Effect of aperture position and size on natural convection heat loss of a solar heat-pipe receiver

A new configuration of heat-pipe receiver is introduced to realize the isothermal light-heat conversion for middle- and high-temperature solar dish system. A 3-D numerical study has been performed to investigate the influence of aperture characteristics, i.e., aperture position and size on natural convection heat loss of this heat-pipe receiver accounting for air property variation with temperature. Temperature and velocity contours as well as the effects of aperture position and size on the natural convection heat loss have been well presented and discussed. It is revealed that the impact of aperture position on the natural convection heat loss is closely related to tilt angle, while the aperture size has similar effect for different tilt angles. The natural convection heat loss approximately is linearly dependent on wall temperature for different aperture positions and sizes. A new simplified Nusselt number correlation that can estimate natural convection heat loss with reasonable accuracy is proposed based on the corresponding numerical results. It is shown that the natural convection heat loss predictions by the present model show smallest deviation from the experimental results as compared to other well-known models regardless a partially or fully opened heat-pipe receiver for middle- and high-temperature solar dish system.