Design and experimental investigation on cut tube absorber for solar parabolic trough collector

In parabolic trough collector, evacuated or non-evacuated glass tubes are more valuable for medium and high-temperature applications to reduce the heat losses from the absorber tube. Use of such glass tubes is not convenient under lower temperature applications because of lower surface temperature and high initial cost. In this work, an effort has been made to improve the performance of the absorber tube by reducing the heat losses without using a glass cover tube. A new technique of cut tube absorber was designed, developed and tested experimentally in the conditioned room by optimizing area with 45% cut on the upper portion of the tube, which does not receive concentrated sunrays and further covered with flat plate. Also, the presence of insulation and coating over cut tube absorber was studied. Water and sigma therm-K was used as a heat transfer medium to examine the heat losses for the working fluid having a temperature range below and above 100 degrees C. Experimental results reveal that reduction in overall surface area of the tube and coating leads to a decrease in thermal heat losses by 16.13% in water and 10.13% in sigma therm-K. Adding insulation would reduce heat losses more by 7.33% in water and 33.43% in sigma therm-K as compared to uncut tube with coating.