Thermal efficiency enhancement of an Evacuated Tube Collector: Experimental, numerical and analytical approach

Abstract

In this work a commercial Evacuated Tube Collector with U-pipe flow system and mini compound parabolic concentrators was investigated analytically, numerically and experimentally. The thermal function of the solar collector was tested experimentally in Athens city (Greece) at 26th of April for water inlet temperatures in the range of 50–75 °C. An analytical approach and a simulation model were utilized and validated through experiments. The comparisons showed mean deviations lower than 6 % from the experimental results, with the non-experimental solutions to appear a mean declination of 1.6 % between them. A detailed thermal analysis was followed using the validated analytical solution for an inlet temperature range of 10–80 °C. The volumetric flow rate was optimized analytically. Two different geometrical characteristics were modified for studying possible enhancement of the collector. These parameters were the number of the evacuated tubes and the diameter of each receiver tube considering the collector’s aperture area as constant. The increment of these parameters had positive effect on the thermal efficiency leading to enhancements greater than 6 %. The experiments were held at the Laboratory of Applied Thermodynamics (Mechanical Engineering Department) of National Technical University of Athens. The design and the numerical simulations of the collector were conducted with Solidworks.