CFD BASED HEAT TRANSFER ANALYSIS OF ARTIFICIALLY ROUGHENED SOLAR AIR HEATER

Abstract

Modem civilization depends completely on power and energy to move ahead. With population explosion and depleting conventional energy sources such coal, oil and gas, the threat of energy crisis is looming. Thus mankind is forced to search for energy sources which are renewable and eco-friendly. Renewable energy sources such as solar energy, wind energy, hydro power and geothermal energy are being explored extensively in recent times. Solar energy can be used for various applications such as water heating, space (air) heating, cooling and refrigeration, power generation and others. Solar air heater finds application in areas such as drying of agricultural products, process heating and others. Solar air heaters have been observed to have generally low heat transfer coefficient from the absorber plate to the air. This low heat transfer coefficient results in relatively higher absorber plate temperature leading to higher thermal losses to the environment and hence low thermal efficiency. Thermal efficiency can be increased by several methods including by increasing heat transfer coefficient with the help of roughness elements attached to the underside of the absorber plate, but it brings about large increase in pumping power consumption also. Therefore, there is a need to select suitable artificial roughness geometry that can yield maximum heat transfer with minimum possible pumping power. A review of literature shows that several investigators have carried out work on performance of solar air heater with roughened duct by providing various types of geometry of roughened elements. The roughness in the form of thin circular wires, rectangular wires, wedge shaped roughness with different orientations such as transverse, inclined, chamfered and combination of different geometries have been investigated. Most of the work is carried out experimentally and very little work has been reported in the