Parallel and Counterflow He II Heat Exchangers

超流氦是指在2.2K以下存在的液氦的低温相，有着众多的技术应用。由于其独特的性质，即极高的导热系数，在某些情况下粘度为零，He II是各种低温设备的首选冷却剂，包括超导磁体系统和空间低温设施。对于这些应用来说，了解基本的HeII热传递机制是很重要的。本项目通过对平行和逆流换热器中的HeII进行分析和实验研究来满足这一需求。分析工作包括求解应用于由换热表面热耦合的两个强迫流热通道的HeII能量方程。需要进行实验测量，以确定分析工作的基准，并提供物理参数，特别是Kapitza电导的量化值。主要的测量数据包括平行/逆流换热器两侧流动的温度分布。改变换热器的长径比、流体速度和浴温，以获得建立关联式所需的一系列参数。虽然这项工作的直接目标是将分析结果与实验测量结果进行比较，但次要目的是利用基础研究得出的关联式或其他经验公式来开发HeII平行/逆流换热器的设计程序。

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.