Evaluating the possibility of utilizing the waste heat of hot water before the cooling towers based on Phase change material

Articles in Press

Document Type : Research Article

Authors

1 Department of Mechanical Engineering, Bushehr branch, Islamic Azad University, Bushehr, Iran

2 Department of Mechanical Engineering, Bushehr branch, Islamic Azad University, Bushehr, Iran.

Abstract

Today, efficient energy use and minimizing waste are crucial. In power plants, hot water with high thermal energy enters a cooling tower, requiring significant water consumption for cooling. In the current research, the possibility of exploiting the thermal energy of hot water between the turbine and the cooling tower has been investigated using shell and tube heat exchangers where the shell is filled with phase change materials (PCM). This research investigates the temperature reduction of the hot water temperature entering the cooling tower and possibility of using the thermal energy of the hot water entering the cooling tower. Two approaches are included: a PCM-based heat exchanger for thermal storage and a heat exchanger to reduce hot water temperature without energy storage capability. Paraffin, a phase change material, is placed between the tube and shell in a heat exchanger, where hot water flows through the tube. The enthalpy-porosity model simulates phase change. Outlet hot water temperature, volume fraction changes, and paraffin temperature in finned and non-finned tubes are compared in different conditions. Also, fines are installed on the shell side to investigate the heat transfer enhancement. Results suggest that with an insulated shell, a thermal storage system should use a heat sink (cold water) to absorb released heat during paraffin solidification. The insertion of fins increases paraffin phase change rate to about 100% which reduces required time to be completed melt from 10 to 4 hours, thus enhancing the heat transfer rate significantly. Results indicate that in a colder climate with temperatures significantly below the melting point, non-insulated heat exchangers can maintain steady performance which can cause a steady two-phase regime of PCM (steady liquid volume fraction about 0.5) and keep the shell temperature constant over time. Finally, it could reduce hot water temperature that enters cooling tower about 6 degrees.

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Iranian Journal of Chemistry and Chemical Engineering

Articles in Press, Accepted Manuscript
Available Online from 14 February 2024

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