heat pipe (LHP) with two differently oriented radiators. Analytical modeling has been made under particular conditions that the LHP of concern is used to reject waste heat generated by thermoelectrical cooling devices. The model is expressed in comparative dimensionless form normalized by specified design parameter values, thus permitting off-design state predictions of an LHP with one evaporator and two condensers. Condidered in that model are Peltier cooling power consumption holding most of the heat load, coupled radiator sink temperatures, a conductive loss and bubble generation in the evaporator wick, an extent of the condenser two-phase region length, a degree of the liquid subcooling, a change of the radiative conductance, a capillary pump head increase/decrease compensating a total pressure loss change, and a hydraulic balance between the condensers arranged in a row. Performance calculations of a modeled LHP have then been done with the sink temperatures as main variables and the mission equipment temperature as an operational parameter. Numerical results are graphically shown in the figures to readily find the heat rejection rate, the cooling coeffiencient of performance, the baseplate/reservoir/radiators temperatures, the subcoolness degree, the capillary/reservoir pressure changes, the capillary pump efficiency, the evaporator temperature effectiveness, the loop axial conductance, and the two-phase factor ratio representing a workability. Some of them are also compared with experimental ones obtained in ground testing to plainly demonstrate availability of the model.