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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]

In the present paper, a comprehensive investigation on thermal and thermohydraulic performance of solar collector for heating air having circular wire rib roughness in the form of arc shape on the back side of absorber plate, has been carried out. A mathematical model incorporating the operating and system parameters has been developed and the results have been computed by using MATLAB for specified range of these parameters. A conventional solar air heater working under similar conditions has also been considered for the purpose of comparison. At rib height-to-duct hydraulic diameter ratio = 0.0422 and flow-attack-angle = 0.3333 the values of maximum thermal and effective efficiencies were found to be 79.84% and 75.24% respectively for the range of parameters used in the investigation. Further, the thermal efficiency, obtained in the present work has been compared with those obtained for other roughness geometries available in the literature for common roughness parameters and operating parameters to validate the results. Optimization of different parameters of wire roughness for optimum thermohydraulic (effective) efficiency of solar air heater duct has also been investigated. [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]

Exergy efficiency analysis is an useful method to evaluate overall performance of solar thermal systems as it takes into consideration of useful energy output and consequent pumping power requirement. In present work, an investigation on exergetic performance evaluation of solar air heater with arc-shaped wire rib roughened absorber plates has been made analytically by employing mathematical model and the results have been compared with a plane absorber plate solar air heater for similar operating conditions. The exergetic efficiency curves as a function of Reynolds number (Re) and temperature rise parameter (ΔT/I) for different roughness parameters have been plotted. The maximum enhancement in exergetic efficiency of roughened solar air heater as compared to smooth absorber plate solar air heater has been found as 56% corresponding to relative roughness height (e/D) = 0.0422. The design plots, exhibiting the optimum combination of roughness parameters, can be used to design arc shaped wire rib roughened solar air heater. [ABSTRACT FROM AUTHOR]