Lower Convective Zone Temperature Research Articles

Thermo-economic evaluation of a combined Kalina cycle and humidification-dehumidification (HDH) desalination system integrated with thermoelectric generator and solar pond

This study aims at introducing a new layout for cogeneration of power and distilled water using thermal heat stored at the lower convective zone (LCZ) of a salinity-gradient solar pond (SGSP). The proposed system consists of a Kalina cycle (KC), a humidification-dehumidification (HDH) unit, and two thermoelectric generators (TEGs). The feasibility of the devised system at the base and optimal modes of operation under the steady-state assumption is carried out, using thermoeconomic and the rmodynamic tools. Later, a parametric study is carried out and the effects of important design factors on the system performance and cost metrics were investigated. The results of multi-objective optimization revealed that the energy utilization factor (EUF), exergy efficiency, and total unit cost of the product (TUCP) can be improved by 14.09%, 5.5%, and 27.93%, respectively, in comparison with the base case. The optimum EUF, exergy efficiency, and TUCP were achieved at 0.756, 27.7%, and 30.54 $/GJ, respectively, when the proposed power/desalination system was designed under the following design parameters: solar pond area of 15326 m2, LCZ thickness of 1.65 m, NCZ thickness of 1.35 m, UCZ thickness of 0.35 m, LCZ temperature of 370 K, the figure of merit of 2.45, desalination flow ratio of 2.45, the turbine inlet pressure of 2500 bar, the pump pressure ratio of 3, and ammonia concentration of 86%. The results of the case study showed that between 20 March and 20 April the system produces the minimum rate of freshwater, which is 0.152 m3/h. On the contrary, the maximum amount of distilled water can be obtained between 21 June and 21 July. Moreover, from 21 May to 21 August is the best time to run the system to produce simultaneous distilled water and electricity.

Improved Thermal Efficiency of Salinity Gradient Solar Pond by Suppressing Surface Evaporation Using an Air Layer

Salinity gradient solar ponds (SGSPs) provide a tremendous way to collect and store solar radiation as thermal energy, and can help meet the critical need for sustainable ways of producing fresh water. However, surface evaporation results in the loss of both water and heat. This study therefore theoretically investigates the effect on temperatures within an SGSP when its surface is covered with a layer of air encased in a nylon bag. An earlier SGSP model was slightly modified to add the air layer and to estimate the temperature distributions of the upper layer or the upper convective zone (UCZ) and the bottom layer or lower convective zone (LCZ). The results for a year-long period showed that adding the air cover increased the LCZ temperature to a maximum of 94°C in July, with a total average increase of about 9% over the uncovered pond. In the UCZ, temperatures showed an average increase of approximately 45%, reaching a maximum of 34°C. The temperature of the air layer was meanwhile found to be close to the ambient temperature and behaved identically. These findings invite future experimental and theoretical investigations into the use of air layers to prevent surface evaporation, thereby enhancing the efficiency of SGSPs as a source of clean energy.

Feasibility investigation of a humidification-dehumidification (HDH) desalination system with thermoelectric generator operated by a salinity-gradient solar pond

Water distillation via solar energy is investigated potentially as an appreciable topic across the globe in recent decades. While many high-efficient solar collectors are developed for this objective, it is discovered that solar pond with big size can be more cost-effective than many types of high-efficient collectors. In pursuance of this objective, plausibility of extracting thermal heat from a salinity-gradient solar pond (SGSP) set-up for water distillation via a humidification-dehumidification (HDH) system is scrutinized under privilege of thermodynamics laws. Furthermore, due to the fact that solar pond's pumps consume more power for their task, two thermoelectric generators (TGEs) are posited to use waste heat of the discarded brine and distilled water to generate electricity for power demands. Single-criterion optimization is executed for the suggested set-up and the results are presented for the Urmia lake in Iran. Considering maximization of distilled water scenario, the findings outlined that 4.5 m3/h distilled water and 3.16 kW net electricity can be generated with cogeneration Gain-Output-Ratio (CGOR) of 1.56 and exergy-based CGOR (ECGOR) of 4.87%. Also, the designed desalination unit generated more fresh water between 22 May and 22 July for Urmia province, while more electricity is generated between 21 April and 21 May. Among all constituents of the introduced SGSP/HDH system, dehumidifier attributed as the major site of loss by exergy destruction of 15.23 kW. At last, an exhaustive parametric evaluation is established to scrutinize impact of some preeminent design parameters on the targets. It is exhibited that the CGOR can be maximized with desalination flow ratio, while the ECGOR can be maximized with lower-convective zone temperature.

A study on exergetic performance of using porous media in the salt gradient solar pond

The transient exergetic performance of the salt gradient solar ponds with porous media added in Lower Convective Zone (LCZ) is investigated. One dimensional transient temperature, energy and exergy models have been developed. Three different porous media materials have been used in the simulation. Findings show that solar pond with cinders gains the highest LCZ temperature and gets the maximum energy and exergy efficiency which are 32.62% and 20.70% respectively, and the lowest one is the case with marbles which are 29.72% and 16.62%. The results indicate that adding porous media with low volume heat capacity and low heat diffusivity to LCZ is beneficial to reach a higher temperature, and high temperature, high volume heat capacity and low thermal diffusivity of the porous media are both positive effect to the solar pond’s energy and exergy storage. Experimental study shows that the numerical energy and exergetic efficiency are both a little higher than experimental ones, and the same temperature difference leads to a bigger exergy difference than energy.

Experimental Investigation on Shallow Solar Pond Using CuO Nano Particles

On the increase of energy needs and rising environmental concern forces the use of renewable and to search the alternative source of energy for the polluting fossil fuels. The best alternative energy is solar which is being emitted by the sun and is collected and is stored in various thermal storage medium. Solar pond is one of the best ways to collect solar energy in that shallow solar pond is one of its type. From the name it implies the pond depth is small so the solar pond can be fabricated in a simple manner with very low cost covering large area. Previous research they have used baffle plates to find out the thermal performance, but this research brings out using CuO nano particles and has been examined experimentally. The shallow solar pond is built with a surface area of 1.7m2 with a depth of 0.5m. The experiment has been carried out during the month of April of 2016 under the climatic conditions of pachapalayam [Latitude 10.950N, Longitude 76.890E]. It was examined for the six successive sunny days and its temperature of lower convective zone varies from 1.3°C to 9.2°C, with the maximum rise in temperature is obtained when adding 0.8% concentration of nano particles.

Investigation on the exergy performance of salt gradient solar ponds with porous media

The exergy performance of solar pond with porous media added in the lower convective zone (LCZ) has been experimentally and theoretically studied. The effect is investigated under three cases, which are solar pond without adding any porous media (case A), with cinder (case B) and with multi-type porous media of cinder and cobblestones (case C), respectively. The results show case C gains the highest LCZ temperature and exergy efficiency, and case A has the lowest temperature and efficiency; and the maximum transient exergy efficiencies of the three cases are found to be 19.23%, 19.83% and 21.61%, respectively. The daily mean exergy efficiency of case C is 2.66% higher than case A, and 1.87% higher than case B. The results indicate that adding porous media, i.e., cinder or the mixture of cinder and cobblestones increases the LCZ temperature of solar pond, and it also improves the exergy performance of solar pond.

Transient model to predict the performance of thermoelectric generators coupled with solar pond

Solar pond has been a reliable supply of heat source for industrial process that requires heat at the temperature <100 °C. In this paper, the prospect of solar pond in generating electricity has been explored with the aid of using TEGs (thermoelectric generators) for converting the heat available at LCZ (lower convective zone) into electricity. By using the transient heat transfer model developed and the testing result of a thermoelectric module, this study has covered the potential of generating electricity for the solar pond operates in the climate of Group A, B, and C under Köppen climate classification. The effect of heat extraction, climatic variation, temperature polarisation, and the conversion efficiency of TEG on the thermal performance and electrical performance of the system has been discussed. The solar pond operates in Riyadh (Group B of Köppen climate classification) possesses the highest potential in generating electricity, which is about 4.834 kWh/year-m2 at heat extraction of 15% of year average horizontal solar radiation (i.e. solar pond yearly efficiency of 15%) while having average LCZ temperature of 80 °C throughout the year. Overall, the thermal-electrical conversion efficiency, ηt of this system is in the range of 1%–1.5% from the heat extracted.

Experimental study of natural brine solar ponds in Tibet

Abstract A salinity gradient solar pond (SGSP) is a simple and effective way of capturing and storing solar energy. The Qinghai-Tibet Plateau has very good solar energy resources and very rich salt lake brine resources. It lacks energy for its mineral processes and is therefore an ideal location for the development and operation of solar ponds. In China, solar ponds have been widely applied for aquaculture, in the production of Glauber’s salt and in the production of lithium carbonate from salt lake. As part of an experimental study, a SGSP using the natural brine of Zabuye salt lake in the Tibet plateau has been constructed. The pond has an area of 2500 m 2 and is 1.9 m deep. The solar pond started operation in spring when the ambient temperature was very low and has operated steadily for 105 days, with the LCZ temperature varying between 20 and 40 °C. During the experimental study, the lower convective zone (LCZ) of the pond reached a maximum temperature of 39.1 °C. The results show that solar ponds can be operated successfully at the Qinghai-Tibet plateau and can be applied to the production of minerals.

Computer Aided Modelling and Performance Prediction of Fertiliser Solar Pond for Agricultural Operations

Performance prediction of a new salt like fertiliser is crucial before it is used in a large solar pond. The heat transfer process in solar pond is modelled and implemented through a computer program for assessing the thermal performance in terms of temperature of lower convective zone (LCZ). The programmed model is validated using the real time data of a working solar pond. The model is found to be in good agreement with the observed data. The program is tested for predicting the solar pond performance using a fertiliser salt, Muriate of Potash. The solar pond is observed to attain steady state after 10, h month of pond operation. The pond started in April attained peak LCZ temperatures quicker than that started in January. The pond behavior is well explained by superimposing temperature surface and contours.

Comparative performance evaluation of fertiliser solar pond under simulated conditions

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.