Mathematical Model of Heat-Controlled Accumulator (HCA) for Microgravity Conditions

It is reasonable to use a two-phase heat transfer loop (TPL) in a thermal control system (TCS) of spacecraft with large heat dissipation. One of the key elements of TPL is a heat-controlled accumulator (HCA). The HCA represents a volume which is filled with vapor and liquid of a single working fluid without bellows. The pressure in a HCA is controlled by the heater.

The heat and mass transfer processes in the HCA can proceed with a significant nonequilibrium. This has implications on the regulation of TPL. This article presents a mathematical model of nonequilibrium heat and mass transfer processes in an HCA for microgravity conditions. The model uses the equations of mass and energy conservation separately for the vapor and liquid phases. Interfacial heat and mass transfer is also taken into account. It proposes to use the convective component k for the level of nonequilibrium evaluation.

The experiments were carried out in microgravity conditions for the estimation of the k value. The heating of the HCA was investigated in the flight experiments. The working fluid was ammonia. It was determined that in the mathematical model, the k low margin is k = 15…30 for the microgravity conditions.

An analysis of the HCA regulation was performed for two values of the k coefficient. It defined that nonequilibrium has a significant impact on the regulation process. It is shown that to ensure a given mode of TPL operation with the HCA equilibrium process (k > 100), a greater HCA heater power is required than in a nonequilibrium process (k = 30).