Corrugated circular dimple absorber for heat transfer augmentation on parabolic trough solar receiver

Abstract

Corrugated circular dimple absorber $($CCD$)$ as a heat transfer augmentation is introduced for line focusing solar receiver. It is designed to increase heat transfer performance with minimal increase of pressure drop. Meanwhile, computational fluid dynamics (CFD) analysis which is widely used is conducted by using ANSYS software to study outlet working fluid temperature, absorber temperature distribution, Nusselt number, specific heat loss, specific pressure drop and performance evaluation criteria (PEC). Heat transfer working fluid is Syltherm 800, a thermal oil which is extensively utilized in concentrating solar thermal power plant. The mass flow rate values are between 0.3 kg/s and 4 kg/s, the inlet temperatures of working fluid are 375 K and 650 K and concentrated heat flux is 100,000 W/m${}^2$. At 375 K inlet working fluid temperature, simulation results showed that corrugated circular dimple absorber can improve outlet working fluid temperature up to 8 K over 4 m absorber length and performance evaluation criteria reaches 3.28. This energy gain is obtained from lower specific heat loss to ambient due to higher Nusselt number. Increasing inlet working fluid temperature to 650 K will reduce thermal energy output since the specific heat loss increases from 137 W/m to 644 W/m due to radiation at higher temperature and emissivity value. Nusselt number rises from 230 to 521 and maximum absorber temperature decreases from 1036 K to 970 K. The specific pressure drop rises from 11 Pa/m in a smooth absorber to 41 Pa/m in a corrugated circular dimple absorber due to surface changes, but the performance evaluation criteria is at 1.31. In conclusion, CCD design can improve heat transfer performance with minimum pressure drop penalty indicated by higher PEC values.