Search

Because of the ultra-high operation temperature in solar thermochemical reactors, radiative transfer accounts for the majority of the total heat transfer. Determining the radiative characteristics of catalysts during solar thermochemical reactions is critical for numerical calculations. Optical constant of material is only determined by the intrinsic properties of materials and not related to the micro-structural morphology. In this study, optical constants of four typical types of metal oxides often used as catalysts during solar thermochemical reactions were obtained by using infrared variable angle spectroscopic ellipsometry. In addition, the variation of optical constant of quartz window with temperature was also investigated using infrared variable angle spectroscopic ellipsometry in the far infrared spectral region. The experimental results indicated that the peak values of the refractive index and extinction coefficient of the optical window decreased with increasing temperature, and the degree of polarization of optical window decreased with increasing temperature and already decreased to 40% at 673 K in the spectral range of 7.2–7.5 μm. In addition, the refractive index and extinction coefficient varied sharply with increasing wavelength for both the catalysts and optical window.

The transient thermal performance response characteristics of porous-medium receiver have a major impact on the operability of a solar thermal power plant (STPP). To investigate the transient thermal performance response characteristics of porous-medium receiver, method coupled to the Monte Carlo ray tracing (MCRT) and finite volume method (FVM) was developed to establish a 2D transient state heat-transfer model using a local thermal non-equilibrium (LTNE) calculation. The effects of the fluid thermophysical characteristics, the fluid-phase type, and the solid-phase thermal conductivity on the unsteady-state heat-transfer performance were investigated to determine the transient thermal performance response characteristics of porous-medium receiver. The numerical results indicated that the variation in the air thermophysical properties due to the high working temperature can induce a very small transient thermal performance response in porous-medium receiver (a maximum deviation of 1.9% was observed in this study). A porous-medium receiver with a high thermal conductivity can benefit from the dispersion of concentrated energy. The dimensionless solid-phase temperature eon the center point of receiver in case of λ = 40 W/(m·K) was 1.05 at t = 240 s, decreasing to 0.92 in case of λ = 120 W/(m·K).