Experimental studies on heat transfer and thermal performance characteristics of thermosyphon solar water heating system with helical and Left–Right twisted tapes

Experimental investigation of heat transfer, friction factor and thermal performance of thermosyphon solar water heater system fitted with helical and Left–Right twist of twist ratio 3 has been performed and presented. The helical twisted tape induces swirl flow inside the riser tubes unidirectional over the length. But, in Left–Right system the swirl flow is bidirectional which increases the heat transfer and pressure drop when compared to the helical system. The experimental heat transfer and friction factors characteristics are validated with theoretical equations and the deviation falls with in the acceptable limits. The results show that heat transfer enhancement in twisted tape collector is higher than the plain tube collector. Compared to helical and Left–Right twisted tape system of same twist ratio 3, maximum thermal performance is obtained for Left–Right twisted tape collector with increase in solar intensity.

Research highlights
► Conventional solar heaters are inefficient due to poor convective heat transfer.
► Twisted tapes improve the heat transfer rate in solar water heater system.
► Increase in outlet water temperature by 15 °C through the use of twisted tapes.
► Thermal performance of twisted tape collector is 19% more than plain tube system.
► Reduces collector area (0.6 m2) whereas area for conventional collector is 1 m2.