Thermal Modeling of High Temperature Energy Storage Using Encapsulated Phase Change Materials

2012 ◽  
Author(s):  
Ali F. Elmozughi ◽  
Weihuan Zhao ◽  
Sudhakar Neti ◽  
Alparslan Oztekin
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Energy Storage ◽  
Phase Change ◽  
Phase Change Materials ◽  
Front Tracking ◽  
System Level ◽  
Flow Conditions ◽  
Tracking Method ◽  
Front Tracking Method

Transient heat transfer analysis is conducted to investigate high temperature energy storage using encapsulated phase change materials (EPCMs) for concentrated solar power applications. The phase change material considered is the eutectic mixture of NaCl-MgCl2 (57 mole% NaCl and 43 mole% MgCl2) encapsulated by stainless steel in a cylindrical shaped capsule (or tube). Energy storage into EPCM and energy retrieval from EPCM is simulated for various flow conditions of the heat transfer fluid. Heat storage/retrieval times are determined from numerical simulations for various sizes of capsules and flow conditions by an accurate modeling of propagating solid/liquid interface. Numerical simulations are conducted by employing a front tracking method and the enthalpy–porosity approach. A two-dimensional horizontally placed cylindrical shaped EPCM capsule is considered in simulations using gas (air) and liquid (VP1-Therminol) as heat transfer fluids. The results predicted by the front tracking method agree well with those predicted by the enthalpy–porosity method. It is illustrated by the present work that enthalpy–porosity method can be employed to simulate the modeling at the single capsule level and system level. System level storage unit is a thermocline that includes an arrangement of several EPCMs.

Robustness Analysis of Various Approaches to Modeling of the Phase Change Front Propagation

2017 ◽  
Author(s):  
Tomas Mauder ◽  
Lubomir Klimes ◽  
Pavel Charvat ◽  
Josef Stetina
Keyword(s):  
Phase Change ◽  
Real Time ◽  
Latent Heat ◽  
Thermal Energy ◽  
Phase Change Materials ◽  
Phase Interface ◽  
Front Tracking ◽  
Computational Time ◽  
Tracking Method ◽  
Front Tracking Method

Latent heat thermal energy storage (LHTES) has recently evolved into a promising approach for energy savings and pollution reduction. Phase change materials (PCMs) and the latent heat accompanying the phase change can be utilized to accumulate, store, are release the thermal energy when needed. The latent heat of the phase change allows for a storage of a relatively large amount of heat in a narrow temperature interval. The solid-liquid phase transition is widely utilized in such LHTES applications. Computer simulation tools are usually applied in the optimal design and real-time control of LHTES devices as the simulations are fast, relatively easy to perform and not expensive. Different numerical methods exist for modeling of heat transfer problems with phase changes. The methods can be assessed in several ways — accuracy, mathematical and programming complexity, demands for computational time and hardware, robustness etc. The well-known enthalpy method, the effective heat capacity method and the temperature recovery method are widely utilized as they are simple and easy to implement. These so-called domain or front capturing methods suffer from a low accuracy in the vicinity of the phase interface and they are quite sensitive to the size of the time step. On the other hand, front tracking methods allow for very precise results near the phase interface, but they are more complex and computationally quite demanding. An important point is also the sensitivity and robustness of a method in relation to the thermal conditions and properties. In particular, the large heat flux at the boundary and the high thermal conductivity often cause numerical difficulties and instabilities. In practice, computer models have to be precise enough and sufficiently fast, especially in real-time applications. However, these two objectives are related in an opposite direction. The paper presents a robustness and sensitivity analysis of the above mentioned methods. The responses and numerical behavior of the methods are investigated and analyzed. The test problems with distinct grid spacing, sizes of time steps and thermophysical properties of phase change materials. The results show that the front tracking method can achieve higher accuracy for coarse mesh sizes than other tested methods. This characteristic compensates for higher computational demands of the front tracking method.

Micro encapsulated & form-stable phase change materials for high temperature thermal energy storage

2018 ◽  
Vol 217 ◽  
pp. 212-220 ◽  
Author(s):  
Guanghui Leng ◽  
Geng Qiao ◽  
Zhu Jiang ◽  
Guizhi Xu ◽  
Yue Qin ◽  
...  
Keyword(s):  
High Temperature ◽  
Energy Storage ◽  
Phase Change ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Phase Change Materials ◽  
Stable Phase

Solid/Liquid Phase Change Heat Transfer in Latent Heat Thermal Energy Storage

2009 ◽  
Author(s):  
D. Zhou ◽  
C. Y. Zhao
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Energy Storage ◽  
Phase Change ◽  
Calcium Chloride ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Phase Change Materials ◽  
Metal Foams ◽  
Chloride Hexahydrate

Phase change materials (PCMs) have been widely used for thermal energy storage systems due to their capability of storing and releasing large amounts of energy with a small volume and a moderate temperature variation. Most PCMs suffer the common problem of low thermal conductivity, being around 0.2 and 0.5 for paraffin and inorganic salts, respectively, which prolongs the charging and discharging period. In an attempt to improve the thermal conductivity of phase change materials, the graphite or metallic matrix is often embedded within PCMs to enhance the heat transfer. This paper presents an experimental study on heat transfer characteristics of PCMs embedded with open-celled metal foams. In this study both paraffin wax and calcium chloride hexahydrate are employed as the heat storage media. The transient heat transfer behavior is measured. Compared to the results of pure PCMs samples, the investigation shows that the additions of metal foams can double the overall heat transfer rate during the melting process. The results of calcium chloride hexahydrate are also compared with those of paraffin wax.

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