Development of an Evaporator Using Porous Wick Structure for a Two-Phase Mechanically Pumped Fluid Loop

The Jet Propulsion Laboratory is developing a two-phase mechanically pumped fluid loop (2PMPFL) thermal control system to enable novel mission designs and greater science return for NASA. Pumped two-phase fluid loops have the potential to provide robust and effective thermal control that combine the best aspects of passive two-phase systems (heat pipes) and mechanically pumped single-phase fluid loops. The current requirements include the development of a system with multiple 1 m2 evaporators, each of which is capable of remaining spatially and temporally isothermal while accommodating heat loads of up to 500 W and local fluxes of up to 5 W/cm2. The goal is to attain this using less than 5 W of power. Such a system would be able to accommodate the next generation of payload and bus electronics while using minimal resources. The most important technology of a 2PMPFL is an evaporator which is able to gather heat efficiently. To develop the evaporator which is spatially and temporary isothermal, a high heat transfer coefficient between the heating plate and vapor is essential. Recently, Odagiri et al. (2017) proposed a theoretical model which can predict heat transfer coefficients in evaporators using porous wick structure. The model is based on thin liquid film evaporation theory and nucleate boiling. In this research, we optimized the shape and properties of the wick structure to achieve a high heat transfer coefficient within the designated heat flux range by applying Odagiri’s model and a multi-optimization method. The evaporator was fabricated via metal additive manufacturing and demonstrated by measurement in the thermal-fluids lab at JPL. The methodology of modeling and optimization are presented. Also, the thermal performance of the optimized evaporator is discussed.