Performance Of Solar Pond Research Articles

A transient model of a laboratory-scale carnalite salt gradient solar pond

The thermal performance of a laboratory-scale salt gradient solar pond has been modeled as a one-dimensional unsteady conduction heat transfer problem with heat generation. The pond is assumed to be cut into horizontal slices and finite difference heat balance equations are solved simultaneously to predict the temperature of each slice at any time. The initial conditions were the temperature profile data. The boundary conditions were determined by studying the heat balance at the bottom of the pond and by assuming the pond surface temperature to be equal to the ambient temperature. Solar radiation attenuation is calculated by the Bryant and Colbeck formula. A computer program is constructed to perform the calculations. In addition, Kooi's model was compared with our model. Similarly the salinity behavior was studied by writing the one-dimensional differential mass balance equation over a small slice with the appropriate boundary and initial conditions. The resultant set of linear equations was solved simultaneously for the unknown new concentrations. A computer program has been constructed to perform the calculations. Fair agreement between experimental and predicted profiles was obtained.

Theoretical and experimental comparison of conventional and advanced solar pond performance

Numerical and physical experiments were carried out to compare the performance of two solar pond systems: (a) a conventional salt gradient solar pond (CSP) and (b) a salt gradient pond operated as an “advanced solar pond” (ASP). The main differences in the ASP, as originally proposed by Osdor[1], are an increase in overall salinity and the introduction of a stratified flowing layer near the bottom of the gradient zone. The increased salinity is meant to reduce evaporative heat loss and make up water requirements, while the additional flowing layer allows extra heat extraction and possibly higher temperatures to develop in the lower convective zone. A numerical study was performed to evaluate the salinity effect and the results show only a minor effect of increased salinity on heat collection efficiency. However, slightly higher collection temperatures are obtained, which may provide some benefit for heat engine efficiency. Physical experiments were performed to test the feasibility of constructing and maintaining the necessary flow system for the ASP and also to compare the performance of the ASP and the CSP under similar laboratory conditions. These tests showed that a stable stratified flowing layer could be maintained and that the ASP configuration produced higher efficiencies.

Saturated solar ponds: 2. Parametric studies

The effects of following parameters on the performance of saturated solar ponds are studied: thickness of upper convective zone, nonconvective zone, and lower convective zone; starting time of the pond; water table depth below the pond; ground thermal conductivity; transmissivity of salt solution; incident radiation; ambient air temperature, humidity, and velocity; thermophysical properties of salt solution; pond bottom reflectivity; convection, evaporation, radiation, and ground heat losses; temperature and rate of heat removal; type of salt. Magnesium chloride and potassium nitrate salt ponds located at Madras (India) are considered for the parametric study. A comparison is also made with an unsaturated solar pond.

The onset of thermohaline convection in the advanced solar pond (ASP)

This manuscript concerns the onset of thermohaline convection in a solar pond subject to field conditions as well as a small scale laboratory test section simulating the solar pond performance. The onset of thermohaline convection is analyzed in this study by means of a linear stability analysis in which the flow field perturbations are expended in sets of complete orthonormal functions satisfying the boundary conditions of the flow field. The linear stability analysis is first performed with regard to an advanced solar pond (ASP) subject to field conditions in which thermohaline convection develops in planes perpendicular to the unperturbed flow velocity vector. In the laboratory simulator of the ASP the width and depth are of the same order of magnitude. In this case it is found that the side walls delay the onset of convection in planes perpendicular to the unperturbed flow velocity vector. The presence of the side walls may cause the planes parallel to the flow velocity to be the most susceptible to the development of perturbations in the flow field. Finite rolls, namely, cells with two non-zero velocity components dependent on all three spatial variables, are predicted. They may develop in planes parallel or perpendicular to the unperturbed velocity vector according to the value of the Reynolds number of the unperturbed flow and the ratio between the width and depth of the ASP simulator.

Closure to “Discussion of ‘Basic Experiments Related to the Advanced Solar Pond (ASP) Performance’” (1991, ASME J. Fluids Eng., 113, p. 123)

Closure to “Discussion of ‘Basic Experiments Related to the Advanced Solar Pond (ASP) Performance’” (1991, ASME J. Fluids Eng., 113, p. 123)

Numerical simulation of thermal performance of a salt-gradient solar pond in a cold climate.

A one-dimensional numerical model which simulates the dynamic thermal performance of stratified salt-gradient solar pond is described. The model simulates the thermal performance in the upper convective layer, the nonconvective layer and the lower convective layer in a cold climate. In addition to the energy flux in the solar pond, the model simulates the varying ice thickness appearing in the upper convective layer during the winter season. From the results, it is noticed that it is important to maintain the optimum thickness of the nonconvective layer and the clearness of the upper convective layer for the high thermal efficiency of the salt-gradient solar pond.

Performance of solar ponds with wind suppressors

Abstract The effect of wind suppressors on the performance of a 4 m 2 solar pond, operating under the environment of the Arabian Gulf area characterized by windy, hot and humid conditions, is investigated experimentally. In addition to using screen nets on the pond's perimeter, two arrangements of wind suppressors of PVC floating pipes are considered. Climatological data relevant to the operation of solar ponds in this area namely wind speeds and evaporation rates are presented. Results of both salinity and temperature over a one year period are presented to evaluate the effect of wind suppressors and thermal insulation on the performance of the pond. The gradient zone was disturbed by invoking localized convective zones of different thicknesses to examine the effect of wind suppressors on the healing of those zones. Results show that wind suppressors of the floating piping type, can considerably slow down the movement of the upper convective-gradient zone interface and prohibit any formation of localized convective zones. Thermal insulation is a prerequisite for operating small solar ponds even in hot climates.

Effect of surface ice on solar pond performance

A solar pond simulation model is described which includes the capability for predicting surface ice growth. The model is a direct extension of a previous numerical wind-mixing model. Ice predictions are based on studies of lake and sea ice growth and dissipation. The model incorporates the effect of salinity on freezing temperature and on the temperature of maximum density. Ice growth rates predicted by the model are verified using data from a simple laboratory experiment. Results from numerical simulations of a hypothetical pond in the Buffalo, New York area are presented and these demonstrate a net positive effect of ice cover, notably in reducing gradient maintenance needs for the surface layer.

Performance of a small solar pond in the tropics

The performance of the 240 m 2 solar pond in Bangalore is discussed. The problems of erosion of gradient zone and formation of internal convective zones is highlighted. The technique of passive salt addition is shown to be a viable alternative for salt recycling. Different techniques of heat extraction are discussed and the use of an immersed copper heat exchanger is shown to be most convenient. A two-zone model for prediction of the seasonal structure of the solar pond performance is proposed. The model is shown to simulate the seasonal structure of the observed variation of the temperature in the storage zone.

The advanced solar pond (ASP): Basic theoretical aspects

This manuscript concerns the possible improvement of the conventional solar pond (CSP) performance by applying a multiselective injection and withdrawal procedure. We apply the term advanced solar pond (ASP), for a solar pond (SP) in which such a procedure is applied. The multiselective injection and withdrawal procedure creates in the SP a stratified thermal layer, namely a flowing layer which is subject to salinity and temperature stratification. This phenomenon is associated with reduction of heat losses into the atmosphere and an increase of the temperature of the fluid layer adjacent to the SP bottom. In the framework of this study transport phenomena in the ASP are analyzed and simulated by applying a simplified mathematical model. The analysis and simulations indicate that the multiselective and withdrawal procedure may significantly improve the performance of the SP.

Computer simulation modelling, thermal performance and design optimisation for solar ponds in Greece

The development of a simple one-dimensional computer model is described here to investigate the effect of various zone geometries and operational parameters on the thermal performance of solar ponds in Greece. Given the necessary meteorological data input and load operational requirements, the model is used to optimise the design and to match properly solar ponds with the load temperature requirements. More specifically, solar pond thermal behaviour is examined under both heat extraction schemes of constant rate and temperature and its heat collection efficiency is dynamically calculated. According to the derived results, it comes out that solar ponds are potential solar devices, and their development in the North-eastern Mediterranean basin will substantially contribute to conservation of energy and reduction of oil consumption in isolated and offshore communities of considerable economic activity.

Effect of the gap spacing on the shallow solar pond performance

It is stated by Garg et al. [ Energy Convers. Mgmt 22, 117 (1981)] that, for a shallow solar pond where the gap spacing is large (300 mm), the convective heat loss is somewhat lower than for a conventional collector with a shorter gap spacing (20 mm). How much the total heat transfer coefficient is lowered, and what is the effect of the gap spacing on the performance of the shallow solar pond were not mentioned. In this study, the effect of gap spacing on shallow solar pond performance is studied. For this purpose, a computer program is constructed and is experimentally tested using a shallow solar pond of 6.6 m 2 area. It is concluded from the results that the effect of gap spacing on the top loss coefficient is independent of the temperature difference between the upper film of the water bag and the glazing of the shallow solar pond. The results also show that the change in gap spacing of the shallow solar pond has not an important effect on the pond performance. Hence, the large gap spacing in the conventional design shallow solar pond (300 mm) cannot be considered as a major difference with the flat plate collector design (20 mm), as Garg et al. stated.

Thermal characteristics and performance of salt gradient solar ponds

A mathematical model with various parameters such as effective absorptivity-transmitivity product and total heat loss factor, including ground losses and angle of refraction, which are related to the physical properties and dimensions of the pond, is developed to study the thermal behaviour of salt gradient solar ponds at different operational conditions. A linear relation is found between the efficiency of the solar pond and the function (ΔT/H). The convective heat loss, the heat loss to the atmosphere due to evaporation through the surface of the pond and ground heat losses have been accounted for in finding out the efficiency of the pond. The dependence of the thermal performance of the solar pond on the ground heat losses is investigated and minimized using low cost loose and insulating building materials such as dry dunes and, Mica powder and loose asbestos at the bottom of the pond. The ground heat losses are considerably reduced with the asbestos (loose) and the retention power of solar thermal energy of the pond increases.

Optical analysis of the behaviour of a salt-gradient solar pond

Summary The three-zone salt-gradient solar pond is a body of saline water that collects solar radiation and stores it in the water as thermal energy. The performance of solar ponds largely depends on the portion of solar radiation which reaches the bottom region (LCZ) and from which heat is extracted subsequently. An analysis is made to determine the form of the attenuation of the solar rays inside the pond as a function of wavelength and depth, taking into consideration that each zone has its extinction coefficient due to its salt concentration. Insertion of partitions between zones (between the UCZ and NCZ and between the NCZ and LCZ) has also been discussed. Equations describing the transmissions and reflection coefficients in the presence of partitions were derived. The portion of the solar energy that is absorbed by the different depths of NCZ has been calculated for Cairo. About 20% of the incident radiation is absorbed by the NCZ, and with the presence of transparent partitions this quantity decreases by about 20%.

Thermal performance of solar ponds under different soil conditions

This paper aims to estimate the ground heat losses from the salt gradient field solar ponds working under natural conditions. The dependence of ground heat losses upon moisture gradient, temperature gradient and ambient temperature is estimated considering the coupled heat, moisture and vapour transport theory. The required expression for the soil thermal conductivity is also developed here considering effective continuous media approximation. The validity of expression is tested by comparing the theoretical values of λ e for moist soil with those of experimental results.

Mathematical modelling of salt gradient solar pond performance

This paper presents a mathematical model of the performance of the salt gradient solar pond. A lumped parameter model of the upper convective zone, non-convective zone and lower convective zone is used. This model enables the temperatures of the upper-convective zone and the lower convective zone of the solar pond to be predicted. The experimental results agree well with theoretically predicted values. The major error in the theoretical results is due to the difference between the theoretical value of the solar radiation inside the water and that observed experimentally. It is found that the experimental value of the solar radiation at a depth of 90 cm is approximately 26 per cent of the total solar radiation falling on the solar pond surface, whereas the corresponding theoretical value is found to be 33 per cent. The results conclude that the lumped parameter model can be used as a simple model to predict the performance of the solar pond.

Applicability of steady state equations for solar pond thermal performance predictions

The steady state thermal performance of solar ponds is compared with hourly numerical simulation results and limitations of the steady-state equations are discussed. The approach to steady-state is described by the definition of a time constant. Based on numerical simulation results, a simple way of evaluating monthly performance is given. The concept of utilizability is extended to solar ponds and it is shown that the yearly utilizability curve is independent of location.

Effect of radiation absorption in saline water on the performance of solar ponds

The effect of the solar radiation absorption characteristics of saline water on the performance of salt-gradient solar ponds under quasi-steady conditions is studied. Several models have been proposed to simulate the absorption of radiation in solar ponds, however, it is shown in this work that experimental data published by many authors militate in favour of representing this absorption simply by a single exponential. Pond performance is strongly influenced by the absorption characteristics. The mean pond temperature of the storage zone and the pond efficiency drop considerably as the turbidity of the water increases. The high values of the extinction coefficient result also in damping the pond temperature fluctuations and increase its time lag with respect to the insolation. The importance of using accurate in-site measured absorption data for pond design and performance prediction is emphasized.

Performance of Shallow Solar Ponds

This investigation is devoted to study the performance of a shallow solar pond composed of two zones, a convective zone and a non-convective zone. Finite difference techniques and a comprehensive iterative procedure were employed to solve the realistic transient energy equations subjected to temperature dependent heat transfer coefficients. Actual solar insolation, wind speed, and ambient temperature were used to evaluate the performance of this shallow solar pond at various time intervals for Alexandria all the year round. Lastly, the effect of varying the percentage of the non-convective zone was also investigated under various environmental and operating conditions.

A numerical study of the effects of solar attenuation modelling on the performance of solar ponds

A numerical study of the effects of solar attenuation modelling on the performance of solar ponds