BOILING OF AQUEOUS SUGAR SOLUTIONS IN A SINGLE TUBE NATURAL CIRCULATION EVAPORATOR

Abstract

The present work embodies an experimental investigation of heat transfer in single vertical tube closed loop natural circulation evanorator for water and sugar solution systems at atmospheric pressure. The vertical tube (test-section) was a copper tube of 940 mm length and 19.02mm inside diameter. The heating of the tube was done by electrical heating •e.lement of nicrome wire (22 gauge) wound externally to provie constant uniform flux. The wall and liquid temperatures were measured by means of -copper-constantan thermocouples fixed at an interval of lOomm length of test section. The heat flux values ranged from 7.108x103to 24.878x103 W/m2. Five concentrations 9.90, 19.45,27.40,43.60 and 57.50 wt% of sugar solutions were used in the study. The experimental results slowed the expected trends aualitatively and quantitatively. The local values of heat-transfer- coefficient were correlated by following equations. Natural convection zone of wa ter : - =8.3.0x105 G p "C) .624 r r 1 •- with a maximum deviation of + 20%. Boiling zone of water:- hB-5 (ZtA F-1-•=7.5x10 zs with a maximum deviation of + 30%. Natural convection zone. of. 19.45 and 27.40 wt% sugar:- Nu=0.913(Gr Pr) (Pr)-C1.26 with a maximum deviation of + 20%. natural convection zone of 43.60 and 57.50 wt% sugar:- ply.0033 (p ) 0.17 u=9.6334 (Gr with a maximum deviation of + 20%. .091 z 12.79) w d Boiling zone of sugar•solutions -4 p c -1.3 - 2.93 hB 2,25x10 iL -1D d (At)stI9 86Lti, ri„ z tw d „ s with a maximum deviation of + 30%. The physical properties used in the correlations of boiling heat transfer were taken at the saturation temperatures of the test liquids while for natural convection region they were taken at arithematic of wall and liquid temperatures corresponding to the location under consideration.