Study On Flow Boiling Heat Transfer Characteristic In Space Thermal Control Evaporator

Thermal control system is a crucial component to provide a stable temperature in space vehicle to guarantee the normal operation of instruments or equipments. With the advancement and development of space technology, thermal control environment in space application is getting worse. In high temperature circumstance where heat loss rate through radiation is low, an evaporator is need as a consumptive heat sink to reject heat. On the other hand, electrical heating is necessary to guarantee the operation of some critical apparatus when spacecraft is in low temperature environment.Flow boiling heat transfer characteristic of two-phase flow is the key consideration in the design of any evaporating heat exchange systems. In this study, an experimental heat transfer coefficient database containing 2783 annular flow data points is built from 26 open literatures. The annular flow database consists of seven working fluids, covering hydraulic diameters of 0.5-14.0 mm, mass velocities of 50-1290 kg/m2s, liquid-only Reynolds numbers of 240-55119, vapor qualities of 0.10-0.98, heat flux of 3.0～240.0kW/m2, liquid Prandtl number of 1.26-5.85 and reduced pressures from 0.01 to 0.77. Nineteen existing prediction methods for flow boiling heat transfer are reviewed and evaluated by the annular flow database. Most of the existing prediction methods fail to provide satisfying prediction accuracy for the database. Therefore, a new correlation for flow boiling heat transfer coefficients in annular flow is developed based on the turbulence annular flow model of Cioncolini and Thome. The new correlation provides better prediction accuracy against the entire database than any other existing prediction methods. The MAE and MRE is 13.7% and 0.4%, respectively, with 66.5% and 89.0% of the data falling within ±15% and ±30% error bands. The new correlation shows good applicability for different tube diameters and fluids.In addition, the influence of Ω shaped grooves on flow boiling heat transfer characteristics is investigated. An experimental system is designed and established to investigate the flow boiling heat transfer characteristics in Ω shaped internally grooved tubes, and the influence of direction of gravity on heat transfer. It’s indicated that the flow boiling heat transfer performance in grooved tubes is evidently improved by strengthen of nucleate boiling effect. The heat transfer coefficient in grooved tube is 1.5 to 3 times higher than smooth tube in horizontal flow and vertical upward flow. And for vertical downward flow, the heat transfer coefficient is up to eight times higher than in smooth tube. However, the flow boiling heat transfer characteristic is notably different in different flow direction, meaning the groove structure fails to affect the flow pattern and guarantee the liquid wetting of tube wall. Nor can the groove structure eliminate the effect of gravity direction.Besides, aiming at heating and temperature control for spacecraft in low temperature circumstance, a series of PTC materials with Curie temperature suitable for thermal control of electronic components are prepared. And the adaptive thermal control performances and its applicability of this kind of PTC materials are investigated both experimentally and theoretically.