Lower Convective Zone Research Articles

Numerical Investigation of Thermal Performance Enhancement of Solar Reservoir using Flash Cycle

The main objective of this research is to model a solar reservoir system located in Dehradun, Uttarakhand, India. Solar reservoir acts as both a collector and long-term storage for thermal energy, potentially providing heat for a full year. Using a single input, the latitude angle, solar radiation for the location is calculated. A one-dimensional time-dependent steady-state model is employed to predict the annual temperature behavior within the storage zone of the solar reservoir. The model analyses the temperature range achievable in the lower convection zone (LCZ) of the reservoir. The findings suggest that the LCZ can reach temperatures as high as 80°C. Additionally, the study demonstrates that an increase in feed temperature can improve overall system efficiency. At the end of summer, temperatures as high as 70 °C were observed in the solar pond at a depth of 1.32 m. It reached 26 °C at its lowest point in early April. In an artificial solar pond, salt water is utilised to inhibit convection. There was a 26% concentration of salt NACL at the lake's bottom. The kind and concentration of salt have an impact on the pond's stability. It was determined that 80 g/kg of water is the ideal salt level for the small solar pond. This study demonstrates the potential for maintaining both salinity gradient and thermal performance over an extended period. Future research efforts could benefit from larger-scale experiments that bridge the gap between controlled environments and real-world applications.

Theoretical analysis to optimize heat extraction from a solar pond integrated with a carbon dioxide heat pump

Heat pumps integrated with renewable energy sources represent an efficient approach to residential heating and cooling, with minimal environmental impact and reduced carbon emissions. While these systems have been extensively researched, there is a necessity to broaden their scope by investigating novel approaches to energy capture and storage that are adopted to the specific characteristics of the region. This study analyzes the effects of different operating parameters on heat extraction from a solar pond integrated with a heat pump using carbon dioxide under transcritical conditions. Subsequently, an optimization examination is conducted to assess and determine the conditions required to achieve the maximum heat extraction rate and the minimum pumping power. The outcomes of this investigation demonstrate that the carbon dioxide mass flux and operating pressure exert a greater influence on the responses compared to the inlet temperature of carbon dioxide and the lower convective zone temperature of the solar pond. Additionally, within the investigated range of mass flux, the highest level of heat extraction occurs at operating pressures near the critical point of carbon dioxide, approximately 7.5 MPa. To meet the demand for maximum heat extraction from the solar pond, the optimal conditions result in an overall performance improvement of 2.61 times compared to the reference state. Furthermore, optimizing the system to maximize heat extraction from the solar pond while using the minimum pumping power results in a total performance enhancement of 4.13 times.

An experimental investigation on winter heat storage in compact salinity gradient solar ponds with silicon dioxide particulates infused paraffin wax

Silicon dioxide particulate which is also called silica, owing to its cost-effective synthesis, abundant availability, and high heat transfer capabilities, present an eco-friendly solution with immense potential for diverse applications, including solar heating systems. This novel study explores the integration of silica microparticles infused in paraffin wax in a compact salinity gradient solar pond for enhanced heat storage during the winter season. Leveraging their biocompatibility, facile functionalization, and expansive surface area, silica microparticles exhibit outstanding attributes such as photoconductivity, optimal thermal expansion, corrosion resistance, and enduring durability, all of which synergistically contribute to system efficiency. During the first day, without any heat storage medium, the three distinctive zones of the compact salinity gradient solar pond exhibited temperatures of 31.2 °C in the upper convective zone, 32.8 °C neutral convective zone, and 35.7 °C in the lower convective zone respectively. Experimental investigations are conducted, employing both paraffin wax and silicon dioxide microparticles as augmenting agents to amplify heat storage capacity within the compact solar pond setup. While using paraffin wax without silica particulates the lower convective zone temperature was 4.2 % lower because of heat storage. The incorporation of trace amounts of silicon dioxide microparticles within paraffin wax establishes a novel hybrid approach. The outcomes highlight the profound impact of this hybridization on thermal characteristics, resulting in a discernible improvement in the compact salinity gradient solar pond's heat behavior. Notably, the phase change material introduces a temperature enhancement of approximately 1.5 %, and the amalgamation further elevates the temperature retained to 56 °C within the lower convective zone. An optimization analysis underscores the pivotal role of the solar pond configuration in dictating temperature changes, surpassing the influence of time considerations. This research underscores the transformative role of silicon microparticles in optimizing thermal performance within compact salinity gradient solar ponds, unlocking avenues for enhanced winter energy utilization.

EXPLORING ENHANCED SOLAR POND CONFIGURATIONS FOR LOW-GRADE THERMAL ENERGY STORAGE: A COMPARATIVE STUDY

This study revolves around the salt gradient solar pond (SGSP) as an environmentally conscious approach for efficiently storing heat. This investigation assesses the impact of adding a coal cinder (CC) additive and integrating an East–West reflector (EWR) on enhancing the energy efficiency of the salt gradient trapezoidal solar pond (SGTSP). The research involves designing, fabricating, and analyzing SGTSP systems with EWR and CC, comparing them with standard SGTSP systems in terms of energy performance. The results indicate a substantial 43.4% rise in average solar intensity when employing the EWR, and incorporating the coal cinder additive elevates the lower convection zone's (LCZ) temperature by 24.5%. In comparison to the conventional SGTSP (SGTSP-C), the SGTSP with the East–West reflector (SGTSP-EWR) and SGTSP with the coal cinder (SGTSP-CC) attain temperatures of 60.75°C and 66.87°C, respectively, representing an increase of 15.49% and 27.12%. Similarly, the maximum energy efficiency of LCZ for SGTSP-EWR and SGTSP-CC were 27.15% and 55.92% higher than the values of SGTSP-C. Ultimately, this research showcases the thermal energy storage potential of SGTSP and provides practical approaches to improve its energy efficiency.

Energy storage investigation of solar pond integrated with PCM and nanoparticles during winter season in Chennai

Solar energy is a highly regarded renewable energy sources that are attracting substantial attention owing to its potential to alleviate climate change and provide sustainable energy. Solar ponds are one approach to collect solar energy by capturing and storing thermal energy inside a pond. However, the effectiveness of solar ponds has been hampered by reasons such as heat loss, evaporation, and inadequate heat transmission. Researchers have investigated the use of phase change materials (PCMs) and nano-additives to improve the performance of solar ponds in order to overcome these issues.Large amounts of heat can be stored and released by substances known as phase change materials as they transition between two states. By adding PCMs into solar ponds, heat may be retained throughout the day and released at night when the sun is not shining. Alternatively, nano-additives have the potential to enhance the efficiency of a solar pond by improving the heat transfer properties of the fluid present in it.To measure the thermal efficiency of the solar pond, multiple phases of an experiment have been undertaken to establish the degree of thermal efficiency. During the experiment, various parameters were employed to measure and track the temperature variations in the lower convective zone (LCZ) of the solar pond. These measurements were recorded on a daily, weekly, and hourly basis, taking into account the depth of the solar pond as a determining factor. There was also an experiment carried out using micro PCMs and paraffin waxes (PCMs) that were combined into the matrix. In this study, nanoparticles with high thermal conductivity, such as carbon nanotubes (CNTs), and hybrid nanoparticles, such as AgTiO2, were utilized.The solar pond without phase change material (PCM) had an average temperature of 45 °C in the lower convective zone (LCZ). When PCM was added to the solar pond, the maximum temperature in the LCZ increased by 2 °C compared to the previous 24 h. Furthermore, when carbon nanotube (CNT) nanoparticles were incorporated into the solar pond with PCM at the base, the temperature was observed to be 1.3 °C higher compared to a typical solar pond that only used PCM for heat storage. In another scenario, the solar pond with PCM and a combination of CNT and AgTiO2 nanoparticles had an average temperature of 52.5 °C in the LCZ during the first week of observation.

Analysis of portable solar concrete ponds by using coal cinder to trap thermal energy of sustainable building using artificial intelligence

Cinder is a waste product made from the coal residue left over from power plant blast furnaces. Solar energy is a promising renewable energy source, but because of its erratic availability, energy storage technologies must be used. Our research suggests employing coal cinder (CC) to boost the thermal energy stored in transportable solar concrete ponds, combining rock mechanics with renewable energy. The concepts of renewable energy and rock mechanics are combined in this invention. Additionally, because it doesn't release any pollutants into the sky, it is great for low heat applications like building cooling and heating. However, due to its sporadic nature, solar energy requires effective energy storage to be used at night and in cloudy weather. By adding coal cinders to the bottom layer of a solar concrete pond in order to increase its heat energy, this work integrates rock mechanics with sustainable energy. A variety of small-scale research use the standard micro solar concrete ponds. Also offered is a numerical calculation for predicting energy development over a sizable area of a solar pond with a salt gradient. The coal cinders may significantly raise the temperature at the pond's bottom. With a constant temperature differential of 30 °C and 20 °C throughout the gradient layer for two different pond sizes with depths of 1.5 m and 1.0 m, this study provides thermal analysis of a salt gradient solar pond using machine learning as Particle Swarm Optimization (PSO) and extracting heat from the Lower Convective Zone (LCZ). Going through the regression indices (RMSE, R2, r), the energy efficiency (heat) of the first 1.5-meter-deep concrete pond varies between 22.1 and 11.3% throughout the winter. The energy performance of a solar pond decreases dramatically when the non-convective zone thickness and its size are decreased. For the two concrete ponds with depths of 1.5 m and 1.0 m, respectively, the annual average efficiencies are 23% and 16%. Hence, the solar pond demonstrates that it is an effective method for utilizing solar energy and may be a useful option for low-temperature energy needs, such as room heating.

Transient behavior of a salinity gradient solar pond under Mediterranean climate

Abstract This paper aims to investigate the transient behavior of a salinity gradient solar pond(SGSP) under Mediterranean climate. For this propose, a 2D numerical model is developed in which the absorption of solar radiation by different layers of saline water, the wind effect at free surface, the heat losses and the development of the double-diffusive convection in the lower and upper convective zones are considered. The governing equations of continuity, momentum, thermal energy and diffusion are solved using the finite volume method with SIMPLE algorithm. The validity of the numerical model developed in Fortran95 is achieved through the comparisons of the results computed with the available numerical and experimental results obtained by literature studies. Results show that the developed numerical model can predict transient behavior of the SGSPs with a good accuracy. As an application of this model, temperature, salt concentration, energy stored and storage efficiency variations of a proposed SGSP are analyzed under Mediterranean climate. The results show that the lower convective zone(LCZ) temperature increases from 15 °C to around 95 °C whereas the temperature of the upper convective zone(UCZ) varies sinusoidally depending on that of the ambient air. Furthermore, the salt concentration of the LCZ decreases from 250kg/m3 to around 248kg/m3 while that of the UCZ increases from50 kg/m3 to about 52kg/m3. Additionally, the thermal energy stored is around 135MJ with an efficiency of about 38% which confirms the capacity of the SGSP to store thermal energy as sensible heat.

Effects of Double-Diffusive Convection on Calculation Time and Accuracy Results of a Salt Gradient Solar Pond: Numerical Investigation and Experimental Validation

The main aim of this study is to investigate numerically and experimentally the effects of double-diffusive convection on calculation time and accuracy results of a Salt Gradient Solar Pond (SGSP). To this end, two-numerical models are developed based on the Fortran programming language. The first one is based on energy balance neglecting the development of double-diffusive convection, while the second is two-dimensional and is based on Navier-Stokes, heat, and mass transfer equations considering the development of double-diffusive convection. The heat losses via the upper part, bottom, and vertical walls, as well as the internal heating of saltwater, are considered. In order to validate and compare both numerical models, a laboratory-scale SGSP is designed, built, and tested indoors for 82 h. Results indicate that the two numerical models developed can predict the SGSP thermal behavior with good accuracy. Furthermore, the average relative error between experimental and numerical results is around 9.39% for Upper Convective Zone (UCZ) and 2.92% for Lower Convective Zone (LCZ) based on the first model. This error reduces to about 5.98% for UCZ and 3.74% for LCZ by using the second model. Consequently, the neglect of double-diffusive convection in the SGSP modeling tends to overestimate the thermal energy stored in the storage zone by about 4.3%. Based on the calculation time analysis, results show that the second model returns a calculation time hundreds of times larger than the first one and, accordingly, an increase in computational cost.

Numerical assessment of a solar pond under transient state with realistic energy extraction from all possible zones

A solar pond from which thermal energy is extracted from its non-convective zone (NCZ), lower convective zone (LCZ) and the ground below is modelled in transient state. The novelty of the study lies in the fact that heat extraction in each of the three zones is considered to be realistic, taking into account temperature drop across the exchanger surfaces. The pertinent weather parameters are described by curve fitting as series of sinusoidal time functions. Using these expressions, implicit finite difference method is used to solve the five coupled partial differential equations involved in the analysis, and the scaled down model is validated with simpler models available in the literature. To quantify the practical utility of pond, the final outgoing water stream heated from the pond is fed to a large scale solar still to assess the usefulness in a desalination application. Annual distillate production of the still coupled to such a pond is calculated and its variation with various manually adjustable parameters is studied. A total of 9 such parameters have been investigated. It is observed that there are five pond parameters related to pond’s operation that possess optimum values that maximize annual distillate production. These are: NCZ and LCZ thicknesses, NCZ and LCZ exchanger pipes’ radii, and ground extraction mass flow rate. An increase in any of the remaining parameters: upper convective zone (UCZ) thickness, ground exchanger pipes’ radius and NCZ, LCZ extraction mass flow rates generate a decrease in distillate produced. It is also revealed that extraction should be carried from how many zones depends on the application coupled to the pond, and in this case, where the application is a solar still, LCZ with ground extraction turns out to be the best choice. Further, the assumption of ideal NCZ and ground extraction used in the literature is seen to overestimate system output by nearly 46%. Therefore, this model is a generalized one and various other single or dual zone extraction models available so far become subsets of it. This generalized model presented here can serve to design such a triple zone extraction based solar pond system in a realistic and practical manner and help evaluate suitable values of user-controlled variables that yield maximum output of the application to which the pond supplies energy.

Effects of inlet operational parameters on the combined salt gradient solar pond-direct contact membrane distillation system

This paper focuses on the performance-analysis of a combined renewable energy system/desalination unit. The renewable energy system consists of a Salt Gradient Solar Pond (SGSP) for the collection and the storage of solar energy while the desalination process uses the Direct Contact Membrane Distillation (DCMD).DCMD processes operate practically at the same range of temperatures obtained from low temperature solar pond. However, while combining DCMD unit with a solar energy source, it is necessary to investigate the effect of energy source fluctuations on the operating parameters. The large fluctuations of solar intensity throughout the day will affect the inlet feed temperature of the DCMD process which in turn affects the permeate flux. The main objective of this study is to evaluate, numerically, the effects of inlet operational parameters on the solar driven combined system for production of fresh water. A mathematical model was built to predict the production rate from the measured temperatures of the Salt Gradient Solar Pond. Coupling the heat and mass transfer, through the membrane, the model with solar energy input is mainly based on the technology of a solar pond with a salt concentration gradient. This solar technology will not really be simulated. Indeed, temperature measurements obtained from solar pond will serve as a basis inputs of the simulation. Obtained results showed that permeate flux increases with Lower Convective Zone (LCZ) temperature of the SGSP and the sundial during the day for a year, but it was less sensitive to the Upper Convective Zone (UCZ) temperature of the SGSP and to the feed water salinity.

Experimental study on improving lithium extraction efficiency of salinity-gradient solar pond through sodium carbonate addition and agitation

The use of salinity-gradient solar ponds (SGSPs) to extract lithium from carbonate salt brine has expanded their applications beyond thermal extraction and into direct mineral exploitation. SGSPs play a significant role in lithium extraction, but the CO32- concentration will decease significantly after a cold winter, resulting in low precipitation efficiency of lithium in SGSPs. Analyzing the characteristics of the brine in the lower convective zone shows the key causative factors of this reduced extraction efficiency to be the imbalances in lithium carbonate concentration and metastability of the water at low temperatures. In this study, this problem was solved by adding sodium carbonate and agitating the LCZ. First, the proportion of sodium carbonate was determined through experiments and the practicality was further verified using SGSPs. Meanwhile, system changes caused by sodium carbonate in the LCZ were investigated and numerical simulation was carried out for thermal efficiency and salt diffusion process. This study found that the addition of sodium carbonate improved the quality of the brine and the seasonally-induced concentration imbalances between the Li+ and CO32-. By agitating the LCZ, the stable low convection state of the brine was broken, the ions were remixed evenly, and the supersaturation of lithium carbonate was increased. By adding 5 % sodium carbonate to the SGSPs and agitating the brine, the ponds’ average lithium yield was increased by 48.3 %, and the grade of the lithium carbonate was increased to over 80 %. This study enriches the application of SGSPs as an industrial tool for mineral exploitation.

Energy, exergy and thermoeconomic analysis of an industrial solar pond

This study evaluates the viability of an industrial salinity gradient solar pond during two operating seasons (2014 and 2015). The Granada solar pond was built to supply low-temperature heat (up to 60 °C) to satisfy the temperature requirements of the flotation unit in a mineral processing plant (Solvay Minerales in Granada (Spain)). Energy analysis indicates that the non-convective zone (NCZ) and the upper convective zone (UCZ) have low efficiencies because these zones have a low capacity to store heat, and no heat extractions are carried out from these zones. In contrast, heat extraction in the lower convective zone (LCZ) has a positive impact on the system because it increases the capacity of the solar pond to store energy. Higher efficiencies were achieved in the second operation period in the LCZ, since higher amount of heat was extracted during this period. The overall exergy efficiency of the LCZ after the first and second operation periods was 1.6% and 2.3%, respectively. The solar pond works at temperatures close to room temperature and thus the exergetic efficiency decreases significantly. Regarding the thermoeconomic analysis, the cost of exergy stored is studied in this work, using two different approaches, by estimating the minimum price for exergy stored or the minimum surface area that ensure the thermoeconomic viability. The price of the stored exergy tends to decrease inversely to the price of fuel oil. Thus, the cost of the stored exergy must be four to five times higher than the price of fuel oil for the solar pond system to be feasible. On the other hand, solar pond technology is affected by economies of scale; the larger the solar pond, the higher the inflation rates and the lower the cost reduction rates that can be accommodated. This implies that estimating the cost of the stored exergy is complex due to the variability of the processes involved and can lead to erroneous interpretations when evaluating the viability of a solar pond from a thermoeconomic perspective.

Experimental study of the temperature regime of the solar pond in the climatic conditions of the south of Uzbekistan

This article is devoted to the experimental study of the temperature regimes of the solar pond in the southern climatic conditions of Uzbekistan. The research was conducted in an experimental version of a solar pond that accumulates low-potential heat. According to research, when taking heat from a salt solar pond, without a coating on its upper surface and comparing the results of a glass-covered experiment is 10-15% higher than that of a glass-covered experiment, when the ambient temperature is 34 °C and solar radiation is 973 W/m2 it is scientifically based that the temperature of saline solar pond water with a concentration of 25-30% rises to a temperature of 53 °C in the lower part of the pond and that the energy storage efficiency of the lower convective zone of the solar pond increases in parallel with increasing solar radiation

Solar ponds-a mini review.

A solar pond is a simple system that collects and stores heat for thermal and electrical applications. Heat storage and heat extraction are the key factors in the solar pond. Salt is added to the pond with fresh water to form a salinity gradient solar pond (SGSP). The solar pond comprises of three zones, namely, the upper convective zone (UCZ), the non-convective zone (NCZ) and the lower convective zone (LCZ). The LCZ is also called the storage zone. Generally, the LCZ stores the heat energy of the incoming solar radiation, and this heat may be used for various applications. In this paper, a review is done on the study of solar ponds with various designs and modifications, heating methods, use of floating devices, use of baffle plates, use of heat exchangers, use of flat plate collectors, use of different types of insulation, etc.

Experimental investigation and optical visualization of a salt gradient solar pond integrated with PCM

The thermal performance of a solar pond is affected by the amount of heat lost to the ground through the lower convective zone (LCZ) in which the heat is stored. Studies are focused on decreasing the heat losses, to maximize the energy stored and guarantee the stability of the thermohaline system over time. Phase change materials (PCMs) can help to achieve all these goals, since they work as thermal energy storage (TES), exploiting the latent heat absorbed during the solid-liquid phase change. This paper presents an experimental application of PCMs in the LCZ of a small solar pond. The paraffin wax was enclosed in aluminium cylinders which have been arranged on the bottom. The temperature of the solution in deep is monitored both with and without the PCM. The stability of the pond is analyzed through a laser shadowgraph technique, to visualize the effect of the thermal convection on the interfaces. Results show that the LCZ of the solar pond with PCM is around 3 °C colder than the reference case after a 6-h heating period. The shadowgraph analysis proves that the thermal convection in the reference case is stronger and damage the interface until break. The monitoring of the solar pond with PCM shows an improved stability. • A solar pond integrated with PCM has been designed and built. • After the heating period, the system with PCM results colder in the LCZ. • PCM stabilized the LCZ-NCZ interfaces, as proved with the shadowgraph technique.

The Effect of a Liquid Cover on the Thermal Performance of a Salinity Gradient Solar Pond: An Experimental Study

Salinity Gradient Solar Ponds (SGSPs) offer the potential to capture and store solar energy for use in a range of domestic and industrial activities in regions with high solar insolation. However, the evaporation of water from these ponds is a significant problem that must be overcome for them to be deployed successfully. Thus, two ponds were constructed in the city of Nasiriya, Iraq. The two ponds were cylindrical with a diameter of 1.4 m and a total depth of 1.4 m. The water body in the two ponds was constructed with layer depths of 0.5, 0.75 and 0.1 m for the lower convective zone (LCZ), non-convective zone (NCZ) and the upper convective zone (UCZ) respectively. One of the two ponds was covered with a thin liquid paraffin layer (0.5 cm) to eliminate evaporation from the surface of the UCZ. The behavior of the standard SGSP and that of the covered pond with evaporation suppressed can be straightforwardly compared. The experimental units were run for six months from 1st of February to 31st of July 2019. It was shown in the first instance that by covering the pond with a thin layer of paraffin, that evaporation could be suppressed. The results showed that for the conventional SGSP, the temperature of the LCZ reached a maximum of ca. 76°C while in the covered pond the temperature of the LCZ was consistently lower than that in the uncovered pond by approximately 5–6°C. The results also indicated that the temperature of the UCZ in the covered pond was higher than that in the uncovered pond by about 10°C in the second half of the study period. However, it was noted that on rainy days the paraffin layer was swept away from the surface; and this could hinder the implementation of thin liquid cover in the large SGSP.

Experimental Investigations on Salt Gradient Solar Pond with Additional Non-Convective Zone for Improved Thermal Performance and Stability

Salt gradient solar ponds are to be designed for thermal efficiency and salinity profile stability. As the salt flux moves upward in the pond, the gradient gets destabilized. This is counteracted by intrusion of salt at different levels as and when required. The density of salt is highest at the bottom and minimum at the top. Hence the destabilization effect is more at top that is at the interface of upper convective zone and non-convective zone (NCZ). In order to keep the interface stable, it is desirable to provide a higher slope of salt gradient near it. However, throughout the non-convective zone, it is not feasible to provide higher slope due to solubility limitations. Hence Husain et al (2012) to divide the NCZ into two parts. The top few centimeters may be given a higher slope and the rest of the zone may be given mild slope as usual. Husain et al (2012) have given analysis for the same and found it to be feasible. However, the experimental feasibility of the same needs to be verified. The present work has done an attempt for the same. In this study, an insulated solar pond with a surface area of 1.40 m2and a depth of 1.14 m is built at the SSBT’s College of Engineering and Technology, Jalgaon in the Maharashtra State (India). The three salty water zones (upper convective, non-convective and heat storage) were formed by filling the pond with salty water of various densities. 6 Thermocouples (type Pt100A) (C+0.2%) were used to measure the temperature profile within the pond. A maximum temperature of 47°C was recorded in the heat storage zone in time span considered for study. The results obtained from experimentation is verified with the concept suggested by Hussain et al (2012) it has been found that they are in a good agreement. The influence of varying the thicknesses of the zones present in a salinity gradient solar pond on the temperatures of the upper convective zone (UCZ) and the lower convective zone (LCZ) is investigated. Also, it is found that by adding the additional non convective zone of 50 mm thickness above the UCZ the heat collection capacity of the LCZ is increased noticeably. The study finds that thickness variation of the zones within the pond is a practical feasibility. The system worked for the entire experimental duration effectively without failure.

Impact of Non-convective Zone and Lower Convective Zone Thickness on the Performance Characteristics of Salinity Gradient Solar Pond

A solar pond technology employs a layer of salinity gradient to prevent heat loss due to convection from the lower convective zone. Thus, the energy received from solar radiation is stored in a lower convective zone. The thickness of various zones significantly affects the behaviour of solar pond temperature. In this present study, a transient numerical investigation is conducted to evaluate the impact of depths of different zones on the performance characteristics of solar pond. The variation in maximum temperature and maturation period under the influence of non-convective zone and lower convective zone thickness is discussed. The energy obtained from a solar pond significantly depends on various losses associated with the zones. Thus, an assessment of conduction and ground heat loss is presented for the variation in thickness of zones. An attempt is also made to study the effect of thickness of zones on the temperature of the lower convective zone. It is found that the configuration of a smaller thickness of LCZ and a higher thickness of NCZ yields maximum LCZ temperature.

Enhancement of solar pond stability performance using an external magnetic field

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.

Transient study of a solar pond under heat extraction from non-convective and lower convective zones considering finite effectiveness of exchangers

The transient performance of a salt gradient solar pond, which experiences heat extraction from both gradient and storage regions has been studied for annual performance via accounting for the overall heat transfer coefficient across heat exchangers. The proposed method after reduced complexities is satisfactorily validated with theory and experiment-based results of pertinent literature. The novelty of the work lies in the fact that, the temperature drop across both non-convective and lower-convective zone exchanger surfaces has been accounted by using a local time and space dependent heat transfer coefficient. Here, it takes into the consideration free convection from the pond to the exchanger surface, and forced convection from the exchanger surface to flowing working fluid. Further, temperature variation of thermo-fluidic parameters of water involving, viscosity, density and thermal conductivity is considered. Detailed numerical investigation reveals that by neglecting this coefficient which is assumed in conventional studies, it can lead to significant errors in the prediction of transient temperature profiles in the pond and the exchangers. Calculations reveal an error of about +69% in the annual extraction efficiency and about −9% in entropy production if the conventional assumption is used as opposed to realistic technique presented herein. Interestingly, the present study reveals that there is an optimum radius of exchanger pipe in each of non-convective and lower convective zones that maximises the annual extraction efficiency. This work presents a useful analysis to assess multi zone extraction from solar ponds under transient state in a more practical and accurate manner.