The use of mixed gas working fluids has become common in Joule-Thomson type cryocoolers for a variety of applications. However, there is a scarcity of data currently available with supporting theory capable of predicting the heat transfer coefficients associated with two-phase, multi-component mixtures at cryogenic temperatures. An experimental facility is designed and constructed to measure heat transfer coefficient and frictional pressure drop for boiling multi-component zeotropic mixtures in small horizontal test sections. The aim of this facility is to enable the collection of high accuracy data to overcome the scarcity of heat transfer and pressure drop data for zeotropic mixtures undergoing a phase change (boiling) at cryogenic temperatures. Results are available for hydrocarbon-nitrogen mixtures and synthetic refrigerant mixtures, which are commonly used in small Joule-Thomson cryocoolers. The heat transfer coefficient measurements have been shown to be repeatable and accurate with an uncertainty of less than 10%. The pressure drop measurements have been calibrated, validated and the facility is capable of measuring the frictional pressure drop under both adiabatic and diabatic conditions. The measured heat transfer coefficient data are presented over a temperature range from 100 K to room temperature along with their sensitivity to parameters such as heat fluxes, mass fluxes, pressures, tube diameters, and mixture compositions. The experimental heat transfer coefficient data is predicted well using Granryd and Little correlations. Granryd shows the best accuracy with an Absolute Average Deviation (AAD) of 15% and predicting 87% of the data with a relative error lower than 30%. The measured frictional pressure drop data are compared to several pressure drop correlations available in the literature. The definition 1 of Awad and Muzychka correlation shows the best prediction with an AAD of 17% and agrees with 86% of our data with a relative absolute error lower than 30%. The second best correlation is Sun and Mishima with an AAD of 18%. In addition, the Cicchitti, Müller-Steinhagen and Heck, and Mishima and Hibiki correlations also show reasonable agreement with the experimental data.
Advisor: Gregory F. Nellis.
Ph.D. University of Wisconsin--Madison 2015.
Includes bibliographical references (pages 194-198).