STUDY OF PERFORMANCE CHARACTERISTICS OF DISCRETE RIB ROUGHENED SOLAR AIR HEATER

Abstract

The thermal performance of conventional solar air heater is generally poor because of low convective heat transfer coefficient between air and the absorber plate. The heat transfer 0 coefficient of the absorber plate can be substantially increased by enhancing turbulence in the duct using of artificial roughness in a solar air heater duct. The artificial roughness increases the pumping loss in the duct so turbulence must be created only in a region very close to the absorber plate to break the viscous sub-layer for augmenting the heat transfer and the core flow should not be unduly disturbed to limit the increase in friction losses. Experimental investigation has been carried out to determine the heat transfer and friction characteristics of the duct covering the range of roughness parameter (relative roughness height (eiD) of 0.037, relative gap position (diW) of 0.25, relative gap width (gie) of 1.0, relative roughness pitch (Pie) of 8.0 and relative roughness angle of 60) and working parameter (Reynolds number, Re from 4000 to 18,000 and heat flux of 1000 W/m2) with one broad wall roughened with inclined rib having two gaps (inclined discrete rib), one from the - trailing edge of the rib and another from the leading edge of the rib. A numerical model of the duct is created and meshing is done in ANSYS WORKBENCH. The computational results - are compared with the experimental results. Two different computational analyses has been carried out, first compared the numerical results with available experimental data having roughness as inclined discrete rib with a gap. In the second analysis, the numerical results are compared with the experimental results obtained from present work having roughness as inclined discrete rib with two gaps, one from the trailing edge of the rib and another from the leading edge of the rib. The results showed nearly similar enhancement of heat transfer rate in both the cases of one gap and two gaps in the inclined ribs as compared with smooth duct. The k-C turbulence model has shown better agreement between the experimental and computational results