Heat Transfer and Pressure Drop Characteristics of R-22, R-134A and R-407C in Microchannel Tubes

Abstract

A study of heat transfer and pressure drop characteristics for single-phase and twophase
\nflow of refrigerants in micro channel tubes was conducted. An existing facility was
\nmodified to perform tests on a single microchannel tube using water flowing in counterflow
\nas the heat sink fluid. Data were collected for sub cooled liquid, superheated vapor and
\ncondensing refrigerant for circular-port microchannel tubes at four different mass flow
\nrates. The refrigerants tested were R-22, R-134a and R-407C. In addition to circularport
\ntubes, square-port tubes were tested with R-22 for both single-phase and two-phase
\nflow. Data were also taken with water flowing inside a square-port microchannel tube.
\nThe Reynolds number for all the flows in this study ranged from 3,000 to 17,000 in the
\nliquid phase and 30,000 to 110,000 in the vapor phase.
\nThe heat transfer coefficients and pressure drop for circular-port micro channel tubes
\nwere compared for R-22, R-134a and R-407C. For sub cooled liquid flow, the heat transfer
\ncoefficient for R-407C was found to be greater than that for R-22 and R-134a. The heat
\ntransfer coefficient for R-22 was found to slightly lesser than the other two refrigerants
\nfor condensing flow.
\nA model was built to predict the heat transfer and pressure drop in the microchannel
\ntube. In most cases, the heat transfer and pressure drop predicted by the model agree
\nvery well with experimental results. A sensitivity analysis revealed that the total heat
\ntransfer is not very sensitive to the refrigerant side heat transfer coefficient.