Heat Efficiency of Trough Solar Vacuum Receiver

2014 ◽  
Vol 521 ◽  
pp. 23-27
Author(s):  
Jun Ming Liang ◽  
Jian Feng Lu ◽  
Jing Ding ◽  
Jian Ping Yang

The heat loss and thermal performance of solar parabolic trough vacuum receiver were experimentally measured and analyzed by heat transfer model. According to the present experiments, the heat loss of solar parabolic trough vacuum receiver has good agreement with the heat loss of vacuum receiver from Solel company. As the wall temperature increase from 108°C to 158°C, the heat loss of solar parabolic trough vacuum receiver remarkably increases from 35 Wm-2to 57 Wm-2. The heat transfer model of parabolic trough solar receiver is then theoretically investigated due to the energy balances between the heat transfer fluid, absorber tube, glass envelope and surroundings. When solar radiation flux is constant, the heat efficiency of solar parabolic trough system decreases with the wall temperature and oil temperature. When solar radiation flux or solar concentration ratio increases, the heat efficiency of solar parabolic trough system increases.

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 1001
Author(s):  
Jianfeng Lu ◽  
Yarong Wang ◽  
Jing Ding

The temperature distribution and thermal efficiency of a molten salt cavity receiver are investigated by a nonuniform heat transfer model based on thermal resistance analysis. For the cavity receiver MSEE in Sandia National Laboratories, thermal efficiency in this experiment is about 87.5%, and the calculation value of 86.93–87.79% by a present nonuniform model fits very well with the experimental result. Different from the uniform heat transfer model, the receiver surface temperature in the nonuniform heat transfer model is remarkably higher than the backwall temperature. The incident radiation flux plays a primary role in thermal performance of cavity receiver, and thermal efficiency approaches to maximum under optimal incident radiation flux. In order to increase thermal efficiency, various methods are proposed and studied, including heat convection enhancement by an increase of flow velocity or the decrease of the tube diameter and number of tubes in the panel, and heat loss decline by a decrease of view factor, surface emissivity and insulation conductivity. According to calculation results by different modes of the nonuniform heat transfer model, the thermal efficiency of the cavity receiver is reduced by nonuniform heat transfer caused by variable fluid temperature or variable circumferential temperature, so thermal efficiency calculated by variable fluid temperature and variable circumferential temperature is lower than that calculated by average fluid temperature and bilateral uniform circumferential temperature for 0.86%.


Energy ◽  
2013 ◽  
Vol 59 ◽  
pp. 666-675 ◽  
Author(s):  
Jianfeng Lu ◽  
Jing Ding ◽  
Jianping Yang ◽  
Xiaoxi Yang

2019 ◽  
Vol 196 ◽  
pp. 807-820 ◽  
Author(s):  
Rafael Aguilar ◽  
Loreto Valenzuela ◽  
Antonio L. Avila-Marin ◽  
Pedro L. Garcia-Ybarra

2019 ◽  
Vol 141 (2) ◽  
Author(s):  
S. Zoller ◽  
E. Koepf ◽  
P. Roos ◽  
A. Steinfeld

This work reports on the development of a transient heat transfer model of a solar receiver–reactor designed for thermochemical redox cycling by temperature and pressure swing of pure cerium dioxide in the form of a reticulated porous ceramic (RPC). In the first, endothermal step, the cerium dioxide RPC is directly heated with concentrated solar radiation to 1500 °C while under vacuum pressure of less than 10 mbar, thereby releasing oxygen from its crystal lattice. In the subsequent, exothermic step, the reactor is repressurized with carbon dioxide as it cools, and at temperatures below 1000 °C, the partially reduced cerium dioxide is re-oxidized with a flow of carbon dioxide. To analyze the performance of the solar reactor and to gain insight into improved design and operational conditions, a transient heat transfer model of the solar reactor for a solar radiative input power of 50 kW during the reduction step was developed and implemented in ANSYS cfx. The numerical model couples the incoming concentrated solar radiation using Monte Carlo ray tracing, incorporates the reduction chemistry by assuming thermodynamic equilibrium, and accounts for internal radiation heat transfer inside the porous ceria by applying effective heat transfer properties. The model was experimentally validated using data acquired in a high-flux solar simulator (HFSS), where temperature evolution and oxygen production results from model and experiment agreed well. The numerical results indicate the prominent influence of solar radiative input power, where increasing it substantially reduces reduction time of the cerium dioxide structure. Consequently, the model predicts a solar-to-fuel energy conversion efficiency of >6% at a solar radiative power input of 50 kW; efficiency >10% can be obtained provided the RPC macroporosity is substantially increased, and better volumetric absorption and uniform heating is achieved. Managing the ceria surface temperature during reduction to avoid sublimation is a critical design consideration for direct absorption solar receiver–reactors.


2013 ◽  
Vol 805-806 ◽  
pp. 1603-1611 ◽  
Author(s):  
Chun Li Tang ◽  
Xiao Wei Zhang

This paper presents a radiant model based on the radiant resistance analysis theory and the results of numerical simulations of double glass window. The two-dimensional steady state model is formulated based upon the radiation and free convection heat transfer at different external and internal ambient conditions.The properties of glass which change with incident wavelength are also considered. Specifically, air and CO2 are used as the medium in the 8mm and 10mm cavity of the double glass window, respectively. Several parameters, including transmitted solar radiation flux, temperature distribution, surface heat transfer coefficient for free convection and total surface heat flux are calculated. The results show that transmitted solar radiation flux is slightly lower when filled with CO2 in the cavity than with air due to their absorption difference. Also, the temperature of gas closing to internal glass sheet and the total surface heat flux of internal glass sheet are decreased when filled with CO2 than with air, although the surface heat transfer coefficient is slightly higher when it is CO2. .The temperature variation curves show that less heat flows into the room when filled with CO2 than air in double glass window.


2000 ◽  
Vol 421 ◽  
pp. 293-305 ◽  
Author(s):  
YU. G. VEREVOCHKIN ◽  
S. A. STARTSEV

Thermal convection in a horizontal water layer being cooled from above and absorbing solar radiation is simulated numerically at the Prandtl number Pr = 7. Three different regimes arising are investigated here. The first is characterized by intermittent convection, the second by steady-state convection, and the third is convection free. The transitions occur at different values of J0/Q, the ratio of downward solar-radiation flux just below the surface to heat flux through the interface (assumed to be constant), but at almost the same Rayleigh number. The generalized heat-conduction law is found to be valid.


2007 ◽  
Vol 21 ◽  
pp. 57-66
Author(s):  
Herry Suhardiyanto ◽  
◽  
Yudi Chadirin ◽  
Titin Nuryawati ◽  
Yayu Romdhonah ◽  
...  

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