The calculation of the heat control accumulator volume of two-phase heat transfer loop of a spacecraft thermal control system

Abstract

Spacecraft thermal control systems based on two-phase mechanically pumped loops have advantages in terms of mass and power consumption for auxiliary needs compared to single-phase thermal control systems. However, the disadvantage of two-phase mechanically pumped loops is that when changing the heat load and heat removal conditions, when switching from single-phase to two-phase operation mode and vice versa, the amount of working fluid in the loop changes significantly, which requires the use of a large volume heat-controlled accumulator. Therefore, determining the minimum required volume of the heat-controlled accumulator for the loop operation is an urgent task due to the need to maintain the performance of the l loop at a minimum and maximum heat loads and minimize the mass of the structure and the working fluid charged. When determining the volume of the heat-controlled accumulator, it is necessary to correctly calculate the mass of the fluid in the loop during the two-phase operation mode. The mass of the fluid depends on the void fraction, which depends significantly on the phase slip. Many models and correlations have been proposed to calculate the phase slip factor. However, they all require justification for the parameters characteristic of spacecraft thermal control systems and weightlessness conditions. The paper presents the results of ground-based experiments, based on which the verification of different models and correlations for phase slip was performed. The validation of models and correlations for the conditions of weightlessness was performed by comparing the results with the horizontal and vertical orientation of the elements of the experimental setup. The working fluid is ammonia. The experiments showed that the best coincidence of calculation and experience is provided by Chisholm correlation. The discrepancy between the calculated and experimental values did not exceed +/-7% in the entire range of study parameters both for horizontal and vertical orientations, which allow us to recommend the Chisholm correlation for determining the coolant mass in the two-phase mechanically pumped loops for parameters characteristic of spacecraft thermal control systems, including zero-gravity conditions.

Keywords

• spacecraft
• weightlessness
• thermal control system
• two-phase mechanically pumped loop
• heat-controlled accumulator
• volume
• ammonia
• slip factor