Performance analysis of double Glazing v trough solar water heater With wing cut twisted tape inserts

Abstract

Theoretical and experimental study of thermal performance andfriction factor of double glazing V-trough (DGVT) solar water heater (SWH)with horizontal wing cut (HWTT) and vertical wing cut twisted tape (VWTT)for twist ratio 6 and 3 were studied. Initially the results were compared withconventional single glazing V-trough (SGVT) SWH. The results show thatthe DGVT augments the heat transfer performance by 8.84 % than SGVT. newlineThis is due to the second glass of double glazed collector which will reducethe transmittance solar radiation, decreases the top heat loss.The results of plain DGVTSWH were compared with the HWTT andVWTT for different twist ratio (6 and 3). The wing cut twisted tape hasenhanced the heat transfer rate by two methods. Firstly secondary flow of newlineflowing fluid creates the extra turbulence inside the riser tube. Secondly thewings act as a fin and enhance the heat transfer rate. Compare with twist ratio6, twist ratio 3 gives higher thermal performance. Thermal performance ofHWTT with twist ratios 3 and 6 is 4.91 % and 3.37 % higher than the tubeequipped with VWTT respectively. But the Friction factor for HWTT withtwist ratios 3 and 6 is 1.003 - 1.01 and 1.002 - 1.013 times of that tube newlineequipped with VWTT respectively.To reduce the friction factor in the HWTT without major drop inthermal performance spacer and rod were kept with various lengths (125, 250 newlineand 500 mm) in twist ratio 3. The percentage reduction of Nusselt number fortwisted tapes fitted with rod of 125 mm, 250 mm and 500 mm length is 3.9 %,8.39 % and 17.43 % as compared to full length twist. newline newline