Measurement of Heat Transfer Coefficients for Non-Azeotropic Hydrocarbon Mixtures at Cryogenic Temperatures

The use of non-azeotropic hydrocarbon mixtures in throttle-cycle refrigeration systems has resulted in large increases in the performance of Joule-Thomson type cryocoolers. However, there is very little data or theory currently available in the literature regarding the thermal-fluid behavior of multi-component, multi-phase mixtures at cryogenic temperatures. The design of these systems is therefore semi-empirical, relying heavily on experimental iteration. In this paper, an experimental apparatus is described that is capable of making precise and controlled measurements of the heat transfer coefficient over a range of cryogenic temperatures, compositions, geometries, and flow rates that are relevant to small-scale, throttle-cycle refrigeration systems. The experimental apparatus is used to carry out a study of the horizontal flow boiling heat transfer coefficient for a non-azeotropic hydrocarbon mixture in a circular cross-section with a constant wall temperature. The measurements are carried out over a range of cryogenic temperatures and the data is presented in the form of heat transfer coefficient as a function of temperature and thermodynamic quality. The experimental uncertainty of the measurements is theoretically estimated to be 10%. Measurements of the single-phase heat transfer coefficient for pure nitrogen fall within 10% of the Dittus-Boelter correlation.Copyright © 2004 by ASME