HEAT TRANSFER STUDIES ON A THERMOSIPHON REBOILER

Abstract

Experimental investigation of heat transfer to boiling of water and water-glycertile mixtures was carried out, in a natural circulation single tube reboiler. The heat trans fer section was an externally heated copper tube of 19.05 mm inside diameter and 940 mm long, The heating element, made of nichrame wire, was uniformly wound on the tube with porcelain beads as electrical insulator. The energy input to the test see tion was measured by wattmeters. Ten copper-oanstantan thermocouples were fixed on the tube wall along the length at intervals of 100 mm starting from the tube inlet to measure the wall temperatures. The liquid temperatures at inlet, exit and along the length were measured by copper constantan thermocouple probes. Different inlet liquid Isubcoolings in the range of 49C to 40°C were used to get varying lengths in tube having single phase natural convections subcooled boiling and bulk boiling regions of heat transfer; Heat flux values ranged from 10.66 x 103 to 24.88 x 103 W/m2. The local values of heat transfer coefficient.in single phase convective region were found to,remain almost unchanged along the tube length measured from the inlet but . they increase sharply in subcooled boiling region, under identical conditions of inlet liquid subcooling and heat 4 flux. The curves were found to shift to higher values of heat transfer coefficient when either the inlet liquid sacooling was decreased or the heat flux was raised. The heat transfer coefficients for water and water-glycerine mixtures in single phase natural convection were correlated by the following equation with a maximum error of .± 20 per cent..............