Double Diffusive Natural Convection in Solar Ponds With Nonlinear Temperature and Salinity Profiles

1986 ◽  
Vol 108 (3) ◽  
pp. 214-218 ◽  
Author(s):  
A. T. Kirkpatrick ◽  
R. F. Gordon ◽  
D. H. Johnson
Keyword(s):  
Fluid Layer ◽  
Salinity Gradient ◽  
Radius Of Curvature ◽  
Length Scale ◽  
Solar Ponds ◽  
Solar Pond ◽  
Thin Region ◽  
Nonlinear Temperature ◽  
Set Up ◽  
The Stability

A solar pond can be used as a thermal energy source provided that convective instabilities do not occur. This paper experimentally examines the stability of a fluid layer with nonlinear salinity and temperature profiles. A nonlinear salt profile was set up in a fluid layer, and the water was heated by a solar radiation simulator. Three stability experiments were conducted. Instabilities occurred at the location of the weakest salinity gradient, and were confined to a thin region, as predicted by theory. A local length scale was used to produce a stability parameter, the ratio of thermal to solute Rayleigh numbers. It is shown that for nonconstant solute and temperature gradients, the appropriate length scale is based on the radius of curvature of the salinity distribution. With this chocie of a length scale, good agreement was found between theory and experiment for the onset of an instability.

Assessing the Maximum Stability of the Nonconvective Zone in a Salinity-Gradient Solar Pond

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
A. A. Abdullah ◽  
K. A. Lindsay
Keyword(s):  
Salinity Gradient ◽  
Fluid Velocity ◽  
Weather Conditions ◽  
Convective Zone ◽  
Heat Extraction ◽  
Solar Pond ◽  
Maximum Stability ◽  
Storage Zone ◽  
The Stability

The quality of the stability of the nonconvective zone of a salinity-gradient solar pond (SGSP) 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 behaviors of the upper and lower convective zones (LCZs). 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 (UCZ) 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.

Thermal Heat Storage Gain of Salinity Gradient Solar Pond Using Evacuated Tube Solar Collectors

2015 ◽  
Vol 1113 ◽  
pp. 800-805 ◽  
Author(s):  
Baljit Singh ◽  
Muhammad Fairuz Remeli ◽  
Alex Pedemont ◽  
Amandeep Oberoi ◽  
Abhijit Date ◽  
...  
Keyword(s):  
Large Scale ◽  
Heat Storage ◽  
Salinity Gradient ◽  
Heat Energy ◽  
Working Fluid ◽  
The Sun ◽  
Solar Ponds ◽  
Solar Pond ◽  
Evacuated Tube Collectors ◽  
Evacuated Tube

This paper investigates the capability of running a system which uses hot fluid from solar evacuated tube collectors to boost the temperature and overall heat storage of the solar pond. The system is circulated by a solar powered pump, producing heat energy entirely from the incoming solar radiation from the sun. Solar evacuated tube collectors use a renewable source of power directly from the sun to heat the working fluid to very high temperatures. Solar ponds are emerging on the renewable energy scene with the capacity to provide a simple and inexpensive thermal storage for the production of heat on a large scale. The results of the performance of the system show a significant heat energy increase into the solar ponds lower convective region, increasing the overall performance of the solar pond.

scholarly journals A theoretical and numerical study of thermosolutal convection: stability of a salinity gradient solar pond

2011 ◽  
Vol 15 (1) ◽  
pp. 67-80 ◽  
Author(s):  
Dalila Akrour ◽  
Mouloud Tribeche ◽  
Djamel Kalache
Keyword(s):  
Stability Analysis ◽  
Boundary Conditions ◽  
Numerical Study ◽  
Salinity Gradient ◽  
Thermosolutal Convection ◽  
Separation Coefficient ◽  
Onset Of Convection ◽  
Solar Pond ◽  
Negative Case ◽  
The Stability

A theoretical and numerical study of the effect of thermodiffusion on the stability of a gradient layer is presented. It intends to clarify the mechanisms of fluid dynamics and the processes which occur in a salinity gradient solar pond. A mathematical modelling is developed to describe the thermodiffusion contribution on the solar pond where thermal, radiative, and massive fluxes are coupled in the double diffusion. More realistic boundary conditions for temperature and concentration profiles are used. Our results are compared with those obtained experimentally by authors without extracting the heat flux from the storage zone. We have considered the stability analysis of the equilibrium solution. We assumed that the perturbation of quantities such as velocity, temperature, and concentration are infinitesimal. Linearized equations satisfying appropriate prescribed boundary conditions are then obtained and expanded into polynomials form. The Galerkin method along with a symbolic algebra code (Maple) are used to solve these equations. The effect of the separation coefficient y is analyzed in the positive and negative case. We have also numerically compared the critical Rayleigh numbers for the onset of convection with those obtained by the linear stability analysis for Le = 100, ?a = 0.8, and f = 0.5.

The Influence of Height of LCZ on the Salinity Diffusion of Solar Pond

2013 ◽  
Vol 448-453 ◽  
pp. 1521-1524
Author(s):  
Chun Juan Gao ◽  
Qi Zhang ◽  
Hai Hong Wu ◽  
Liang Wang ◽  
Xi Ping Huang
Keyword(s):  
Solar Energy ◽  
Fresh Water ◽  
Salt Water ◽  
Salinity Gradient ◽  
Good Method ◽  
Convective Zone ◽  
Solar Ponds ◽  
Solar Pond ◽  
Salt Gradient ◽  
And Diffusion

The solar ponds with a surface of 0.3m2were filled with different concentration salt water and fresh water. The three layer’s structure of solar ponds was formed in the laboratory ponds by using the salinity redistribution. The performance and diffusion of salinity were xperimentally in the solar pond. The measurements were taken and recorded daily at various locations in the salt-gradient solar pond during a period of 30 days of experimentation. The experimental results showed that the salinity gradient layer can sustain a longer time when the lower convective zone is thicker, which is benefit to store solar energy. Therefore, properly increasing the height of LCZ is a good method to enhance the solar pond performance.

Effect of Water Distribution Ways on the Operation of Solar Pond

2013 ◽  
Vol 805-806 ◽  
pp. 74-77
Author(s):  
Chun Juan Gao ◽  
Qi Zhang ◽  
Liang Wang ◽  
Ying Wang ◽  
Xi Ping Huang
Keyword(s):  
Water Distribution ◽  
Salinity Gradient ◽  
Convective Zone ◽  
The Body ◽  
Solar Ponds ◽  
Solar Pond ◽  
Storage Zone ◽  
Small Model ◽  
Laboratory Tank ◽  
Salt Diffusion

An experimental study on the evolution of the salinity profiles in the salinity gradient solar ponds was executed using a small model pond. The body of the simulated pond is a cylindrical plastic tank, with 50 cm height and 45 cm diameter. The salinity gradient was established in the laboratory tank by using the salinity redistribution technique. The measurements were taken during a period of 20 days of experimentation. This period of time allowed the existence of salt diffusion from the storage zone to the surface. Results obtained from this study show that when the ratio of brine/water is 1/1, the salinity gradient layer can sustain a longer time and the lower convective zone is thicker, which is benefit to store solar energy.

scholarly journals Exact energy stability of Bénard–Marangoni convection at infinite Prandtl number

2017 ◽  
Vol 822 ◽  
Author(s):  
Giovanni Fantuzzi ◽  
Andrew Wynn
Keyword(s):  
Prandtl Number ◽  
Energy Method ◽  
Marangoni Convection ◽  
Fluid Layer ◽  
Finite Amplitude ◽  
Linear Instability ◽  
Energy Stability ◽  
Thermal Boundary Conditions ◽  
Set Up ◽  
The Stability

Using the energy method we investigate the stability of pure conduction in Pearson’s model for Bénard–Marangoni convection in a layer of fluid at infinite Prandtl number. Upon extending the space of admissible perturbations to the conductive state, we find an exact solution to the energy stability variational problem for a range of thermal boundary conditions describing perfectly conducting, imperfectly conducting, and insulating boundaries. Our analysis extends and improves previous results, and shows that with the energy method global stability can be proven up to the linear instability threshold only when the top and bottom boundaries of the fluid layer are insulating. Contrary to the well-known Rayleigh–Bénard convection set-up, therefore, energy stability theory does not exclude the possibility of subcritical instabilities against finite-amplitude perturbations.

Two-Dimensional Computer Simulation of Salinity Gradient Solar Pond Operation

2014 ◽  
Author(s):  
Minoo Mehdizadeh ◽  
Goodarz Ahmadi
Keyword(s):  
Solar Radiation ◽  
Salt Concentration ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Salinity Gradient ◽  
Radiation Absorption ◽  
Small Scale ◽  
Two Dimensional ◽  
Solar Ponds ◽  
Solar Pond

This study is concerned with computer modeling of flow and thermal analysis of solar ponds with a salinity gradient. Solar ponds have been used as an efficient and environmentally friendly approach for collection of solar energy for low temperature thermal applications. A two-dimensional unsteady computational fluid dynamic (CFD) model was developed and used for numerical study of stability analysis of the pond, as well as heat and mass transfer in the salt gradient solar ponds. Salinity gradient was created in order to stabilize the pond and to restrict convective motions induced by buoyancy driven solar radiation heating during the period of operation. Fluent® commercial software was enhanced with the implementation of User Defined Functions (UDF) and was used in these simulations. The user defined scalar model was included for analyzing the convection and diffusion of the salt concentration in the solar pond. In addition, user defined functions were developed for relating the water density to temperature and salt concentration, as well as, the amount of solar radiation absorption in the solar pond as functions of thermo-physical properties. In the absence of flow exchange, the natural convection in the pond was simulated and the stability of the pond was verified. Development of salt concentration was also studied, and time evolution of temperature distribution in a small scale salinity gradient solar pond was analyzed. For the case of flow exchange at the bottom of the pond, the energy production was evaluated, and the temperature, concentration and flow field were simulated.

Gradient-Zone Erosion by Extraction in Solar Ponds

1995 ◽  
Vol 117 (2) ◽  
pp. 144-150 ◽  
Author(s):  
J. Estevadeordal ◽  
S. J. Kleis
Keyword(s):  
Steady State ◽  
Salinity Gradient ◽  
Operating Conditions ◽  
Density Difference ◽  
Finite Density ◽  
Gradient Zone ◽  
Solar Ponds ◽  
Solar Pond ◽  
Flow Parameters ◽  
Storage Zone

The erosion the dynamically stable gradient zone of a salinity-gradient solar pond, due to the extraction of fluid from the storage zone, is numerically investigated. The effects of fluid withdrawal rate, density stratification level, pond and diffuser geometries, and diffuser placement are considered. It is found, for a typical salinity-gradient solar pond with uniform salinity in the storage zone and a continuous salinity gradient above that a finite amount of fluid entrainment from the gradient zone is inevitable. That is, a finite density difference across the interface is always required for a finite extraction rate under steady-state conditions. The magnitude of the density difference is predicted as function of the geometric and flow parameters. From the results, it is possible to predict the total amount of fluid entrained from the gradient zone as the pond reaches steady-state for prescribed operating conditions.

Effects of Friction and Extraction on the Stability of Solar Ponds

1983 ◽  
Vol 105 (4) ◽  
pp. 356-362 ◽  
Author(s):  
Y. S. Cha ◽  
W. T. Sha ◽  
S. L. Soo
Keyword(s):  
Experimental Results ◽  
Stability Criteria ◽  
Solar Ponds ◽  
Solar Pond ◽  
Salt Gradient ◽  
The Stability ◽  
Cellular Motion

Experimental results were compared to theoretical stability criteria of a salt gradient solar pond. Cellular motion in the nonconvective layer may be caused by instablity. Extension of stability criteria suggests use of stabilizing barriers via friction. Stability of longitudinal extraction assures optimum availability of energy from a solar pond.

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