Development of a Recirculation Ejector for a Cryogenic Heat Sink for ECLSS

In the development of advanced thermal control systems for use in hydrogen-powered space vehicles, utilization of the on-board hydrogen fuel as a heat sink for equipment cooling has many advantages. There are, however, significant challenges preventing the cryogenic temperatures of the stored fuel from causing heat transport fluid freezing. A shell and tube heat exchanger was developed to transfer heat from an ECLSS thermal control coolant loop to the cryogenic hydrogen fuel. To mitigate the potential for coolant freezing, it was necessary to recycle hydrogen from the heat exchanger outlet back to the inlet to moderate heat exchanger inlet temperatures. A recycle compressor could have been used with penalties in weight and reliability due to it's complexity. A superior solution was to use an ejector which has no moving parts, and uses the pressure head of the incoming hydrogen to develop the necessary pumping head and transport the hydrogen through the heat exchanger. This paper will present the design, development and testing of a recirculating ejector for a cryogenic heat sink for ECLSS.