Effects of double windows on optical and thermal performance of solar receivers under concentrated irradiation

To fulfill the working condition at high pressure and temperature, a double-windowed pressurized volumetric receiver (DW-PVR) was proposed in this work. A computation model combining Monte-Carlo Ray Tracing method (MCRTM) and Finite Volume method (FVM) was established to evaluate the temperature field, energy losses, and efficiencies of the receiver. The model also includes a gray-band approximation to consider the spectral properties of windows. The performance of receiver with two windows and with single one (SW-PVR) was compared with each other. Based on the model, effects of five influential factors were fully studied. It is found that the total efficiency is improved by increasing cavity size, inner window thickness, emissivity of inner surfaces and distance between windows. Compared with SW-PVR, the DW-PVR gets a higher thermal efficiency at the expense of a lower optical efficiency. With a relatively large distance between windows and relatively small cavity size, the total efficiency of DW-PVR can be higher than that for SW-PVR. The peak temperature of the outer window in DW-PVR is 38.6-82.6 K lower than that in SW-PVR. The present work can provide a deeper understanding of characteristics of DW-PVRs.