Numerical Study of Porous Parabolic - Finned Receiver for Solar Parabolic- Trough Concentrator

Abstract

Solar energy is now developing as the biggest alternative to the fossil fuels , and in this field one of the most developing field is CSP. The overall efficiency of the CSP depends on the heat transfer between the receiver to the working fluid , so to enhance the heat transfer fins can be employed inside the receiver tube. Fins have been used as an extended surface , which leads to the enhancement in the heat transfer . The primary function of providing a fin is to increase the heat transfer area, so as to increase the convection heat transfer. In a pipe flow for a constant heat flux condition the heat flow does not change in x direction , so we can imply that convective heat transfer coefficient is constant over the length of the pipe. The T hence is constant over the pipe length. If we need to increase the efficiency of heat transfer by fins than the primary importance is by increasing the heat transfer area , which if done by varying the size of fin is impractical , as due to the limitation of the space inside the fin. The number of the pores provides high surface area hence the convection heat transfer coefficient increases . In the present work porous fin of parabolic profile fins are used to enhance the heat transfer in a solar receiver. It is been observed that by increasing the porosity of the fins the heat transfer due to forced convection increases, but at the expense of pressure. If the pressure loss is too high than the pumping cost increases so we need to optimise the heat transfer so that the pressure loss is bearable and heat transfer is high. The aspect ration of the fin is changed and the result is been compared for the both ratios , and it is been found that by increasing the aspect ratio the Nusselt number increases. Previously the work is been done on linear profile longitudinal fins , but in this study comparative study is done between heat transfer enhancement of rectangular fins and parabolic fin. The variation of surface Nusselt number with respect to the Reynolds number is plotted and it is validated with the analysis of Akansu (2006). A three dimensional model of the receiver pipe with the porous fins of parabolic profile is been analysed. The turbulence model used in ANSYS 15 is k-ε RNG solver in the CFD package FLUENT. The forced convection heat transfer inside the receiver pipe is compared using parabolic fins by varying porosity .