Thermal performance evaluation of direct flow solar water heating system using exergetic approach

This communication presents the thermal performance evaluation of a direct flow evacuated tube collector-based solar water heater using energy, exergy analyses and some other thermodynamic parameters such as fuel depletion ratio, productivity lack, relative irreversibility and exergetic factor. The present solar water heating system was fabricated using total nine numbers of evacuated tubes having U-shape copper tubes being inserted inside the glass tube for flowing water through it. This arrangement was made for controlled flow rate of water having better heat and mass transfer mechanism. The experiments were carried out for different volume flow rates of water such as 10, 15, 20, 25 and 30 litres per hour (LPH) being supplied from the overhead tank directly. The performance of the present system is found to be the maximum for 15 LPH, while it is found to be the minimum for 30 LPH of volume flow of water among different volume flow rates analysed and presented in this study. It has also been found that the present water heating system performs better than those of other ETC water heating systems investigated by earlier. Also, the energy efficiency was found to be higher than that of the exergy efficiency for all the flow rates which is due to the fact that energy represents the quantity of energy, while exergy represents the quality of energy and also includes the irreversibilities associated with this system.