Experimental studies on heat transfer and friction factor characteristics of thermosyphon solar water heating system fitted with regularly spaced twisted tape with rod and spacer

• Compared to full length twist.
• Nusselt number decreases 3–31% for twist with rod of 125–500 mm.
• Nusselt number decreases 6–38% for twist with spacer of 125–500 mm.
• Friction factor decreases 9–42% for twist with rod of 125–500 mm.
• Friction factor decreases 11–62% for twist with spacer of 125–500 mm.

Experimental investigation of heat transfer and friction factor characteristics of thermosyphon solar water heater with full length helical twist of twist ratio 3, twist with rod and spacer of lengths 125, 250 and 500 mm has been studied. The experimental data for plain tube collector has been compared with fundamental equation falls within the acceptable limits for Nusselt number and friction factor. Findings shows that the Nusselt number decreases with increase in rod and spacer length and the pressure drop increases with decrease in rod and spacer length when compared with full length twist. Further the correlations developed for friction factor and Nusselt number has predicted the experimental data satisfactorily. The heat transfer enhancement in twist fitted with rod is found to be superior when compared with twist fitted with spacer.