The influence of a novel ribbed wave tape on the enhancement of heat transfer in a solar air heater operating in a transitional flow regime: an experimental study

The effect of a novel ribbed wave tape on the augmentation of heat transfer in a solar air heater operating in a transitional flow regime is experimentally examined. Three different wave ratios are used, and the tube is uniformly heated using heat fluxes while the Reynolds number varied from 521 to 10,194. The transition for plain tube begins at 2810 and ends at 3724. For tube with ribbed wavy tapes, transition begins early and ends at higher Reynolds number than plain tube. For 2 kW/m2 of heat flux, the transition for wavy tape having wave ratio 3 begins at Reynolds number 2589 while at heat flux of 4 kW/m2, the transition begins at Reynolds number 2745. The end of transition takes place at Reynolds number 3969 and 4139 for wave ratio 3 at heat fluxes 2 and 4 kW/m2, respectively. The length of transition decreases with increase in the wave ratio at uniform heat flux. The average enhancement in Nusselt number for ribbed wavy tapes having wave ratio 3 at 4 kW/m2 heat flux was 262% and 85% for laminar and turbulent flow regime, respectively. Two empirical correlations were developed to predict the Nusselt number and friction factor for all the flow regimes.