Experimental studies on the effect of using phase change material in salinity-gradient solar pond

• Solar pond with and without phase change material (PCM) investigated experimentally.
• PCM decreases thermal efficiency of solar pond.
• PCM assisted solar pond decreases the temperature difference and better thermal stability.
• Solar pond with PCM leads to more salinity against heat extraction.

Performance of adding phase change material (PCM) to small salinity-gradient solar pond was studied experimentally. Two ponds with an area of 3.4 m2 and depth of 1 m were chosen. Horizontal cylindrical capsules containing Paraffin Wax as PCM were used in one of the pond’s lower convective zone. The capsules were made of black iron whose thermal conductivity was about 80 W/m °C and its height and diameter were 0.5 m and 75 mm respectively. The study was covered within period of summer for 6 weeks. An internal heat exchanger was used in the lower convective zone of pond. The hourly as well as daily variation of temperatures of the storage zone, surface zone, ambient, inlet and outlet of the internal heat exchanger have been measured and analyzed for ponds. It was shown the assisted PCM pond decreases the temperature difference between night and day. In addition, the pond had more thermal stability over environmental condition and more thermal and salinity stability on heat extraction. Hence the maximum temperature of the pond, outlet water temperature of heat exchanger, and, accordingly, the thermal efficiency decreased by using PCM. However, the heat exchanger outlet water temperature and, accordingly, the thermal efficiency, can be constant by increasing the length of the heat exchanger pipe. Therefore, based on this study, in such applications which one needs lower temperature difference and more uniform temperature, or where applications need a specific temperature range or controlled maximum temperature, PCM with a suitable melting point might be beneficial.

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