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research-article  
Abdullah A. Abdullah and Kenneth Alan Lindsay
J. Sol. Energy Eng   doi: 10.1115/1.4036773
The quality of the stability of the non-convective zone of a salinity-gradient solar pond is investigated for an operating protocol in which the flushing procedure exactly compensates for evaporation losses from the solar pond and its associated evaporation pond. The mathematical model of the pond uses simplified, but accurate, constitutive expressions for the physical properties of aqueous sodium chloride. Also realistic boundary conditions are used for the behaviours of the upper and lower convective zones. The performance of a salinity-gradient solar pond is investigated in the context of the weather conditions at Makkah, Saudi Arabia, for several thickness of upper convective zone and operating temperature of the storage zone. Spectral collocation based on Chebyshev polynomials is used to assess the quality of the stability of the pond throughout the year in terms of the time scale for the restoration of disturbances in temperature, salinity and fluid velocity underlying the critical eigenstate. The critical eigenvalue is found to be real and negative at all times of year indicating that the steady state configuration of the pond is always stable, and suggesting that stationary instability would be the anticipated mechanism of instability. Annual profiles of surface temperature, salinity and heat extraction are constructed for various combinations for the thickness of the upper convective zone and storage zone temperature.
TOPICS: Stability, Solar energy, Temperature, Storage, Evaporation, Operating temperature, Fluids, Heat, Boundary-value problems, Eigenvalues, Polynomials, Sodium, Steady state
research-article  
Xinping Zhou, Yangyang Xu and Yaxiong Hou
J. Sol. Energy Eng   doi: 10.1115/1.4036774
In this paper, a theoretical model of solar chimney power plants (SCPPs) is presented based on compressible ideal gas law assumptions. The theoretical optimal turbine pressure drop factors (TPDFs) for constant and non-constant densities (CD and NCD) are studied, and the effects of flow area parameters examined. Results show that the theoretical optimal TPDF for CD is equal to 2/3 and is independent of the flow area parameters. Results also show that the theoretical optimal TPDF for NCD is close to 1 and is affected by the flow area parameters. However, the theoretical maximum fluid power obtained for NCD is never attained in real life. For the actual states, the theoretical optimal TPDF for NCD is still effectively high enough. The TPDF and the fluid power for NCD increase with the reduction of the collector inlet area, and more precisely with the reduction of the chimney inlet area. The TPFD and the fluid power definitely increase with larger chimney flow area. The increase in the fluid power due to shape optimization of the SCPP is limited compared to that due to higher input heat flux of collector. Divergent-top and upward slanting roof shapes are recommended for the solar chimney and the solar collector, respectively for better SCPP performance. Additionally, locations exposed to strong solar radiation are preferred for SCPPs.
TOPICS: Flow (Dynamics), Fluids, Power stations, Solar energy, Turbines, Pressure drop, Roofs, Shapes, Heat flux, Shape optimization, Solar collectors, Solar radiation
research-article  
Rajneesh Kumar, Varun Goel and Anoop Kumar
J. Sol. Energy Eng   doi: 10.1115/1.4036775
The fluid flow characteristics and heat transfer in triangular duct solar air heater (SAH) has been studied experimentally and numerically for Reynolds number ranges for 4000 to 18000. In the present paper, three different models of triangular duct solar air heater were considered, namely, Model 1 which has simple triangular duct, Model 2 which has rounded corner on one side of triangular flow passage, and Model 3 contains rounded corner on one side of triangular duct with roughness on the absorber plate of SAH. The absorber plate and apex angle value assumed as constant in all three models of SAH i.e., 160 mm and 60°, respectively. The three-dimensional numerical simulations performed by discretizing computational domain using finite volume method (FVM) and they are analyzed with the help of computational fluid dynamics (CFD) code. Experiments are performed to validation of numerical results by comparing the distribution of absorber plate temperature along the length of the SAH. Whereas, a detailed analysis of different models of solar air heater is carried out by solving flow governing equations numerically on ANSYS Fluent 12.1. A close match has been observed between the simulated and experimental results of SAH with the maximum percentage deviation of approximately ±5% in absorber plate temperature. The rounded apex improves velocity distribution near the corner region and helps in improving heat transfer. In three studied models of solar air heater, the best performance is observed in the case of Model-3.
TOPICS: Heat transfer, Computational fluid dynamics, Solar energy, Fluid dynamics, Ducts, Corners (Structural elements), Flow (Dynamics), Temperature, Finite volume methods, Computer simulation, Reynolds number, Surface roughness
Technical Brief  
Cheng Zhang, Yanping Zhang, Xiaolin Lei and Wei Gao
J. Sol. Energy Eng   doi: 10.1115/1.4036725
Parabolic trough solar concentrating technology is a new and clean way to replace the conventional fossil fuel technology to generate steam for heavy oil recovery in oilfield. A computational model was constructed with simulated direct normal irradiance from nearby similar climate locations. Different system configurations were analyzed with the model, such as with single- and dual-loop, with and without heat storage system. Finally, several solar field configurations with different collector field layouts were compared by the cost of unit generated steam. Results show that using heat storage can effectively improve the stability of steam production, and in a certain oilfield, an optimum steam production amount and optimum heat storage time exist for lowest steam cost. The methods and results in the paper provide useful suggestions for the implementation of a solar thermal oilfield steam production system.
TOPICS: Design, Solar energy, Manufacturing systems, Steam, Parabolic troughs, Oil fields, Heat storage, Stability, Petroleum extraction, Climate, Fossil fuels
research-article  
Soukaina El Alj, Ahmed Al Mers, Ossama Merroun, Abdelfattah Bouatem, Noureddine Boutammachte, Hamid Ajdad, Sara Benyakhlef and Yousra Filali Baba
J. Sol. Energy Eng   doi: 10.1115/1.4036726
Recently, linear Fresnel reflectors (LFR) arouse an increasing interest by the scientific and industrial community and have had a really fast development in the domain of concentrated solar power. LFR is considered promising technology which could produce an optical performance lower than those of parabolic trough collector, but its component simplicity would allow high cost reductions in its manufacturing compared to high investment costs of parabolic troughs. The purpose of this paper is to analyse the optical performances of a LFR prototype developed in the framework of CHAMS project, Morocco. The development of this prototype comes to supply industrial applications needing heat at small to medium temperature levels. To achieve this objective, an optical code based on Monte-Carlo ray tracing technique was developed for optical optimization purposes. The developed code identifies geometrical parameters that have a greater influence on optical efficiency of the LFR system as the mirror spacing arrangement, the receiver height, the receiver geometrical configuration taking into account the secondary reflector shape and the absorber tube diameter. An analysis is conducted to identify the contribution of each mode of optical losses (blocking, shading, cosine…) in the optical efficiency of the system. Then an optimization procedure is applied to enhance the optical performances of the prototype.
TOPICS: Solar collectors, Engineering prototypes, Modeling, Optimization, Parabolic troughs, Concentrating solar power, Mirrors, Ray tracing, Shapes, Heat, Temperature, Manufacturing, Optical mirrors, Shades and shadows

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