Abstract: Mechanistically pumped two-phase loop (MPTL) is a two-phase heat transfer device, which possesses the strong heat transfer ability through the release of latent heat of liquid and vapor phase change during flow boiling process. MPTL shows a promising prospect in thermal control of spacecraft.The objective of the present study is to focus on the working characteristics and stability of MPTL under the microgravtiy environment on orbit. One MPTL, which included one shield centrifugal pump, one two-phase temperature controlling accumulator and one micro channel evaporator, was designed and constructed to investigate the characteristics of start-up, phase-changing heat transfer, and temperature-controlling for MPTL aboard one satellite. Test results shows that MPTL shows good working performance and stable operating behavior in microgravity environment. The two-phase accumulator presents good heat transfer performance under microgravity condition. Its temperature control accuracy reaches to ±0.1K. The passive cooling function of accumulator is validated, and its cooling rate reaches to 1℃/min. The temperature difference between the measuring points of vapor and liquid phase for the accumulator are in the range of 0.3～1.0K when the pump is working. The temperature control accuracy of the evaporator is in the range of ±0.1～±0.3K at the two rotation speeds. Superheating phenomenon takes place during the phase changing process of the loop and it leads to a higher 7～8K temperature at the evaporator’s outlet than the temperature control point. By comparing the results under the two rotation speeds, the superheat time and superheat temperature are related with the rotation speeds. The two-phase temperature controlling accumulator using the capillary structures can assure the function of high-precision temperature control and high-efficiency two-phase fluid management and control for MPTL under the microgravity condition. The phase transition characteristic for vapor-liquid is related to the mass flowrate of the loop. The stability of temperature on the evaporator is related to the fluid quality of its interior fluid. The study would contribute to the engineering design basis for the technology of two-phase flow and heat transfer, and would promote the development of active two-phase thermal control technology for space.

Key words: spacecraft thermal control, mechanically pumped two-phase loop (MPTL), on-orbit testing, convection heat transfer, microgravity