Thermodynamics of Energy Storage by Melting Due to Conduction or Natural Convection

1990 ◽  
Vol 112 (2) ◽  
pp. 110-116 ◽  
Author(s):  
M. De Lucia ◽  
A. Bejan
Keyword(s):  
Energy Source ◽  
Natural Convection ◽  
Energy Storage ◽  
Phase Change ◽  
Phase Change Material ◽  
Melting Process ◽  
Absolute Temperature ◽  
Design Parameters ◽  
Environment Temperature ◽  
Change Material

This paper describes the most basic thermodynamic aspects of the process of energy storage by melting of a phase change material when the energy source is a stream of hot single-phase fluid. The first part of the paper considers the melting process ruled by pure conduction across the liquid phase, and the second part deals with the quasi-steady melting dominated by natural convection. The paper establishes the relationship between the total irreversibility of the melting process and design parameters such as the number of heat transfer units of the heat exchanger placed between the energy source and the phase change material, the duration of the melting process, and the position of the energy storage process on the absolute temperature scale. It is shown that the exergy transfer to the melting material is maximized when the melting temperature (Tm) equals the geometric average of the environment temperature (Te) and the temperature of the energy source (T∞), in other words when Tm=(TeT∞)1/2. This conclusion holds for both conduction-dominated melting and convection-dominated melting.

Thermodynamic Optimization of Phase-Change Energy Storage Using Two or More Materials

1992 ◽  
Vol 114 (1) ◽  
pp. 84-90 ◽  
Author(s):  
J. S. Lim ◽  
A. Bejan ◽  
J. H. Kim
Keyword(s):  
Energy Storage ◽  
Melting Point ◽  
Phase Change ◽  
Phase Change Material ◽  
Finite Thickness ◽  
Melting Process ◽  
Two Phase ◽  
In Series ◽  
Optimal Melting ◽  
Change Material

This paper documents the relative merits of using more than one type of phase-change material for energy storage. In the case of two phase-change systems in series, which are melted by the same stream of hot fluid, there exists an optimal melting point for each of the two materials. The first (upstream) system has the higher of the two melting points. The second part of the paper addresses the theoretical limit in which the melting point can vary continuously along the source stream, i.e., when an infinite number of different (and small) phase-change systems are being heated in series. It is shown that the performance of this scheme is equivalent to that which uses an optimum single phase-change material, in which the hot stream remains unmixed during the melting process. The time dependence, finite thickness and longitudinal variation of the melt layer caused by an unmixed stream are considered in the third part of the paper. It is shown that these features have a negligible effect on the optimal melting temperature, which is slightly higher than (T∞Te)1/2.

scholarly journals Numerical investigation on the phase change process of different shaped macro encapsulated PCM

2018 ◽  
Vol 7 (4.5) ◽  
pp. 587
Author(s):  
Jay R. Patel ◽  
Manish K. Rathod
Keyword(s):  
Energy Storage ◽  
Phase Change ◽  
Phase Change Material ◽  
Melting Process ◽  
Complex Flow ◽  
Ansys Fluent ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Convection Dominated ◽  
Change Material

Latent heat energy storage using macro encapsulated phase change material is an emerging technique for thermal energy storage applica- tions. The main aim of the present investigation is to investigate the melting process of phase change material filled in different shaped configurations. The selected different cavities are square, circular and triangular. A mathematical model based on convection dominated melting is required to be developed, especially in view of the complex flow geometries encountered in such problems. Thus, an attempt has been made to develop a model using ANSYS Fluent 16.2 to investigate the heat transfer rate and solid-liquid interface visualization of PCM filled in different shapes of cavity. It is found that triangular shaped macro encapsulated PCM melts faster than square and circu- lar shaped encapsulated PCM.   

scholarly journals Phase Change Material Melting Process in a Thermal Energy Storage System for Applications in Buildings

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3254 ◽  
Author(s):  
Túlio Nascimento Porto ◽  
João M. P. Q. Delgado ◽  
Ana Sofia Guimarães ◽  
Hortência Luma Fernandes Magalhães ◽  
Gicelia Moreira ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Storage ◽  
Heat Exchanger ◽  
Phase Change ◽  
Phase Change Material ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Melting Process ◽  
Average Heat ◽  
Change Material

The development of thermal energy storage systems is a possible solution in the search for reductions in the difference between the global energy supply and demand. In this context, the ability of some materials, the so-called phase change materials (PCMs), to absorb and release large amounts of energy under specific periods and operating conditions has been verified. The applications of these materials are limited due to their low thermal conductivity, and thus, it is necessary to associate them with high-conductivity materials, such as metals, to make the control of energy absorption and release times possible. Bearing this in mind, this paper presents a numerical analysis of the melting process of a PCM into a triplex tube heat exchanger (TTHX) with finned copper tubes, which allowed for the heat transfer between a heating fluid (water) and the phase change material to power a liquid-desiccant air conditioning system. Through the analysis of the temperature fields, liquid fractions, and velocities, as well as the phase transition, it was possible to describe the material charging process; then, the results were compared with experimental data, which are available in the specialized literature, and presented mean errors of less than 10%. The total required time to completely melt the PCM was about 105.5 min with the water being injected into the TTHX at a flow rate of 8.3 L/min and a temperature of 90 °C. It was observed that the latent energy that accumulated during the melting process was 1330 kJ, while the accumulated sensitive energy was 835 kJ. The average heat flux at the internal surface of the inner tube was about 3 times higher than the average heat flux at the outer surface of the TTHX intermediate tube due to the velocity gradients that developed in the internal part of the heat exchanger, and was about 10 times more intense than those observed in the external region of the equipment.

scholarly journals Melting of a phase change material in a horizontal annulus with discrete heat sources

2015 ◽  
Vol 19 (5) ◽  
pp. 1733-1745 ◽  
Author(s):  
Hooshyar Mirzaei ◽  
Abdolrahman Dadvand ◽  
Mohammad Mastiani ◽  
Seyed Sebti ◽  
Sina Kashani
Keyword(s):  
Energy Storage ◽  
Phase Change ◽  
Phase Change Material ◽  
Liquid Fraction ◽  
Outer Cylinder ◽  
Melting Process ◽  
Cylinder Wall ◽  
Heat Sources ◽  
Discrete Heat Sources ◽  
Change Material

Phase change materials have found many industrial applications such as cooling of electronic devices and thermal energy storage. This paper investigates numerically the melting process of a phase change material in a two-dimensional horizontal annulus with different arrangements of two discrete heat sources. The sources are positioned on the inner cylinder of the annulus and assumed as constant-temperature boundary conditions. The remaining portion of the inner cylinder wall as well as the outer cylinder wall is considered to be insulated. The emphasis is mainly on the effects of the arrangement of the heat source pair on the fluid flow and heat transfer features. The governing equations are solved on a non-uniform O type mesh using a pressure-based finite volume method with an enthalpy porosity technique to trace the solid and liquid interface. The results are obtained at Ra=104 and presented in terms of streamlines, isotherms, melting phase front, liquid fraction and dimensionless heat flux. It is observed that, depending on the arrangement of heat sources, the liquid fraction increases both linearly and non-linearly with time but will slow down at the end of the melting process. It can also be concluded that proper arrangement of discrete heat sources has the great potential in improving the energy storage system. For instance, the arrangement C3 where the heat sources are located on the bottom part of the inner cylinder wall can expedite the melting process as compared to the other arrangements.

scholarly journals Study of Thermal Behavior of a Horizontal Two Fins Annular Tube Heat Exchanger with Melting Phase Change Material: Fins Orientation Effects

2021 ◽  
Vol 45 (2) ◽  
pp. 141-151
Author(s):  
Nesrine Boulaktout ◽  
El Hacene Mezaache ◽  
Abdelghani Laouer
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Phase Change ◽  
Phase Change Material ◽  
Melting Process ◽  
Initial Time ◽  
Tube Heat Exchanger ◽  
Change Material ◽  
Annular Tube

This paper investigates the effect of fins orientations of a horizontal two fins annular tube heat exchanger on enhancing the heat transfer during the melting process of n-eicosane, as phase change material (PCM) used in thermal storage systems. Based on the enthalpy-porosity method, two-dimensional model is performed and solved by Ansys Fluent. The impact of the fins orientation on melting rate, thermal conduction and natural convection, as the angle of the system varied from 0º (vertical fins) to 90º (horizontal fins) are discussed. Numerical predictions are validated by comparison with experimental data and numerical results reported in the literature. Good agreements are achieved. The results show that at initial time of the melting process, the conduction heat transfer is dominant. During the melting process, the heat transfer in the horizontal fins is more effective while the upper half of PCM melts and less effective as the lower half of PCM melts because fin arrangement resists natural convection occurs. However, the effectiveness of heat transfer and convection in the vertical fins is almost constant during the entire melting process. From comparison, better heat transfer performance is achieved with vertical fins system; complete melting was reduced 250% compared to horizontal fins case.

scholarly journals Characterization and Experimental Investigation of NaNO3 : KNO3 as Solar Thermal Energy Storage for Potential Cooking Application

2016 ◽  
Vol 2016 ◽  
pp. 1-6 ◽  
Author(s):  
Elias Wagari Gabisa ◽  
Abdulkadir Aman
Keyword(s):  
Energy Source ◽  
Experimental Investigation ◽  
Energy Storage ◽  
Phase Change ◽  
Phase Change Material ◽  
Thermal Energy ◽  
Thermal Characteristics ◽  
Solar Thermal ◽  
Solar Thermal Energy ◽  
Change Material

Household cooking is a major energy intensive activity in most of the Ethiopian households. Replacing the existing inefficient cooking stoves and the polluting energy source with a renewable source of energy plays a paramount role in conserving the environment and reducing the indoor pollution. In this study an energy storage phase change material is proposed to store solar thermal energy for a potential household cooking application. The selected phase change material has a melting point range which is well fitted to the operating range of temperatures for most of the household cooking activities. The solar energy source is simulated with electrical heating for experimental investigation of the thermal characteristics. Also it is intended to study the thermal characteristics of the mixture using deferential scanning calorimeter to identify at which mass ratio the mixture shows better thermal characteristics. From the laboratory analysis it is found that the 60% NaNO3 and 40% KNO3 by mass have shown promising thermal characteristics. For applying the selected salt mixture for cooking application, an experiment was conducted on two Ethiopian local meals, shiro wet and potato meal, to know how much energy is required to cook them and what amount of the PCM is required to store the required energy. The result reveals that 2.38 kWh energy is required for cooking the two meals for five family members for lunch and dinner. To store the energy required 4 kg of the PCM was required. Experiments were conducted to see the charging and discharging time of 60% NaNO3 and 40% KNO3 by mass. From the experimental result for 1.4 kg of the PCM, charging time of 50 minutes up to 300°C and a discharging time of 4.5 hours (from 300°C to 100°C) are required.

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