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

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.

Valve for two-phase fluid loop

Improvement of heat transfer efficiency of the spacecraft thermal control subsystem constitutes a relevant problem for today space industry. Two phase thermal control system presents the most suitable solution for this problem. Implementation of reliable thermal control loop elements constitutes one the major prerequisites for reliability of thermal control systems featuring the operating pressure of 4.8 MPa and ammonia as heat fluid. This paper presents the design and test results of manual valve and fill and drain valve to be operated within the spacecraft two phase thermal control subsystem. The paper provides considerations and detailed description of the technical solutions adopted to ensure compliance with the specification requirements such as operating pressure and plug seat leak tightness under the operating pressure and 160 open/close cycles. Valve plug torque selection criteria are described. The employed design and technical solutions as well as qualification test results have proven that the units designed feature outstanding combination of performances such as leak tightness, life cycle with ammonia as heat fluid.

Heat Transfer in Evaporator of Thermal Sink in Presence of Subcooled Boiling Section

The paper proposes a model of heat transfer in the evaporator of the spacecraft thermal control system. The model allows to calculate the average temperature of the evaporator wall and to build a "boiling curve" in a wide range of thermal loads. Adequacy of the model is confirmed by experimental studies on an aluminum thermal sink with high longitudinal thermal conductivity in the range of parameters typical for the thermal control systems of spacecrafts. Ammonia is used as a working fluid. The model might be recommended for use in zero gravity and normal ground conditions.

“Spacecraft Thermal Control Technologies”

Into my hands came an exciting new book about space. “Spacecraft Thermal Control Technologies” is written by Professor Jianyin Miao, Qi Zhong, Professor Qiwei Zhao and Professor Xin Zhao. All the authors of this book are part of the Institute of Spacecraft System Engineering, China Academy of Space Technology (CAST), Beijing, China. Jianyin Miao is a head scientist of heat pipes at CAST and a Massachusetts Institute of Technology (MIT, USA) visiting professor, and is an academic leader for space thermal control technology at China Aerospace Science. Qi Zhong is a research fellow at CAST and his expertise is in the field of aerospace thermal control. Qiwei Zhao is a professor at CAST with expertise in the field of space thermophysics. Professor Xin Zhao has served as a chief designer of thermal control subsystems. He serves on the professional committee at CAST. He has received several national and ministerial awards for his work in this field. The series editor Peijian Ye, (China Academy of Space Technology, Beijing, China) is a Chinese aerospace engineer. He is a professor at the Beijing University of Aeronautics and Astronautics, China, and is a professor at the Harbin Institute of Technology, China. He is a research fellow and chief engineer at CAST. He is also the Chief Commander and Chief Designer of the Chinese Lunar Exploration Program. In his honour the inner main-belt asteroid 456677 Yepeijian, discovered by the Purple Mountain Observatory Near-Earth Object Survey Program at the XuYi Station, China, took his name in 2007.