Mechanical Stability Analysis to Determine the Optimum Aspect Ratio of Rock Caverns for Thermal Energy Storage

Heat transfer analysis of a high aspect ratio thermal energy storage (TES) device was carried out numerically. The three dimensional numerical study was performed to understand the heat transfer enhancement which results from internal natural convection in a high aspect ratio vertical unit. Octadecane was used as phase change material (PCM) inside TES system, which consisted of six corrugated panels filled with PCM. Each panel had a total of 6 tall cavities filled with PCM, which were exposed to external flow in a concentric TES system. Unlike traditional concentric-type TES devices where heat transfer by conduction is the dominant heat transport mechanism, the high aspect ratio TES configuration used in the study helped promote density-gradient based internal convection mechanism. The numerical model was solved based on the finite volume method, which captured the whole transient heat transfer process effectively. The time-dependent temperature profiles of the PCM inside a single TES panel are compared with the experimental results for two cases. Numerical and experimental results of the two cases showed a reasonable agreement. Furthermore, convection cells were formed and sustained when the PCM melted within the space between the solid core and the walls. The promising results of this numerical study illustrate the importance of internal natural convection on the speed of the PCM melting (charging) process.

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Effects of aspect ratio and mushy-zone parameter on melting performance of a thermal energy storage unit filled with phase change material

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2020-0182 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Azim Memon ◽

Anoop K. Gupta

Keyword(s):

Energy Storage ◽

Aspect Ratio ◽

Mushy Zone ◽

Phase Change ◽

Phase Change Material ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Aspect Ratios ◽

Zone Parameter ◽

Change Material

Abstract An intermittent supply of energy from renewable or unconventional resources has resulted in the use of phase change materials (PCM) in thermal energy storage (TES) systems. In this work, melting and heat transfer characteristics in a rectangular enclosure of different aspect ratios (width to height) filled with a phase change material (PCM) have been studied numerically. The n-octadecane has been selected as the PCM (melting temp = 301.35 K, Prandtl number ∼ 60). We considered five different aspect ratios (AR) of the enclosure to delineate the effects of 9-fold variation in the aspect ratio. The simulations were carried out using ANSYS Fluent 19.2. In particular, extensive results have been presented and discussed in terms of the temperature contours, rate of melting and energy storage, and total time required to reach the fully melt condition. Additionally, the effect of the mushy zone parameter (A mush ) on the melting performance has also been investigated. Low values of the A mush were seen to predict the higher rate of melting. At a fixed value of A mush , ∼ 3 times faster melting rate was observed as the value of AR was reduced from 3 to 1/3. Finally, it can be concluded that melting and energy storage rate largely depends on the aspect ratio of the enclosure and the optimal choice of the value of the A mush .

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Cyclic mechanical stability of thermal energy storage media

E3S Web of Conferences ◽

10.1051/e3sconf/202020507008 ◽

2020 ◽

Vol 205 ◽

pp. 07008

Author(s):

Henok Hailemariam ◽

Frank Wuttke

Keyword(s):

Energy Storage ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Heat Storage ◽

Mechanical Performance ◽

Mechanical Stability ◽

Storage Systems ◽

Supply And Demand ◽

Storage System ◽

Industrial Applications

Closing the gap between supply and demand of energy is one of the biggest challenges of our era. In this aspect, thermal energy storage via borehole thermal energy storage (BTES) and sensible heat storage systems has recently emerged as a practical and encouraging alternative in satisfying the energy requirements of household and industrial applications. The majority of these heat energy storage systems are designed as part of the foundation or sub-structure of buildings with load bearing capabilities, hence their mechanical stability should be carefully studied prior to the design and operation phases of the heat storage system. In this study, the cyclic mechanical performance of a commercial cement-based porous heat storage material is analyzed under different amplitudes of cyclic loading and medium temperatures using a recently developed cyclic thermo-mechanical triaxial device. The results show a significant dependence of the cyclic mechanical behavior of the material, such as in the form of cyclic axial and accumulated plastic strains, on the different thermo-mechanical loading schemes.

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Shape Factor in the Latent-Heat-Thermal-Energy-Storage Systems

10.1115/imece2001/htd-24226 ◽

2001 ◽

Author(s):

Sergei Fomin

Keyword(s):

Energy Storage ◽

Aspect Ratio ◽

Latent Heat ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Storage Systems ◽

Melting Rate ◽

Energy Storage Systems ◽

Cross Sectional ◽

Thermal Energy Storage Systems

Abstract An approximate mathematical model of contact melting of an unfixed material in an elliptical capsule is developed. The main characteristic scales and non-dimensional parameters, which describe the principal features of the melting process, are found. Choosing the special heat flux distribution on the wall of the capsule allows us to derive a closed-form evolution equation for the motion of the solid, which also determines the melting rate. It is shown that the melting rate depends on the shape of the capsule. The elliptical capsules show higher rate of melting than the circular ones. The vertically elongated capsules provide more effective melting than the horizontally elongated ones, even though they have the same aspect ratio and vertical cross-sectional areas. The time required for complete melting can be achieved by the right choice of the shape of the capsule, which is specified by the value of the aspect ratio. This is especially important for the design of practical latent-heat-thermal-energy-storage systems.

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