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A simulation method consisting of Monte Carlo Ray-Trace and Finite volume coupled model is proposed in the present work for simulation of complex photo-thermal conversion in the particle entrapped cavity receiver. The solar heat flux distribution in the cavity receiver was simulated by using the Monte Carlo ray tracing, while the convection-radiation-conduction process taking place in the cavity receiver was simulated by the Finite Volume Method. Solar heat flux was introduced as a source term in the energy equation for the Finite Volume Method part, and correlations for flow boiling heat transfer were chosen to calculate the surface temperature of the boiling tubes. Based on the simulation model, the thermal performance of the receiver, the temperature distribution and the mean square deviation of temperature at the outer surface of the boiling tubes were analyzed at varying albedo ω , diameter D and time (8:00–16:00). It was revealed that the temperature distribution on the outer surface of the boiling tubes can be uniformed by entrapping carbon particle sin the receiver. The results indicate that the collision between photon and carbon particles resulted in scattering and absorbing, with a tendency to decrease the maximum heat flux and temperature gradient at the surface of tubes. Although the thermal efficiency of the receiver decreases by 4.5%, the maximum temperature was reduced from 665 K to 630 K and the mean square deviation of temperature on the outer surface of backpanel was reduced from about 43 K to 26 K at noon. The results are useful for choosing suitable parameters for entrapped particles in cavity receivers to improve efficiency and operational safety. • MCRT and FVM methods were applied to evaluate the thermal efficiency of a cavity receiver. • Thermal efficiency of the cavity receiver at varying sun positions along the passage of day was evaluated. • Effects of particle's radiation properties on thermal performance of the receiver were investigated. • Carbon aerosol was used to achieve uniform heat flux distribution and overcome the localized heating problem. [ABSTRACT FROM AUTHOR]

An uneven heat flux distribution on the receiver's surface can lead to a highly non-uniform temperature distribution and high local temperature on the receiver tubes which results in fatigue failure. In the present work, a carbon aerosol entrapped cavity receiver of "DAHAN" power plant was numerically simulated to achieve homogenized heat flux distribution with improved safety of the receiver. A three-dimensional Monte Carlo Ray Tracing (MCRT) and Finite Volume Method (FVM) coupled model was developed to simulate the radiation-conduction-convection heat transfer in the receiver. Firstly, the MCRT method is used to simulate the solar heat flux distribution on the surface of the receiver. Then, the thermal performance and heat losses in the receiver were investigated by the coupled model. Finally, the levelized cost of energy (LCOE) was calculated and stress analysis was performed to predict the lifespan of the receiver. Moreover, with this strategy, the peak solar heat flux on the back panel significantly dropped from 290 kW/m2 to 135 kW/m2, while the peak temperature dropped from 652K to 620K. Carbon aerosol particle slightly decreases the thermal performance of the receiver. However, it decreases stress concentration on the receiver panels. Also, the economic analysis revealed that carbon aerosol entrapped receiver is more economical. • Thermal performance of carbon aerosol entrapped receiver is evaluated through a 3D MCRT-FVM coupling model. • Effects of the varying carbon aerosol density on heat flux and temperature distribution on the tube surfaces are examined. • Effect of varying carbon aerosol density on the thermal performance and heat losses of the cavity receiver is evaluated. • Economic and stress analyses of the receiver are performed with varying carbon aerosol density. [ABSTRACT FROM AUTHOR]

A non-uniform solar flux leads to a non-uniform temperature distribution on the walls of cavity receiver. There exists a large temperature gradient, which can cause great challenges for the safety and high-efficiency operation of concentrating solar power system (CSP). To overcome this problem, micron particles with strong properties of absorption, scatter and radiation are added into the cavity receiver to improve the non-uniform heat flux distribution on the wall. In the present research, a coupled simulation method based on Monte Carlo Ray Tracing (MCRT) method and Finite Volume Method (FVM) is established to simulate the complex photo-thermal conversion process of a two-dimension square solar cavity filled with air-carbon particle mixtures. In the model, first, the solar heat flux distribution on the surface of cavity receiver is simulated by MCRT and the photo-thermal conversion process in the receiver is modeled by FVM. Then both are coupled in the cavity receiver by transferring the absorbed solar energy computed by MCRT to FVM, and this energy is applied as a source term for the energy equation in the FVM part. Based on the coupling model, the thermal performance and the temperature distribution characteristics on the wall of the cavity receiver are studied at various particle densities. The results show that as carbon particle density increases, the heat flux and temperature distribution on the walls of the receiver becomes more uniform and the effects of different L / D and N on σ T of the receiver are further investigated. [ABSTRACT FROM AUTHOR]

Cavity receiver is one of the main components of efficient concentrating solar collector systems. It has the ability to operate at relatively higher temperature and efficiency. The safety and thermal efficiency of solar cavity receiver can affect the efficiency of the whole power system. However, the non-uniform distribution of heat flux and temperature inside the cavity tends to cause the operation instability and bring damage to the tube as well. In the present work, a comprehensive numerical model was developed by coupling Monte Carlo Ray Tracing (MCRT) and Finite Volume Method (FVM) to simulate the thermal performance of a 2D square solar cavity filled with air-carbon particle mixture. Firstly, the complicated photon transmission in the air-carbon particle mixture absorber is simplified as the transmission process in the statistically homogenous and isotropic turbid media. The solar heat flux distribution from the aperture to the wall is simulated by MCRT, and the photo-thermal convection process in the cavity receiver is modeled by FVM. Then the two parts are coupled in the cavity receiver by transferring the absorbed energy computed by MCRT to FVM, and this energy is applied as a source term of the energy equation in the FVM part. Based on this model, the temperature and heat flux characteristics of the cavity receiver were studied at various carbon densities. The result indicated that the air-carbon particle mixture can actively take part in the radiation and it appears that it has a remarkable effect on the temperature homogenization. It decreases the temperature of wall 3 dramatically and increases the temperature of wall 2 and wall 4. The relationships between the temperature unevenness and the number particle density were also analyzed. The temperature unevenness on the wall 3 drops most with the increase of number density of carbon particle, from 25.0K to 2.4K. The unevenness of temperature on the top and bottom walls also decreases slightly by 3K. In addition, the present model is proved to be accurate and reliable for studying the complex energy convection process in the cavity filled with air-carbon particle mixture. The result of the cavity receiver study can also provide a method to effectively improve the uniformity of the heat flux distribution on the wall. [ABSTRACT FROM AUTHOR]