Flow Boiling Heat Transfer Characteristics of R-134a in Horizontal and Vertical Mini-Channels Available to Purchase

Heat transfer experiments are carried out to obtain the data of R-134a during flow boiling in a circular mini-channel having a diameter of 1.75 mm and a length of 600 mm. The DC power supply generating 80 A at 12 V is used to apply heat to the test section. T-type thermocouples are installed at the inlet and outlet of the test section to measure the system temperature. The 10 thermocouples are installed on the top and bottom sides at equal distances along the tube to measure the wall temperature. Variable area type flow meters calibrated specially in the range 0.02–0.2 LPM for R-134a by the manufacturer are used to measure the refrigerant flow rate. A transparent tube is installed to match up with the test section outlet and to serve as a viewing window for visualisation. Two sets of the horizontal flow and vertical upward flow data are analysed. Flow regime map and heat transfer coefficient tend to be dependent with flow direction under the certain experimental conditions.