The Characteristics of Flow Boiling Heat Transfer and Pressure Drop in Small Tube with the Pipe Sections Having Increased Diameters

Abstract

This study presents an experimental investigation of the characteristics of the flow boiling heat transfer and pressure drop for refrigerant of R134a flowing in a small - diameter evaporative tube with the pipe sections having increased diameters. The experiments were performed at the saturation temperature of 5°C , heat flux of 5.12 ~ 10.96 ( KW/m2), mass flux of 200~600 ( kg/m2s), different length-to-diameter ratios of the test tubes and refrigerant quality of 0.07~0.78, and based on the same surface area of heat transfer. The enhancement performance ratios, θa/s for the tubes with the pipe sections having increased diameters relative to the smooth tube are higher than 1 (about 1.01~1.10). It means that the augmented tubes show the better overall performance than the smooth tube under study.