Numerical Investigation On Combined Heat Loss Characteristics Of Cavity Receiver Applied In Phase-change Type Solar Dish Thermal Power System

As a critical component in dish solar thermal power system,the thermal properties of the cavity receiver have a significant impact on the thermal efficiency of the system.Therefore, it is necessary to investigate the combined heat losses of the cavity receiver.In this research, the cavity receiver applied in phase-change system is treated as the study object. Based on the thermal boundary condition that only the bottom wall is in a constant temperature while other walls without heating, the effects of cavity inclination,bottom wall temperature, surface emissivity, wind speed and incidence angle(in wind cases) on the combined convection, radiation and conduction heat losses were conducted by 3D numerical simulation method. According to the results, the average convective and radiant heat loss Nusselt number Nuc and Nur in the given range for natural convection and wind conditions were proposed respectively.Results show that under natural convection conditions Nuc decreases with the increase of ?, while Nur increases slowly. For a given cavity inclination, both Nuc and Nur increase as the increase of the bottom wall temperature Tb and surface emissivity ?.However, compared with the gentle change of Nuc, the variation of Nur with Tb and ? is relatively sharp. Meanwhile, the proportion of convective heat loss in the total heat loss decreases with the increase of ?, Tb and ?, and it should be noted that the effect of ? is dominant. Nevertheless the variation of the radiation heat loss is presented with an opposite tendency with the increase of these variable, and mainly depends on Tb and ?.Moreover, the percentage of conduction heat loss decreases with ? while increases with Tb and ?.In wind conditions, Nuc is generally greater than that in natural convection cases,but in some conditions of low wind speed, the result may be exactly opposite. For inclined cavity, Nuc in different wind directions increases with the increase of wind speed V, but the variation is much more complex when cavity is horizontal. Compared with back-side wind conditions, the impact of V on Nuc is greater in front-side winds.There exists a wind incidence angle ? varying from 30° to 45° making Nuc reach a maximum value. At low wind speed, Nuc gradually decreases with the increase of ?,while at higher wind speed, it will rise up initially and then decline. At the same time,contrary to Nuc, Nur changes slightly with V, ? and ?, but rather sharply with Tb and ?,which illustrates that in wind conditions the convection heat loss is mainly depends onV, ? and ? while the radiation heat loss is mainly up to Tb and ?. In addition, with the change of V, ? and ?, the variation of convection heat loss proportion in the total heat loss is similar to that of Nuc, but the change with Tb and ? turns out to be opposite to Nuc.Furthermore, the variation of radiation heat loss ratio with the parameters considered is opposite to that of the convection heat loss, and the proportion of conduction heat loss shows to be gently variable.