Parallel and Counterflow He II Heat Exchangers

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HeII (superfluid helium), the low temperature phase of liquid helium existing below 2.2 K, has numerous technical applications. Because of its unique properties, namely extremely high heat conductivity and in some cases vanishing viscosity, He II is the preferred coolant for a variety of low temperature devices, including superconducting magnet systems and space based cryogenic facilities. An understanding of basic HeII heat transfer mechanisms is important for these applications. This project addresses this need through analytical and experimental studies of HeII in parallel and counterflow heat exchangers. The analytical work consists of obtaining solutions to the HeII energy equation applied to two forced flow HeII channels thermally coupled by a heat exchange surface. Experimental measurements are required to benchmark the analytical work as well as to provide quantitative values for physical parameters, particularly the Kapitza conductance. The primary measurements consist of temperature profiles within the flowing HeII contained on both sides of a parallel/counterflow heat exchanger. Heat exchanger length-to-diameter ratio, fluid velocity and bath temperature are varied to obtain a range of parameters necessary for developing correlations. Although the immediate goal of the work is a comparison of analytical results with experimental measurements, a secondary purpose is to develop a design procedure for HeII parallel/counterflow heat exchangers using correlations or other empirical expressions derived from our fundamental studies.