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.

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.

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.

Simulation of the Hygrothermal Behavior of a Building Envelope Based on Phase Change Materials and a Bio-Based Concrete

Phase Change Materials(PCMs)have high thermal inertia,and hemp concrete(HC),a bio-based concrete,has strong hygroscopic behavior.In previous studies,PCM has been extensively combined with many materials,however,most of these studies focused on thermal properties while neglecting hygroscopic aspects.In this study,the two materials have been combined into a building envelope and the related hygrothermal properties have been studied.In particular,numerical studies have been performed to investigate the temperature and relative humidity behavior inside the HC,and the effect of adding PCM on the hygrothermal behavior of the HC.The results show that there is a high coupling between temperature and relative humidity inside the HC,since the relative humidity changes on the second and third days are different,with values of 8%and 4%,respectively.Also,the variation of relative humidity with temperature indicates the dominant influence of temperature on relative humidity variation.With the presence of PCM,the temperature variation inside the HC is damped due to the high thermal inertia of the PCM,which also leads to suppression of moisture evaporation and thus damping of relative humidity variation.On the second and third days,the temperature changes at the central position are reduced by 4.6%and 5.1%,compared to the quarter position.For the relative humidity change,the reductions are 5.3%and 5.4%on the second and third days,respectively.Therefore,PCM,with high thermal inertia,acts as a temperature damper and has the potential to increase the moisture buffering capacity inside the HC.This makes it possible for such a combined envelope to have both thermal and hygric inertia.

Fatty Acid/Expanded Graphite Encapsulating Form-Stable Phase Change Materials for Energy Storage

The lauric-myristic-palmitic acid( LA-MA-PA) ternary eutectic mixtures/expanded graphite( EG) composite phase change materials( PCMs) were prepared by absorbing LA-MA-PA into the porous network of EG. The optimum ratio of ternary eutectic mixtures to EG was determined to be 93∶7 without liquid LA-MA-PA leakage from the composite PCMs. In order to make the structure more stable, the composite PCMs were encapsulated by surface treatment agent to prepare LA-MA-PA/EG encapsulating form-stable PCMs which were characterized by scanning electron microscope( SEM),Fourier transformation infrared spectroscope( FT-IR),differential scanning calorimetry( DSC) and thermal treatment. The results showed there was no chemical reaction between surface treatment agent and LA-MA-PA,and the samples were compactly encapsulated which left almost no imprint on the filter paper after thermal treatment. The phase change temperature and latent heat of LA-MA-PA/EG encapsulating form-stable PCMs were tested to be29. 32 ℃ and 96. 20 J/g,respectively. Additionally,the heat transfer efficiency of heat storage was improved by the addition of EG.

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.

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.

Preparation and phase change performance of Na_2HPO_4·12H_2O@poly(lactic acid) capsules for thermal energy storage

Micro-encapsulated phase-change materials(micro PCMs) with Na_2 HPO_4·12 H_2 O encapsulated in poly(lactic acid)(PLA) shell were prepared by a solvent evaporation–precipitation method that involves the use of a coaxial needle. The effects of PLA concentration, stirring speed, injection rate of core and shell solutions, and polyvinyl alcohol(PVA) concentration on phase change properties were investigated. The thermal properties of microP CMs were characterized by differential scanning calorimetry(DSC). The capsules prepared under the optimal conditions are about 2 mm in diameter and show a latent heat of up to 122.2 J·g^(-1).

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.

Melting and Solidification Heat Transfer Characteristics of a Phase-Change Material in a Latent Heat Storage Vessel: Effects of a Perforated Partition Plate and Metal Fiber

Today, latent heat storage technology has advanced to allow reuse of waste heat in the middle-temperature range. This paper describes an approach to develop a latent heat storage system using middle-temperature waste heat (~100oC - 200oC) from factories. Direct contact melting and solidification behavior between a heat-transfer fluid (oil) and a latent heat storage material mixture were observed. The mixture consisted of mannitol and erythritol (Cm = 70 mass %, Ce = 30 mass %) as a phase-change material (PCM). The weight of the PCM was 3.0 kg and the flow rate of the oil, foil, was 1.0, 1.5, or 2.0 kg/min. To decrease the solidified height of the PCM mixture during the solidification process, a perforated partition plate was installed in the PCM region in the heat storage vessel. PCM coated oil droplets were broken by the perforated partition plate, preventing the solidified height of the PCM from increasing. The solidification and melting processes were repeated using metal fiber. It was found that installing the metal fiber was more effective than installing the perforated partition plate to prevent the flow out problem of the PCM.

Numerical Investigation on Heat Transfer Characteristics of Microencapsulated Phase Change Material Slurry in a Rectangular Minichannel

Microencapsulation phase change material slurry(MEPCMS) becomes a potential working fluid for cooling high energy density miniaturized components,thanks to the latent heat absorption of particles in the heat transfer process.In this work,the Discrete Phase Model(DPM) based on the Euler-Lagrangian method is used to numerically investigate the convective heat transfer characteristics of MEPCMS flowing through a rectangular minichannel with constant heat flux.The results show that particles of MEPCMS are mainly subjected to drag force during the flow.Even so,they can migrate from the high-temperature region to the low-temperature region driven by the thermophoretic force,affecting the particle distribution and phase change process.Moreover,the Nux of the MEPCMS fluctuates due to particle phase change with varying specific heat capacities.Specifically,the value increases first,then decreases,and eventually increases again until it approaches the fully developed value of the pure base fluid as the particles gradually melt.Furthermore,the heat transfer performance of the MEPCMS is influenced by the combination of fluid inlet temperature fluid inlet velocity(v),and mass concentration(c_(m)) of MEPCM particles.The result shows that the maximum reduction of the maximum bottom wall temperature difference(ΔT_(w)) is 23.98% at T_(in)=293.15 K,v=0.15 m·s^(-1),c_(m)=10%.

A one-step method for producing microencapsulated phase change materials

This short communication reports our recent work on the synthesis and characterisation ofmicrocapsules of phase change materials using silica as the shell material through a one-step method. The method uses no surfactants or dispersants for stabilising the capsules. The results show that the one-step method allows the tuning of the size and polydispersity of the capsules, and the use of different core materials. Analyses of the capsules show that they contain about 65% phase change materials. The results also suggest no need for a stabilising agent due to self-stabilisation by the amine groups. Further work is underway to investigate the mechanical and thermal properties of the microcapsules and the scale-up of the method.

Experimental Investigation of the Operating Characteristics of a Pulsating Heat Pipe with Ultra-Pure Water and Micro Encapsulated Phase Change Material Suspension

The specific heat capacity of working fluid is an important influence factor on heat transfer characteristic of the pulsating heat pipe(PHP).Due to the relatively large specific heat capacity of micro encapsulated phase change material(MEPCM) suspension,a heat transfer performance experimental facility of the PHP was established.The heat transfer characteristic with MEPCM suspension of different mass concentrations(0.5% and 1.0%) and ultra-pure water were compared experimentally.It was found that when the PHP uses MEPCM suspension as its working fluid,operating stability is impoverished under lower heating power and the operating stability is better under higher heating power.At the inclination angle of 90°,the temperature at heating side decreases compared to ultra-pure water and the temperature at heating side decreases with the raising of MEPCM suspension mass concentration.The heat transfer characteristic of the PHP is positively correlated with the inclination angle and the 90° is optimum.The unfavorable effect of the inclination angle decreases with heating power increasing.When the inclination angle is 90°,the PHP with MEPCM suspension at 1.0% of mass concentration has the lowest thermal transfer resistance and followed by ultra-pure water and MEPCM suspension at 0.5% of mass concentration has the highest thermal transfer resistance.When the inclination angles are 60° and30°,the effect of gravity on the flow direction is reduced to 86.6% and 50% of that on the inclination angle of 90°,respectively,and the promoting effect of gravity on the working fluid is further weakened as the inclination angle further decreases.Due to the high viscosity of MEPCM suspension,the PHP with ultra-pure water has the lowest heat transfer resistance.When the inclination angles is 60°,the thermal resistance with MEPCM suspension at0.5% of the mass concentration is lower than that at 1.0% at the heating power below 230 W.The thermal resistance of MEPCM suspension tends to be similar for heating power of 230-250 W.At the heating power above 270 W,the thermal resistance with MEPCM suspension at 1.0% of the mass concentration is lower than that at 0.5%.

Flow frictional characteristics of microencapsulated phase change material suspensions flowing through rectangular minichannels

An experimental investigation was conducted on the laminar flow frictional characteristics of suspensions with microencapsulated phase change material (MEPCM) in water flowing through rectangular copper minichannels. The MEPCM was provided at an average particle size of 4.97 μm, and was mixed with distilled water to form suspen- sions with various mass concentrations ranging from 0 to 20%. The experiment was per- formed to explore the effect of MEPCM mass concentration on friction factor and pressure drop in the minichannels. The Reynolds number ranged from 200 to 2000 to provide laminar and transitional flows. It was found that the experimental data for the suspensions with 0 and 5% concentration agree well with the existing theoretical data for an incom- pressible, fully developed, laminar Newtonian flow. For the suspensions with mass con- centrations higher than 10%, there is an obvious increase in friction factor and pressure drop in comparison with laminar Newtonian flow.

Synthesis and Characterization of Storage Energy Materials Prepared from Nano-crystalline Cellulose/Polyethylene Glycol

This paper gives a brief report of the synthesis of a new kind of solid-solid phase change materials （SSPCMs）, nano-crystalline cellulose/polyethylene glycol （NCC/PEG）. These PCMs have very high ability for energy storage, and their enthalpies reach 103.8 J/g. They are composed of two parts, PEG as functional branches for energy storage, and NCC as skeleton. The flexible polymer PEG was grafted onto the surface of rigid powder of NCC by covalent bonds. The results of DSC, FT-IR were briefly introduced, and some comments were also given.

Microencapsulation of stearic acid with polymethylmethacrylate using iron(Ⅲ) chloride as photo-initiator for thermal energy storage

Aiming to identify the validity of fabricating microencapsulated phase change material(PCM) with polymethylmethacrylate(PMMA) by ultraviolet curing emulsion polymerization method using iron(III) chloride as photoinitiator,SA/PMMA microcapsules were prepared and various techniques were employed to determine the ignition mechanism,structural characteristics and thermal properties of the composite.The results shown that the microcapsules containing SA with maximum percentage of 52.20 wt% formed by radical mechanism and only physical interactions existed in the components both in the prepared process and subsequent use.The phase change temperatures and latent heats of the microencapsulated SA were measured as 55.3 °C and 102.1 J·g^(-1) for melting,and 48.8 °C and 102.8 J·g^(-1) for freezing,respectively.Thermal gravimetric analysis revealed that SA/PMMA has good thermal durability in working temperature range.The results of accelerated thermal cycling test are all shown that the SA/PMMA have excellent thermal reliability and chemical stability although they were subjected 1000 melting/freezing cycles.In summary,the comparable thermal storage ability and good thermal reliability facilitated SA/PMMA to be considered as a viable candidate for thermal energy storage.The successful fabrication of SA/PMMA capsules indicates that ferric chloride is a prominent candidate for synthesizing PMMA containing PCM composite.

The Application of Microcapsule in the Infrared Stealth Camouflage

Infrared radiation is one of the main exposure symptoms of military targets. Infrared radiation differences between targets and backgrounds should be eliminated to the greatest extent to fight against all kinds of infrared reconnaissance. In addition to the employment of the camouflage paint with low emissivity, reducing the surface temperature of targets is an urgent and difficult challenge. PCM (phase-change material) can be used to effectively solve this problem. The application of microcapsule in the infrared stealth materials greatly promotes the development of infrared stealth technology.