Coupled heat extraction from gradient and storage zones and its effect on base insulation effectiveness of a salt gradient solar pond

Engineering notes

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Chinese explanation / 中文解读

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Original abstract

Abstract Solar ponds are a type of solar thermal energy storage devices which comprise three distinct zones: the top zone, the gradient zone, and the storage zone. Among these zones, heat for industrial applications is primarily extracted from the gradient and storage zones. The base layer insulation plays a very important role, as it governs the heat loss from the base of the pond. However, in the literature, the optimum base insulation thickness for salt gradient ponds was evaluated under energy extraction from the storage zone alone. This work is an attempt to carry the same investigation by including gradient zone energy extraction as well, and to quantify how much error this additional heat extraction introduces into the calculation. A transient heat transfer model is used to calculate year-round extraction temperatures based on the zone thicknesses, the pond cross-sectional area, and the mass flow rate of water in the gradient/storage heat exchanger. While calculating the best base thermal insulation thickness, the selected criterion is the insulation thickness at which the increase in maximum extraction temperature is less than 0.01 oC. The study is extended for four different mass flow rates of working fluid in the gradient zone heat exchanger: 0.00, 0.02, 0.04,0.06 kg.s-1, and the storage zone heat exchanger: 0.00, 0.02, 0.04,0.06 kg.s-1. It is seen that the operation of the gradient zone exchanger drastically reduces the required amount of base insulation thickness. The reduction in optimal base insulation thickness at gradient zone exchanger mass flow rates of 0.02 kg.s-1, 0.04 kg.s-1and 0.06 kg.s-1 is 18.46%, 38.46%, and 56.92% respectively, compared to the no gradient zone heat extraction case. It is also observed that the optimum base insulation thickness increases with an increase in pond area and decreases with an increase in all other parameters mentioned in the study.

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