Heat transfer and friction factor correlations for impinging jet solar air heater

Experimental investigation has been carried out to study heat transfer and friction factor characteristics using impinging jets in solar air heater duct. The effect of flow and geometrical parameters, especially the jet diameter, streamwise and spanwise pitch has been studied. The experiments encompassed the flow Reynolds number in the range 3800–16,000. The jet diameter, streamwise pitch and spanwise pitch each normalized by hydraulic diameter of the duct are in the range: 0.043–0.109; 0.435–1.739; 0.435–0.869 respectively. The air through the jets is impinged normally onto the absorber surface which was heated with uniform heat flux of 1000W/m2. The heat transfer and friction factor data obtained is compared with that of parallel flow solar air heater under similar geometrical and flow conditions. The results show that there is considerable enhancement in heat transfer and friction factor by 2.67 and 3.5 times respectively. Correlations for Nusselt number and friction factor have been developed in terms of above parameters which reasonably correlate the experimental data.