Modeling and Experimental Evaluation of the Effects of Reflective Film and Vacuum on the Performance of Concentric Double Tube Direct Flow Solar Collector

The present study is focused on investigating experimentally and numerically the four versions of a concentric double tube solar collector with and without vacuum, and with and without a reflective solar film. The conservation equations were used to formulate the thermal model and treated numerically to develop a homemade numerical code in Matlab. An experimental setup is constructed to test the four versions of the collector under outdoor conditions and hence validate both the thermal model and the numerical procedure. The tests were performed during the summer and autumn seasons. The numerical outcomes agreed well with the experiments showing a maximum error of about 2.1%. The results indicated that the vacuum effect is significant and enhanced the efficiency by about 13.6% in the presence of the reflective film. An average increase of 6.6% was found in the case of the collector without reflective film but with the vacuum. The reflective solar film increased the efficiency by about 4.3% for all cases with or without a vacuum.