Solar Thermal Power Generation Research Articles

Optical Efficiency Analysis of Primary Mirror in LFR-CSP

The linear Fresnel solar thermal power generation system is one of the most representative forms of solar thermal power generation system at present. The primary mirror, as the main mirror, plays a key role in the photothermic conversion process of the collector tube. In this paper, the solar position and the optical efficiency of the primary mirror in LFR-CSP are modeled and analyzed. The light reflection process of primary mirror by solar position through four dimensions of solar declination angle, solar time angle, altitude angle and azimuth angle is studied, and the distribution law of solar position parameters in different seasons and different times throughout the year is analyzed. It is found that the variation range of chord efficiency of a single mirror element in the whole day is 75 %-93 %. The position of a mirror element in winter solstice has the greatest impact on the end loss of more than 1 %, but the summer solstice has no effect.

Multi-model adaptive predictive control of superheated steam temperature of DSG solar parabolic-trough collector based on heat-steam ratio and its reference trajectory

The direct steam generation (DSG) solar thermal power generation system has obvious inertia and nonlinearity in the response of superheated steam temperature. Due to the intermittent and random fluctuations of solar irradiation, the DSG system frequently undergoes large changes in operating conditions, which results in a very complicated problem of controlling the superheated steam temperature at the collector outlet. This paper proposed a multi-model adaptive control scheme based on the heat-steam ratio and its reference trajectory for the control problem of the outlet steam temperature of the DSG solar parabolic-trough collector. Firstly, through analyzing the dynamic characteristics of the superheated steam temperature, the main factors and the main nonlinear characteristics that lead to the nonlinearity of the steam temperature response are revealed. Secondly, taking the ratio of solar irradiation to the outlet steam flow (heat-steam ratio) as the characteristic parameter based on the nonlinear characteristics of the system, the DSG collector system is divided into several linearized subspaces, and then the corresponding steam temperature predictive sub-model set and steam temperature adaptive predictive control scheme are established. Finally, a smooth switching strategy based on the reference trajectory of the nonlinear characteristic parameter (heat-steam ratio) is established in response to the frequent or large switching of the controller caused by the large changes in the operating conditions, which effectively improved the stability of the temperature control process of the superheated steam at the DSG collector outlet. In this paper, the effectiveness of the above-mentioned control scheme has been preliminarily verified through simulation experiments.

Coordination control for Integrated Solar Combined Cycle thermoelectric coupling

Improving the utilization of solar energy and promoting the development of integrated energy systems, solar thermal power generation systems are researched and widely used. In the integrated solar combined cycle thermoelectric system, traditional power generation equipment as an auxiliary energy source mitigates fluctuations because of solar energy’s intermittent nature and uncertainty. However, because of the difference in response speed of different power generation equipment, it leads to imbalance of supply and demand power, which affects the smooth operation of the system. This paper proposes a novel coordination control method for integrated solar combined cycle thermoelectric coupling system. To solve the different energy response speed mismatches problem, an inertial power compensation scheme is proposed based on the established solar energy cogeneration system model, and the dynamic performance and robustness of the system are improved. In this paper, the intelligent optimization algorithm is used to optimize the parameters to improve the control precision of the controller. Finally, the paper carries out multi-scenario simulation with the 50MW solar thermal power generation and the 50MW gas turbine to verify the effectiveness and stability of the proposed coordination control method.

An additively-manufactured molten salt-to-supercritical carbon di-oxide primary heat exchanger for solar thermal power generation – Design and techno-economic performance

The design and techno-economic performance of a compact additively manufactured (AM) molten salt (MS)-to-supercritical carbon di-oxide (sCO2) primary heat exchanger (PHE) for solar thermal application is described. The PHE design consists of sCO2 flow through an array of microscale pin fins while the MS flows through mm-scale rectangular channels. Constraints imposed by AM using laser powder bed fusion method are considered in the design. Structural and fluid flow simulations are performed to arrive at a viable design of the core and headers. A simplified one-dimensional steady state model for the PHE is developed including the impact of surface roughness from the AM process. A process-based cost model is used to determine the tradeoff between thermofluidic design and manufacturing cost.A parametric study is performed using the thermo-fluidic and cost models to determine the set of geometrical and flow variables that result in high power density and low cost, while restricting the pressure drop on the sCO2 side to less than 2% of line pressure. Flow rates of MS and sCO2 were varied over heat capacity rate ratios ranging from 0.2 to 1. Results indicate that it is possible to design a low-pressure drop AM PHE with an effectiveness of 90% and a power density in excess of 10 MW/m3 (including headers). Fabrication of representative nickel superalloy specimens are shown to demonstrate that low-porosity parts with the requisite dimensional tolerance of PHE core can be generated.

Dual Fresnel lens and segmented mirrors based efficient solar concentration system without tracking sun for solar thermal energy generation

We propose and experimentally demonstrate a combination of two large Fresnel lenses and six segmented mirrors for concentrating sunlight efficiently within a common area throughout the day without mechanical tracking the sun. The proposed system was used for efficient solar thermal power generation, i.e., efficient heating of water. The angular position of two lenses is designed and mounted in such a way that the lenses are in direct line-of-sight with the sun for efficient sunlight collection during early morning, mid-day and for evening hours. Further, the height gap between Fresnel lenses and receiver unit is sufficient enough such that there is no shadow effect on the receiver unit hence the receiver unit is also exposed to direct sunlight rays throughout the day. Due to concentration of sunlight throughout the day the efficiency of solar thermal system is significantly enhanced. This is due to the fact that with the help of the proposed system, apart from concentrated sunlight made incident on to the solar thermal receiver it is also exposed to direct sunlight. The thermal receiver unit is placed in the common area and fluid is heated very fast. The design of system using ray optics in ZEMAX and experimental study of the direct and collected incident sunlight radiations using the proposed concentrating system on the receiver unit is analyzed. The thermal performance of the proposed system is compared with combination of single large Fresnel lens and segmented mirrors. The instantaneous thermal efficiency of the proposed system is around 20% or more in comparison to single lens concentrating system. The result shows that this type of system is highly efficient, and very much useful for countries where sunlight is available in plenty. Therefore, the proposed system is very much helpful for sustainable development of country.

Preparation and characterization of corundum ceramics doped with Fe2O3 and TiO2 for high temperature thermal storage

High-temperature thermal storage materials have received urgent attention for efficient thermal transfer in solar thermal power generation. Corundum ceramics doped with Fe2O3 and TiO2 were prepared via a pressureless sintering. A Fe2O3–TiO2 system with different Fe2O3/TiO2 ratios was applied to corundum ceramics. Phase composition, microstructural evolution, sintering properties, high temperature resistance and thermophysical properties were evaluated. The results indicated that Fe2O3 and TiO2 rendered the grains highly active and enhanced the bonding between grains due to existing stably in the lattice of corundum. In addition, decrease in the Fe2O3/TiO2 ratio led to a new phase of FeAlTiO5, which refined the grains. These effects gave the samples good sintering properties and thermal shock resistance, but the thermal expansion coefficient mismatch between FeAlTiO5 and corundum deteriorated the high-temperature (1300 °C) stability. Formula C1 (Fe2O3/TiO2 ratio of 9:1) sintered at 1600 °C had the optimum comprehensive properties, possessing a bending strength loss rate of 1.54% after 30 cycles of thermal shock (1100 °C-room temperature, air cooling) and a constant strength retention rate of approximately 71.34% after 90 h high-temperature cycle. The corresponding thermal conductivity and specific heat capacity were 18.81 W/(m·K) and 1.02 J/(g·K) at 25 °C, which was suitable as a high-temperature thermal storage material.

Technical Requirement Analysis of Regulation Characteristics of CSP Station with Heat Storage System

Using solar energy to generate thermal power is often called concentrating solar power (CSP), is a grid friendly clean energy utilization mode with unique development advantages. Large capacity heat storage system with relatively mature technology and low cost can be configured to ensure stable and controllable power generation. The method can be. Solar thermal power generation has become a strategic emerging industry supported by many countries around the world. Spain, the United States, India, South Africa and other countries have carried out commercial operation of power technology with solar thermal, and installed capacity is growing steadily. China has also given key support to CSP generation technology, which has been vigorously developed. As the most promising new energy technology, CSP generation from molten salt heat storage tower is one of the main technical approaches of CSP generation. The key is to store the absorbed solar heat through thermal storage materials and release it stably for a long time, so as to achieve continuous and stable power generation independent of solar radiation changes. Through analysis, this paper puts forward the key technology research and scheme of molten salt regenerative CSP generation system, promotes the research on the bidirectional relationship between CSP station and power grid, and realizes the innovation of renewable energy technology. Relevant research results and technical schemes can be popularized and applied in demonstration power stations, and can also be used for operation control of newly-built molten salt heat exchange and storage tower power stations in the future.

Study on Dynamic Model and Dynamic Characteristics of Solar Field of 50 Mw Trough Solar Thermal Power Generation Plant

Solar thermal power generation solves the problem of fluctuation and intermittency through energy storage system, and can bear the basic power load and peak load regulation. It is an important technical way for China's energy structure transformation. As a complex thermal system with multivariable disturbance, large inertia and large delay, the operation control of the solar field is a difficult issue. In this paper, the solar field of the first 50 MW trough solar thermal demonstration power plant in China is taken as the research object. Based on the topological structure and working principle of the solar field and the basic laws of optics and thermodynamics, the hydrodynamic calculation model and the heat transfer dynamic model are developed. The correctness of the model is verified by comparing the simulation results with the actual operation data. On this basis, the disturbance simulations are carried out. In addition, the dynamic response curves of step disturbance and the inertia time constant of the heat collecting loops are obtained. The conclusions of this paper have important guiding significance for the operation control strategy formulation and system optimization design of trough solar thermal power generation system.

Modeling and Simulation Analysis of Solar Thermal Electric Plants Based on Petri Net

At present, solar thermal power generation is in the demonstration stage, and the large-scale production is affected by many factors. In view of the characteristics of different operating modes of photothermal power generation, it is analyzed that the turbine needs to be started and stopped frequently due to different operating modes, which will lead to the instability of the output energy and the reduction of power generation efficiency. In this paper, the dynamic equation of energy conversion process is established by using the law of conservation of energy and conservation of mass. Combined with the logic switching criterion of the system, the system model was established by using the extended differential Petri net, and the validity and accuracy of the model were verified. Through the Petri net model of the system, the system’s working mode switching and power generation situation are analyzed due to the difference of direct normal irradiation intensity (DNI). Finally, the accuracy of the model is proved by comparing it with experimental data of the photovoltaic and thermal demonstration projects that have been connected to the grid.

Power Generation System of Solar Heat using Stirling Engine

Renewable energy, a domestically produced energy source, is attracting increasing attention as an important sustainable energy source in terms of improving energy self-sufficiency and reducing greenhouse gas emissions. In this regard, renewable energy utilization technologies are expected to realize sustainable development. In this research, we aim to construct a system that can collect sunlight and solar heat with a parabolic dish and generate electricity with a Stirling engine (SE). First, we evaluated the operational performance of the α-model SE, which employs a spirit lamp and an electric heater as heat sources. Finally, we executed a performance test of the constructed parabolic dish/SE combined solar thermal power generation system. As a result, when the total solar radiation amount is about 900 W/m2, a temperature difference of about 180°C is obtained between the SE heat cap and the surface of the low temperature side cylinder in about 3 minutes, and it is confirmed that the LED load lights up at an output voltage of 2V.

Experimental investigation of solar organic Rankine cycle with parabolic trough concentrator using nitrate salt as heat transfer and storage fluid

Nitrate salt with low melting point as heat transfer and storage fluid simplifies the heat transfer, storage, and exchange processes, and organic Rankine cycle as heat and power conversion system can realize the distributed energy supply. This study experimentally investigated the solar organic Rankine cycle with parabolic trough concentrator using nitrate salt as heat transfer and storage fluid, and the main problems and phenomena during the operation process have been described and analyzed in detail. Experimental results showed that the temperature difference of collector tube changes with direct normal irradiation and lags behind the changes of direct normal irradiation. Molten salt heat storage system can effectively restrain the temperature fluctuation at the collector tube outlet. The abrupt temperature drop at the evaporator inlet was caused by the heat imbalance between R123 and nitrate salt and inappropriate design of the evaporator. The effects of expander inlet pressure and expansion ratio on the ORC electrical power output were obtained at different superheating degrees of the expander inlet. The researches on each component are instructive to the technology of the parabolic trough concentrated solar power generation system with molten salt as heat transfer and storage fluid and provide some guides for the subsequent research. Furthermore, the energy and exergy analyses on overall system were developed, and results indicated the system average efficiency can reach 1.5%. Novelty statement Experimental study on parabolic trough concentrated solar ORC system with nitrate salt as heat transfer and storage medium were firstly analyzed. Single screw expander was firstly applied in a real solar thermal power generation system and showed a stable performance. Dynamic changes on the temperatures of PTC, molten salt tanks, and ORC were shown, and energy and exergy analyses on overall system were carried on.

Numerical analysis of the thermal and hydraulic characteristics of CO2/propane mixtures in printed circuit heat exchangers

The supercritical CO2 Brayton cycle has great prospects for application in the field of solar thermal power generation,where the thermoelectric conversion efficiency is significantly affected by the ambient temperature. Meanwhile, the real gas effect and thermal efficiency advantage of CO2 can only be fully used near the critical temperature. In this case, a scheme of using CO2-based mixtures as heat transfer fluids is proposed. As an important component of the supercritical Brayton cycle, a printed circuit heat exchanger (PCHE) is used as the object with CO2/propane mixtures as the heat transfer fluid. The thermal and hydraulic performance of the PCHE is investigated by numerical analysis. The general regulation of mixture components on heat transfer and friction features is obtained for various pressure ratios, inlet temperatures and mass flow rates. The results indicate that CO2/propane mixtures exhibit lower pressure loss and higher heat transfer coefficients as heat transfer fluids. The fanning friction factor decreases by 8.3% and the Nusselt number increases by 16.9% when the molar fraction of propane varies from 0 to 0.5. The heat transfer capacity of the mixture does not change significantly with pressure since its specific heat decreases slightly with increasing pressure. Compared with mixtures, the pressure drop of pure CO2 is more obviously affected by the mass flow rate. New thermal–hydraulic correlations explaining the thermophysical property variations and the mixing ratio effects are proposed which predict all data with errors of less than ±2%.

Capacity optimization of renewable energy microgrid considering hydropower cogeneration

This paper proposes a renewable energy system based on photovoltaic power generation, wind power generation and solar thermal power generation, combining thermal power plants with low-temperature multi-effect distillation. Through the electric heater and the thermal storage system photovoltaic and wind power will spare capacity in the form of heat energy, at the same time by thermal power generation system to maintain the stability of the power supply, run under constant output scheduling policy, to the levelling of the smallest energy cost and the design of power rate of maximum satisfaction as the goal, using multi-objective particle swarm optimization (PSO) algorithm to find the best combination of capacity, this system is established. At the same time, combined with low-temperature multi-effect distillation, compared with reverse osmosis seawater desalination cost is lower, reduce energy consumption, has a good application prospect.

Study on the preparation and thermal properties of binary mixed chloride salts

Nitrate phase change materials (PCMs) are the most widely used PCMs in solar thermal power generation technology. The maximum service temperature of Nitrate phase change materials is only 600°C. Therefore, to find a phase change material with large heat capacity, wide temperature range, low heat loss and low price is the focus of current research. According to different mass ratios, nine binary molten salt mixtures were prepared by mixing lithium chloride and sodium chloride. The phase change temperature and latent heat of phase transition of them were studied by differential scanning calorimeter (DSC). The experiment results showed that since the melting point of sodium chloride was high, when the content of sodium chloride in the binary mixture of lithium chloride and sodium chloride was large, a small amount of lithium chloride could not reduce the melting point of the mixture below 600°C, the mixture could not be melted. Meanwhile, when sodium chloride and lithium chloride were melted, the phase transition temperature of lithium chloride and sodium chloride remained at about 540°C and floated at ±15°C. The melting temperature and crystallization temperature of the binary mixture of 90% lithium chloride and 10% sodium chloride were quite different, and the latent heat of phase transformation was relatively high. Therefore, the binary mixed molten salt can be used in the heat transfer and storage technology of solar power generation.

Design and performance analysis of compressed CO2 energy storage of a solar power tower generation system based on the S-CO2 Brayton cycle

Two kinds of S-CO2 Brayton cycle tower solar thermal power generation systems using compressed CO2 energy storage are designed in this paper. The energy storage system uses excess solar energy to compress CO2 near the critical point to a high-pressure state for energy storage during the day, and the high-pressure CO2 is heated by a gas-fired boiler or the heat of stored high-temperature molten salt at night, so that it enters the turbine for work and drives the generator to generate electricity. The traditional molten salt heat storage scheme and the proposed compressed CO2 energy storage system model are established with Ebsilon software, and then the equipment selection, structure layout, and parameter design processes are carried out for the energy storage and heating systems. The thermoeconomic and technoeconomic indexes of the three energy storage schemes are calculated under the operating conditions of a typical day. The results show that the efficiency of the combined cycle is higher than that of other organic working fluids when T-CO2 is used as the bottom cycle working fluid. The integrated scheme of compressed CO2 energy storage and auxiliary combustion has the highest average daily efficiency (26.62% on summer solstice and 23.04% on winter solstice) and the lowest initial equipment investment. However, due to the additional cost of natural gas, the scheme has the highest levelized cost of energy (LCOE) at $0.1168/kWh. The LCOE of the integrated scheme of compressed CO2 energy storage and molten salt heat storage was the lowest at $0.1046/kWh.

Performance assessment of convective heat transfer in tubes with a temperature difference in the high‐temperature solar power generation system

Heat transfer enhancement technology provides many advantages in heat exchanger applications. Thermal energy storage is a technology that stocks thermal energy by heating or cooling a storage medium so that the stored energy can be used later for heating and cooling applications and power generation. The experimental investigation was carried out for heat convection in tubes with significant temperature differences (400 and 600°C), which were used convective heat transfer in a tube with air-water steam and heat conduction oil in the high temperature solar thermal power generation system. From the experiment, the results recorded with an average maximum temperature for air, water, and steam up to 422.4, 413.9, and 405.7℃, respectively, with the outer wall temperature of 600℃. Similarly, for an external wall temperature of 400°C, the average maximum temperature was obtained up to 351.2, 310.9, and 308.1℃, respectively. Therefore, from the experimental results, when the diameter of the flow pipe is higher than that of pipe diameter, then the effect of flow velocity on heat flow temperature was uncertain. At last, from the results, we conducted that the empirical correlation of convective heat transfer in a tube with temperature difference exceeding 100℃ obtained. The results showed that the increase of temperature thermal energy storage system could effectively enhance heat transfer and the calculation results can be used to optimize the performance of the high-temperature thermal energy storage system. Novelty impact statement Assessment of convective heat transfer in tubes with a temperature difference in the high-temperature is performed. The increase of temperature in thermal energy storage system could effectively enhance heat transfer. Carried out the study for different temperature thermocouples tube bundles with Nu, Re, and Pr. Conducted the empirical correlation of convective heat transfer in a tube with temperature difference.

Pulsed Electrophoretic Deposition of Carbon Nanotube Based Low-Reflective Coatings for Space Applications

Space observatory missions requires the development of low-reflectivity surfaces/coatings for space-borne instruments, such as seeker telescopes, optical sensors, etc., to minimize stray and reflected light across the visible and infrared wavebands for facilitating the direct exoplanet detection and characterization. All space application materials require lightweight, good thermo-structural properties, and durability when exposed to harsh environments, such as UV, atomic oxygen, vacuum, etc. The excellent mechanical, thermal, optical, and electrical properties of carbon nanotubes (CNTs) make them as ideal coating materials for obtaining low reflectivity surfaces for space applications.In this presentation, Faraday Technology Inc. will discuss an innovative electrophoretic deposition (EPD) manufacturing process, based on the use of pulsed electric fields, for controlled, reproducible, scalable application of low reflective CNT based coatings. The low-reflectivity CNT coatings have been successfully deposited on a variety of geometries: flat coupons, curved surfaces, sharp edges, and internal and external surface of square tubes using the FARADAYIC® EPD process with different anode-cathode configurations (Figure 1 A). The CNT coatings show the total hemispherical reflection of ~ 1% across visible to near infrared (NIR) wavebands, which is 5 times better than the reflectance of the typically used Z306 black paint (Figure 1 B). Most importantly, the CNT coating shows no measurably discernible spectral reflectance changes after 2500 equivalent solar hours (ESH) UV/VUV illumination (Figure 1B). As a comparison, Z306 black paint shows more than 2% reflectance increases with same ESH UV/VUV illumination. These CNT coatings also withstood simulated launch conditions vibrational tests, and demonstrated no weight loss or optical degradation. Furthermore, the CNT coatings were evaluated for atomic oxygen erosion resistance in a simulated low earth orbit (LEO) environment, and showed enhanced resilience when compared to Kapton and HOPG.In summary, a scalable manufacturing process for fabricating CNT based coatings with low reflectivity across visible to near infrared wavebands has been demonstrated and shown great potential in facilitating space observatory missions by minimizing stray and reflected light on targeted telescope and baffle materials and construction. The CNT based coatings will also be beneficial for optoelectronic fields for minimizing unwanted surface reflections for solar thermal power generation and storage, solar-driven steam generation for sanitization and water purification, and so on. Acknowledgements: The financial support of NASA SBIR program through contracts No. 80NNSC18P2062 & 80NSSC19C0177 is acknowledged. The authors acknowledge Alan Hopkins, Peter Fuqua, Amber Hennessy, Aura C Labatete-Goeppinger, Martin Ciofalo, and Lee Wizda from the Aerospace Corporation for simulated launch conditions vibration tests, optical characterization, and UV radiation effect tests. David Oakes and Alan Hoskinson from Physical Sciences Inc. are acknowledged for the atomic oxygen erosion tests on the CNT based coatings. Figure 1

Comparative Study of Conventional and Water Circulating-Heat Sink Cooling Base Thermoelectric Generator System for Optimum Solar Thermal Waste Heat Recovery

A novel technique for waste heat recovery in solar thermal power generation is investigated through experimentation and systematically presented. Power generation using Thermoelectric Generator (TEG) is a promising technique in waste heat recovery application. In this topology, TEG array is directly attached to the back of the solar Photovoltaic panel (model AP-AM15) to receive the transmitted heat at the back of the PV panel as waste heat. More so, a circulating water-heat sink is attached to the TEG cold side to improve the temperature gradient. Base on Seebeck effect, the TEG directly converts the temperature difference into electricity. The experimental result shows that efficiency between the range of 2.1% and 4.7% for the conventional cooling system while the output power approximately ranges between 0.05W and 0.47W, the circulating water-heat sink technique has efficiency ranging between 2.9% and 10.3% with output power between the range of 0.10W and 2.2W. The daily average increase in efficiency was found to be 263.76%. This shows that the daily average power is improved by a factor of 2.6376 with the water circulating water-heat sink technique. This is an indication of waste heat recovery from the solar thermal power generation.

Combined use of volumetric expanders and Scheffler receivers to improve the efficiency of a novel direct steam solar power plant

This research proposes an innovative solar thermal plant able to generate mechanical power through an optimized system of heliostats with Scheffler-type solar receivers coupled with screw-type steam expanders. Scheffler receivers appear to perform better than parabolic trough collectors due to the high compactness of the focal receiver, which minimizes convective and radiative heat losses even at high vaporization temperatures. At the same time, steam screw expanders are volumetric machines that can be used to produce mechanical power with satisfactory efficiency also by admitting two-phase mixtures and with further advantages compared to steam turbines: low working fluid velocities, low operating pressures, and avoidance of overheating. This study establishes a mathematical model to assess the energetic advantages of the planned solar thermal power system by evaluating the solar-to-electricity efficiency for different off-design working conditions. For this purpose, a numerical model on the Scheffler receiver is initially investigated, thus assessing all the energy losses which affect the heat transfer phase. A thermodynamic model is then developed to evaluate the energy losses and performance of the screw expander under real working conditions. Finally, parametric optimization of the solar energy conversion is performed in a wide range of operating conditions by establishing thermodynamic formulations related to the whole solar electricity generation system. Water condensation pressure and vaporization temperature are so optimized with respect to global energy conversion efficiency which, under the best operating conditions achieved in this research, rises from 10.9% to 14.4% with increasing solar irradiation intensity. Hence, the combined use of screw expanders and Scheffler receivers for solar thermal power system application can be a promising technology with advantages over parabolic dish concentrators. Novelty statement This research proposes an innovative direct steam solar power plant based on an SRC, with water utilized as both heat transfer and working fluid, equipped with Scheffler solar receivers as a thermal source and screw expanders as work-producing devices. Technical studies and energy assessments of this kind of SEGS at part-load operation do not exist in scientific literature; after reviewing the literature, it was determined that volumetric expanders have been rarely combined with Scheffler receivers for solar thermal power system application. In effect, combined use of screw expanders and Scheffler-type solar concentrator in a direct steam solar power system represents a completely new plant configuration; however, as a promising DSG solar system, at present numerical model of this new sort of SEGS is lacked in literature and the optimum operating conditions have yet to be defined. For this reason, the chief objective of this paper is to define a first parametric optimization of all thermodynamic variables involved to maximize global efficiency of the proposed solar thermal power generation system for ordinary working conditions.

Numerical Simulation Study on Turbulent Heat Transfer Characteristics of Supercritical Fluid in Micro-Fin Tubes

In consideration of the technical requirements for compact and efficient heat-exchange equipment in industrial fields, such as sludge incineration heat utilization, solar thermal power generation and aerospace, this paper analysed the supercritical nitrogen flow and heat transfer processes in square straight micro-fin tube, triangle straight micro-fin tube and smooth circular tube under different Re numbers, and obtained the changes in velocity field, local turbulence intensity, average Nusselt number and resistance coefficient of supercritical fluid in micro-fin tubes. Moreover, it was found that the introduction of micro fin was able to improve the turbulent heat transfer performance of supercritical fluid in tubes within certain Re number range.