Heat loss analysis of three coil cylindrical solar cavity receiver of parabolic dish for process heat

摘要

The share of solar thermal energy for process heat at sub cooled temperature is estimated about 30% of the total demand. The assessment of heat loss from tubular receiver used for the process heat is necessary to improve the thermal efficiency and consequently the cost effectiveness of the parabolic dish receiver system. The study considers a modified three coil solar cavity receiver of wall area three times (approximately) as compared to the existing single coil receiver and experimentally investigates the effect of increases in cavity inner wall area, fluid inlet temperature (50-75oC), and cavity inclination angle (θ = 0-90o) on the combined (total) heat loss from receiver under no wind condition. This paper also develops an analytical model to estimate the different mode of heat losses from the downward facing receiver. In the mean fluid temperature range of 50oC to 70oC, the total heat loss from three coil receiver is reduced up to 40.98% at 90o and 20% at 0o inclination, as compared to single coil receiver. The analytical modeling estimates very low heat loss from conduction (1-3%) and radiation (2-8%) and high heat loss from convection (97-89%). The heat loss by natural convection decreases sharply with increase in cavity inclination, while the heat loss by radiation and conduction increases slowly with inclination. A three coil cavity receiver might be considered in the design to reduce heat loss from parabolic dish receiver system to improve the thermal performance and cost effectiveness.