Transition Flow Heat Transfer and Pressure Drop in a Uniformly Heated Inclined Solar Air Heater Fitted with Wavy Tapes

Mixed convection heat transfer and pressure drop in a circular inclined solar air heater fitted with wavy tapes for assisting flow under uniform heat fluxes is carried out in transition flow regime using experimental and numerical technique. The working range of Reynolds number is 500–7005. Both experiments and simulations were carried out with three wavy tapes uniform wave ratio of 0.75, width ratio of 0.6, 0.7 and 0.8 and free length of 2000 mm at uniform heat flux of 2 kW/m2. This study has investigated the effect of the wave ratio, heat flux and inclination angle of the tube on the mixed convection heat transfer and pressure drop process. The results obtained from the investigation show shifting in the transition flow regime. For plain horizontal channel, the transition begins at Reynolds number 2983 and ends at Reynolds number 3346. At a 15° inclination angle, the transition begins at Reynolds number 3012 while ends at Reynolds number 3349. This is due to the buoyancy effect. At inclined position, the effect of buoyancy forces lessens which causes the transition to start at delayed Reynolds number. Along with this enhancement in the heat transfer and pressure drop was also observed. At the inclined position of 15°, a slight decrease in the Nusselt number was observed. A further decrease in the Nusselt number was observed when inclination angle is changed to 30°. However, friction factor shows very minute appreciation when position is changed from horizontal (0°) to inclined (30°). Correlations were also developed to predict the Nusselt number and friction factor in laminar, transition and turbulent flow regime.