A Two-Dimensional Numerical Study of Hydrodynamic, Heat and Mass Transfer and Stability in a Salt Gradient Solar Pond

Abstract

Abstract:In this work, the problem of hydrodynamic, heat and mass transfer and stability in a salt gradient solar pond has been numerically studied by means of computational fluid dynamics in transient regime. The body of the simulated pond is an enclosure of height H and length L wherein an artificial salinity gradient is created in order to suppress convective motions induced by solar radiation absorption and to stabilize the solar pond during the period of operation. Here we show the distribution of velocity, temperature and salt concentration fields during energy collection and storage in a solar pond filled with water and constituted by three different salinity zones. The bottom of the pond is blackened and the free-surface is subjected to heat losses by convection, evaporation and radiation while the vertical walls are adiabatic and impermeable. The governing equations of continuity, momentum, thermal energy and mass transfer are discretized by finite-volume method in transient regime. Velocity vector fields show the presence of thin convective cells in the upper convective zone (UCZ) and large convective cells in the lower convective zone (LCZ). This study shows the importance of buoyancy ratio in the decrease of temperature in the UCZ and in the preservation of high temperature in the LCZ. It shows also the importance of the thickness of Non-Convective Zone (NCZ) in the reduction of the upwards heat losses.

Numerical temperature and concentration distributions in an insulated salinity gradient solar pond

“…In order to ensure the accuracy of numerical results, we validated the numerical code specifically developed for the present work in three ways. The results obtained from this study, which were published in Boudhiaf et al (2012) and Boudhiaf and Baccar (2014) and hence are not repeated here for the sake of space, have shown a good comparison. The study of the grid independence, the validation of the numerical code specifically developed for the present research, and the algorithm of the numerical method have been detailed elsewhere (Boudhiaf et al 2012;Boudhiaf and Baccar 2014;Boudhiaf 2013).…”

“…The Prandtl and Schmidt numbers are kept constant (Pr = 6 and Sc = 1000), which correspond to the average characteristics of salty water (Hammami et al 2007;Boudhiaf et al 2012;Boudhiaf and Baccar 2014). The results are generated for fixed values of thermal Rayleigh number, internal Rayleigh number, and aspect ratio (Ra T = 10 7 , Ra I = 1.4 × 10 8 , and A = 3).…”

“…In very recent works, the authors have studied the hydrodynamic, heat, and mass transfer behaviors of a twodimensional salinity gradient solar pond in transient regime (Boudhiaf et al 2012;Boudhiaf and Baccar 2014). The results have shown, in particular, that the internal Rayleigh number, the buoyancy ratio, and the aspect ratio have an important effect, respectively, on the thermal performance of the pond, on the stability, and on the distribution of temperature and velocity fields in the salinity gradient solar pond.…”

Constructal design of salt-gradient solar pond fields

“…There are many one-dimensional studies in steady or transient conditions [8,28,29], and more sophisticated two-dimensional models that analyze in detail the hydrodynamics inside the pond [30][31][32]. In general, the one-dimensional steady models provide a good first approximation to determine the thermal performance of a solar pond, especially for analyzing changes in performance against parameter variations [6,[33][34][35][36].…”

“…where q i is the incident radiation, and r (=0.06) is the reflectance of the solar radiation at the water surface [32]. Because the temperature in the NCZ is not uniform, the analysis in this zone is different than that of the UCZ and LCZ.…”