Fusion Of Phase Change Materials Research Articles

Modelling a latent heat thermal storage demonstrator and identification of the model key-parameters

Latent Heat Thermal Energy Storage (LHTES) has a great potential to reduce CO2 emissions in urban areas, when associated to a district heating network. It facilitates the flexibility of the network by decoupling the production and consumption. Thus, consumption peaks that are often managed with fossil fuels will be managed by unloading the storages of the network. LHTES based on tube and shell is the most widely studied technology, as it combines low cost, high maturity, and high compactness factor. This paper presents a numerical model to simulate the thermohydraulic behaviour of a shell-and-tube LHTES, based on a 1D approach for the heat transfer fluid (HTF) and a 1.5D approach for the Phase Change Material (PCM). The objective is to develop a model representing a whole system, faster than a Computational Fluid Dynamic approach while keeping a sufficient degree of accuracy. The paper focuses on the presentation of the model and its validation against experimental data from a real-scale 180 kWh demonstrator, currently in operation in the substation of the urban heating network of Grenoble, France. The validation against three different charges is presented, two charges at a constant flow rate (0.6 and 1.6 kg/s-1) and one at constant power (60 kW). The model gives results with an accuracy superior to 95 % and >80 % of the points are between the experimental uncertainty curves. It has also been found that the model loses its accuracy when the inlet HTF temperature abruptly decreases and the top collector does not behave as a stratified tank anymore (the relative error on total energy accumulated reaches 35 %). In the second part of the paper, a sensitivity study to the main parameters of the model shows that the model is sensible to the discretization of the collectors, the precision of the Nusselt correlation for convective transfers in the tubes, and the fusion temperature of the PCM. These parameters can induce up to respectively 22 % (0D model for the collectors' volume), 4.5 % to 9 % (considering the annular space as a flat plane or a cylindrical tube) and 3 % to 6 % (error of 0.5 to 1 °C in the PCM fusion temperature) error.

An experimental investigation of a PCM-based heat sink enhanced with a topology-optimized tree-like structure

A heat sink filled with phase change material (PCM) is an efficient thermal management device which utilizes the high latent heat of fusion of PCM in the cooling process. To improve the thermal performance of the PCM-based heat sink, a topology optimization (TO) strategy is devised to develop a new class of enhanced structures. This is achieved by carrying out a comprehensive numerical study to identify the effects of various thermal transport mechanisms on the TO design by considering two different heat transfer problems, i.e., steady-state heat conduction and transient heat conduction with phase change. To enable easy fabrication and performance evaluation of the new heat sink design predicted by the TO process, the resulting heat sink with tree-like structure was fabricated by selective laser melting (SLM), a metal additive manufacturing (AM) technique. Experimental characterization of the TO heat sink was carried out using three different types of PCMs, i.e., RT35, RT35HC and RT44HC and heat fluxes ranging from 4.00 kW/m2 to 7.24 kW/m2. Our experimental results show that the TO tree-like structure heat sink has better performance, exhibiting up to 4 °C lower wall temperatures, than the conventional fin-structure heat sink. At low heat fluxes, the best thermal performance can be obtained with RT35HC whereas at high heat fluxes, lower wall temperatures were achieved with RT44HC. In addition, the tree-like structure increases operational time by up to 13% as compared to the fin-structure heat sink. The better thermal performance of the tree-like structure heat sink is due to its optimized heat conduction paths that allow heat from the concentrated heat source to be efficiently dissipated to the PCM. This work not only demonstrates the potential of enhancing electronics cooling with TO PCM-based heat sinks, but it also outlines key guidelines for the design and implementation of TO structures for other cooling applications.

Building bricks with phase change material (PCM): Thermal performances

In certain Moroccan regions, weather conditions are extreme; the outside ambient temperature varies between 45 °C during the day and 25 °C at night in the estival period. Under such conditions, residential and tertiary buildings, which have lightweight walls, may be vulnerable to internal overheating. Heat waves penetrating the building lead to occupant’s discomfort and dissatisfaction. Creating an internal climate, which is independent or slightly dependent on external conditions, can be an appropriate solution to mitigate temperature fluctuations. The adoption of new approaches to improve the thermal inertia of lightweight walls is currently among the most widely accepted techniques in literature. In this study, the integration of phase change material (PCM) in building hollow bricks (widely used in Morocco construction) is proposed to improve the thermal performance of external walls. High latent heat of fusion of PCMs will help to dampen the heat flow through the envelope. Physical modeling and numerical analysis of heat transfer through the hollow bricks containing PCM has been carried out. A parametric study was conducted to evaluate the effect of weather conditions on the thermal response of this building element, also the influence of PCM properties are studied and discussed. It is found that the use of PCM in building bricks stabilizes and reduces the indoor temperature fluctuation.

Thermal reliability and corrosion characteristics of an organic phase change materials for solar space heating applications

The increasing interest in solar thermal energy storage necessitates the identification of new latent heat based phase change materials (PCMs). Testing the reliability and corrosion of newly identified PCMs upon repeated thermal charging and discharging cycles helps to evaluate the long term feasibility of latent heat storage system. Phenyl acetic acid (PAA) is an organic PCM with phase transition temperature of 75–80 °C and latent heat of 152 J/g. In this present work the thermal reliability on thermo-physical properties and corrosive nature of phenyl acetic acid is studied for 2000 accelerated thermal cycles. The experimental result shows that phase transition temperature and latent heat of fusion of PCM varies only ±1–3% and also has less corrosive nature to aluminium and stainless steel than copper metal containers throughout the thermal cycles. This study also comprises of experimental investigation on thermal performance of solar air heater (SAH) with built-in latent heat thermal energy storage. The solar air heater with PCM has outlet air temperature higher than ambient by 2–13 °C for 2.5 h and 1–8 °C for 2 h after solar hours at the mass flow rate of 30 and 45 kg/hr.m2 respectively. Therefore the newly identified phenyl acetic acid is a promising PCM for solar space heating applications due to good heat storage properties, long term thermal reliability and less corrosive nature.

Numerical investigations of optimal phase change material incorporated into ventilated walls

Phase change materials (PCMs) have been extensively integrated with ventilated walls to improve their thermal performance and the indoor thermal comfort, and the optimal PCM could gain the best improvement. However, there were few studies on the optimal PCM incorporated into ventilated walls. To accurately obtain the optimal PCM, a series of numerical models, including indoor air, soil and an active-passive ventilated wall with PCM, were developed and validated by an experiment. Then both phase change temperature and heat of fusion of PCM were changed and written into the developed models, and their effect on different performance indicators, namely heat storage density, heat storage efficiency and minimum indoor air temperature, was discussed. Finally, the optimal PCM was determined with different objectives, and potential PCMs were recommended. The results showed that the change trend of the optimal heat of fusion of PCM was opposite with different with different objectives, but the relationship between the optimal phase change temperature and the optimal heat of fusion was fitted into a curve. With the multiple objectives of maximizing all of the proposed performance indicators, the optimal PCM was at the connection point between the minimum indoor air temperature curve and the relationship fitting curve.

Multiscale Transient Modeling of Latent Energy Storage for Asynchronous Cooling

This paper establishes a multiscale design evaluation framework that integrates performance models for a thermal energy storage (TES) unit and a subsystem heat exchanger (HX). The modeling facilitates the analysis of transient input and extraction processes for the TES device which uses solid–liquid phase change to store thermal energy. We investigate sensible and latent heat transfer through the unit's matrix structure which contains phase change material (PCM) in the interstitial spacing. The heat transfer is driven by a temperature difference between fluid flow passages and the PCM matrix which experiences sensible heat transfer until it reaches the PCM fusion point; then it undergoes melting or solidification in order to receive, or reject, energy. To capture these physics, we establish a dimensionless framework to model heat transfer in the storage device much like effectiveness-number of transfer units (NTU) analysis methods for compact HX. Solution of the nondimensional governing equations is subsequently used to predict the effectiveness of the transient energy input and extraction processes. The TES is examined within the context of a larger subsystem to illustrate how a high efficiency design target can be established for specified operating conditions that correspond to a variety of applications. The general applicability of the model framework is discussed and example performance calculations are presented for the enhancement of a Rankine power plant via asynchronous cooling.

Composite of wood-plastic and micro-encapsulated phase change material (MEPCM) used for thermal energy storage

Application of phase change materials (PCMs) in lightweight building is growing due to the high latent heat of fusion of PCMs and their ability to control temperature by absorbing and releasing heat efficiently. Wood-plastic composites (WPC) are materials used in the interior parts of buildings that have improved properties compared to conventional materials. However, these materials have low energy storage capacity, which can be improved by incorporating PCM in them. Leakage of PCM is a major obstacle to the industrial applications, which can be solved through the use of microencapsulated PCM (MEPCM). This paper presents the performance tests conducted for a composite of wood-plastic-MEPCM for using in buildings for thermal storage. The wood-plastic-MEPCM composites were produced in this project using compression molding and their thermal and mechanical properties were investigated using DSC analysis, cycling test, leakage test, and three point bending analysis. The results showed that there is no leakage of PCM during phase change. The results also indicated that the composite has reasonable thermal properties, but its mechanical properties need to be improved by increasing the pressure during the molding process or by using extrusion method. The produced composites can be used as a building material for thermal energy management of building.

Performance characteristics of microencapsulated phase change material slurry in a helically coiled tube

Flow and heat transfer characteristics of microencapsulated phase change material (MPCM) slurry as a heat transfer fluid (HTF) in a heated helically coiled tube have been investigated experimentally. Thermophysical properties of MPCM slurry were determined experimentally. A fully instrumented helical coil system was designed, built, and characterized to conduct pressure drop and heat transfer experiments at different mass fractions of MPCM slurries under turbulent flow conditions. Pressure drop and friction factor of MPCM slurry in the coiled tube were measured and correlated using the Dean number. Local convective heat transfer of MPCM slurry flowing through the coiled tube was characterized under turbulent flow and constant heat flux conditions. In addition, useful correlations have been postulated to predict Nusselt number of MPCM slurry. Furthermore, overall thermal performance analyses have been conducted to determine the benefits of using MPCM slurry in terms of heat transfer and heat capacity, respectively. The results showed that the enhancement in heat transfer performance is restricted due to the high viscosity and low latent heat of fusion of phase change material (PCM), but MPCM slurry still exhibits enhanced heat capacity when compared to water. Also, it was found that a helically coiled tube is more appropriate for convection of MPCM slurry than a straight tube.

Numerical analysis for the optimal location of a thin PCM layer in frame walls

The thermal performance of building walls can be improved using phase change materials (PCMs). The objective of this study was to estimate the optimal location of a “thin” PCM layer to be incorporated into frame walls, parallel to the frame and insulation, for the purpose of increasing thermal mass and reducing peak heat fluxes through the wall. Based on a mathematical model built in this paper, it was found that an optimal location of this “thin” PCM layer can be estimated, and it was affected by the thermal properties of PCM and the environmental conditions. The optimal locations for the PCM layer were found to be closer to the exterior surface of the wall when the thickness of PCM layer, the heat of fusion of PCM, and the PCM melting temperature were increased, while the optimal location was closer to the interior surface of the wall when the interior surface temperature of the wall was increased.

Experimental Investigation of Solar Paraffin Wax Melting Unit Integrated with Phase Change Heat Energy Storage by Using Phase Change Material

An Experimental study on phase change heat energy storage system (PCHES) using Erythritol as a phase change material (PCM) has been carried out. Simple and popularly used domestic solar thermal applications make use of direct radiation energy of the sun for cooking, liquid heating, drying and many others as it is the remarkable potential renewable energy source. Effective utilization of such energy can be made with the development of economically operating phase change heat energy storage (PCHES) which is elemental in spanning the gap between supply and demand of energy. PCHES that stores the latent heat of fusion of phase change materials is provocative because of its huge storage density. An integrated Solar wax melting unit with phase change thermal energy storage using ethylene glycol as heat transfer fluid(HTF) to transfer the heat from parabolic dish collector to the wax melting unit is investigated. In this experimental setup, the paraffin wax container is kept in an insulated heat retrieval unit. Heat stored during the daytime by the PCHES is utilized in the off sunshine hours.

Melting and solidification enhancement using a combined heat pipe, foil approach

Abstract Melting and solidification of a phase change material (PCM) is investigated, experimentally and computationally, using a novel heat pipe–metal foil approach. By embedding a PCM within a metal foil matrix, and delivering (or extracting) thermal energy to (or from) the matrix with a vertically-oriented heat pipe, overall thermal resistances between a working fluid and the PCM solid–liquid interface can be reduced. This leads to increased phase change rates relative to configurations involving only the heat pipe, or only a solid rod of the same physical dimensions as the heat pipe. For a small (approximately 1%) volume fraction of foil in the PCM–foil matrix, measured and predicted melting (solidification) rates associated with heat pipe–foil configurations are increased by approximately 300% (900%) relative to configurations involving the rod with no foil. Melting and solidification rates relative to configurations involving the heat pipe with no foil, are increased by approximately 200% and 600%. The influence of the heat pipe evaporator-to-condenser length ratio, as well as the overall temperature difference between the working fluid and the PCM fusion temperature, is also reported.

Modelling of a Phase Change Material melting process heated from below using spectral collocation methods

Purpose – Mathematical and numerical models are developed to study the melting of a Phase Change Material (PCM) inside a 2D cavity. The bottom of the cell is heated at constant and uniform temperature or heat flux, assuming that the rest of the cavity is completely adiabatic. The paper used suitable numerical methods to follow the interface temporal evolution with a good accuracy. The purpose of this paper is to show how the evolution of the latent energy absorbed to melt the PCM depends on the temperature imposed on the lower wall of the cavity. Design/methodology/approach – The problem is written with non-homogeneous boundary conditions. Momentum and energy equations are numerically solved in space by a spectral collocation method especially oriented to this situation. A Crank-Nicolson scheme permits the resolution in time. Findings – The results clearly show the evolution of multicellular regime during the process of fusion and the kinetics of phase change depends on the boundary condition imposed on the bottom cell wall. Thus the charge and discharge processes in energy storage cells can be controlled by varying the temperature in the cell PCM. Substantial modifications of the thermal convective heat and mass transfer are highlighted during the transient regime. This model is particularly suitable to follow with a good accuracy the evolution of the solid/liquid interface in the process of storage/release energy. Research limitations/implications – The time-dependent physical properties that induce non-linear coupled unsteady terms in Navier-Stokes and energy equations are not taken into account in the present model. The present model is actually extended to these coupled situations. This problem requires smoother geometries. One can try to palliate this disadvantage by constructing smoother approximations of non-smooth geometries. The augmentation of polynomials developments orders increases strongly the computing time. When the external heat flux or temperature imposed at the PCM is much greater than the temperature of the PCM fusion, one must choose carefully some data to assume the algorithms convergence. Practical implications – Among the areas where this work can be used, are: buildings where the PCM are used in insulation and passive cooling; thermal energy storage, the PCM stores energy by changing phase, solid to liquid (fusion); cooling and transport of foodstuffs or pharmaceutical or medical sensitive products, the PCM is used in the food industry, pharmaceutical and medical, to minimize temperature variations of food, drug or sensitive materials; and the textile industry, PCM materials in the textile industry are used in microcapsules placed inside textile fibres. The PCM intervene to regulate heat transfer between the body and the outside. Originality/value – The paper's originality is reflected in the precision of its results, due to the use of a high-accuracy numerical approximation based on collocation spectral methods, and the choice of Chebyshev polynomials basis in both axial and radial directions.

On the use of a reduced model for the simulation of melting of solutions in DSC experiments

It is known that when studying the fusion of phase change materials (PCM) in differential scanning calorimetry (DSC) experiments, the geometry of the samples is not well known. Yet, some studies show that a numerical model, needing obviously to clearly define the shape of the sample, may reproduce the experimental DSC curve. In particular, such methods are currently applied to identification process based on inversion methods applied to the thermodynamical parameters governing the numerical model. Consequently, it means that if several numerical models are able to reproduce the thermal behavior of a PCM undergoing phase transition, the best one is the simplest one, that is to say the one which is the fastest to solve.Recently, we have thus shown that for pure substances PCM, a reduced model based on a spherical assumption for the shape of the sample leads to similar DSC curves that a more general model based on cylindrical shape.Clearly, if this result may be extended to other kinds of PCM, this will promote the capability of this method to be used in inversion process involved by identification process. The aim of the present paper is therefore to further study this method by considering non-pure materials, i.e. binary solution in the present case.

Thermal analysis of a double layer phase change material floor

Phase change materials (PCMs) can be used to shift the cooling or heating load from the peak period to the off-peak period. In this paper, a new double layer phase change material (PCM) floor is put forward. The two layers of PCM have different melting temperature. The system is used to store heat or cold energy in the off-peak period and release them in the peak period during heating or cooling. According to the numerical model built in this paper, the thermal performances of the floor are analyzed. The results show that the optimal melting temperatures of PCMs exist. The fluctuations of the floor surface temperatures and the heat fluxes will be reduced and the system still can provide a certain amount of heat or cold energy after the heat pump or chiller has been turned off for a long time. Compared to the floor without PCM, the energy released by the floor with PCM in peak period will be increased by 41.1% and 37.9% during heating and cooling when the heat of fusion of PCM is 150 kJ/kg.

Modelling and simulation of cyclic thermal regenerators utilizing encapsulated phase change materials (PCMs)

The operational behaviours of thermal storage systems utilizing the latent heat of fusion of phase change materials (PCM) are simulated for symmetric balanced/unbalanced conditions. A unified two-phase model, which accommodates the performance prediction of cyclic thermal regenerators with encapsulated PCM or conventional packing, is solved numerically by finite difference method. Extensive numerical results revealed the effect of various parameters on the performance of such systems. The comparison of the results with the literature data proves the accuracy of the developed model. Copyright © 2003 John Wiley & Sons, Ltd.

A simplification of the differential thermal analysis method to determine the latent heat of fusion of phase change materials

A simplified version of differential thermal analysis has been developed resulting in an inexpensive apparatus for determining the latent heat of fusion of phase change materials. The experimental results performed with three samples show that the present method yields results which agree within 5% with the measurements of sophisticated differential scanning calorimetry apparatus.