International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 05 Issue: 07 | July-2018 www.irjet.net p-ISSN: 2395-0072 © 2018, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 165 Parametric optimization of system parameters and characteristics of solar air heater with different geometries. Mayank Mani Pandey 1 , Rahul Bahuguna 2 1 Faculty of Technology, Uttarakhand Technical University Dehradun , Uttarakhand, India 2 Asst. Professor, Dept. of Mechanical Engineering, Faculty of Technology, Uttarakhand Technical University Dehradun , -----------------------------------------------------------------------------***---------------------------------------------------------------------------- Abstract - The scope of this study deals with the parametric optimization of the system parameters based on effective efficiency criterion of the impingement jets of the various geometries. The optimum values required of the system parameters will be useful to determine the geometrical set of parameters which delivers the higher Nusselt Number and lower Friction Factor. Key Words: Heat transfer coefficient; jet impingement; Nusselt number; Reynolds number; thermal efficiency; effective efficiency. 1.INTRODUCTION The thermal efficiency of a solar air heater is significantly low because of low convective heat transfer coefficient between the absorber plate and air, leading to high absorber plate temperature and greater amount of heat losses to the ambient. It has been found that the main thermal resistance to the convective heat transfer is due to the formation of boundary layer on the heat transferring surface. Efforts for enhancing heat transfer have been directed towards artificially destroying or disturbing this boundary layer. 1.1 Improvement of heat transfer from the absorber plate The thermal efficiency of a solar air heater is generally low because of low heat transfer coefficient between absorber plate and air flowing in the duct, which leads to higher absorber plate temperature, thus higher thermal losses. By lowering the temperature of the absorber plate these thermal losses can be reduced which enhances the rate of heat transfer between absorber plate and air. The thermal losses can be reduced by using:  Extended surface on the absorber plate  Porous material in the air flow duct  Turbulence promoters 1.2 Artificial Roughness The artificial roughness in the form of repeated ribs is one of the effective and economic ways of improving the performance of a solar air heater. Ribs break the viscous sub layer and create local wall turbulence due to separation and reattachment of flow without disturbing the core turbulent flow resulting in improvement of convective heat transfer coefficient between air and the absorber plate. The application of artificial roughness in the form of fine wires or ribs of different geometry on the heat transfer surface has been recommended to increase the heat transfer coefficient by several investigators. Several different types and shapes of geometries of artificial roughness have been proposed and investigated. The types include transverse, inclined, v-shaped, rib-grooved, ribs with gaps, discrete or continuous, multiple-v ribs, v with gap, chamfered, wedge shaped ribs, dimpled, expanded metal mesh, arc-shaped ribs etc. It has been found that each shape is represented by sets of geometrical dimensionless parameters that characterize the geometry. Such parameters include relative roughness height, relative roughness pitch, angle of attack, relative groove position, relative gap width, relative gap position etc. Several investigators have experimentally investigated the heat transfer and fluid flow characteristics of these different geometries and developed correlations for Nusselt number and friction factor as a function of geometrical parameters. They have also discussed the relative enhancement in Nusselt number achieved by the use of artificial roughness. The performance of solar air heaters as a result of the use of artificial roughness on the underside of absorber plate of solar air heater has been investigated and the enhancement in thermal efficiency as a function of roughness parameters has been presented and discussed. However, it is pointed out that an enhancement in heat transfer and hence thermal performance is accompanied by substantial increase in friction factor and hence pressure losses and energy expenditure to make the air flow through the