Ph.D. Proposal Presentation by Biswajit Mitra
Monday, February 14, 2005

(Dr. Srinivas Garimella, Chair)

"Supercritical Gas Cooling and Condensation of Refrigerant R410A at Near-Critical Pressures"

Abstract

A study of heat transfer and pressure drop of refrigerant blend R410A during condensation and supercritical cooling at near-critical pressures is proposed. Local heat transfer coefficients and pressure drops will be obtained at five nominal pressures, 0.8, 0.9, 1.0, 1.1 and 1.2 ´ P crit , for the mass flux range 200 < G < 800 kg/m 2 -s in 6.2 and 9.4 mm diameter tubes. The entire vapor-liquid region will be traversed in small quality increments for the condensation tests, while for the supercritical tests, refrigerant temperature will be varied from 30-110 ° C in small increments. Local heat transfer coefficients will be measured using a thermal amplification technique that measures heat duty accurately while also providing refrigerant heat transfer coefficients with low uncertainties.

The measured heat transfer coefficients and pressure drops will be analyzed and compared with the limited heat transfer and pressure drop models available in the literature for similar situations, and explanations for agreements/disagreements will be provided. Flow-regime-specific condensation heat transfer and pressure drop models will be developed using flow regime maps available in literature. Supercritical heat transfer and pressure drop models will be developed by accounting for the sharp variations in the thermophysical properties in the vicinity of the critical point, and defining liquid-like, gas-like, and pseudo-critical transition regions.

It is believed that the proposed study will lead to better understanding of phase-change and near-critical pressure cooling of the refrigerant, and the development of heat transfer and pressure drop models that can be used for designing components for high-temperature-lift vapor-compression space-conditioning and water heating systems.