Quantification of thermal stratification and its impact on energy efficiency in solar hot water storage tanks

Baihong Liu, Wenfeng Gao, Qiong Li, Huai Chen, Yougang Zhang and Xiang Ding

Energy, 2025, vol. 326, issue C

Abstract: Improving thermal stratification is recognized as the most effective method to enhance the energy efficiency of thermal storage devices. It is essential to accurately evaluate thermal stratification and establish a quantifiable relationship between the thermal stratification level (TSL) and energy efficiency. Therefore, we propose a method of dimensionless exergy analysis to quantify the TSL. In this paper, a series of three-dimensional numerical simulations were carried out to explore the combined effects of the height/diameter aspect ratio (H/D), dimensionless initial temperature (Θ), Reynolds number (Re), and dimensionless temperature stratification parameter (s) on the TSL and discharge efficiency of solar hot water storage tanks. The mixing mechanism, temperature distribution, and thermal stratification in the tank are analyzed. An empirical formula is established to quantify the relationship between the TSL and the combined effects of these parameters (H/D, Re, Θ, and s). This formula can predict both the TSL and discharge efficiency based on the geometric dimensions and operational parameters. The results show that the tank with a larger aspect ratio, higher initial temperature, lower Reynolds number, and higher temperature stratification parameter all result in a higher TSL and discharge efficiency. Additionally, discharge efficiency increases parabolically with the TSL. A 77.5 % increase in TSL leads to a 50 % increase in discharge efficiency. Thus, this study can contribute significantly to the optimized design of thermal storage devices and the maximization of energy storage and utilization.

Keywords: Thermal stratification quantification; Solar hot water storage tank; Detailed numerical model; Novel combined index; Discharge efficiency (search for similar items in EconPapers)
Date: 2025
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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:326:y:2025:i:c:s0360544225018857

DOI: 10.1016/j.energy.2025.136243

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