A Multi-Zone Unsteady Heat Transfer Model for an Open Volumetric Air Receiver: A Step Towards Scale-Up and Design Optimization
TL;DR: In this article , a multi-zone, unsteady heat transfer model is developed for a straight absorber pore-based open volumetric air receiver, which includes heat exchange between the porous absorbers, absorbers and receiver casing.
Abstract: A comprehensive, multi-zone, unsteady heat transfer model is developed for a straight absorber pore-based open volumetric air receiver. This includes heat exchange between the porous absorbers, absorbers and receiver casing, and absorbers and return air. The validation revealed its predictive capability within an uncertainty of ±7%. The model is used for the scale-up of receiver design with several intermediate absorber layers. The major recommendations for scale-up are a) multiple absorber layers is beneficial for mitigating thermal stress, b) higher flux concentration is required for non-volumetric heating, to achieve the desired air temperature, compared to volumetric heating, c) air return ratio should be 0.6, d) absorber porosity should be 0.6 for volumetric heating and higher for non-volumetric heating, e) absorber gap to length ratio should be 0.15 -0.25, f) the radiative heat loss is substantial for non-volumetric heating; therefore, the exposed surface area to ambient should be reduced, and g) absorber diameter to length ratio should be 1-2. The developed approach is generic and adaptable for the different open volumetric air receiver designs.
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01 Jan 2023
TL;DR: In this paper , an integrated solar power generation unit using a tubular solid oxide fuel cell (SOFC) is designed, which features the utilization of concentrated solar power for the heat supply of the SOFC.
Abstract: An integrated solar power generation unit using a tubular solid oxide fuel cell (SOFC) is designed in this paper. The unit features the utilization of concentrated solar power for the heat supply of the SOFC. A mathematic model of the unit is developed and validated against the experimental data from published literature. Then the model is used to analyze the unit performance. The normal operation of the unit is proved by the hydrogen and current density distribution. The SOFC fuel utilization ratio and efficiency are 73% and 44%, respectively. To lower the impact of solar irradiation fluctuation on the unit, adjusting the inlet air velocity may be one solution. It seems increasing the inlet air velocity proportional to the solar irradiation can effectively stabilize the fuel cell efficiency (the max variation is only −1.5%).
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TL;DR: In this article, a review of the central receiver designs for concentrating solar power applications with high-temperature power cycles is presented, which includes low-cost and durable materials that can withstand high concentration ratios (~1000 suns), heat-transfer fluids, and low radiative and convective heat losses leading to a thermal efficiency >90%.
Abstract: This paper reviews central receiver designs for concentrating solar power applications with high-temperature power cycles Desired features include low-cost and durable materials that can withstand high concentration ratios (~1000 suns), heat-transfer fluids that can withstand temperatures >650 °C, high solar absorptance, and low radiative and convective heat losses leading to a thermal efficiency >90% Different receiver designs are categorized and evaluated in this paper: (1) gas receivers, (2) liquid receivers, and (3) solid particle receivers For each design, the following information is provided: general principle and review of previous modeling and testing activities, expected outlet temperature and thermal efficiency, benefits, perceived challenges, and research needs Emerging receiver designs that can enable higher thermal-to-electric efficiencies (50% or higher) using advanced power cycles such as supercritical CO 2 closed-loop Brayton cycles include direct heating of CO 2 in tubular receiver designs (external or cavity) that can withstand high internal fluid pressures (~20 MPa) and temperatures (~700 °C) Indirect heating of other fluids and materials that can be stored at high temperatures such as advanced molten salts, liquid metals, or solid particles are also being pursued, but challenges include stability, heat loss, and the need for high-temperature heat exchangers
587 citations
TL;DR: A chronological review of the volumetric receivers of most interest for electricity production, identifying their different configurations, materials and real and expected results, and pointing out their main advantages and conclusions based on the multitude of international and national projects reports and references.
Abstract: Deployment of the first generation of grid-connected plants for electricity production, based on Solar Thermal Power Plants with Central Receiver System technology using large heliostat fields and a solar receiver placed on the top of a tower, is currently being boosted by the first commercial plants in Spain, PS10, PS20, and Gemasolar. Therefore one of the main goals of solar technology research is the study of existing receivers and development of new designs to minimize heat losses. In this context, volumetric receivers appear to be the best alternative to tube receivers, mainly due to their functionality and geometric configuration. They consist of a porous material that absorbs concentrated radiation inside the volume of a structure and transfers the absorbed heat to a fluid passing through the structure. Solar radiation is first converted into thermal energy or chemical potential, and then at a later stage, into electricity. This volumetric receiver technology has been under development since the early 1990s in various research and development projects. This paper is a chronological review of the volumetric receivers of most interest for electricity production, identifying their different configurations, materials and real and expected results, and pointing out their main advantages and conclusions based on the multitude of international and national projects reports and references. This study also deals with other important issues surrounding the volumetric receiver, such as the basic plant configuration, flow stability phenomenon and the main problems of a windowed design for pressurized receivers.
523 citations
TL;DR: The technical feasibility of the CRS power plants technology can be valued as sufficiently mature after the pioneering experience at the early 1980s of several pilot plants in the 0.5-10 MW power range and subsequent improvement of key components like heliostats and solar receiver in many projects merging international collaboration during the past 15 years.
Abstract: Central Receiver Systems that use large heliostat fields and solar receivers located on top of a tower are now in the position to deploy the first generation of grid-connected commercial plants. The technical feasibility of the CRS power plants technology can be valued as sufficiently mature after the pioneering experience at the early 1980s of several pilot plants in the 0.5-10 MW power range and the subsequent improvement of key components like heliostats and solar receiver in many projects merging international collaboration during the past 15 years. Solar-only plants like Solar Tres and PS10 or hybrid schemes like SOLGAS, CONSOLAR, or SOLGATE are being developed and supply a portfolio of alternatives leading to the first scaling-up plants during the period 2000-2010. Those projects with still non-optimized small sizes of 10-15 MW are already revealing a dramatic reduction of costs versus previous feasibility studies and give the path for the formulation of a realistic milestone of achieving a LEC of $0.08/kWh by the year 2010 and penetrating initial competitive markets by 2015 with LECs between $0.04/kWh-$0.06/kWh.
312 citations
TL;DR: In this article, the macroscopic temperature distribution of the fluid and solid phases in volumetric solar air receivers is analyzed, and the effects of velocity, porosity, mean cell size and the thermal conductivity of the solid phase on the temperature fields are analyzed.
Abstract: Ceramic foams are promising materials for the absorber of volumetric solar air receivers in concentrated solar thermal power (CSP) receivers. The macroscopic temperature distribution in the volumetric solar air receiver is crucial to guarantee that volumetric solar air receivers work steadily, safely and above all, efficiently. This study analyzes the temperature distribution of the fluid and solid phases in volumetric solar air receivers. The pressure drop in the ceramic foams and the interfacial heat transfer between the flowing fluid and solid are included in the model. The radiative heat transfers due to concentrated solar radiation absorption by the ceramic foam and the radiation transport in the media were modeled with the P 1 approximation. The energy fields of the fluid and solid phases were obtained using the local thermal non-equilibrium model (LTNE). Comparison of the macroscopic model with experimental results shows that the macroscopic model can be used to predict the performance of solar air receivers. Sensitivity studies were conducted to analyze the effects of velocity, porosity, mean cell size and the thermal conductivity of the solid phase on the temperature fields. The results illustrate that the thermal non-equilibrium phenomena are locally important, and the mean cell size has a dominant effect on the temperature field.
224 citations
TL;DR: In this paper, the non-uniform solar flux features in four CSP technologies including the parabolic-trough collector, the linear Fresnel collector and the solar power tower were reviewed, and a recommendation for the optimization of the solar collector was provided.
Abstract: Concentrated solar flux distribution in the concentrated solar power (CSP) systems is extremely non-uniform, which can lead to high local temperature and large temperature gradient in solar receivers that will cause great challenges for the safety and efficient operation of the system. This paper introduces the non-uniform flux features in four CSP technologies including the parabolic-trough collector, the linear Fresnel collector, the solar power tower, and the parabolic-dish collector. Challenges including degeneration of the materials, thermal stress and deformation, and overburning are summarized. The corresponding solutions proposed to tackle these challenges are emphatically reviewed, and a recommendation for the optimization of the solar collector is provided from this review, which is that the solar flux distribution and the heat transfer ability of the heat transfer fluid (HTF) should match with each other as well as possible. From this point of view, the existing solutions are classified into two groups. One is optimizing the heat transfer ability of the HTF to match with the flux distribution, which is called the passive approach. The other is homogenizing the flux distribution to match with the heat transfer ability of the HTF, which is called the active approach. This review can help to have a better understanding of the non-uniform solar flux features in CSPs, and provide guidance for solving the corresponding challenges.
186 citations