Simple mathematical model of a thermal storage with PCM (original) (raw)
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Latent heat thermal storage (LHTS) using phase change materials (PCMs) is one of the efficient and useful technologies in conservation and retention of thermal energy. One of the main advantages of this technology is the utilization of such systems in cooling/heating applications where the air is the heat transfer fluid (HTF). Generally , the heat transfer rate in a LHTS unit and its efficiency depends on the difference between the melting temperature of the PCM and the HTF temperature. If a single PCM is used, the temperature difference between the PCM and the HTF along the flow direction will be decreased. This leads to a decrease in the heat transfer rate and efficiency. In this case, nearly a constant temperature difference between the PCM and the HTF can be maintained during phase change. Therefore, the heat transfer rate to/from the PCM is constant. This work presents a two-dimensional numerical investigation of the performance of the LHTS unit which is composed of several rectangular PCM slabs. The enthalpy method is used to solve the governing equations for the melting process in PCMs. The convective heat transfer inside the air channels is analyzed by solving the energy equation, which is coupled with the heat conduction equation in the PCM wall. The general equations of temperature and the local liquid fraction are discretized with the finite difference method and are solved by a fully implicit scheme. The effect of geometrical parameters of storage such as the PCM slab thickness and the length as well as the effect of air flow rate in the outlet air temperature of storage are investigated.
Study of phase change modeling for a rectangular PCM container exposed to constant heat flux
Latent heat storage is one way of storing thermal energy that is capable of storing much more amounts of energy than the sensible heat storage. It has also the advantage of storing energy in a nearly isothermal phase change process. There are many phase change materials known, changing phase in a wide range of temperatures, which makes them suitable for different applications. In this study, temperature behavior of paraffin as a phase change material has been studied with two different numerical methods. Further the results have been verified with experimental data.
Thermal behaviour study of phase change material of a latent heat storage system
Materials Today: Proceedings, 2016
An Experimental study on latent heat storage system (LHS) using Erythritol as a phase change material (PCM) has been carried out to analyze the thermal characteristics. The study is part of testing aimed at observation of PCM to store solar energy to melt paraffin wax for candle making. The trial inspected the effect of inlet temperatures (T h) of heat transfer fluid (HTF) on the thermal behaviour of the LHS system. The outcome revealed that the suitable inlet temperature (T h) for charging the system is 143° C. The trial plan also examined the temperature gradient in the axial directions during charging to help predict heat transfer in the system during phase change of Erythritol. Time bound temperature curves were used to analyse the results. An LHS was fabricated of shell and tube (bundle) type heat exchanger for this study. Thermocouples connected to a data logger were used to measure the temperature of the PCM along the direction of flow.
Performance Analysis of Latent Heat Storage Systems
Storage of heat in the form of latent heat using phase change materials (PCMs) is an effective way of storing the thermal energy. PCMs have been used in many applications such as thermal energy storage in solar thermal power plants, thermal conditioning of buildings, thermal comfort in vehicles, cooling of electrical equipments, etc. In the present paper, numerical experiments carried out to analyse the performance of latent heat storage (LHS) systems using PCM have been presented. Effective heat capacity method is employed to account the latent heat of PCM. Boussinesq approximation has been included in the model to incorporate the buoyancy effect of the molten layer of PCM. For proper modelling of velocities in the mushy region, Darcy law’s source term has been added. In the current study, Paraffin RT 50 has been selected as the PCM and water has been selected as the heat transfer fluid (HTF). Melting time of PCM packed in three different cylindrical configurations viz. pipe model, cylinder model and shell-and-tube model is compared. The mathematical model is validated with the data available in the literature. The thermal characteristics of the models have been analysed using isothermal contour plots and temperature time curves. The phase change in the shell-and-tube model was dominated by the effect of convective heat transfer. Numerical results shown that for the same mass of PCM and surface area of heat transfer, shell-and-tube model takes the minimum time for melting the PCM.
Experimental Investigation of Thermal Behaviour of Phase Change Material in a Thermal Store
This paper reports on an experimental thermal energy storage system using phase change material (PCM) and comprising a bench top test rig based on a plate heat exchanger design concept. The research explores the unique properties of PCMs and how they may be used to alleviate peak electricity loads and costs that result from use of heat pumps in domestic buildings by taking advantage of off-peak electricity tariffs. Thermo-physical properties of three different PCMs were tested using a differential scanning calorimeter (DSC) and Hot disk instrument. Paraffin wax (RT 58) with a melting point range of 54 – 62°C was selected for the experimental work. A test rig was made from extruded polypropylene sheet with channels that can carry water, representing one of the plates in the thermal store heat exchanger, and PCM contained on one side of it. A computational model was developed to investigate heat exchange between the heat transfer fluid, polypropylene sheet and the PCM in the store. Th...
Numerical analysis of latent heat thermal energy storage system
Energy Conversion and Management, 2007
This paper presents a comparative study of the total melting time of a phase change material (PCM) packed in three containers of different geometric configurations, viz. rectangular, cylindrical and cylindrical shell, having the same volume and surface area of heat transfer. Employing a slightly modified enthalpy method, which enables decoupling of the temperature and liquid fraction fields, the governing equation for one dimensional isothermal phase change is discretized using the Crank-Nicholson finite difference scheme. While the resulting system of algebraic equations for temperature is solved using the Thomas algorithm, the liquid fraction field is updated explicitly using the currently known temperature field. The results are presented for different masses of PCM filling the containers and inlet temperature of the heat transfer fluid (HTF). On the basis of detailed discussion of these results, it is concluded that for the same mass of PCM and surface area of heat transfer, cylindrical shell containers take the least time for equal amounts of energy storage, and this geometric effect is more pronounced with an increase in the mass of the PCM. It is also found that for cylindrical shell containers, an increase in the inlet temperature of the HTF from its lower range of values results in a drastic decrease in energy storage time, while this effect of inlet temperature of the HTF diminishes sharply at higher and higher values. Further, it is observed that as the mass of the PCM in the cylindrical shell container having a fixed surface area of heat transfer increases, the reduction in total melting time due to an increase in the inlet temperature of the HTF becomes more and more pronounced.
Applied Thermal Engineering, 2017
Thermal energy storage in general, and phase-change materials (PCMs) in particular, have been a major topic of research for the last thirty years. Due to their favorable thermo-dynamical characteristics, such as high density, specific heat and latent heat of fusion, PCMs are usually employed as working fluids for thermal storage. However, low thermal conductivities of organic PCMs have posed a continuous challenge in its large scale deployment. This study focuses on experimental and numerical investigation of the melting process of industrial grade paraffin wax inside a semi-cylindrical enclosure with a heating strip attached axially along the center of semi-cylinder. During the first part of the study, the solid-liquid interface location, the liquid flow patterns in the melt pool, and the spatial and temporal variation of PCM temperature were recorded. For numerical simulation of the system, open source library OpenFOAM ® was used in order to solve the coupled Navier-Stokes and energy equations in the considered system. It is seen that the enthalpy-porosity technique implemented on OpenFOAM ® is reasonably well suited for handling melting/solidification problems and can be employed for system level design. Next, to overcome the inherent thermal limitations of PCM storage material, the study further explored the potential of coupling the existing heat source with copper-water heat pipes, so as to help augment the rate of heat dissipation within the medium by increasing the effective system-level thermal conductivity. Integration of heat pipes led to enhanced transport, and hence, a substantial decrease in the total required melting time. The study provides a framework for designing of large systems with integration of heat pipes with PCM based thermal storage systems.
Thermal Performance of the Thermal Storage Energy with Phase Change Material
Acta Mechanica et Automatica
Values of energy supply and demand vary within the same timeframe and are not equal. Consequently, to minimise the amount of energy wasted, there is a need to use various types of energy storing systems. Recently, one can observe a trend in which phase change materials (PCM) have gained popularity as materials that can store an excess of heat energy. In this research, the authors analysed paraffin wax (cheese wax)’s capability as a PCM energy storing material for a low temperature energy-storage device. Due to the relatively low thermal conductivity of wax, the authors also analysed open-cell ceramic Al2O3/SiC composite foams’ (in which the PCM was dispersed) influence on heat exchange process. Thermal analysis on paraffin wax was performed, determining its specific heat in liquid and solid state, latent heat (LH) of melting, melting temperature and thermal conductivity. Thermal tests were also performed on thermal energy container (with built-in PCM and ceramic foams) for transient...
Study of Heat Transfer in Energy Storage System Using Phase Change Material
2020
The usage of phase change materials to store heat in the form of latent heat is increased, because large quantity of thermal energy is stored in smaller volumes. A cylindrical thermal storage device is composed of an inner aluminum pipe having inner/outer diameter of 20/30 mm and length of 1000 mm. The pipe passes through a cylindrical storage device have a radius of 300 mm, fill with paraffin wax. In the present work, a numerical study of the effects of convection, number of fins and heating surface temperature on the storage characteristics of annular latent heat energy storage system (LHESS) using the CFD software FLUENT6.3.26. The results show that the effect of convection cannot be neglected, but it decreases when the space between fins decreases which occurs when numbers of fins increase. The heat transfer increases as the number fins increases and found that after 12 hours the rate of energy stored increased to 116.5% and 89.6% and 89.6% for 3 fins, 8 fins and 13 fins respect...