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The objective of present work is to predict the thermal performance of wire screen porous bed solar air heater using artificial neural network (ANN) technique. This paper also describes the experimental study of porous bed solar air heaters (SAH). Analysis has been performed for two types of porous bed solar air heaters: unidirectional flow and cross flow. The actual experimental data for thermal efficiency of these solar air heaters have been used for developing ANN model and trained with Levenberg-Marquardt (LM) learning algorithm. For an optimal topology the number of neurons in hidden layer is found thirteen (LM-13).The actual experimental values of thermal efficiency of porous bed solar air heaters have been compared with the ANN predicted values. The value of coeffi- cient of determination of proposed network is found as 0.9994 and 0.9964 for unidirectional flow and cross flow types of collector respectively at LM-13. For unidirectional flow SAH, the values of root mean square error, mean absolute error and mean relative percentage error are found to be 0.16359, 0.104235 and 0.24676 respectively, whereas, for cross flow SAH, these values are 0.27693, 0.03428, and 0.36213 respectively. It is concluded that the ANN can be used as an appropriate method for the prediction of thermal performance of porous bed solar air heaters. [ABSTRACT FROM AUTHOR]

In present article a mathematical model of arc shape wire roughened solar air heater, on the basis of energy and exergy output rates, entropy generation rate and augmentation entropy generation number, has been developed. A parametric study leading to entropy generation minimization has also been performed. In the analysis the geometric and operating parameters which have been considered as variable are: inlet air temperature, duct depth, collector width to duct depth ratio, mass flow rate per unit collector area, and temperature rise parameter . Results have been presented to see the effects of these values on the energy and exergy output rates of the roughened solar air heater. Effect of different values of wire rib roughness parameters on entropy generation has also been presented. Finally, design curves and optimization for different rib roughness parameters on the basis of minimum entropy generation number with temperature rise parameter, have been presented and optimum values also have been found out 0.004 to 0.010 (Km2)/W. The entropy generation rate obtained for the system, in the present work has been compared with those obtained for solar air heater with different roughness geometries on absorber plates available in the literature for common roughness parameters and operating parameters which validate the present results. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on optimal thermohydraulic performance of a solar air heater having arc-shaped wire rib roughness on underside of the absorber plate. The use of artificial roughness on the absorber plate of a solar air heater causes enhancement in rate of the heat transfer between absorber plate and flowing air, by creating turbulence, however, there is substantial increase in the frictional resistance which leads to more pumping power consumption. The effective efficiency is evaluated on the basis of useful thermal energy gain minus equivalent thermal energy to the power required to propel the air through solar air heaters. A mathematical model and procedure for prediction of effective efficiency of an arc shaped wire rib roughened absorber plate solar air heater has been presented and the effects of roughness and various geometrical and operating parameters on effective efficiency have been worked out. The effective efficiency of the roughened absorber plate solar air heater has also been compared with smooth absorber plate solar air heater operating under similar conditions. It is observed that effective efficiency of a roughened solar air heater has an optimum value corresponding to a certain Reynolds number and specific values of operating and geometrical conditions. A correlation between system and operating parameters that delivers optimum effective efficiency has been developed and presented, which can be used for optimal design of such systems. [ABSTRACT FROM AUTHOR]