Design of a Helium Recovery System for a Hypersonic Expansion Tunnel Facility

An upcoming facility at Rutgers - New Brunswick is under design with the goal of creating airflow with Mach numbers and enthalpy levels suitable for simulating hypersonic flight in Earth's atmosphere, operating on the principle of an expansion tunnel. Helium is used for its low molecular weight, which provides favorable characteristics for generation of high-velocity, high-enthalpy shockwaves; a system for recovering, purifying, and storing helium gas has been designed in order to minimize the cost of operation and ensure the successful creation of suitable test conditions. This recovery system will use one of two configurations based on pending quotes from two currently competing equipment suppliers; the more mature design of the two is presented. In preparation for an experiment, several sections of the tunnel are filled with helium gas at very high, or very low, pressures. The purity of helium in these sections at the beginning of a test influences the test conditions, with higher purity levels yielding higher velocities and enthalpy levels. Operating requirements for the recovery system are determined with estimation of the required purity levels for given test conditions. This investigation determines these requirements, and investigates tradeoffs in different procedures for operation of the recovery system.