Time-Temperature Charge Function of a High Dynamic Thermal Heat Storage with Phase Change Material

A thermal heat storage system with an energy content of 40 kWh and a temperature of 58°C will be presented. This storage system is suitable for supporting the use of renewable energies in buildings and for absorbing solar heat, heat from co-generation and heat pumps or electric heat from excess wind and solar power. The storage system is equipped with a plate heat exchanger that is so powerful that even with small temperature differences between the flow temperature and the storage temperature a high load dynamic is achieved. The storage system has a performance of 2.8 kW at 4 K and 10.6 kW at a temperature difference of 10 K. Thus, large performance variations in solar thermal systems or CHP plants can be buffered very well. Further a storage charge function Q(T, t) will be presented to characterize the performance of the storage.

The Effects of Thickness and Location of PCMon the Building’s Passive Temperature-Control–A Numerical Study

Building energy consumption and building carbon emissions both account for more than 20%of their total national values in China.Building employing phase change material(PCM)for passive temperature control shows a promising prospect in meeting the comfort demand and reducing energy consumption simultaneously.However,there is a lack of more detailed research on the interaction between the location and thickness of PCM and indoor natural convection,as well as indoor temperature distribution.In this study,the numerical model of a passive temperature-controlled building integrating the developed PCM module is established with the help of ANSYS.In which,the actual weather condition of Beijing city is set as the boundary conditions and the indoor natural convection is simulated with the consideration of radiation model.The effects of PCM’s thickness and location on the internal temperature field are analyzed and discussed.The results show that the room could maintain within the human comfort temperature range with the longest ratio of 94.10%and the shortest ratio of 51.04%as integrating PCM.In comparison,the value is only 26.70%without PCM.The room’s maximum temperature fluctuation can also be improved;it could be lowered by 64.4%compared to the normal condition.When the quantity of PCM is sufficient,further increasing the PCM amount results in a temperature fluctuation reduction of less than 0.1°C and does not increase the comfort time.Placing PCM on the wall induces an apparent variation in indoor temperature along the vertical direction.Conversely,placing PCM on the roof can lead to a heat transfer rate difference of up to seven times.The optimal placement of PCM depends on the difference between the environmental and phase change temperatures.If the difference is positive,placing PCM on the roof is more effective;conversely,the opposite holds.According to the results over the entire cycle,PCM application on vertical walls yields better performance.The significant difference in natural convection caused by the same thickness of PCM but different application positions,coupled with the influence of air movement on the melting and solidification of PCM,further impacts indoor temperature fluctuations and comfort.This study can provide guidance for the application location and thickness of PCM,especially for scenarios where temperature regulation is required at a specific time.

Numerical Investigation of the Thermal Behavior of a System with a Partition Wall Incorporating a Phase Change Material

The work deals with the thermal behavior of a conventional partition wall incorporating a phase change material(PCM).The wall separates two environments with different thermal properties.The first one is conditioned,while the adjacent space is characterized by a temperature that changes sinusoidally in time.The effect of the PCM is assessed through a comparative analysis of the cases with and without PCM.The performances are evaluated in terms of dimensionless energy stored within the wall,comfort temperature and variations of these quantities as a function of the amount of PCM and its emplacement.

Performance of a Phase Change Material Battery in a Transparent Building

This research evaluates the performance of a Phase Change Material(PCM)battery integrated into the climate system of a new transparent meeting center.The main research questions are:a.“Can the performance of the battery be calculated?”and b.“Can the battery reduce the heating and cooling energy demand in a significant way?”The first question is answered in this document.In order to be able to answer the second question,especially the way the heat loading in winter should be improved,then more research is necessary.In addition to the thermal battery,which consists of Phase Change Material plates,the climate system has a cross-flow heat exchanger and a heat pump.The battery should play a central role in closing the thermal balance of the lightweight building,which can be loaded with hot return or cold outdoor air.The temperature of the battery plates is monitored by multi-sensors and simulated by the use of PHOENICS(Computational Fluid Dynamics)and MATLAB.This paper reports reasonable agreement between the numerical predictions and the measurements,with a maximum variance of 10%.The current coefficient of performance for heating and cooling is already high,more than 27.There is scope for increasing this much further by making use of the very low-pressure difference of the battery(below 25 Pascal),low pressure fans and the ventilation system as a whole.

Study on Phase Change Material in Grooved Bricks for Energy Efficiency of the Buildings

Phase change materials(PCMs)are an interesting technology due to their high density and isothermal behavior during phase change.Phase change material plays a major role in the energy saving of the buildings,which is greatly aided by the incorporation of phase change material into building products such as bricks,cement,gypsum board,etc.In this study,an experiment has been conducted with three identical small chambers made up of normal,grooved and PCM-treated grooved bricks.Before the inclusion of PCM in grooved bricks,PCM material behavior has been studied by different techniques such as DSC,TG/DTA,SEM,and XRD.Thermal properties and thermal stability were investigated by differential scanning calorimeter(DSC)and thermogravimetric analyzer(TGA)respectively.Scanning electron microscopy(SEM)and X-ray diffraction(XRD)were used to determine the microstructure and crystalloid phase of the PCM before and after the accelerated thermal cycling test(0,60,120).These three identical model rooms built were exposed at a temperature just above 40°C with a heater.When the maximum outdoor temperature was 40-41°C,then the temperature of the PCM-treated grooved chamber was 32-33°C.The PCM-treated wall was tested and compared with a conventional and grooved wall.The difference between the PCM-treated grooved chamber and the untreated one was 8-9°C.PCM-treated bricks provided more efficient internal heat retention in summer when the outside temperature increased.

Feasibility Research of Using Phase Change Materials to Reduce the Inner Temperature Rise of Mass Concrete

In order to evaluate the feasibility of using phase change materials to reduce the inner temperature rise of mass concrete, the interior temperature of normal concrete specimen under semi-adiabatic curing condition was measured. The effect of embedding phase change material(PCM) and replacing water with suspension of phase change material(SPCM) as cooling fluid were compared in the experiment. The cooling effect and the affecting factors were analyzed and calculated. The research results showed that the peak of inner temperature could be decreased obviously by the method of pre-embeding PCM in concrete, however, this method is only effective in the initial stage of cement hydration process. Besides, the volume of PCM is rather big and the PCM can not be used circularly, which means that this method can only be used under special condition and the feasibility is low. When SPCM was used as cooling fluid, the interior temperature rise of mass concrete was reduced more effectively, and the temperature grads peak around the cooling pipe was also reduced. Besides, both the SPCM consumption amount and the circulation time were decreased, and most important is that the SPCM is recyclable. The technical and economical feasibility of using SPCM to reduce the inner temperature rise of mass concrete is high.

Application of phase diagram calculations to development of new ultra-high temperature structural materials

In-situ refractory metal intermetallic composites(RMICs) based either on (Nb, Si) or (Mo, Si, B) are candidate materials for ultra-high temperature applications (>1400 ℃). To provide a balance of mechanical and environmental properties, Nb-Si composites are typically alloyed with Ti and Cr, and Mo-Si-B composites are alloyed with Ti. Phase diagrams of Nb-Cr-Ti-Si and Mo-Si-B-Ti, as prerequisite knowledge for advanced materials design and processing development, are critically needed. The phase diagrams in the metal-rich regions of multicomponent Nb-Cr-Ti-Si and Mo-Si-B-Ti were rapidly established using the Calphad (Calculation of phase diagram) approach coupled with key experiments. The calculated isotherms, isopleths, and solidification paths were validated by experimental work. The important heterogeneous multiphase equilibria in both quaternary systems identified will offer engineers the opportunity to develop materials with a balance of properties for high-temperature applications.

Direct incorporation of paraffin wax as phase change material into mass concrete for temperature control: mechanical and thermal properties

Taking advantage of heat absorbing and releasing capability of phase change material(PCM),Paraffin wax-based concrete was prepared to assess its automatic temperature control performance.The mechanical properties of PCM concrete with eight different Paraffin wax contents were tested by the cube compression test and four-point bending test.The more Paraffin wax incorporated,the greater loss of the compressive strength and bending strength.Based on the mechanical results,four contents of Paraffin wax were chosen for studying PCM concrete's thermal properties,including thermal conductivity,thermal diffusivity,specific heat capacity,thermal expansion coefficient and adiabatic temperature rise.When the Paraffin wax content increases from 10%to 20%,the thermal conductivity and the thermal diffusivity decrease from 7.31 kJ/(m·h·°C)to 7.10 kJ/(m·h·°C)and from 3.03×10−3 m2/h to 2.44×10−3 m2/h,respectively.Meanwhile the specific heat capacity and thermal expansion coefficient rise from 5.38×10−1 kJ/(kg·°C)to 5.76×10−1 kJ/(kg·°C)and from 9.63×10−6/°C to 14.02×10−6/°C,respectively.The adiabatic temperature rise is found to decrease with an increasing Paraffin wax content.Considering both the mechanical and thermal properties,15%of Paraffin wax was elected for the mass concrete model test,and the model test results confirm the effect of Paraffin wax in automatic mass concrete temperature control.

High-stability temperature control and frequency-domain analysis of sandwich-like insulation design based on phase change materials for satellite thermal management

High-stability thermal management is critical for the measurements of high sensitivity for temperature, but also challenging because any small thermal disturbances could lead to unacceptable temperature fluctuations. The present work delivers a design for passive temperature control, customized for a component in the satellites for gravitational wave detection. A novel sandwichlike structure is proposed with the configurations of proper materials, consisting of a layer of insulation material and two layers of nanocomposite phase change materials, bringing an integration of heat insulation and absorption/storage. Its performance is examined using an improved thermal network model and the revised transfer function method(TFM). The basic results of the two methods are validated by present COMSOL simulations and available numerical and experimental data in the literature. An effective reduction of temperature fluctuation is achieved to the scale of 0.1 K, even under two thermal disturbances from different directions: a radiative heat flux of 20 W m~(-2)(inside) and a temperature fluctuation of about 20 K(outside). Moreover,the TFM is employed to analyze the effects of the frequency of thermal disturbance: excellent damping performance is obtained for over 3.2 mHz and the underlying mechanism is discussed. Overall, the present design is expected to be combined with active temperature control to explore more possible ways for temperature control with higher stability.

PDMS包封CPCM制备三明治结构织物及热性能分析

为解决正十八烷在使用过程中的相泄露问题,以细菌纤维素膜为支撑载体、聚二甲基硅氧烷为包封材料,通过真空浸渍和热固处理制备形稳性复合相变材料。正十八烷浸渍率高达84.9%,潜热能为212.70 J/g,可经受100次热循环测试。经180°弯折后回弹角为156.4°,回弹角相较于包封前提高了131.7%。以复合相变材料为中间层、涤棉混纺织物为外层,经由聚二甲基硅氧烷粘合和固化处理,制得三明治结构织物。吸热饱和后,三明治织物表面温度比普通织物延时降温310 s,在日照模型和人体热管理测试中其覆盖的空间内部温度比普通织物覆盖处降低0.9℃,显示出优异的储热和隔热性能。

Preparation and Properties of Paraffin/PMMA Shape-stabilized Phase Change Material for Building Thermal Energy Storage

The composite phase change material(PCM) consisting of phase change paraffin(PCP) and polymethyl methacrylate(PMMA) was prepared as a novel type of shape-stabilized PCM for building energy conservation through the method of bulk polymerization. The chemical structure, morphology, phase change temperature and enthalpy, and mechanical properties of the composite PCM were studied to evaluate the encapsulation effect of PMMA on PCP and determine the optimal composition proportion. FTIR and SEM results revealed that PCP was physically immobilized in the PMMA so that its leakage from the composite was prevented. Based on the thermo-physical and mechanical properties investigations, the optimal mass fraction of PCP in the composite was determined as 70%. The phase change temperature of the composite was close to that of PCP, and its latent heat was equivalent to the calculated value according to the mass fraction of PCP in the composite. For estimating the usability in practical engineering, thermal stability, reliability and temperature regulation performance of the composite were also researched by TG analysis, thermal cycling treatments and heating-cooling test. The results indicated that PCP/PMMA composite PCM behaved good thermal stability depending on the PMMA protection and its latent heat degraded little after 500 thermal cycling. Temperature regulation performance of the composite before and after thermal cycling was both noticeable due to its latent heat absorption and release in the temperature variation processes. The PCP/PMMA phase change plate was fabricated and applied as thermal insulator in miniature concrete box to estimate its temperature regulation effect under the simulated environmental condition. It can be concluded that this kind of PCP/PMMA shape-stabilized PCM with the advantages of no leakage, suitable phase change temperature and enthalpy, good thermal stability and reliability, and effective temperature regulation performance have much potential for thermal energy storage in building energy conservation.

Heat transfer and parametric studies of an encapsulated phase change material based cool thermal energy storage system

This work investigates the transient behaviour of a phase change material based cool thermal energy storage (CTES) system comprised of a cylindrical storage tank filled with encapsulated phase change materials (PCMs) in spherical container integrated with an ethylene glycol chiller plant. A simulation program was developed to evaluate the temperature histories of the heat transfer fluid (HTF) and the phase change material at any axial location during the charging period. The results of the model were validated by comparison with experimental results of temperature profiles of HTF and PCM. The model was also used to investigate the effect of porosity, Stanton number, Stefan number and Peclet number on CTES system performance. The results showed that increase in porosity contributes to a higher rate of energy storage. However, for a given geometry and heat transfer coefficient, the mass of PCM charged in the unit decreases as the increase in porosity. The St number as well as the Ste number is also influential in the performance of the unit. The model is a convenient and more suitable method to determine the heat transfer characteristics of CTES system. The results reported are much useful for designing CTES system.

Role of Composite Phase Change Material on the Thermal Performance of a Latent Heat Storage System: Experimental Investigation

Paraffin wax is a perfect phase change material(PCM)that can be used in latent heat storage units(LHSUs).The utilization of such LHSU is restricted by the poor conductivity of PCM.In the present work,a metal foam made of aluminium with PCM was used to produce a composite PCM as a thermal conductivity technique in PCM⁃LHSU and water was used as heat transfer fluid(HTF).An experimental investigation was carried out to evaluate the heat transfer characteristics of LHSU using pure PCM and composite PCM.The study included time⁃dependent visualization of the PCM during the melting and solidification processes.Besides,a thermocouple network was placed inside the heat storage to record the temperature profile during each process.Results showed that better performance could be obtained using composite PCM⁃LHSU for both melting and solidification processes.The melting time of composite PCM⁃LHSU was about 83%faster than that of a simple PCM⁃LHSU,and the percentage decreasing in the solidification time was about 85%due to the provision of metal foam.

Parametric Study on Phase Change Material Based Thermal Energy Storage System

The usage of phase change materials (PCM) to store the heat in the form of latent heat is increased, because large quantity of thermal energy is stored in smaller volumes. In the present experimental investigation, sodium thiosulphate pentahydrate is employed as phase change material and it is stored in stainless steel capsules. These capsules are kept in fabricated tank and hot water is supplied into it. The experimental design is prepared by considering the parameters: flow rate, heat transfer fluid inlet temperature and PCM capsule shape. Experiments are conducted according to the experimental design and responses are recorded. The effect of selected parameters on TES using PCM is studied by analyzing experimental data. The experimental data are also analyzed using Fuzzy Logic to find the optimal values of flow rate, heat transfer fluid inlet temperature and PCM capsule shapes. The present work utilizes Fuzzy Logic to find the optimal parameters for designing the effective Thermal Energy Storage System (TES).

Green's function solution for transient heat conduction in annular fin during solidification of phase change material

The Green＇s function method is applied for the transient temperature of an annular fin when a phase change material （PCM） solidifies on it. The solidification of the PCMs takes place in a cylindrical shell storage. The thickness of the solid PCM on the fin varies with time and is obtained by the Megerlin method. The models are found with the Bessel equation to form an analytical solution. Three different kinds of boundary conditions are investigated. The comparison between analytical and numerical solutions is given. The results demonstrate that the significant accuracy is obtained for the temperature distribution for the fin in all cases.

Optimum Distribution of Two Different Phase Change Materials between Various Components of Roof Air-Conditioned Room, Suitable to Reduce Annual Energy Consumption

Obviously, the outside annual climate change caused either by a major solar input during the hottest period or by a temperature drop during the coldest period leads to discomfort in inside buildings. This effect can be reduced by storing heat transmitted in phase change materials (PCM) as latent heat, in order to ensure a good situation of thermal comfort during all months of the year. In this work, thermal behavior of two roofing systems is studied. One roof is constituted only by usual materials in building. In the other, two phase change materials (PCM) are introduced according to three configurations. Study is interested to assess incorporation effect of two PCMs within the roof and to evaluate the optimum locations to reduce the energy consumption of air-conditioned room. Mono-dimensional numerical model validated analytically and experimentally, is used to carry out a parametric analyzes to determine characteristics of the layers in which the roofs are formed regardless of external climate effect. Numerical calculations are performed for three configurations of roof. Results show that insertion of phase change materials in roof provides best energy consumption saving regardless annual climate change. Generally, the three configurations lead to different results, depending on the combination of PCMs. This difference becomes less important when selection of PCMs take account the thermal comfort level and temperatures of hottest and coldest periods.

A New Kind of Shape-stabilized Phase Change Materials

Based on the lowest melting point and Schroeder’s theoretical calculation formula,nano- modified organic composite phase change materials（PCMs）were prepared.The phase transition temperature and the latent heat of the materials were 24℃and 172 J/g,respectively.A new shape-stabilized phase change materials were prepared,using high density polyethylene as supporting material.The PCM kept the shape when temperature was higher than melting point.Thus,it can directly contact with heat transfer media.The structure,morphology and thermal behavior of PCM were analyzed by FTIR,SEM and DSC.

Effect of Phase Change Materials on the Thermal Protective Performance of the Multi-layered Fabrics Examined by TPP Tester under Flash Fire

Cotton fabrics treated with phase change materials( PCMs)were used in multi-layered fabrics of the fire fighter protective clothing to study its effect on thermal protection. The thermal protective performance( TPP) of the multi-layered fabrics was measured by a TPP tester under flash fire. Results showed that the utilization of the PCM fabrics improved the thermal protective performance of the multi-layered fabrics. The fabric with a PCM add on of 41. 9% increased the thermal protection by 50. 6% and reduced the time to reach a second degree burn by 8. 4 s compared with the reference fabrics( without PCMs). The employment of the PCM fabrics also reduced the blackened areas on the inner layers. The PCM fabrics with higher PCM melting temperature could bring higher thermal protective performance.

Heat Transfer Characteristics of Work Fluid Including Phase Change Material That Flow into Heating Surface from Narrow Path

Use of the low temperature (less than 100°C) energy contributes to effective use of heat resources. The cost recovery by power generation is difficult by using an existing system (the binary cycle or the thermoelectric conversion element), because the initial investment is large. The final purpose of this research is development of the low temperature difference drive engine supposing use in a hot-springs resort as a power source for electric power generation. In order that a traveler may look at and delight a motion of an engine, it is made to drive at low-speed number of rotations. An engine cycle of this study is aimed at the development of Stirling cycle engine which can maintain high efficiency in small size. This kind of engine has simple structure;it brings low cost, and it is easy to perform maintenance. However, it is difficult to obtain enough output by this type of engine, because of its low temperature difference. This paper deals with the heat transfer characteristic that the working fluid including a phase change material flows into the heating surface from the narrow path. In order to increase the amount of the heat transmission, Diethylether is added to the working fluid. Diethylether is selected as a phase change material (PCM) that has the boiling point which exists between the heat source of high temperature and low temperature. The parameters of the experiment are additive amount of PCM, rotational speed of the displacer piston and temperature of heat transfer surface. It is shown that it is possible to make exchange of heat amount increase by adding phase change material. The result of this research shows the optimal condition of the difference in temperature in heat processing, number of revolutions, and addition concentration of PCM.

Diphylleia Grayi-Inspired Intelligent Temperature-Responsive Transparent Nanofiber Membranes

Nanofiber membranes(NFMs) have become attractive candidates for next-generation flexible transparent materials due to their exceptional flexibility and breathability. However, improving the transmittance of NFMs is a great challenge due to the enormous reflection and incredibly poor transmission generated by the nanofiber-air interface. In this research, we report a general strategy for the preparation of flexible temperature-responsive transparent(TRT) membranes,which achieves a rapid transformation of NFMs from opaque to highly transparent under a narrow temperature window. In this process, the phase change material eicosane is coated on the surface of the polyurethane nanofibers by electrospray technology. When the temperature rises to 37 ℃, eicosane rapidly completes the phase transition and establishes the light transmission path between the nanofibers, preventing light loss from reflection at the nanofiber-air interface. The resulting TRT membrane exhibits high transmittance(> 90%), and fast response(5 s). This study achieves the first TRT transition of NFMs, offering a general strategy for building highly transparent nanofiber materials, shaping the future of next-generation intelligent temperature monitoring, anti-counterfeiting measures, and other high-performance devices.