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.
Highlights
Solar radiation constitutes a huge energy source which is abundant and available almost everywhere.A salt gradient solar pond is a large solar energy collection pool which absorbs an important amount of solar energy radiation and stores it as thermal energy in the same medium for a long period of time.Solar ponds can be employed to supply thermal energy in many applications, e.g., heating of buildings, production of electricity, desalination of sea water, textile processing and food industries, etc.In this work a solar pond was filled with salty water of different concentrations to form three distinct zones
We have numerically studied the problem of hydrodynamic, heat and mass transfer and stability in a two-dimensional salt-gradient solar pond
The buoyancy ratio has a very important effect to prevent convection motions induced by solar radiation absorption and to stabilize the layers of salty water in the solar pond
Summary
Solar radiation constitutes a huge energy source which is abundant and available almost everywhere.A salt gradient solar pond is a large solar energy collection pool which absorbs an important amount of solar energy radiation and stores it as thermal energy in the same medium for a long period of time (months, seasons or even a year).Solar ponds can be employed to supply thermal energy in many applications, e.g., heating of buildings, production of electricity, desalination of sea water, textile processing and food industries, etc.In this work a solar pond was filled with salty water of different concentrations to form three distinct zones. The second convective zone is situated at the bottom of the solar pond and called lower convective zone (LCZ), which has a high temperature, and a maximum salt concentration In this zone, solar radiation is absorbed and transformed to thermal energy. It is an absorption and storage zone These two zones are characterized by uniform concentration and separated by the important gradient zone called the non-convective zone which functions as a transparent insulator, permitting solar radiation to be trapped and stored in the bottom of the solar pond. In this zone, the salt concentration and the temperature increase with depth
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