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A small seawater solar pond with a dimension of 2. 8 m X 2. 3 m X 0. 8 m was constructed. The pond was filled with bittern and the solution of coarse salt in water. The temperature in the pond and the radiation intensity during experimental period were measured. Based on the experimental data and the diffusive radiation absorbed by wall shadow, the temperature distribution in the pond with a one-dimension transient model considering the turbidity of the solar pond water was simulated. There is a better agreement on the experimental data and the simulating temperature distributions. Both the results suggest that temperature in the small solar pond with probably insulated rose up in short time, so it is better to extract heat in warm seasons. [ABSTRACT FROM AUTHOR]

Abstract: Solar pond is an artificially constructed pond in which significant temperature rises are caused to occur in the lower regions by preventing convection. To prevent convection, salt water is used in the pond. Those ponds are called “salt gradient solar pond”. In the last 15 years, many salt gradient solar ponds varying in size from a few hundred to a few thousand square meters of surface area have been built in a number of countries. Nowadays, mini solar ponds are also being constructed for various thermal applications. In this work, various design of solar pond, prospects to improve performance, factors affecting performance, mode of heat extraction, theoretical simulation, measurement of parameters, economic analysis and its applications are reviewed. [Copyright &y& Elsevier]

In an attempt to improve the daily productivity of the single effect solar stills, a single-slope single-basin solar still integrated with a shallow solar pond (SSP) was studied to perform solar distillation at a relatively high temperature. The energy balance equations of various elements of the considered system were formulated and solved analytically. Suitable computer programs were prepared for optimizing and predicting the thermal performance of the considered system. Numerical calculations were carried out on typical summer and winter days in Tanta (latitude 30° 47′N) for different thicknesses and mass flow rates of the flowing water to study the effect of these parameters on the daily productivity and efficiency of the system. To validate the proposed theoretical model, comparisons between calculated and measured results were carried out. Good agreement has been achieved. The year-round performances of the still with and without the SSP were also investigated. The optimum values of the flowing water thickness and the mass flow rate for this typical configuration of the SSP-active solar still were obtained as 0.03m and 0.0009kg/s. The annual average values of the daily productivity and efficiency of the still with the SSP were found to be higher than those obtained without the SSP by 52.36% and 43.80%, respectively. [Copyright &y& Elsevier]

Abstract: We have developed a wind-wave-surge coupled process-based numerical model for simulating storm surge, consisting of a meso-scale atmospheric model (MM5), a third-generation spectral wave model (WW3) and a coastal ocean model (POM). We introduced an additional sea surface shear stress by wave dissipation into the model to consider the process of energy transfer from winds to currents through whitecap breaking. We demonstrate the importance of this energy transfer path through a hindcast simulation of a cyclone surge in April, 1991 in the Bay of Bengal: it helps generate mean current and has wave effects on wind-induced current fields in extremely shallow water areas. [Copyright &y& Elsevier]

Abstract: Solar thermal electricity (STE) generation offers an excellent opportunity to supply electricity with a non-CO2 emitting technology. However, present costs hamper widespread deployment and therefore research and development efforts are concentrated on accelerated cost reductions and efficiency improvements. Many focus on the latter, but in this paper we rather focus on attaining very low levelised electricity costs (LEC) by designing a system with very low material cost, while maintaining appreciable conversion efficiency and achieving low maintenance cost. All investigated designs were dimensioned at a 50MW scale production. Calculated LECs show that a new proposed hybrid of ocean thermal energy conversion with an offshore solar pond (OTEC–OSP) may have the lowest LEC of 0.04€/kWh. Addition of a floating offshore solar pond (OSP) to an OTEC system increases the temperature difference in the Rankine cycle, which leads to an improved efficiency of 12%, while typical OTEC efficiencies are 3%. This higher efficiency leads to much lower investments needed for power blocks, while the OSP is fabricated using very low-cost plastic foils. The new OTEC–OSP design can be located in many sunny coastal areas in the world. [Copyright &y& Elsevier]

In this study, a solar pond having dimensions 1.5x1.5x1.5 m was constructed in the campus area of Süleyman Demirel University. It was added two semi cover having insulating and reflecting property for focusing more solar radiation on to the pond surface and reducing thermal losses from upper layer. In the computer model, optimum angle of reflector was determined in order to focus more solar radiation to the pond. Theoretical and experimental results were presented as graphically. [ABSTRACT FROM AUTHOR]

Abstract: Conservation in oil and gas, as well as environmental protection programs strategies need to be looked at carefully to avoid dumping tones of polluting CO2 into atmosphere which have a great hazards on health and environment. This and others make the solar energy option as a clean energy source a favorable option. In this study the solar energy is used as an energy source in a salinity gradient solar pond for water desalination. A mathematical model is used to study the factors affecting the size of solar pond to serve adequate thermal load sufficient to operate the desalination unit for the entire period of operation. One could conclude from this work that there is a linear relation between the required thermal load for the desalination unit and the surface area of the solar pond. This study has also highlighted the clear effect of the thickness of each layer in the solar pond showing that the optimum thickness for the upper convecting zone is 0.3 m, for the non-convecting zone, it is 1.1 and 4 m for the lower convecting zone. [Copyright &y& Elsevier]

A theoretical study of the thermal behavior of salt-gradient solar pond located in Cairo (latitude angle 30°05'N and longitude angle 31°17'E) is presented in this work. The present model is chosen for thermal analysis of six salt-gradient layers of the solar pond. One-dimensional time-dependent solar energy absorbed in six layers of the solar pond of the present solar pond is applied using Fresnel's equations. The vertical temperature variation through six layers during the days of the month year round is presented. The daily temperature fluctuations are smallest for larger depths and about 12°C for the 137.5 cm. The theoretical form of the absorption of solar radiation by salt gradient of water layers is presented. The solar radiation transmission through the layers of the present pond is illustrated. The amount of energy absorbed by the layers of the salt gradient is predicted during the days of the month around the year. The mean amount of absorption energy in the layer (1) is 55,196.1 cal/cm2/day at 12.5 day hour. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present an experimental and theoretical investigation of the exergetic performance of a solar pond (with a surface area of 4 m2 and a depth of 1.5 m) which was built at Cukurova University in Adana, Turkey. The system was filled with salty water to form three zones (e.g., upper convective, non-convective and heat storage) accordingly. A data acquisition device was used to measure and record the temperatures hourly 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). An exergy model is developed to study the exergetic performance of the pond and its three zones in terms of exergy efficiencies which are then compared with the corresponding energy efficiencies. The reference environment temperature is specified for exergy analysis as the average representative temperature of each month of the year (for example, it is taken as an average temperature of 28 °C for August). Thus, the highest energy and exergy efficiencies are found for August to be: 4.22% and 3.02% for the upper convective zone, 13.80% and 12.64% for the non-convective zone, and 28.11% and 27.45% for the heat storage zone, respectively. [Copyright &y& Elsevier]

Abstract: Solar evaporators are widely used in salt mining from seawaters or saline waters. The potash industry in Jordan and other countries utilized solar energy in the evaporation process to concentrate seawater where salt starts to deposit. In this work, the thermal performance of such evaporators was analyzed and modeled on lumped basis. The developed model indicates that the efficiency of any solar evaporator is limited by the optical absorptivity of the saline water as an upper limit. [Copyright &y& Elsevier]

Abstract: Comparison between theoretical and experimental analysis of a mini solar pond assisted solar still is presented in this paper. In a mini solar pond, experiments were conducted for different salinity. It was found that the optimum value of salinity in the mini solar pond is 80 g/kg of water. Effect of sponge cubes in the still, effect of integrating mini solar pond with the still and combination of both are discussed. The average daily production of solar still is found to be increased considerably, when it is integrated with a mini solar pond. Theoretical analyses were made using conservation of energy and the results obtained give very good agreement with the experiments. [Copyright &y& Elsevier]

Abstract: Salt management in irrigated agriculture is critical to the economies of the San Joaquin Valley of California and many other areas around the world. Purified salts can be recovered as marketable products through fractional crystallization following concentration of final stage drainage water from integrated on-farm drainage management systems. To obtain recovered salt and use as a commercial product, new systems which can perform with higher efficiency and lower environmental impact than solar evaporation basins or solar ponds that have previously been used for the final stage are in need of development. For this purpose, a number of solar-assisted brine concentration concepts have been explored, including an open liquid film-type using a tilted evaporation surface described here. Model performance was conceptually evaluated and then experimentally verified. A transient model was developed from energy and component mass balances and employed constitutive heat and mass transfer relationships from various other sources for simulating concentration of agricultural drainage water using a liquid film solar-assisted concentrator. Measured maximum evaporation rate and productivity were between 1.3 and 1.5kgm−2 h−1, and 80kgm−2 over a 7day experimental period respectively which was about a third better performance compared with a shallow basin horizontal concentrator. Measurements were in good agreement with model predictions: within 2°C at the peak and 4°C at the lowest evaporation, and 0.2kgm−2 h−1 for evaporation rates during the peak evaporation periods of the day when compared with independent data sets. Cumulative evaporation rates were from 75 to 85kgm−2 for the tilted concentrator model and 60 to 65kgm−2 for the horizontal concentrator model after 7days. The tilted concentrator yielded productivity and efficiency that were 33% higher than the horizontal concentrator according to the experimental result for the same period and location. [Copyright &y& Elsevier]

Abstract: Solar ponds are a type of solar collector used for storing solar energy at temperature below 90°C. Absorption heat transformers (AHTs) are devices used to increase the temperature of moderately warm fluid to a more useful temperature level. In this study, a theoretical modelling of an absorption heat transformer for the temperature range obtained from an experimental solar pond with dimensions 3.5×3.5×2 m is presented. The working fluid pair in the absorption heat transformer is aqueous ternary hydroxide fluid consisting of sodium, potassium and caesium hydroxides in the proportions 40:36:24 (NaOH:KOH:CsOH). Different methods such as linear regression (LR), pace regression (PR), sequential minimal optimization (SMO), M5 model tree, M5′ rules, decision table and back propagation neural network (BPNN) are used for modelling the absorption heat transformer. The best results were obtained by the back propagation neural network model. A new formulation based on the BPNN is presented to determine the flow ratio (FR) and the coefficient of performance (COP) of the absorption heat transformer. The BPNN procedure is more accurate and requires significantly less computation time than the other methods. [Copyright &y& Elsevier]

The purpose of this study is to evaluate temperature and density profiles of an experimentally investigated salt gradient solar pond (SGSP) by using artificial neural network (ANN). The input parameters of the ANN are solar pond depth, ambient temperature, radiation absorption coefficient of salty solution in the pond, initial density values of the pond and time of day. The output parameters of the ANN are temperature and density profiles in the pond. The experimental data set consists of 168 values. These divided into two groups, of which the 134 values were used for training/learning of the network and the rest of data (34 values) for testing/validation of the network performance. According to the ANN predicted results compared to the experimental results, the mean relative error (MRE) is 2·30% for temperature and 0·63% for density. The correlation coefficients (R2) between the experimentally measured and the ANN predicted results are 0·9632 for temperature and 0·9855 for density in the test/validation data set. The calculated errors of proposed ANN model are in acceptable ranges. These results indicated that the ANN approach could be considered as an alternative and practical technique to evaluate the temperature and density profiles of a SGSP. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a mathematical model of absorption heat transformer (AHT) operating with the aqua/ammonia was developed to simulate the performance of these systems coupled to a solar pond in order to increase the temperature of the useful heat produced by solar ponds and used a special ejector located at the absorber inlet. By the use of the ejector, the obtained absorber pressure becomes higher than the evaporator pressure and thus the system works with triple-pressure-level. The ejector has two functions: (i) aids pressure recovery from the evaporator and (ii) upgrades the mixing process and the pre-absorption by the weak solution of the ammonia coming from the evaporator. The other advantage of the system with ejector is increased absorber temperature. Therefore, pressure recovery and pre-absorption in the ejector improves the efficiency of the AHT. Under the same circumstances, when compared to an AHT with and without an ejector, the system''s COP and exergetic coefficient of performance (ECOP) were improved by 14% and 30%, respectively and the circulation ratio (f) was reduced by 57% at the maximum efficiency condition. Due to the reduced circulation ratio, the system dimensions can be reduced; consequently, this decreases overall cost. The maximum upgrading of the solar pond''s temperature by the AHT was obtained at 57.5°C and gross temperature lift at 97.5°C with coefficients of performance of about 0.5. The maximum temperature of the useful heat produced by the AHT was ∼150°C. In addition, exergy losses for each component in the system were calculated at different working temperatures and the results of both systems with and without an ejector were compared. Exergy analysis emphasised that both the losses and irreversibilities have an impact on the system performance and exergy analysis can be used to identify the less efficient components of the system. Exergy analyses also showed that the exergy loss of the absorber of AHT with ejector was higher than those of other components. [Copyright &y& Elsevier]

Abstract: The problem of the development of salt concentration profiles in a solar pond is investigated, the thermodiffusion contribution is also taken into account, using a one-dimensional mathematical model and a finite-difference approach. A novel scheme of heat extraction from the solar pond is presented, along with preliminary two-dimensional computational fluid dynamics (CFD) simulations. [Copyright &y& Elsevier]

Abstract: The thermal performance of a shallow solar pond (SSP) under an open cycle continuous flow heating mode for heat extraction has been investigated. A serpentine heat exchanger (HE), either welded to the absorber plate or immersed in the pond water, has been used for extracting the heat. Suitable computer programs have been developed based on analytical solutions of the energy balance equations for the various elements of the SSP in the presence of the HE. Numerical calculations have been performed to study the effect of different operational and configurational parameters on the pond performance. In order to improve the pond performance, optimization of the various dimensions of the pond with the HE has been performed. The effects of the design parameters of the HE’s tube, i.e. length L he, diameter D and mass flow rate of the fluid flowing through the HE, on the pond performance have been investigated. The outlet temperature of the HE’s fluid T fo is found to increase with increase of the HE length L he, and it decreases with increase of the mass flow rate of the HE’s fluid up to typical values for these parameters. Typical values for L he and are found to be 4m and 0.004kg/s beyond which the change in T fo becomes insignificant. Experiments have been performed for the pond under different operational conditions with a HE welded to the absorber plate. To validate the proposed mathematical models, comparisons between experimental and theoretical results have been performed. Good agreement has been achieved. [Copyright &y& Elsevier]

Abstract: The objective of this study is to investigate experimentally and theoretically whether sodium carbonate (Na2CO3) salt is suitable for establishing a salinity gradient in a salt-gradient solar-pond (SGSP). For this purpose, a small-scale prismatic solar-pond was constructed. Experiments were conducted in the laboratory under the incident radiation from two halogen-lamps acting as a solar simulator. Furthermore, a one-dimensional transient mathematical model that describes the heat and mass transfer behaviour of the SGSP was developed. The differential equations obtained were solved numerically using a finite-difference method. It was found from the experiments that the density gradient, achieved using sodium carbonate salt, can suppress convection from the bottom to the surface of the pond. [Copyright &y& Elsevier]

Abstract: In this study, an experimental and theoretical investigation of temperature distributions in an insulated solar pond, particularly during daytimes and nighttimes, is presented. Several temperature sensors connected to a data acquisition are placed vertically inside and the bottom of the pond and also horizontally and vertically in the insulated side walls, and used to measure temperature changes with time and position. In addition, we model the solar pond to compute theoretical temperature distributions and compare with the experimental measurements, and hence a good agreement is found between experimental and theoretical temperature profiles. There is a large amount of heat losses between daytimes and nighttimes, depending upon the temperature difference, and these present a significant potential for energy savings and storage. During the months of January, May and August, it is found that the total heat losses from the inner surface of the pond and its bottom and side walls, as a function of temperature difference, are determined to account for 227.76MJ (e.g., 84.94% from the inner surface, 3.93% from the bottom and 11.13% from the side walls, respectively). [Copyright &y& Elsevier]

Highly regulated salinity gradients in solar salt pond concentrating sequences provide an opportunity to investigate in situ salinity impacts on aquatic flora and fauna. The Shark Bay Salt solar ponds at Useless Inlet in Western Australia vary in salinity from seawater to four times seawater over the pond sequence. We observed a shift from planktonic to benthic primary productivity as salinity increased. Water column photosynthesis and biomass decreased markedly with increasing salinity, while benthic productivity increased as cyanobacterial mats developed. Correspondingly, productivity shifted from autotrophy to heterotrophy in the water column and from heterotrophy to autotrophy in the benthos. Both shifts occurred at intermediate salinity (S = 110 g kg−1, ρ = 1.087 g cm−3) in the pond sequence, where there was little production by either. Within individual ponds, productivity, algal biomass and physico-chemical conditions were relatively constant over one year, with only water column photosynthesis significantly different between seasons, mostly due to greater winter production. Transitions between benthic and planktonic production and their relative magnitudes appear to be driven mostly by direct responses to salinity stress, but also by changes in nutrient availability and grazing, which are also influenced by salinity. [ABSTRACT FROM AUTHOR]

Abstract: An experimental study on the evolution of the temperature and salinity profiles in a salinity gradient solar pond was executed using a small model pond. The body of the simulated pond is a cylindrical plastic tank, with 1 m height, 0.9 m diameter. The tank was insulated by 150 mm of polyurethane. The salinity gradient was established in the laboratory tank by using the salinity redistribution technique The base of the tank is black painted. Solar radiation was simulated by a 2000 W light projector that presents a spectrum similar to the solar one. The measurements were taken during a period of 29 days of experimentation. This period of time allowed to show the existence of salt diffusion from the storage zone to the surface. The temperature profile was established in the small model pond after 5 days of heating. The maximum temperature attained in the storage zone was 45°C carrying out a difference in temperature between the bottom and the surface of the pond of 23°C when the projector is put of and 17°C when it is put on. A comparison between the temperature and salinity profiles obtained experimentally in the model pond and those calculated by the empirical relation of Newell show a good agreement. [Copyright &y& Elsevier]

Abstract: An alternative method of heat extraction from salinity-gradient solar ponds is investigated with the aim of increasing the overall energy efficiency of collecting solar radiation, storing heat and delivering this heat to an application. In this alternative method, heat is extracted from the non-convecting gradient layer of a solar pond as well as, or instead of, from the lower convective zone (LCZ). A theoretical analysis of combined gradient-layer and LCZ heat extraction is conducted to obtain expressions for the variation of temperature with depth in the pond, and the temperature gradient with depth. The dependence of the overall energy efficiency of the pond on thickness of the gradient-layer, temperature of delivered heat, and various combinations of gradient layer and LCZ heat extraction rates, including the limiting cases of gradient-layer heat extraction only, and LCZ heat extraction only, is then explored. This theoretical analysis suggests that heat extraction from the gradient layer has the potential to increase the overall energy efficiency of a solar pond delivering heat at a relatively high temperature by up to 50%, compared with the conventional method of heat extraction solely from the LCZ. The potential gain in efficiency using gradient-layer heat extraction is attributed to the lowering of heat losses by conduction to the upper convective (surface) zone that can be achieved with this method. Experimental investigations are proposed to test the predictions of the theoretical analysis in practice, and assess the impact of a number of idealized assumptions made on the findings reported here. [Copyright &y& Elsevier]

Abstract: The origin and continuation of mankind is based on water. Water is one of the most abundant resources on earth, covering three-fourths of the planet''s surface. However, about 97% of the earth''s water is salt water in the oceans, and a tiny 3% is fresh water. This small percentage of the earth''s water—which supplies most of human and animal needs—exists in ground water, lakes and rivers. The only nearly inexhaustible sources of water are the oceans, which, however, are of high salinity. It would be feasible to address the water-shortage problem with seawater desalination; however, the separation of salts from seawater requires large amounts of energy which, when produced from fossil fuels, can cause harm to the environment. Therefore, there is a need to employ environmentally-friendly energy sources in order to desalinate seawater. After a historical introduction into desalination, this paper covers a large variety of systems used to convert seawater into fresh water suitable for human use. It also covers a variety of systems, which can be used to harness renewable energy sources; these include solar collectors, photovoltaics, solar ponds and geothermal energy. Both direct and indirect collection systems are included. The representative example of direct collection systems is the solar still. Indirect collection systems employ two sub-systems; one for the collection of renewable energy and one for desalination. For this purpose, standard renewable energy and desalination systems are most often employed. Only industrially-tested desalination systems are included in this paper and they comprise the phase change processes, which include the multistage flash, multiple effect boiling and vapour compression and membrane processes, which include reverse osmosis and electrodialysis. The paper also includes a review of various systems that use renewable energy sources for desalination. Finally, some general guidelines are given for selection of desalination and renewable energy systems and the parameters that need to be considered. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

This paper involves the prediction of convective layers on the sidewalls of a solar pond. A three-dimensional finite-volume method for incompressible flows with different initial and boundary conditions is applied for the solution of convective layers generated on solar pond walls. A parametric study was conducted to predict the effects of wall tilt angle and salt concentration on the characteristics of the convective layers.Comparison of the present numerical results with experimental data from previous studies shows that it is possible to capture the flow features of the convective layers. Furthermore, the trends predicted for the effects of the tilt angles and the salt concentrations agrees well with that obtained from experimental data. [Copyright &y& Elsevier]

The salt-gradient solar ponds are considered in this work in order to study its performance numerically. Governing equations of the upper convective zone, nonconvective zone, and lower convective zone of a salt gradient solar pond are deduced as a set of non-linear partial differential equations. The equations are solved numerically to predict the thermal performance of the solar pond over a long time. The meteorological data of Egypt such as incident solar radiation, ambient temperature, air velocity, and relative humidity are taken into considerations in the model. Heat transfer modes considered between the upper convective zone and the ambient are convection, evaporation, and radiation. The present model is used to study the development of temperature inside the three zones of salt gradient solar pond. The optimum thickness of each layer is obtained with close agreement of previous results. [ABSTRACT FROM AUTHOR]

The thermal performance of a shallow solar pond (SSP) under the batch and open cycle modes of heat extraction has been investigated experimentally. Experiments have been performed during the summer season of 2001 under different operational conditions for the two modes of heat extraction. The pond performance is investigated in terms of the heat loss coefficients and the rates of energy losses and energy collected. It is found that using an additional glass cover reduces the top Ut and total Ul loss coefficients by 54 and 44%, respectively. The highest value of the rate of energy collected &Qdot;coll. of 644 W has been achieved when the pond is used with double glass cover and an outer mirror. Further, the tap water is used as a fluid flowing through a heat exchanger (HE), welded to the pond absorber plate, to extract the heat under the open cycle mode. The outlet temperature of the HE’s fluid Tfo is found to decrease with the increase of the mass flow rate &mdot;f. The maximum values of Tfo are found to be 55.5, 46.5 and 43.5 °C when &mdot;f equals 0.00054, 0.0030 and 0.00798 kg/s, respectively. Comparisons between the two modes of heat extraction are performed based on the efficiency and the successive operation of the pond. The long-term performance of the pond under the best operational conditions has been investigated by computer simulation for a whole year. It is inferred that the present SSP can be used as a source for the warm water required for domestic applications under climatic conditions similar to Tanta city (latitude 30°47′). [Copyright &y& Elsevier]

In a previous study, the authors presented a simple mathematical model for predicting the ratio of the evaporation pond area to that of a salt gradient solar pond area. The evaporation pond idea provides a very attractive method of salt recycling by evaporation, especially in areas of high evaporation and low rates of rain as it is the case for North Africa.In this paper, the model was elaborated upon and applied to two types of surface water flushing (fresh water and seawater) under the prevailing conditions of Tripoli, Libya (latitude=32.86°N). All the results presented were predicted for the first three years of operation. The daily variations of brine concentration in the of Tajoura''s Experimental Solar pond and those based on different designs were predicted and discussed under different scenarios. The quantities of brine provided by the evaporation pond and that required by were predicted for both cases of surface water flushing (fresh water and seawater) under the different design conditions. It was predicted that the can provide 20–40% during the first year and 45–95% during the third year depending on the design selected. [Copyright &y& Elsevier]

In this paper, the thermal performance of a shallow solar-pond (SSP) under the batch mode of heat extraction has been investigated theoretically and experimentally. A transient mathematical model has been proposed. A computer program has been developed based on an analytical solution of the energy-balance equations of different elements of the pond. Numerical calculations have been carried out to study the effects of various configurational and operational parameters on the pond''s performance. To improve the pond''s performance, an outer mirror is hinged outside the pond to increase the amount of solar radiation incident on the pond cover. Optimization of various dimensions of the pond has been carried out. Effects of the pond''s water-depth Xw, wind speed V, the sides’ Xs and back Xb insulation thicknesses as well as the height C and width W of the outer mirror have been investigated. The influence of the number of glass covers over the pond during the night have also been studied. Comparisons between experimental and theoretical results showed that good agreement has been achieved. Experiments indicated that the pond could provide 88 l of hot water at a maximum temperature of 60 °C at sunset. The pond can retain hot water till 7.00 a.m. next day at a temperature of 47 °C: this is suitable for domestic applications. [Copyright &y& Elsevier]

The El Paso salinity gradient solar pond, initiated in 1983, has been in operation since 1985. Through 16 years, of research and operation, the El Paso Solar Pond has successfully demonstrated applications including desalination, waste brine management, industrial process heat production, and electricity generation; and has developed and implemented key technical advancements to improve the technical viability and economic feasibility of salinity gradient solar ponds, including: 1) an automated instrumentation monitoring system, 2) a stability analysis strategy and high temperature (60-90°C) gradient maintenance methods, 3) a scanning injection technique for improved salinity gradient construction and maintenance, 4) new liner technology, and 5) an improved heat extraction system. [ABSTRACT FROM AUTHOR]

Absorption thermal systems are attractive for using waste heat energy from industrial processes and renewable energy such as geothermal energy, solar energy, etc. The Absorption Heat Transformer (AHT) is a promising system for recovering low-level waste heat. The thermal processes in the absorption system release a large amount of heat to the environment. This heat is evolved considerably at temperature, the ambient temperature results in a major irreversible loss in the absorption system components. Exergy analysis emphasises that both losses and irreversibility have an impact on system performance. Therefore, evaluating of the AHT in exergy basis is a much more suitable approach. In this study, a mathematical model of AHTs operating with the aqua/ammonia was developed to simulate the performance of these systems coupled to a solar pond in order to increase the temperature of the useful heat produced by solar ponds. A heat source at temperatures not higher than 100 °C was used to simulate the heat input to an AHT from a solar pond. In this paper, exergy analysis of the AHT were performed and effects of exergy losses of the system components on performance of the AHT used to increase solar pond’s temperature were investigated. The maximum upgrading of solar pond’s temperature by the AHT, is obtained at 51.5 °C and gross temperature lift at 93.5 °C with coefficients of performance of about 0.4. The maximum temperature of the useful heat produced by the AHT was ~150 °C. As a result, determining of exergy losses for the system components show that the absorber and the generator need to be improved thermally. If the exergy losses are reduced, use of the AHT to increase the temperature of the heat used from solar ponds will be more feasable. [Copyright &y& Elsevier]

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Bioaccumulation of selenium (Se) in wetlands and evaporation ponds has created serious hazards to fish and waterfowl in the western United States. Agricultural drainage water is the main source for Se contamination in this region. Treatment technologies currently being evaluated to reduce the Se load in agricultural drainage water include physical, chemical and biological methods. This article focuses on ion-exchange, reverse osmosis, solar ponds, chemical reduction with iron, microalgal-bacterial treatment, volatilization, biological precipitation, and flow-through wetlands to remove Se in water. Advantages and disadvantages of each technology are evaluated and assessed in terms of cost-effectiveness and practical applications in dealing with large volumes of drainage water. With intense research in treatment technologies, it is feasible that a combination of biological, chemical and physical techniques may be employed in the development of a cost-effective strategy to treat agricultural drainage water. [ABSTRACT FROM AUTHOR]

Two simple formulations for estimation of net available radiation at a depth in solar pond are proposed. The first formulation uses the correlation of Bryant and Colbeck [Solar Energy 19 (1977) 321] and extends the same to incorporate the reflected part of radiation coming from bottom and surface of the pond. The other formulation is an empirical fourth order polynomial function. The universal functions of Hull [Solar Energy 29 (5) (1982) 385] are taken as a base line for comparison of accuracy in estimation of radiation flux. The proposed formulations provide a substantial saving of computational time, much simplicity in analytical calculations, and reasonably good accuracy in estimation of radiation flux at a depth in solar pond. Their impact of these formulations is also analyzed on accuracy in prediction of pond’s long-term thermal behavior and gain in terms of computational speed. It provides a 20–25% saving in computational time as compared to Hull’s method with comparable accuracy. [Copyright &y& Elsevier]

A theoretical and experimental study is made for underfloor heating system using solar collectors. Also a study for a similar system using solar ponds is made under the same local conditions. Results obtained show that the solar collector system is 7% more efficient than the solar pond system. Economic analysis show that the Solar Collector System (SCS) will break even earlier than the Solar Pond System (SPS). Practical considerations show that the SCS requires less operation and maintenance work. [Copyright &y& Elsevier]

A one-dimensional transient mathematical model is used for the study of the salt diffusion and stability of the density gradient in a solar pond. A finite difference method with a diffusion coefficient dependent on both temperature and salt concentration is used to solve the salt diffusion equation. On the basis of simple considerations we analyze the influence of the salinity-gradient thickness on the useful energy which can be withdrawn from the bottom layer of the solar pond. Finally some considerations on the effect of the velocity of injected brine in rising solar ponds are presented, making use of the Rayleigh analysis of the small perturbations in order to study the stability of the system. [Copyright &y& Elsevier]

In salt gradient solar ponds, the clarity of water and absorptivity of the bottom are important concerns. However, both are practically difficult to maintain beyond a certain limit. The reflectivity of the bottom causes the loss of a fraction of the incident radiation flux, resulting in lower absorption of flux in the pond. Turbidity hinders the propagation of radiation. Thereby it decreases the flux reaching the storage zone. Both these factors lower the efficiency of the pond significantly. However, the same turbidity also prevents the loss of radiation reflected from the bottom. Hence, the combined effect is compensatory to some extent. The present work is an analysis of the combined effect of the bottom’s reflectivity and water turbidity on the steady state efficiency of solar ponds. It is found that in the case of a reflective bottom, turbidity, within certain limits, improves the efficiency of pond. This is apparently contradictory to the conventional beliefs about the pond. Nevertheless, this conclusion is of practical importance for design and maintenance of solar ponds. [Copyright &y& Elsevier]

A comparative study between two types of solar ponds is presented. The first type has its free surface covered by a thin layer of transparent paraffin oil. The second type is covered by transparent glass floating devices. Each device disposes an air-vacuum chamber. The free water surface between these devices is covered by transparent paraffin oil also. The thermal storage efficiency of each pond is estimated during two time periods: between sunrise and sunset and from midnight to midnight. The calculated efficiency between sunrise and sunset corresponds to the average transmittance–absorptance product. This is estimated using linear regression and also a maximum likelihood identification technique. The behavior of the system was studied by solving numerically the heat transfer equations of the system. Also an ARMAX (AutoRegressivie Moving Average with eXogenous signal) model allowing the assessment of its performance was presented. This efficiency is larger for the first pond during the sunrise to sunset period and smaller when calculated from midnight to midnight. Thus, the first type of pond could be preferred for a use just after the sunset of the same day, while the second for use after one or more days of heat storage. [Copyright &y& Elsevier]

We are interested in the modeling and control of a salt gradient solar pond (SGSP) in the south of Tunisia. We developed a model of a closed cycle salt gradient solar pond (CCSGSP) that ensures successful year round operation. This model was used to study the response of the solar pond (SP) to various control techniques. It takes into account heat and salt diffusion within the pond and simulates the transient behavior of a SGSP. Furthermore, we investigated the dynamic process, which involves internal gradient stability, boundary behavior between the gradient zone and the convective zones. We thus incorporated the double diffusive processes into the SP model by using the one dimensional stability criterion produced by linear theory. The governing differential equations are solved numerically by using a control-volume scheme.The results show that successful operation of a SP requires three things: the maintenance of the storage zone temperature through heat extraction and brine injection, the use of surface washing to control the deepening of the upper mixed layer and a well designed initial salt stratification to prevent the formation of instability within the gradient. Using linear salinity profile as an initial condition, three round year simulations were run using average meteorological data with the result that adequate stability (Rρ≻2 throughout the gradient and Rρ≅10 at the interfaces) was maintained. Numerical results show also that 10–30% efficiency could have been reached if heat extraction is performed routinely especially when one considers that the storage temperature is within 40–80 °C. The model is validated against data taken from the operation of the UTEP SP. Close correlation between computed and measured data was obtained. [Copyright &y& Elsevier]

An investigation of the thermal stability of large area saltpan solar ponds under different climatic conditions is presented. The study focuses on time taken by the pond to reach its stable conditions with heavy rainfall and the effect of wind-mixing process for the stability of the pond. Investigations were carried out over a period of 60 days on a large-area solar pond of 90 cm deep. The temperature and density profiles obtained 34 days after filling showed that the pond had attained its stability with a bottom temperature of 63 °C. Results reveal that heavy rainfall is the prime cause for the pond to reach stability in a time period of about 30 days. Strong wind-induced mixing prevailed during the second half of the investigation, which contributed to the erosion of the nonconvecting zone is the cause for observed destabilization of the pond. The estimated critical wind speed for complete destruction of the nonconvecting zone is about 25 km/h. [Copyright &y& Elsevier]

The salt gradient solar pond is a long-term heat storage system with a considerable warm-up time. A pond is efficient when it reaches the desired temperature quickly and maximum heat is subsequently retrieved at steady state. This requires optimum sizing of the non-convective zone. In the present work, the optimum size of the non-convective zone for fast warm-up is determined. This is found to differ considerably from the optimum size of the steady state criterion. The possibility of achieving both performance parameters, i.e. fast warm-up and maximum heat collection later on, is analyzed. It is suggested that when commissioning a pond, the size of the non-convective zone should at first be the optimum value from the warm-up rate criterion, but may later be changed to the optimum size from the steady state criterion. [Copyright &y& Elsevier]

This paper investigates a few mathematical aspects of computer simulation of salt gradient solar pond’s thermal behavior. The basic equation governing heat flow in the non-convective zone of solar pond is solved by finite difference approach using the Crank–Nicholsen method. Stability and convergence of the method, specifically for the case of solar pond, is examined over a wide range of depth difference (Δx) and time difference (Δt). It is observed that the mesh ratio parameter (r = K Δt/√ of ρCpΔx2) which is used to define the stability and convergence of the method does not have an absolute value, rather its value varies with Δx. While using an actual set of Δx and Δt, the stability must be tested with reference to the set being used. Few other mathematical aspects pertaining to the actual application of the method are also investigated. Also, the effect of fineness of ambient input data on long term performance of the pond is investigated. It is observed that the diurnal variation of ambient input data yields the same accuracy as the hourly variation. Different approaches of calculating the heat losses from upper convective zone are compared for long term performance of the pond. A simple method is suggested to calculate the radiation flux at a depth which results due to multiple reflections between bottom and surface of the pond. The method saves computational time when used for simulation and is also suitable for hand calculations. [Copyright &y& Elsevier]

An experimental test rig for solar pond simulation was developed to study the chosen fertiliser salt, Muriate of Potash (MOP) for use in a solar pond under simulated conditions with provisions to vary the heating input and maintain a particular lower convective zone temperature. The performance, in terms of temperature and density profiles, was studied for MOP and was compared with that of sodium chloride and saltless solar ponds for different heating regimes and lower convective zone temperatures. The formation of three zones viz., upper convective zone, nonconvective zone, and lower convective zone was distinct at all heating combinations for both MOP and sodium chloride salts under simulated conditions. The temperature and density gradients were not affected significantly by intermittent no-heating spells of the solar ponds. Maintaining lower convective zone temperature of 70 °C and above led to the initiation of minor internal convective zone under simulated conditions. The temperature decay of lower convective zone (LCZ) was at lesser rate for different LCZ temperatures associated with both the heating regimes, for a MOP pond over a 24 h period of cessation of heating as compared to sodium chloride and saltless ponds. [Copyright &y& Elsevier]

Applications of simple methods to reduce the maintenance of a small solar pond are discussed in this paper. It was found that floating rings along with continuous surface flushing could effectively control and maintain a relatively thin upper convective layer. A novel system of salt replenishment (a salt charger) is introduced. It is shown that the application of the proposed system is capable of controlling the position of the lower interface. Criteria governing the design of a salt-charger for a salinity-gradient solar pond are developed theoretically and verified experimentally. The design procedures are presented. Experiences relating to the utilization of brine shrimps to improve the transparency of the pond are described. [Copyright &y& Elsevier]

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Presents a study which presented the results of a mathematical model for predicting the ratio of the evaporation pond area to that of a Salt Gradient Solar Pond (SGSP) area in water flushing. Zones that compose a SGSP area; Types of surface water flushing.

Fertiliser salts are considered in the place of sodium chloride for operating solar ponds. A study was conducted to identify the potentially viable candidate fertiliser salts for Indian conditions. Muriate of potash, a potassic fertiliser, is found to have properties comparable to that of sodium chloride, and can generate energy at cheaper cost than urea. [ABSTRACT FROM AUTHOR]

Presents a study of the natural brine solar pond in the South East of Tunisia. Description of the natural reserves; Experimental details; Comparison between the natural and the artificial brine solar ponds; Conclusion.

Brine released from desalination plants is extremely high in salinity and contains various chemicals, which are harmful to the ecosystem. The disposal of brine has raised great concerns for the desalination industry around the world due to its detrimental impact on fauna and flora. This review complies with various zero liquid discharge technologies that have been proposed for successful brine disposal which aims to minimize the impact of brine discharge. Moreover, it highlights some of the detrimental impacts of brine discharge on marine fauna and Flora. It also discusses both thermal and membrane technologies for recovering freshwater, energy, and minerals from waste brine, in addition to the recent advances in a solar pond, membrane distillation, pressure retarded osmosis, etc. In Driver-Pressure-State-Impact-Response (DPSIR) framework was used in this review to analyze the water resource system in Qatar. This review also facilitates and provides a comprehensive approach in minimizing the potential impact of brine discharge which can be practiced and applied in countries where desalination plants are set up. This promotes cleaner production, sustainability, and recycling of waste that will help protect and preserve the country's natural water resources. [ABSTRACT FROM AUTHOR]

• Active method by external magnetic field is proposed to improve solar pond stability. • Improvement of heat storage capacity and stability is analyzed quantitatively. • Magnetic field effectively represses interface erosion in solar pond. • Nondimensionalized magnetic field effect on solar pond performance is discussed. A solar pond is a simple and reliable system that collects and stores solar energy for applications with low-grade heat supply. The main obstacle to the long-term stable operation of a solar pond is interface erosion induced by double-diffusive convection. In this study, an active method of using an external magnetic field is proposed to repress the intense convection region and improve its corresponding operating stability. A two-dimensional transient model is developed and solved using the lattice Boltzmann method with multiple-relaxation-time collisions. The double-diffusive convection, variation of solar energy absorption to depth, and changes in solution electrical conductivity are considered in the model. The fluid flow, heat, and mass transfer characteristics were investigated under continuous high illumination with or without an external magnetic field. When magnetic control is exerted on a solar pond, the decrease in the nonconvective zone thickness caused by interface erosion changes from 14.75% to 0. The state of the solar pond is transformed from a thermally unstable state to a theoretically stable state after 35 h of continuous high illumination. Further, the external magnetic field can delay concentration homogenization and improve the heat storage performance of a lower convective zone. A Hartmann number above 56.67 is recommended to enhance the stability of the solar pond. This research sheds new light on methods to improve the long-term stability of solar ponds. [ABSTRACT FROM AUTHOR]