Thermal Stratification and Heat Loss in Underground Thermal Storage Caverns with Different Aspect Ratios and Storage Volumes

Abstract

Thermal stratification in heat stores is essential to improve the efficiency of energy storage systems and deliver more useful energy on demand. It is generally well known that the degree of thermal stratification in heat stores varies depending on the aspect ratio (the height-to-width ratio) and size of the stores. The present study aims to investigate the effect of the aspect ratio and storage volume of rock caverns for storing hot water on thermal stratification in the caverns and heat loss to the surroundings. Heat transfer simulations using a computational fluid dynamics code, FLUENT were performed at different aspect ratios and storage volumes of rock caverns. The variation of thermal stratification with respect to time was examined using an index to quantify the degree of stratification, and the heat loss to the surroundings was evaluated. The results of the numerical simulations demonstrated that the thermal stratification in rock caverns was improved by increasing the aspect ratio, but this effect was not remarkable beyond an aspect ratio of 3-4. When the storage volume of rock caverns was large, a higher thermal stratification was maintained for a relatively longer time compared to caverns with a small storage volume, but the difference in thermal stratification between the two cases tended to decrease as the aspect ratio became larger. In addition, the numerical results showed that the heat loss to the surrounding rock tended to increase with an increase in aspect ratio because the surface area of rock caverns increased as the aspect ratio became larger. The total heat loss from multiple small caverns with a reduced storage volume per cavern was larger compared to a single cavern with the same total storage volume as that of the multiple caverns.

Status of Thermal Stratification Research on Piping System in Korea Nuclear Power Plant

“…5)에 의한 배관 고주기 열피로 평가 방법을 제안하고 있다 (34,35) . (42,43,44,45,46) , 열에너지의 거대한 지하 암반공동 저 장시의 열성층 유동특성 및 열손실 등을 해석적으로 검토하고 있다 (47,48,49) .…”