Two-phase flow issues in space nuclear reactor and nuclear propulsion systems
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Nuclear technologies in space for power and propulsion as part of the new exploration initiative are being considered along with a number of power conversion systems including liquid metal Rankine power cycles. Although studies of the liquid metal Rankine cycle as a power conversion system were completed in the 1960s and 1970s, some important issues related to multiphase flow and heat transfer remain for development of space nuclear systems. The Interphase Transport Phenomena Laboratory at Texas A&M University has studied microgravity two-phase flow phenomenology pertaining to space nuclear reactor and propulsion systems for 20 years. This work has been conducted principally in reduced gravity aircraft testing as wells as one week long space shuttle test. Specifically, this work includes microgravity flow regime mapping, phase separation technology, phase distribution within manifolds, and boiling and condensation behavior. Texas A&M has completed work predicting flow regimes resulting from various fluids and flow conditions providing fundamental information necessary to develop pressure drop and heat transfer models important for thermal hydraulic design. The removal of gas generated in the liquid metal coolant of the primary as well as gas/liquid separation in the power conversion system requires a device that has a high volumetric throughput, is not sensitive to changes in inlet quality, and provides a high degree of separation. Due to the complications of microgravity phase separation, a unique, stationary vortex separator which provides centripetally driven phase separation in microgravity was developed. A model of split two-phase flow in manifold under reduced gravity was developed and validated experimentally. Several flight experiments were conducted to evaluate the affect of the flow regime and flow quality on the heat transfer coefficient in a boiler/condenser. The purpose of this paper is to discuss issues related to microgravity two-phase flow and the development of space nuclear systems while demonstrating work undertaken at Texas A&M University.
