STUDY OF POOL BOILING OF REFRIGERANT OVER A HORIZONTAL TUBE

Abstract

Boiling is a form of convection heat transfer since it involves fluid motion. But boiling heat transfer coefficients and rates are generally much larger than those of convection heat transfer without phase change, because of combined latent heat and buoyancy-driven flow effects. Among different. regions of pool boiling curve, nucleate pool boiling region is one of the most efficient mode of heat transfer. Heat transfer coefficient and rate increases very rapidly in this region. Heat transfer in nucleate boiling is a highly complex phenomenon as it depends on several parameters like thennophysical properties of liquid, input heat flux and heating surface conditions. This study investigates heat transfer performance on horizontal stainless steel tube for refrigerant R-410A and R-245fa, having zero ozone-depleting potential. R-410A is a high pressure refrigerant and R-245fa is a low pressure refrigerant. The experimental set up is specially designed to accommodate high vapour pressure refrigerant R-410A. This setup is used for the measurement of the wall heat flux, wall super heat and fmally heat transfer coefficients for both the refrigerants are calculated. An auto transformer is used to generate uniform heat flux on the tube. Data are taken in the order of increasing heat flux from 10 to 80 kW/m2 with an interval of 10 kW/m2. Test results showed that nucleate pool boiling heat transfer coefficients of refrigerants increase as the heat flux and vapour pressure increase. Measurements showed that the refrigerant of a higher vapour pressure has a higher heat transfer coefficient