Phase Change Material Container Research Articles

Experimental investigations on stable supercooling performance of sodium acetate trihydrate PCM for thermal storage

Abstract Experiments have been performed on the stable supercooling characteristics of sodium acetate trihydrate (CH 3 COONa:3H 2 O) within three shapes of thermal storage units: sharp rectangular, rounded rectangular, and cylindrical. The phase change material (PCM) in the rounded rectangular unit was prone to be more stably supercooled than the PCM in the sharp rectangular one. The cylindrical unit is also desirable for stable supercooling but contains much less PCM. The effects of several factors on stable supercooling were then investigated in the rounded rectangular unit; these included charging time, cooling rate, the inner surface roughness of the PCM container, the carboxymethyl cellulose (CMC) content, and the salt–water mass ratio in mixture. The experimental results showed that more stable supercooling could be achieved with longer charging periods for fully melting crystals, a relatively lower cooling rate, an appropriate CMC content, and a lower inner surface roughness. Additionally, stable supercooling is achieved with the salt–water mass ratios of 3:2, 1:1, and 2:3 in mixture. The results in this paper will be useful for the unit and system design of solar energy seasonal storage for space heating, by utilizing the supercooled inorganic phase change materials.

Investigation of the corrosive properties of phase change materials in contact with metals and plastic

Phase change material (PCM) is used as a means of storing thermal energy. The method of PCM containment in thermal energy storage (TES) systems is important as the material is in direct contact with metal piping, plates and housing units which can be damaged if the material is corrosive. The compatibility of PCM with various materials for use in TES applications has been investigated using the immersion corrosion method and suggestions to minimise their corrosive behaviour or to mitigate it by using an alternative PCM have been presented and are described in the following paper. The metals and plastics tested were copper, brass, aluminium, stainless steel, mild steel and Perspex. These were immersed in five different PCM, three fatty acids, a salt hydrate and Micronal® for a period of 722 days. Stainless steel was determined to be the most suitable of all the PCM investigated. Aluminium can be used with all fatty acids, however caution is advised as the maximum corrosion rate was found to be 12.4 m g/cm2year. Copper and brass can be encapsulated using fatty acid and again caution is advised as corrosion rates were found to be 22.15 g/cm2year and 1.67 g/cm2year, respectively.

Heat transfer characteristics of coconut oil as phase change material to room cooling application

Thermal comfort in a room is one of human needs in the workplace and dwellings, so that the use of air conditioning system in tropical countries is inevitable. This equipment has an impact on the increase of energy consumption. One method of minimizing the energy use is by using the phase change material (PCM) as thermal energy storage. This material utilizes the temperature difference between day and night for the storage and release of thermal energy. PCM development on application as a material for air cooling inlet, partitioning and interior needs to be supported by the study of heat transfer characteristics when PCM absorbs heat from ambient temperature. This study was conducted to determine the heat transfer characteristics on coconut oil as a phase change material. There are three models of experiments performed in this research. Firstly, an experiment was conducted to analyze the time that was needed by material to phase change by varying the temperature. The second experiment analyzed the heat transfer characteristics of air to PCM naturally convection. The third experiment analyzed the forced convection heat transfer on the surface of the PCM container by varying the air velocity. The data of experimental showed that, increasing ambient air temperature resulted in shorter time for phase change. At temperatures of 30°C, the time for phase change of PCM with the thickness of 8 cm was 1700 min, and it was stable at temperatures of 27°C. Increasing air temperature accelerated the phase change in the material. While for the forced convection heat transfer, PCM could reduce the air temperature in the range of 30 to 35°C at about 1 to 2°C, with a velocity of 1-3 m/s.

Effect of PCM on temperature fluctuation during the door opening of a household refrigerator

ABSTRACTTemperature fluctuation inside the cabinet of a household refrigerator significantly affects the quality of preserved food. Phase change material (PCM) is a latent heat storage system that can store and release the heat energy by changing its phase from liquid to solid and solid to liquid respectively. Therefore, use of PCM inside the refrigerator cabinet has the potential for minimizing the temperature fluctuation during the door opening and the power failure. However, very few studies in the literature were dedicated to investigating the role of PCM to reduce the temperature fluctuation. The aim of this work is to experimentally investigate the effects of PCM on temperature fluctuation inside the cabinet of a household refrigerator during the door opening and power failure. The results found that a significantly lower temperature fluctuation can be obtained using PCM. It was found that during the door opening condition the air temperature in the cabinet rose rapidly. However, when a PCM container was used, temperature variation was reduced to 3–5°C. During the power failure, the system with PCM maintained a lower temperature inside the storage chamber for a long period of time (about 2 hours). Moreover, the test results indicate that PCM maintains more stable temperature in the foodstuffs inside the refrigerator. This reduction of temperature fluctuation ultimately improves the quality of preserved food.

응고/융해 잠열을 이용한 위성용 열제어장치의 실험적 연구

고상-액상 상변화물질(PCM, Phase Change Material)을 이용한 위성부품 열제어장치를 설계 및 제작하였으며 열환경시험을 수행함으로써 온도제어 성능을 분석하였다. 설계온도에 부합하는 n-Hexadecane을 PCM으로 채용하였고, 낮은 열전도도를 보완하기 위하여 내부에 전열휜이 장착된 용기를 Al6061로 제작하였다. 위성에 장착하였을 때와 동일한 작동조건을 확보하기 위하여, 부품과 방열판 사이를 열관으로 연결하였으며 열관의 단열부가 관통하도록 PCM 열제어장치를 설치하였다. 동일한 모양과 부피의 열적완충질량(TBM, Thermal Buffer Mass)도 제작하여, 주기적인 가열-냉각 실험을 수행하였다. 실험결과 상변화 잠열에 의한 PCM의 열제어 성능을 확인할 수 있었으며, TBM에 비하여 질량과 보온히터의 소모전력을 절감할 수 있음을 확인하였다. The thermal control device using solid-liquid phase change material (PCM) is designed, manufactured, and experimented in thermal environment chamber. The n-Hexadecane is selected as a PCM and its melting point is placed within the component working temperature range. The PCM container is made of Al6061 and has the thermal spreading fins inside. To simulate the working condition for on-orbit satellite the heat pipes are used to connect the heater and radiator and the PCM thermal control device (PCMTD) is installed at the middle portion of heat pipes. The thermal buffer mass (TBM), which is same configuration and volume with PCMTD, is also manufactured to compare the thermal control performance. As a result, the PCMTD is not only more efficient than TBM in their temperature control features but both mass and power of compensation heater are reduced.

The novel use of phase change materials in an open type refrigerated display cabinet: A theoretical investigation

In this paper, 2D CFD models have been developed for a prototype refrigerated open type multi-deck display cabinet with and without integrated phase change material (PCM). The models can predict the effect of adding a PCM container on cabinet efficiencies, air temperature distributions, product temperatures and air flow patterns inside the cabinet at a range of operating conditions including space air temperatures and evaporator air velocities. To validate the cabinet models, the prototype cabinet was mounted in an air conditioned chamber and extensive experiments were conducted at constant space air temperature and relative humidity. The cabinet models have therefore been validated through comparison with experiment results for air temperatures at different locations of the airflow path and of food products. Simulation results show that significant energy can be saved through the installation of a PCM container. Further benefits include greater stabilization of product temperatures during defrost periods for the modified display cabinet. Consequently, the validated models can be used to explore and analyse the cabinet performance and control strategies at various operating and design conditions.

Effect of installation angle of fins on melting characteristics of annular unit for latent heat thermal energy storage

Latent heat thermal energy storage (LHTES) technology can solve the problem of a mismatch between energy supply and demand in time, space and intensity and thus has become a research on focus in energy and environmental protection. The low thermal conductivity of phase change materials (PCMs) is the primary bottleneck of the popularization application of LHTES technology. An effective way to solve this problem is adding fins into the PCM container to enhance heat transfer, there has been no report on the effect of the installation location of fins on the heat transfer characteristics of the PCM in a LHTES unit. To study the effect of fins installed at different locations on the heat transfer, this work have investigated the melting characteristics of PCM in an annular with different installation angle of fins (θ) via a numerical simulation method, which is based on an enthalpy-porous medium model. In addition, the numerical calculation results are verified via experimentation. On this basis, the melting processes of the PCM in horizontal, annular units with fins installed at five different values of θ under three fixed wall temperature conditions (60, 70, and 80°C) have been simulated. The simulation results have been compared to those of the unit without fins. The results show that although fins inhibit natural convection, the addition of fins can lead to an increase in the melting rate and a decrease in the melting time due to an increase in the total amount of heat exchanged. Considering the entire melting process, the melting rate of the PCM in the unit with fins installed at θ=0° is maximum. When θ reaches 45°, the further increase of θ has no marked impact on the melting rate of the PCM in the unit. Based on the trend of the change of the mean Nusselt number with the Fourier number (Fo), the heat transfer of the melting process of the PCM is divided into four stages. Additionally, the dimensionless criterion relationship between the melting fraction (f) and SteFoRa1/6 when θ=0° is fitted as f=0.24X3-1.13X2+1.82X, where X=SteFoRa1/6.

Thermal stress analysis of PCM containers for temperature smoothing of waste gas

This article develops an analytical and numerical approach to evaluate thermal stress in a phase change material (PCM) system, used for temperature smoothing of waste gas of Electric Arc Furnace, in which the PCM is encapsulated in a cylindrical steel container. Thermal analysis shows that temperature distribution in the PCM system can be considered as uniform at any time instant according to the lumped capacitance method; the thermal behaviour of PCM system is thus simulated as a sequence of steady state analyses. Mechanical analysis adopts an axialsymmetric plane analytical model to compare elastic thermal stress distribution for different stainless steels and to identify AISI 316 as the most suitable material for the PCM container. A simple two-bars model and a stress index are also used to allow a physical understanding and a satisfactory interpretation of the PCM system response. Mechanical analysis shows that thermal stresses exceed the yield point of both stainless steels used in the container. A finite element elastic-plastic model is then developed to estimate the extension of the plastic zone. Finally, an alternative PCM system geometry based on concentric pipes is designed to keep the maximum stresses in the PCM container below the yielding point. A sensitivity analysis shows that the most relevant design parameters of the alternative geometry are the diameter of inner pipe and thickness of the external pipe.

Experimental investigation of thermoelectric generator (TEG) with PCM module

In the paper, the results of experimental investigation of thermoelectric generator (TEG) are presented. The model of TEG was designed for the use of solar radiation as a heat source. An important feature of the design under study is the method of cooling of thermoelectric modules. Phase change material (PCM) absorbs heat during its melting, thus stabilizing temperature of the cool side of TEG. Basic performance characteristics, i.e. voltage and current generated vs. time, were measured during tests conducted for different electrical configurations of the unit, and for different heat fluxes on hot side of TEG. Temperature distributions in PCM container during the operation of TEG were also recorded. The reverse operation of TEG, i.e. when heat earlier accumulated in PCM is utilized, was tested as well. The results confirmed the potential of the application of phase change materials as a cooling/heating media in TEGs.

Numerical Investigation on Vertical Generator Integrated with Phase Change Materials in Vapour Absorption Refrigeration System

A model has been established based on numerical calculation to analyze a vertical tube in tube stainless steel generator with forced convective boiling. Refrigerant vapour is generated from the weak refrigerant-absorbent solution takes place in the middle tube of the generator, when hot water through the outer side is used as boiling medium and the pipe arrays inserted is the phase change material containment. This paper shows the results of the TRNSYS modeling and simulation of a solar absorption cooling system under the weather conditions of Chennai in order to partially satisfy the thermal demand of a building room. The maximum hourly thermal load reaches 165 kW. The suggested model operates with concentrating parabolic collectors, a NH3-H2O single effect absorption air-conditioning system, hot water storage with PCM and an external auxiliary boiler. As a result of the method simplifying for the varying climate and different orientation of the components are analyzed. These outcomes show that the prime system could succeed a yearly solar fraction of 0.58.

Integration of PCM in domestic hot water tanks: Optimization for shifting peak demand

Most of the current domestic hot water tanks store heat in sensible form. Latent heat storage systems have become popular recently due to their capacity of storing energy in high density with slight temperature variation. They use phase change materials (PCMs) as the storage medium which have a high heat of fusion and are able to store and release large amount of energy.This paper reports the outcomes of implementing PCM in a standard domestic hot water tank, on energy consumption and the discharge period and suggests a method for optimization of the tanks regarding their discharge time. Geometrical aspects of PCM containers and the amount of PCM inside the tank were design parameters of this study. TRNSYS was used to simulate the behavior of the tank with PCM. Artificial neural network was used to find a correlation between design parameters of the tank and the discharge time. Genetic Algorithm was then used in order to find the optimum amount of PCM needed for a desired peak shift.Finally, a comparison between an optimized tank with PCM and a tank without PCM was performed and it was concluded that an optimized tank is able to provide hot water while consuming less energy compared to the regular one (without PCM). Furthermore, by applying a certain amount of PCM, electrical energy consumption could be shifted completely to off peak periods characterized by less power demand.

Lattice Boltzmann application on the PCM solidification within a rectangular finned container

This work presents an application of lattice Boltzmann method (LBM) for solidification of phase change material (PCM) within a rectangular finned container. To do this, an implicit lattice Boltzmann method is applied into two rectangular containers. At first the problem of PCM solidification within a rectangular fined container with constant wall temperatures is solved and compared with available approximate analytical results. The LBM results are compared with results of finite volume method (FVM), and then it was used to analyze accuracy condition for presenting the analytical solutions. Second, the LBM is used to obtain the temperature distribution through the composite plane wall containing rectangular PCM container with convective boundary conditions. The effect of PCM within the composite plane wall is studied as a heat source during freezing. It is shown that locating the PCM container inside the wall could efficiently prevent the heat losses, when it is exposed to the cold air flow, and the rate of solidification is extremely controlled by containers material. Also, it is confirmed that the current LBM effectively saves the running time several times compared to finite volume method.

Review on Heat Transfer Mechanisms and Characteristics in Encapsulated PCMs

Latent heat storage (LHS) is a particularly promising technique compared with the conventional sensible heat storage (SHS) as it provides a high-energy storage density with a small volume. However, there are difficulties in practical engineering applications of LHS due to the heat releasing/absorbing, which involves phase transition and moving boundary problems and the unacceptable low thermal conductivity of the phase-change material (PCM). Furthermore, the encapsulation would affect the heat transfer characteristics of PCM significantly, depending on the parameters of various encapsulations and boundary conditions. Hence, this review analyzes heat transfer mechanisms during the phase-change process and numerical analysis for heat transfer in macroencapsulated PCMs according to the shape of containment. The effective heat capacity method and the enthalpy method, two of the most widely used numerical approaches for phase-change problems, are presented in detail. Besides numerical models for different PCM containment such as spherical, rectangular, and cylindrical containment models, PCM-based heat-sink models are reviewed, including several heat transfer enchantment technologies: finned structure and porous matrix. Finally, the challenges in numerical modeling and designing an LHS unit are also summarized in this article.

An experimental study on heat transfer characteristics of paraffin wax in horizontal double pipe heat latent heat storage unit

An experimental study is conducted to investigate the melting and solidification processes of paraffin wax as a phase change material (PCM) in horizontal double pipe heat latent heat storage unit. The present work on phase change process includes study of temperature variations along the axial distances in PCM, determination of heat transfer coefficient as well as the heat flow rate. A series of experiments was conducted to investigate the effect of increasing the inlet temperature and the mass flow rate of the heat transfer fluid (HTF) both on the charging and discharging processes of the PCM. The experimental results show that the PCM melts and solidifies congruently, and the melting front moves from the left to right side of the PCM container whereas the solidification front moves from right to the left along the axial distances in the PCM container. The results indicate that natural convection dominates the melting process in the liquid phase due to buoyancy effects. On the other hand, the solidification process is dominated by conduction. The flow rate and inlet temperature of the HTF in the experiment range has a significant effect on the phase change processes. The results also indicate that the heat transfer coefficient between the HTF and the PCM was affected by the Reynolds number more during the melting process than during the solidification process. Heat flow rate during the melting and solidification process increased by 25% and 11%, respectively, in the case of increase or decrease by 2°C of the inlet HTF temperature. The results of this study show that by increasing the inlet water temperature from 70°C to 74°C, total melting time can be decreased by 31%.

An experimental investigation on the combined use of phase change material and rock particles for high temperature (∼350 °C) heat storage

The intermittent nature of solar energy requires integration of an energy storage system with solar collector devices in order to have un-interrupted supply of energy in the absence of the availability of solar energy. The use of Phase Change Material (PCM) and rock bed for heat storage has been studied in the past decades. However, limited knowledge exists on the use of the combination of PCM and rock particles for high temperature heat storage with air as the medium of heat transfer. The aim of this paper is to show experimentally by means of comparison, the thermal behaviours of thermal energy storage with only rocks and that with rocks and PCM. A heat storage consisting of only rocks and that with rocks and PCM has been designed and built. The PCM material used is a mixture of NaNO3 and KNO3 in the ratio of 60:40 percent (mol%). The charging and thermal de-stratification profiles were investigated for both cases. The results showed that the introduction of PCM cylinders in a bed of rocks for heat storage does not only increase the energy content of the storage but it also increases the vertical thermal conductivity. The increase in vertical thermal conductivity is attributed to the high thermal conductivity of the PCM container material.

Parametric studies on packed bed storage unit filled with PCM encapsulated spherical containers for low temperature solar air heating applications

The focus of the present work is to perform parametric studies on the performance of a packed bed storage unit filled with phase change material (PCM) encapsulated spherical containers, suitable for low temperature solar air heating applications. A parametric analysis was carried out using the validated enthalpy based numerical model that considers the thermal gradient inside the PCM container. The results of simulation analysis showed that the size of the PCM ball, fluid inlet temperature and the mass flow rate of the heat transfer fluid (HTF) influenced respectively the heat transfer area in the packed bed, temperature difference between the HTF and PCM and the surface convective heat transfer coefficient between the HTF and PCM balls. The poor thermal conductivity of the PCM has only negligible effect on heat transfer due to high surface convective resistance provided by the air. The influence of various parameters for the selected range of values were analyzed using the charging time, instantaneous heat stored and cumulative heat stored during the charging process.

Analysis of a thermal energy storage system for air cooling–heating application through cylindrical tube

In order to reduce building energy consumption, thermal energy storage (TES) system has been explored as an alternative solution for air cooling–heating application. Different types of phase change materials (PCMs) along with the different geometries of TES system have been investigated for this application. In this work, a theoretical model was used to analyse the TES system for air cooling–heating application. The heat transfer phenomena in a phase change material (PCM) outside a double wall circular tube with heat transfer fluid (HTF) as air inside the tube were studied. Potassium fluoride tetrahydrate was used as a PCM for the TES system. Laminar forced convection with varying wall temperature was considered to analyse this system. Here, some important design parameters like inner radius and thickness of the tube for HTF flow were also investigated. It was found that an optimum inner radius and thickness of the tube should be considered to design a TES system. Since, significant change in outlet air temperature from the system was observed for reducing inner radius and increasing the thickness of the tube. The coefficients of performances (COPs) for cooling were found 8.79 and 7.20 for 15mm and 25mm inner radiuses of the PCM container respectively. Hence, the system can be optimized by reducing the volume of the PCM container. Furthermore, better COP was observed for higher inlet air temperature while the outlet air temperature was almost identical.

Exact solution of thermal energy storage system using PCM flat slabs configuration

An analytical investigation of thermal energy storage system (TESS) consisting of several flat slabs of phase change material (PCM) is presented. The working fluid (HTF) circulating on laminar forced convection between the slabs charges and discharges the storage unit. The melting and solidification of the PCM was treated as a radial one dimensional conduction problem. The forced convective heat transfer inside the channels is analyzed by solving the energy equation, which is coupled with the heat conduction equation in the PCM container. The comparison between the present exact solution with the numerical predictions and experimental data available in literature shows good agreement. The charging/discharging process is investigated in terms of liquid–solid interface position, liquid fraction, total heat transmitted to the PCM and thermal storage efficiency for various HTF working conditions and different design parameters such as PCM slab length, fluid passage gap and thickness of PCM duct container.

Root zone temperature control with thermal energy storage in phase change materials for soilless greenhouse applications

A new root zone temperature control system based on thermal energy storage in phase change materials (PCM) has been developed for soilless agriculture greenhouses. The aim was to obtain optimum growing temperatures around the roots of plants. The candidate PCMs were 40% oleic acid–60% decanoic acid mixture and oleic acid alone. Field experiments with these PCMs were carried out in November 2009 with Cucurbite Pepo and March 2010 with Capsicum annum plants. No additional heating system was used in the greenhouse during these periods. In the November 2009 tests with zucchini, 40% oleic acid+60% capric acid mixture was the PCM and a temperature increase in the PCM container (versus the control container) was measured as 1.9°C. In our March 2010 tests with peppers, both PCMs were tried and the PCM mixture was found to be more effective than using oleic acidalone. A maximum temperature difference achieved by the PCM mixture around the roots of peppers was 2.4°C higher than that near the control plants.

Corrosion of metal and polymer containers for use in PCM cold storage

Transport and storage of low temperature sensitive products is an issue worldwide due to changes of the lifestyle and population increase. In the recent years, thermal energy storage (TES) using phase change materials (PCMs) is being highly studied and developed for cold storage applications. Furthermore, the PCM are normally encapsulated in containers and added in the available systems, usually in food processes. Therefore safety constraints as the compatibility of the PCM with other materials have to take into account. Hence the main goal of the paper is to study the corrosion effect of different metals and polymer materials in contact with some PCM used in low temperature applications. Results show that copper and carbon steel must be avoided as PCM containers, and aluminium is not recommended; stainless steel 316 is recommended when in contact with the tested PCM. Moreover, PP, PS, PET, and HDPE are not affected by a process of degradation and are also compatible with the PCM studied.