Analytical performance investigation of parabolic trough solar collector with computed optimum air gap.

Parabolic trough collectors have a wide range of industrial as well as domestic applications. This study analytically investigates the performance of non-evacuated absorber tube with glass cover of parabolic trough collector (PTC) in terms of overall heat loss from the absorber. The impact of different parameters such as diameter of absorber tube, mean temperature of absorber tube, wind velocity, emissivity of absorber and ambient temperature have been studied and find the optimum value of air gap. The optimum value of air gap has been computed considering one-dimensional steady state model, where heat loss due to convection plus radiation is equal to heat loss due to conduction plus radiation from absorber tube to glass cover under steady state. Optimum air gap is found to be approximately 7mm and 8 mm for an absorber tube of diameter in range of 1.2-3.18cm and 4.5-7.62cm, respectively. Corresponding to optimum air gap, minimum overall heat loss has been observed. Overall heat loss increases with increase in absorber temperature, wind velocity and emissivity of absorber, whereas decreases with increase in air temperature for different absorber tube diameters. Absorber tube with diameters in the range of 3.18-4.5cm gives better performance. From the obtained data, correlations have been developed, which can be further utilized for designing the PTC system for getting desired output. [ABSTRACT FROM AUTHOR]