Numerical and experimental study of effect of paraffin phase change heat storage capsules on the thermal performance of the solar pond

Hua Wang,Xinmin Zhang,Yanyang Mei,Anchao Zhang,Zhang Liugang,Ma Xiaomeng

doi:10.1177/0144598720974160

Hua Wang, Xinmin Zhang + Show 4 more

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https://doi.org/10.1177/0144598720974160

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Abstract

In this paper, the effect of adding the composite PCM (Phase Change Material) heat storage capsules to the heat storage layer of the salt gradient solar pond on the thermal performance of the solar pond was studied numerically and experimentally. Based on the program-controlled temperature simulation of the solar pond experimental platform, the effect of adding the composite PCM (48–50°C and 58–60°C melting point paraffin) heat storage capsules on the solar pond temperature and stability was studied, and a numerical simulation model was established to be compared by the experimental results. The results showed that the experimental temperature was consistent with the simulation results; the solar pond with PCM capsules had a smaller temperature change range than the conventional solar pond during the phase change process, but it did not have such effect in the non-phase transition process; in terms of flow, the addition of the PCM phase change units could reduce the flow rate of the heat storage zone, and the PCM with a larger latent heat had a more obvious suppression effect on the flow. Therefore, within a certain temperature range, adding PCM units to the solar pond had a positive effect on maintaining the stable temperature and stability of solar pond.

Highlights

The increase of effective supply of the various clean energy sources such as solar energy is one of the basic ways to realize China’s commitment to the world on energy conservation and emission reduction in 2030 (Zhao et al, 2017)
The solar pond is a salt water pond with increasing salinity from surface to bottom. This increasing density gradient in the depth direction suppresses the thermal convection caused by the temperature gradient, so that the solar energy reaching the bottom can only be lost to the environment in the form of heat conduction through the thicker gradient zone, so a stable salt gradient zone is the most basic guarantee for the solar pond operation (Wang et al, 2011)
Solar pond is generally composed of three zones: the Upper Convection Zone (UCZ) composed of fresh or brackish water; the Non-convection Zone or gradient zone (NCZ) where the brine concentration gradually increases with depth and the heat can only be transferred in the form of heat conduction; and the Lower Convection Zone (LCZ) composed of concentrated brine with uniform concentration

Summary

Introduction

The increase of effective supply of the various clean energy sources such as solar energy is one of the basic ways to realize China’s commitment to the world on energy conservation and emission reduction in 2030 (Zhao et al, 2017). The salt gradient solar pond (the following is abbreviated as solar pond), as a low-cost solar heat utilization integrating solar energy absorption and storage, can store large-capacity low-temperature thermal energy for a long time (Abdullah et al, 2016). The solar pond is a salt water pond with increasing salinity from surface to bottom. This increasing density gradient in the depth direction suppresses the thermal convection caused by the temperature gradient, so that the solar energy reaching the bottom can only be lost to the environment in the form of heat conduction through the thicker gradient zone, so a stable salt gradient zone is the most basic guarantee for the solar pond operation (Wang et al, 2011). LCZ is called heat storage layer because convective flow occurs uniformly and it absorbs and stores solar radiation energy

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