Heat Transfer and Friction Factor Data for Gap-Helical Screen Fin Counterflow Heat Exchanger

Abstract

A counterflow heat exchanger for a small cryogenic gas refrigerator has been designed, built, and tested at the M.I.T. Cryogenic Engineering Laboratory. This heat exchanger was designed specifically for the integral heat exchanger/expander cryocooler that was also developed at this laboratory. Two annular gaps between three concentric tubes make up the counterflow passages of the heat exchanger. A helical screen fin within the low pressure passage of the heat exchanger provides large heat transfer area at relatively low pressure drop loss and conduction loss. A very small annular gap within the high pressure passage of the heat exchanger provides a large heat transfer coefficient with relatively small dead volume. Measured steady-state heat transfer coefficients and friction factors are presented and compared with those predicted by theory.