Experimental study on thermal behavior of new mixed medium phase change material for improving productivity on salt grad
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Experimental study on thermal behavior of new mixed medium phase change material for improving productivity on salt gradient solar pond Mohammad Reza Assari1 · Mohammad Hossein Tahan1 · Alireza Jafar Gholi Beik1 · Hassan Basirat Tabrizi2 Received: 6 April 2020 / Accepted: 28 September 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Five identical cylindrical salinity-gradient solar ponds (SGSPs) with internal heat exchanger were constructed and operated. In order to optimize the performance of the SGSPs, mixtures of NaCl and Na2SO4 were used. Radiation flux, temperature of the zones, ambient temperature, inlet, and outlet temperature of the internal heat exchangers were measured. It was shown a controlled amount of N a2SO4 improves the thermal and salinity stability of the pond in the normal operation and heat extraction and lowers the pond temperature drop ratio to the water outlet temperature drop during the heat extraction, which means an improvement in the energy storage capacity. The pond with higher percentage of Na2SO4 requires less time to stabilize. Higher percentage Na2SO4 reduces the density gradient between the upper and lower convective zones of the pond and leads to rapid destruction of the upper layer. Maximum ability of heat extraction corresponds to the pond with 0.75% Na2SO4. In addition, to prevent the algae growth at higher percentage N a2SO4, spraying of HCl on the pond surface was used. Keywords Phase change materials · Salts combination · Solar-gradient pond · Thermal efficiency · Salinity stability · Heat extraction List of symbols Ao External surface area of the heat exchanger (m2) ASP Area of the solar pond (m2) Cprel Ratio (specific heat capacity of fluid heat exchanger to specific heat capacity of fluid LCZ) ( ) CPS Specific heat capacity of fluid LCZ J Kg−1 ◦ C CPW (Specific heat ) capacity of fluid heat exchanger JKg−1 ◦ C G Solar radiation at the surface of the pond (W m-2) HCl Hydrochloric acid mlcz Mass of LCZ (Kg) mrel Ratio of (mass flow rate in heat exchanger to mass of LCZ) (Kg) ṁw Mass flow rate in heat exchanger (Kg/ s) * Mohammad Reza Assari [email protected]; [email protected] 1
Mechanical Engineering Department, Jundi-Shapur University of Technology, Dezful, Iran
Mechanical Engineering Department, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran
2
n Heat extracted time intervals NaCl Sodium chloride Na2SO4 Sodium sulfate PE Polyethylene Q̇ Rate of heat extraction from the LCZ per unit area of the solar pond (W/ m2) Ti Inlet temperature of the internal heat exchanger (°C) Tiw Initial temperature of heat exchanger (°C) To Outlet temperature of the internal heat exchanger (°C) Tow Final Temperature of Heat exchanger (°C) TP Temperature of pond (°C) TP1 Initial temperature of LCZ (°C) TP2 Final temperature of LCZ (°C) U Overall heat transfer coefficient based on external surface area (W/ m2°C) Abbreviation IHE Internal heat exchanger JSUT Jundi-Shapur University of Technology LCZ Lower convective zo
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