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A volumetric solar receiver with composite porous structure is proposed, where a porous foam with different pore parameters from that in the other region of receiver is placed in the inlet near-wall region. Thermal performance of the solar receiver is numerically investigated. The local thermal non-equilibrium model is utilized to represent the energy transport within the porous foam. Radiative transfer in the porous foam due to high temperature combined with the transport of concentrated solar radiation inside the receiver is solved using the P1 approximation. Thermal behavior comparison is made between the receiver with composite porous structure and that with single porous layer. The effects of different pore parameter designs are discussed. The results indicate that there exists a large temperature gradient in the solid phase for a solar receiver with single porous layer. Using low porosity and small mean cell size in the inlet near-wall region for the receiver with composite porous structure can reduce the solid temperature gradient and increase the mean fluid outlet temperature. [ABSTRACT FROM AUTHOR]

Volumetric receivers have become a promising technology for the solar thermal conversion. The absorption of concentrated solar radiation and the heat transfer to the working fluid are the two dominant processes. To effectively investigate the thermal performance of receiver, a numerical model coupling the solar radiation transport and the internal heat transfer is presented. Solar radiation transport from the dish concentrator to the interior of receiver is simulated with the Monte Carlo ray tracing method. Combining the distribution of absorbed solar energy in the receiver, the local thermal non-equilibrium model with P1 approximation is used to solve the internal heat transfer. Two other treatment approaches for the concentrated solar radiation are compared. One considers the solar radiation on the front surface of receiver as thermal boundary condition (TBC) and the other as a collimated incident radiation (CIR) beam. The results show that the porosity and mean cell size have a great effect on the distribution of absorbed solar radiation. Compared with the coupling approach, the TBC approach overestimates the solid temperature near the front surface with a deviation up to 76.4%, while the CIR approach provides acceptable temperature field with a deviation less than 3.4%. In addition, the fluid and solid temperatures both decrease as the slope error of concentrator increases. [ABSTRACT FROM AUTHOR]

In this article, a newly designed volumetric solar receiver (VSR) using cup-shaped Al 2 O 3 porous absorber is studied through numerical simulations and experimental verification. The absorber achieves several advantages including lower heat loss and higher uniformity of heat flux. The ray tracing method is adopted to obtain the external radiation source. The inner radiative exchange within the cavity is solved with the aid of User Defined Function (UDF). The heat transfer performance has been compared based on different parameters including window reflectivity, porosity and mass flow rate. The theoretical advantages of using cup-shaped Al 2 O 3 absorber are presented. The experimental verification is adopted based on sixteen-dish concentrator (SDC) platform. [ABSTRACT FROM AUTHOR]

The absorption of concentrated solar radiation within volumetric receiver is the key step that governs the global efficiency of solar thermal systems. An integrated radiative transfer model combined the dish concentrator, solar window and porous absorber is developed. The distribution of absorbed radiation energy in the porous absorber and the optical performance of the entire system are investigated by a Monte Carlo ray tracing simulation. The detailed radiation transport within the solar window and porous absorber is fully considered. The effects of porous structure parameters, slope error of concentrator and the alignment error of receiver are analyzed. The results show that the optical losses due to the back scattering from porous absorber and the absorption and reflection of solar window have a significant influence on the optical performance of system. The porous structure parameters greatly affect the distribution of solar radiative source within the porous absorber. In addition, the optical efficiency decreases noticeably when the slope error and alignment error exist. [ABSTRACT FROM AUTHOR]

Space Solar Power Station (SSPS) is a very potential candidate for supplying abundant electrical energy. Symmetrical two-stage flat reflected concentrator (STFC) has many advantages when used in SSPS. However the steady performance and control method on orbit has become a big problem which will be discussed in this paper. The actual posture of entire station is analyzed in detail due to the requirements of good flux uniformity, circular concentrated spot and controlled concentration ratio. Here two regulating directions are studied. And the most optimal method in multidimensional space of adjusting parameters is developed. In order to verify the correctness and reliability, the concentrating characteristics in different cases are simulated by Monte-Carlo ray tracing method (MCRTM). Based on the optimal adjusting parameters, solutions for the arrangement of transverse truss are proposed. After that the effect and regulating method for tracking error is investigated to improve the tolerance performance as highly as possible. Finally the construction of concentrators is much important to the realizability, cost and working performance. A flat hexagon module concept and the regular pattern are investigated to build the optical model. The flux distribution on solar panel based on different big number of modules is simulated, which provides certain reference for the build of SSPS. [ABSTRACT FROM AUTHOR]

The crossed compound parabolic concentrator (CCPC) is one of the most efficient non-imaging solar concentrators used as a stationary solar concentrator or as a second stage solar concentrator. In this study, the CCPC is modified to demonstrate for the first time a new generation of solar concentrators working simultaneously as an electricity generator and thermal collector. The CCPC is designed to have two complementary surfaces, one reflective and one absorptive, and is named as an absorptive/reflective CCPC (AR-CCPC). Usually, the height of the CCPC is truncated with a minor sacrifice of the geometric concentration. These truncated surfaces rather than being eliminated are instead replaced with absorbent surfaces to collect heat from solar radiation. The optical efficiency including absorptive/reflective part of the AR-CCPC was simulated and compared for different geometric concentration ratios varying from 3.6× to 4×. It was found that the combined optical efficiency of the AR-CCPC 3.6×/4× remained constant and high all day long and that it had the highest total optical efficiency compared to other concentrators. In addition, the temperature distributions of AR-CCPC surfaces and the assembled solar cell were simulated based on those heat flux boundary conditions. It was shown that the addition of a thermal absorbent surface can increase the wall temperature. The maximum value reached 321.5 K at the front wall under 50° incidence. The experimental verification was also adopted to show the benefits of using absorbent surfaces. The initial results are very promising and significant for the enhancement of solar concentrator systems with lower concentrations. [ABSTRACT FROM AUTHOR]