Thermo-hydraulic characterization and design optimization of dimpled/protruded absorbers in solar heat collectors

In the present study, the thermo-hydraulic characterization of the dimpled/protruded absorbers in solar heat collectors have been studied. The process control factors pertaining to these types of absorbers which affects the thermal and hydraulic behaviour have also been discussed along with their effect towards optimal shape and position. The study is concentrated around four performance attributes viz. Nusselt number, friction factor, effective and exergetic efficiency. Since, different combinations of control factors present different behaviour for each performance attribute, the entropy and the weight of the attribute has been determined using Shannon's Entropy method. Further, the VIKOR method is used to evaluate the benefit and regret measure and finally the VIKOR index based upon which the alternative sets are ranked from the best to the worst. Enhancement in each performance attribute has been identified on the optimal control factor combination for each absorber and duly compared with the conventional flat plate collector. It has been observed that the Nusselt number for dimpled arc and protruded arc is 2.24 and 3.65 times while friction factor enhancement is 2,65 and 1.6 times respectively. Also, enhancement of 1.22 and 1.23 times for effective efficiency and 1.36 and 1.09 times for exergetic efficiency than that of conventional collector is observed respectively for dimpled-arc and protruded-arc absorbers.