Thermal behaviour of salt gradient solar ponds (original) (raw)
Related papers
A Technical Note on Fabrication and Thermal Performance Studies of a Solar Pond Model
Journal of Renewable Energy, 2013
A solar pond has been fabricated to analyze the thermal behavior of it, in the climatic conditions of Moradabad, Uttar Pradesh. Sodium chloride (NaCl) has been used to form a salt gradient for better performance, and a dark-colored (blackened) rigid surface bottom with 1 mm irregularities has been considered for trapping the heat in a good amount. A solar pond with a surface area of 2.56 m 2 and a depth of 1 m has been filled with salty water of various densities to form three salty water zones (upper convective, nonconvective, and heat storage). A few investigations have been carried out to evaluate the thermal efficiencies of three different zones of the solar pond. An attempt is also made to improve the thermal performance of the salt gradient solar pond.
Experimental study of laboratory salt gradient solar pond thermal behaviour
Heat Recovery Systems and Chp, 1988
Aktraet--Experimental studies have been performed on two identical small scale laboratory solar ponds which consisted of rectangular tanks made of reinforced concrete having dimensions 0.40 × 0.40 x 0.90 m, with wall thickness 0.03 m. The measurements have been obtained by operating the pond at one fourth, one third and a half full using 15% and 20% concentrations of the sodium chloride solution. The pond surface was made up by adding fresh water to the brine in the pond. Stable density gradients were developed at room temperatures approximately one month after estabfishment. The ponds were then heated from the bottom to temperatures of 35°C, 40°C, 45°C and 50°C and density profiles as well as temperature profiles were obtained for every operating temperature. Dry dune sand with variable thickness (6era and 12cm) has been used as a thermal insulator around the walls of the pond. In this study, the following effects are considered: the heat transfer from the pond to the surrounding ground; the change of the salt gradient due to the diffusion of salt; the local occurrence of thermal convection. The effect of the variation of the thickn__~__ of the upper, lower and non-convective zones with the variation of the heating temperature and the filling depths of the pond are discTassed qualitatively. It is noticed that the thermal performance of the pond is improved by taking proper care of the above mentioned facts. t a, Greek letters ~.l thermal conductivity of the wall of the pond [Win -t °C -I ] ~.2 thermal conductivity of imulating material [W m -~ °C -~ ] ~.w thermal conductivity of saline water [W m-t °C-t ]
Comparison of Thermal Behavior of Solar Ponds with Flat and Corrugated Bottom
The heat extraction from the lower convective zone or storage zone of salinity gradient solar pond with corrugated bottom is investigated with the aim of increasing the overall efficiency of collecting solar radiation, storing heat and delivering this heat to different applications. The energy balance equations for each zone have been used to develop the expression of temperature distribution in the solar pond. Then this equation has been used to develop the equation for efficiency of the solar pond. The analysis is based on the boundary conditions at the interface between the zones and the matching conditions. In this method, heat is extracted from the storage zone of the solar pond. A theoretical analysis is conducted to obtain expression for the variation of temperature with depth of solar pond. The dependence of the energy efficiency of the solar pond on the thickness of storage zone, temperature of delivered heat, variation combinations of the pond and storage zone heat extraction only explored. The theoretical analysis suggests that heat extraction from the storage zone has the potential to increase the overall efficiency of a solar pond delivering heat at a relatively high temperature by up to 50 %, compared with the conventional solar pond method of heat extraction solely from the storage zone. The potential gain in efficiency using storage zone heat extraction is attributed to the storage zone that can be achieved with this method. The results are then obtained by computer simulation. The effects of system and operating parameters of the solar pond like area enhancement factor (β), heat extraction rate, heat capacity rate and depth of the pond on the temperature distribution and efficiency have been developed. It has been found that the temperature distribution in the solar pond is a strong function of system and operating parameters.
Thermal Behavior of a Large Salinity-Gradient Solar Pond in the City of Mashhad
Iranian Journal of Science and Technology Transaction B-engineering, 2005
By applying a model of finite differences, the thermal behavior of a large solar pond in the city of Mashhad in the north east of Iran, is studied in this paper. The 32-year data of sunny hours to day-length ratio are used for the estimation of global radiation. The temperature data of a similar duration are used for evaluating the ambient temperature. The effects of the variation of different zone thicknesses on pond performance are studied. It is observed that the upper convective zone thickness should be as thin as possible, the non-convective zone might be from 1 to 2 m and the lower convective zone thickness may be designed based on the application needs. A thicker non convective zone provides more insulation against heat losses, and a thicker lower convective zone supplies a higher storage capacity, though with a lower operating temperature. The heat may be extracted from the pond by either a constant or a variable loading pattern. The appropriate loading pattern can be select...
Applied Energy, 2008
An experimental salt gradient solar pond having a surface area of 3.5 Â 3.5 m 2 and depth of 2 m has been built. Two covers, which are collapsible, have been used for reducing the thermal energy loses from the surface of the solar pond during the night and increasing the thermal efficiency of the pond solar energy harvesting during daytime. These covers having reflective properties can be rotated between 0°and 180°by an electric motor and they can be fixed at any angle automatically. A mathematical formulation which calculates the amount of the solar energy harvested by the covers has been developed and it is adapted into a mathematical model capable of giving the temporal temperature variation at any point inside or outside the pond at any time. From these calculations, hourly air and daily soil temperature values calculated from analytical functions are used. These analytic functions are derived by using the average hourly and daily temperature values for air and soil data obtained from the local meteorological station in Isparta region. The computational modeling has been carried out for the determination of the performance of insulated and uninsulated solar ponds having different sizes with or without covers and reflectors. Reflectors increase the performance of the solar ponds by about 25%. Finally, this model has been employed for the prediction of temperature variations of an experimental salt gradient solar pond. Numerical results are in good agreement with the experiments.
Thermal behavior of a small salinity-gradient solar pond with wall shading effect
Solar Energy, 2004
The thermal behavior of a small-scale salinity-gradient solar pond has been studied in this paper. The model of heat conduction equation for the non-convective zone has been solved numerically with the boundary conditions of the upper and lower convective zones. The variation of the solar radiation, during a year, and its attenuation in the depth of the pond has been discussed. The wall shading area for a vertical wall square pond has been elaborated and its effect on the reduction of the sunny area has been included in the model. The temperature variation of the storage zone has been calculated theoretically and compared with the experimental results. The sensitivity analysis demonstrates the importance of the side and bottom insulation and the thickness of the non-convective zone, as well as the wall shading effect on the performance of the pond. The application of several loading patterns gives an overall efficiency of 10% for the small pond.
Performance comparison of aboveground and underground solar ponds
Thermal Science, 2016
This paper deals with the modeling of two different solar ponds which has some different structural parameters such as aboveground and underground, and its performance evaluation. The solar pond system generally consists of three zones, and the densities of these zones decrease from the bottom of the pond to the surface. The most significant decrease in the density distribution of the salt between bottom and up of the pond is the gradient zone. The convective heat loss in the solar pond is prevented with this zone. In this study, aboveground and underground solar ponds were modeled at the same dimensions, but different structural parameters in the same conditions. In this model, the temperature distributions of the solar pond were obtained during a year. The thermal performances of the solar pond were calculated and the results were compared with an experiment. This study shows that the efficiency of the aboveground solar pond is observed to be a maximum of 25.93% in July, a minimum...
The purpose of this analysis is the development of salt gradient solar pond design to improve the performance of solar pond. The study of previous treatment of internal reflection is considered by dividing the spectrum into a finite no. of spectral wavelength bands. To evaluate the performance of solar pond various method of augmentation are included. Such as based on depth cold sea water as heat sink, auxiliary heat source at high temperature, waste heat, fossil fuels and biomass fuels. In this paper the heat extraction from the lower convective zone or storage zone of salt gradient solar pond with corrugated bottom is investigated with the aim of increasing the overall efficiency of collecting solar radiation. A theoretical analysis is conducted to obtain expression for the variation of temperature with depth of solar pond. The efficiency of the solar ponds depends on thickness of storage zone, temp of delivered heat, the analysis suggests that heat extraction from the storage zone has potential to increase the overall efficiency of solar pond delivering heat at a relatively high temp up to 50% compared with the conventional solar pond the potential gain in efficiency using storage zone heat extraction is attributed to the storage zone that can be achieved with this method. The effects of system and operating parameters of the soar ponds like area enhancement factor (), heat extraction rate, heat capacity rate, depth of the pond on the temp distribution and efficiency have been developed.
Journal of Energy Technologies and Policy, 2013
A numerical investigation on the non-convective salt-gradient solar pond was carried out to study the effect of different variables on the solar pond performance. A numerical computer program was performed to show the relations between the different pond variables. The investigation analysis was performed at selected days (1, 15, and 20 th) of December 2012 at Jordan-Amman climate. The results of investigation show that the temperature of storage zone will increase by decreasing the depth of both UCZ and LCZ and increasing the depth of NCZ.
Performance investigation of a solar pond
Applied Thermal Engineering, 2006
This work consists of both experimental and theoretical parts. In the experimental part, an insulated solar pond with a surface area of 4 m 2 and a depth of 1.5 m was built at Cukurova University in Adana, Turkey to conduct performance experiments. The system was filled with salty water of various densities to form three salty water zones (upper convective, non-convective and heat storage). During the months of January, May and August, a data acquisition device was used to measure and record the temperature readings at various locations in the pond (distributed vertically within and at the bottom of the pond, and horizontally and vertically within the insulated side-walls). In the theoretical part, we developed a performance model to determine the thermal efficiencies of the pond and its various zones. Temperature difference was seen to be the key driving force in heat transfer, particularly in heat rejection. As expected, the highest thermal efficiency was obtained for August as follows: 4.5% for the upper convective zone, 13.8% for the non-convective zone and 28.1% for the heat storage zone, respectively.