Performance Optimization Research Of Salt Gradient Solar Pond

Salt-gradient solar pond combines solar energy collection with long-term storage.Salt gradient solar pond are composed of three layers:Upper Convective Zone(UCZ),Non-convective Zone(NCZ)and Lower Convective Zone(LCZ).In practical engineering application,the gradient layers and salt concentration have great influence on performance and stability of solar pond,and it is directly related to the construction cost and maintenance cost.However,up to now,there are few reports on the performance about gradient layers and salt concentration of solar pond.In this study,the experimental study and numerical simulation are used to analysis the influence laws and mode about heat collection and heat storage on performance of solar pond,moreover,from economic and convenient maintenance consideration,the paper is intended to choose the best NCZ layers and concentration distribution.The experimental results of NCZ layers on performance of the solar pond were shown as follows:the performance of heat collection became weaken with increasing the NCZ layers.The collected energy in the SGSP without NCZ was respectively 1.11,2.52,and 4.03 folds of the ponds with one,two,and three NCZ layers,and the pond’s effectiveness respectively was 1.39.2.86 and 5.21 folds of those.However,the heat release in night decreased with increasing the NCZ layers,and in no-NCZ pond it was 3,56 times in the pond with three layers.The experimental results of NCZ salt concentration was shown that decreasing of the salt concentration was beneficial to the heat collection and thermal storage performance of solar pond:the maximum temperature、average heat collection and heat storage were respectively 57.5℃、0.48 MJ、3.42 MJ(31h)with 52 g/L of NCZ concentration,while 20%of NCZ concentration were respectively 54.3℃、0.45 MJ、1.51 MJ.Numerical simulation results on the performance about NCZ layers were shown that:the salt concentration distribution was at the same with different NCZ layers;they were gradually increasing with time,and the more NCZ layers,the shorter the time to reach the linear steady state of solar pond;Similarly,the NCZ layers also affected heat collection and heat storage performance of solar pond,with increasing of the NCZ layers,the effect of heat collection was reduced,but the thermal insulation performance was improved.In no-NCZ solar pond,the heat collection performance was 2.0435 times with three NCZ layers after the operation about 100 days;while,the heat transfer rate in no-NCZ layers was 1.3603 times with three NCZ layers of solar pond.In addition,the maximum average temperature and thermal efficiency were 74.23 and 16.38%respectively in no-NCZ solar pond,and 73.8℃和16.8%in solar pond with three NCZ layers.The simulation results were in agreement with the experimental results.The results about the effect of gradient concentration on performance of solar pond was that:the salt concentration change on different gradient zone had different effect on the performance of solar pond.In LCZ,the heat collection performance was improved with the increasing of salt concentration,but the rate of heat loss was reduced.When 298 g/L salt concentration of the LCZ,the maximum heat collection was 938.69 MJ.About UCZ,with the increasing of salt concentration,the temperature,heat collection,heat storage,thermal efficiency were all reduced of solar pond,thus,the heat collection and heat storage performance has been suppressed.When UCZ was fresh water,the maximum heat collection was 1.05 times with concentration of 31 g/L,while the average thermal efficiency was 1.29 times.The numerical simulation analysis was confirmed that the salt concentration on performance of solar pond,as follows:with the increase of UCZ concentration,the maximum temperature was reduced in heat storage zone,after the operation of 100 days,the fresh water of UCZ had the highest temperature about 60.05℃,while 60.00℃in the solar pond with 31 g/L of UCZ concentration.The highest temperature was basically the same,and the temperature performance was similar in the solar pond.Through the research of this topic,it was indicated that the SGSP construction must be based on adequately investigating the climate and application,and set opportune NCZ layers and gradient salt concentration for high heat effectiveness and economic benefits.