Phase Change Material Particles Research Articles

Analysis of micro-dispersed PCM-composite boards behavior in a building's wall for different seasons

The integration of phase change materials (PCMs) in buildings especially in their walls is the subject of more than a decade of growing interest due to their potentialities for energy saving and enhancement of thermal comfort. The present investigation concerns the applications related to thermal insulation. The idealized composite wall considered here numerically can be thought of as resulting from the incorporation of shape-stabilized PCM particles in a polymer matrix. A novel model is developed to study the thermal behavior of this PCM-composite when used as a planar insulating material submitted to variable thermal modulations on one of its faces. The numerical model couples the heat transfer in the wall with the heat transfer and the crystallization/melting process within PCM inclusions considered as spherical. Both processes are modeled by a finite volume approach combined with the enthalpy method to account for the phase change. Simulation results are used to monitor the temperatures in the wall and quantify the energy exchanges between its two sides. The thickness of the wall and the volume fraction of the incorporated PCM were varied in this study. This analysis permits to point out the configurations for which the negative effect of the higher thermal conductivity of the PCM outweighs the benefits related to its latent heat. The analysis is extended to different external temperature modulations representing different typical seasons/climates. The results show the impact of the choice of the PCM phase change temperature on the wall thermal efficiency over the year. For the case investigated, it was shown that a PCM composite board with increased performances during a summer day exhibits a degraded behavior during a winter day when compared to a pure (without PCM) insulation material.

Numerical simulation of the heat transfer characteristics of a U-shaped thermosyphon containing a PCM suspension

The present study investigates the heat transfer characteristics of a U-shaped vertical closed-loop thermosyphon filled with a phase change material (PCM) suspension using numerical simulation. The loop is made of a copper pipe (outer diameter/inner diameter=1.46). The heating section and the cooling section are located at the bottom and top of the loop, respectively, and octadecane is used as the PCM. Parametric simulations were conducted using the pertinent physical parameters of a loop with a fixed geometrical configuration with the following parameter ranges: modified Rayleigh number Ra∗=5×103-5×105, modified Stefan number Ste∗=0.05-5, PCM suspension concentration fp=0–10%, PCM particle dimensionless diameter Dp=0.23–0.0023, and modified subcooling factor Sc∗=0.2-1.0. The results show that Ste∗ presents a critical value under the given parametric conditions; when Ste∗ is less than the critical value, the latent heat effect becomes significant, and the temperatures in the heating and adiabatic sections of the loop decrease considerably.

An experimental study of the latent functionally thermal fluid with micro-encapsulated phase change material particles flowing in microchannels

Phase change material holds a good promise as a media of thermal energy storage and intensive heat flux removal. In this context, experiments were conducted to investigate the hydrodynamic and thermodynamic properties of a latent thermal fluid, which consisted of water and well dispersed micro-encapsulated phase change material (MEPCM) particles, flowing in parallel microchannels. It is suggested that MEPCM particles loading induces much higher pressure drop, which is very sensitive to temperature. Compared against water, the heat transfer performance of MEPCM slurry performs much better owing to particles aggregation, collision and micro-convective around the particles. Besides these, latent heat absorbed during phase change process makes the key contribution. It is found that with melting occurrence, Nusselt number of the slurry with only 2% MEPCM particles would increase remarkably and achieves 1.36 times as that of pure water, which is very benefit to the thermal management system.

Properties of cementitious mortar and concrete containing micro-encapsulated phase change materials

More efficient energy usage in buildings with increased thermal mass and better thermal insulation has attracted considerable attention in recent years. As one the most widely used construction materials in the building industry, concrete has a great potential to be converted to a high performance thermal storage material by using phase change materials (PCMs). To demonstrate this, mortar and concrete mixes were blended with microencapsulated PCM as part replacement of fine aggregates and assessed for improved thermal performance. Specimens with varying amount of microencapsulated PCM were tested using calorimetry, differential scanning calorimetry (DSC), thermogravimetry (TGA), scanning electron microscopy (SEM), compressive strength and thermal conductivity. Results show that high specific surface of microencapsulated PCM particles has induced an acceleration of the cement hydration. However, the compressive strength at 28days is still decreased when fine aggregates were substituted by PCM. Contrary to past observations, microencapsulated PCM is observed to remain intact in the cementitious matrices and contributed significantly to improve the heat capacity as well as to reduce the thermal conductivity of the mixes tested. A blend with 20%·v/v replacement was identified as the optimum PCM replacement.

Thermophysical properties and thermal characteristics of phase change emulsion for thermal energy storage media

A great deal of attention has been paid to energy saving devices in place of conventional air-cooled and water-cooled devices. The thermal energy storage system that uses the latent heat of a PCM (phase change material) for air-conditioning or heating has recently become popular because it does not require high electric power and it saves energy. An emulsion dispersed nano-size particles of phase change material is produced. We discuss with the thermophysical properties, the stability of emulsion, and the heat transport characteristics as a thermal functional fluid. The testing emulsion, which has nano-size particles as the discrete phase, is produced with a d-phase emulsification method. The diameter of discrete phase in the emulsion is measured for evaluation of the long-term stability of emulsion. In addition, the DSC (differential scanning calorimetry) curve of emulsion is determined. Thermophysical properties such as viscosity and thermal conductivity of emulsions were studied in this work, and was compared with that of the base fluid. The results reveal that the emulsion with the d-phase emulsification method has the superior stability. From the differential thermal analysis, the DSC curve of present emulsion indicates a discontinuous change at the phase change temperature of phase change material due to its latent heat.

Building Energy Storage Panel Based on Paraffin/Expanded Perlite: Preparation and Thermal Performance Study.

This study is focused on the preparation and performance of a building energy storage panel (BESP). The BESP was fabricated through a mold pressing method based on phase change material particle (PCMP), which was prepared in two steps: vacuum absorption and surface film coating. Firstly, phase change material (PCM) was incorporated into expanded perlite (EP) through a vacuum absorption method to obtain composite PCM; secondly, the composite PCM was immersed into the mixture of colloidal silica and organic acrylate, and then it was taken out and dried naturally. A series of experiments, including differential scanning calorimeter (DSC), scanning electron microscope (SEM), best matching test, and durability test, have been conducted to characterize and analyze the thermophysical property and reliability of PCMP. Additionally, the thermal performance of BESP was studied through a dynamic thermal property test. The results have showed that: (1) the surface film coating procedure can effectively solve the leakage problem of composite phase change material prepared by vacuum impregnation; (2) the optimum adsorption ratio for paraffin and EP was 52.5:47.5 in mass fraction, and the PCMP has good thermal properties, stability, and durability; and (3) in the process of dynamic thermal performance test, BESP have low temperature variation, significant temperature lagging, and large heat storage ability, which indicated the potential of BESP in the application of building energy efficiency.

Dust ignition of pure and encapsulated paraffin phase change materials

In this study, the dependence of the flammable concentration on particle size is investigated for Phase Change Material (PCM) and Encapsulated Phase Change Material (EPCM) particles using a novel continuous particle dispersion apparatus into which a propane flame is introduced creating a test akin to the flash-point test for liquids. The results show that the threshold concentration is a strong function of particle size. For tested particles with size ranging from 290 μm to 750 μm, the threshold concentration is above the predictions based on an instantaneous heat transfer limit, and is approximately linear with the particle size, following a heat transfer limited ignition model. For sizes above ≈1 mm, the particles behave like the bulk material, and ignition is not observed for the concentrations tested. The results obtained here are important for the safe construction, handling, and operation of systems using PCM and other particles.

Predicting Mechanical and Thermal Behavior of Multiphase Composite Containing Phase Change Material (PCM) by Micromechanical Approaches

This work is devoted to the study of thermal and mechanical properties (stiffness and thermal conductivity tensors) of multiphase composite materials (mortar with PCMs). A micro-macro modeling is presented in order to predict these properties by using some classical homogenization schemes. The effective thermo-mechanical behavior is then analyzed by considering various PCM particle forms, concentrations, and orientations.

Modeling on heat storage performance of compressed air in a packed bed system

Compressed Air Energy Storage (CAES) incorporates a Packed Bed Thermal Energy Storage (PBTES) represents a promising larger scale storage technology. The heat storage performance of compressed air (CA) in PBTES is presented and numerically analyzed in this paper. Phase change material (PCM) particles are used as the filler. The unsteady two-phase energy conservation equations considering the phase change phenomena inside the PCM particles are developed and solved numerically by finite difference method. This model has been validated with Izquierdo-Barrientos’ experimental data. Then, the effects of porosity (ε), PCM particle diameter (dp), CA inlet pressure (P) and filling approach on PBTES thermal behaviors (such as temperature profiles, heat storage capacity and charge efficiency) are investigated.It was found that increasing particle diameter results in a decrease in the charge efficiency, and the charge efficiency increases with an increase in CA inlet pressure. The PBTES filled with three kinds of materials has better charge efficiency compared with the packed bed filled with single PCM or rock.

Microencapsulation of metal-based phase change material for high-temperature thermal energy storage.

Latent heat storage using alloys as phase change materials (PCMs) is an attractive option for high-temperature thermal energy storage. Encapsulation of these PCMs is essential for their successful use. However, so far, technology for producing microencapsulated PCMs (MEPCMs) that can be used above 500°C has not been established. Therefore, in this study, we developed Al-Si alloy microsphere MEPCMs covered by α-Al2O3 shells. The MEPCM was prepared in two steps: (1) the formation of an AlOOH shell on the PCM particles using a boehmite treatment, and (2) heat-oxidation treatment in an O2 atmosphere to form a stable α-Al2O3 shell. The MEPCM presented a melting point of 573°C and latent heat of 247 J g−1. The cycling performance showed good durability. These results indicated the possibility of using MEPCM at high temperatures. The MEPCM developed in this study has great promise in future energy and chemical processes, such as exergy recuperation and process intensification.

Experimental heat transfer coefficients between a surface and fixed and fluidized beds with PCM

This work presents an experimental study to determine the capacity of a phase change material (PCM) in granular form to be used in fixed and bubbling fluidized beds for thermal energy storage. The experimental measurements are focused on determination of the heat transfer coefficient between a heated surface immersed in the bed and the granular PCM. The flow rate is varied to quantify its influence on the heat transfer coefficient. The PCM used is Rubitherm GR50 with a phase change temperature of approximately 50° C. The PCM is available in two different particle sizes, 0.54 mm and 1.64 mm, of which the finer is used in the fluidized bed and the coarser is used in the fixed bed. In addition, the results obtained for the PCM are compared with the heat transfer coefficients measured for sand, a material commonly used for thermal storage.In comparing the heat transfer coefficients for fixed and fluidized beds, the heat transfer coefficients in the fluidized bed with PCM are nearly three times higher than those for the fixed bed at the same gas flow rate. This increase in the heat transfer is a result of two main factors: first, the continuous renewal of PCM particles from the heated surface when they are fluidized, and second, the large quantities of energy in latent form absorbed by the PCM. In the fixed bed there is no renovation of particles, consequently only a small percentage of particles are able to change its phase. Hence, there is no increase in the heat transfer coefficient due to this fact.

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.

Functionalization of mortars for controlling the indoor ambient of buildings

This paper reports on the use of nanoparticles of titania (nT), superabsorbent polymer (SA) and phase-change material (PCM) in order to obtain the functionalization of mortars. Single, binary and ternary mixtures with 0–1wt.% nT, 0–1wt.% SA, 0–20wt.% PCM were based on flow table measurements (∼140mm) to estimate the individual and interactive effect between the additives. In general, the mentioned additives showed distinct behaviors, but the PCM particles predominate on most of properties and also on the performance of others additives. SA particles exhibited quite different rheological behavior if compared with other additions, due to high affinity with the water and stronger absorption levels. The PCM-containing mortars attenuate and delayed the temperature changes, while 1SA particles resulted in higher hygroscopic capacity. Moreover, the photocatalytic degradation of NOx reached 40–45%. In addition, the moisture buffering value of 1SA, 1nT and 20PCM mortars were classified as good according to the Nordtest method.

Thermal, mechanical and microstructural analysis of concrete containing microencapsulated phase change materials

This paper studies the thermal, mechanical and microstructural aspects of concrete containing different amounts of microencapsulated phase change materials (PCMs). In addition, numerical simulation is carried out to study the potential application of PCM-modified concrete for reduction in summer surface temperature. It is shown that increasing PCM content in concrete led to lower thermal conductivity and an increase in the heat storage ability of concrete. However, the compressive and flexural strength of concrete significantly decreased. Microstructural analysis showed that PCMs appear to remain intact during mixing; however, PCM particles appear to fail by bursting under loading, creating hemispherical voids and crack initiation points as well as possible entrapped air behaviour. The result of numerical simulation revealed that reduction in summer concrete pavement surface temperature by several degrees was possible, with implications for reduction in concrete thermal stresses, shrinkage and urban heat island effect.

Investigation into thermal performance of nanosized phase change material (PCM) in microchannel flow

PurposeHeat capacity enhancement is important for variety of applications, including microchannel cooling and solar thermal energy conversion. A promising method to enhance heat capacity of a fluid is by introducing phase change particles in a flow system. The purpose of this paper is to investigate heat capacity enhancement in a microchannel flow with the presence of phase change material (PCM) particles.Design/methodology/approachDiscrete phase model (DPM) and homogeneous model have been compared in this study. Water is used as the carrier fluid and lauric acid as the PCM particles with different volume concentrations, ranging from 0 to 10%. Both the models neglect the particle‐particle interaction effects of PCM particles.FindingsThe DPM indicates that presence of 10% volume concentration of PCM particles does not cause an increase in the pressure drop along the channel length. However, prediction from the homogeneous model shows an increase in the pressure drop due to the addition of nanoparticles in such a way that 10% volume concentration of particles causes 34.4% increase in pressure drop.Research limitations/implicationsThe study covers only 10% volume concentration of PCM particles; however, the model may be modified to include higher volume concentrations. The laminar flow is considered; it may be extended to study the turbulence effects.Practical implicationsThis work provides a starting framework for the practical use of different PCM particles, carrier fluid properties, and different particle volume concentrations in electronic cooling applications.Originality/valueThe work presented is original and the findings will be very useful for researchers and engineers working in microchannel flow in cooling and thermal storage applications.

미니에멀젼 중합에 의한 파라핀 왁스의 나노캡슐화 및 상변환물질로서의 열적 특성

폴리스티렌을 쉘 물질로 하여 상변환물질인 파라핀 왁스 코어 물질을 나노캡슐화하는 방법과 형성된 입자들의 열적 특성을 연구하였다. 나노캡슐화의 방법으로는 미니에멀젼 중합법을 채택하였다. 중합시 사용된 가교제의 성질, 유화제의 양, 상변환 물질과 단량체의 비율, 개시제의 친수성 등이 나노캡슐화된 상변환물질의 열적 특성에 미치는 영향을 분석하였다. 오스왈드 숙성에 의한 입자의 크기 변화, 형태 변화는 캡슐 입자의 열적 특성에 가장 큰 영향을 미치는 것으로 나타났으며, 또한 폴리스티렌 쉘의 친수성과 가교밀도도 캡슐 입자의 형태 변화와 이로 인한 열적 특성에 영향을 주는 것으로 나타났다. Encapsulation of a paraffin wax core as a phase change material with polystyrene shell and the its thermal characteristics caused by the encapsulation were studied. For the nanoencapsulation, the miniemulsion polymerization method was selected. The factors affecting the thermal properties of prepared nanocapsule particles of phase change material were analysed in aspect of the structure of crosslinking agents, amounts of surfactant, ratio of paraffin wax to monomer, and hydrophilicity of initiators. It was assumed that Oswald ripening plays the most important role in the changes of particle size, particle morphology, and thermal capacity of nanocapsule core. It was elucidated that the thermal capacity was also dependent on the hydrophilicity and crosslinking density of polystyrene shell components.

Physical Property and Thermal Physical Property of Microencapsulated Phase Change Material Slurry

Microencapsulated phase change material (PCM) slurry is a kind of novel heat transfer fluid called latent functionally thermal fluid. Unlike conventional (sensible) materials, when the PCM reach the temperature at which they begin phase change (its melting point), they absorb large amounts of heat with little or no temperature change. Due to this, the heat transfer ability and energy transport ability can be obviously improved. Therefore, they have many potentially important applications in some fields such as energy storage, thermal conditioning of buildings, waste heat recovery, off peak power utilization, heat pump systems, space applications. In present study, the core materials are encapsulated with membrane of synthetic material. And the core materials are composed of several kinds of n-paraffin waxes (mainly nonadecane) and the membrane is a type of melamine resin. The range of diameter of the PCM particles is distributed from 0 μm to 4.5 μm, and its average diameter is 0.74 μm. The thickness of melamine resin is about 11nm. The melting point of the PCM is about 304K. Physical properties, such as density, diameter and its distribution of microencapsulated PCM slurry are investigated. Meanwhile, the thermal physical property, apparent specific heat, is determined by a Differential Scanning Calorimeter (DSC). Also, the influence of mass concentration has been discussed.

Characterization and Thermal Properties of the Microencapsulated PCM Slurry

The microencapsulated phase change material (PCM) slurry is a kind of mixture with the PCM microcapsule particles and water. The actual PCM in the microcapsule is composed of several kinds of paraffin waxes (mainly nonadecane), and the membrane is a type of melamine resin. This study is focused on preparation, characterization, and thermal properties of the microencapsulated (PCM) slurry. The microencapsulated PCM particles are prepared by in-situ polymerization method. Four different levels of mass concentration Cm of the PCM will be used such as Cm=10%, 20%, 30% and 40%, respectively. The diameter of the particles is distributed in the range of 0µm~4.5µm, and most (61%) of them occur in the range of 0.5µm~1.5µm. The average volumetric diameter of the PCM microcapsule particle is about 0.78µm. And the average membrane thickness is about 11nm.Thermal properties of the microencapsulated PCM slurry are determined using differential scanning calorimeter (DSC). From DSC analysis, the melting and freezing temperatures and the latent heats of Cm=30% are measured as 38°C and 25°C, and 37.9 kJ/kg, respectively. The rheological properties are measured by a rotating cylinder type of rheometer, which the slurry shows the pseudo plastic non-Newtonian fluid behavior with the power-law fluid index n.

Microencapsulated phase change slurries for thermal energy storage in a residential solar energy system

Phase change materials (PCMs) are attractive for use in thermal energy storage applications and thermal regulation/control due to their high-energy storage density over a small temperature range. The direct use of phase change materials for energy storage and/or heat transfer applications has been limited due to the low thermal conductivity of the PCM particularly when solidifying on the heat transfer surface. A Phase change slurry (PCS) consists of small micro-encapsulated PCM particles suspended in a carrier fluid which enhances the heat transfer to the PCM. The PCS can serve not only as the thermal storage media but also as the heat transfer fluid, and hence may have many potentially important applications including in the field of heating, ventilation and air-conditioning (HVAC), refrigeration, solar energy and heat exchangers. A test system to examine PCS performance in residential thermal energy storage applications has been developed to both observe and characterise the thermal processes that occur in a thermal store with a helical coil heat exchanger. These test results will be used to improve the system design and identify limitations when used for intermittent application.

Thermo-mechanical analysis of ceramic encapsulated phase-change-material (PCM) particles

Thermal energy storage (TES) is of growing importance, and involves the storage of both sensible and latent heat. Latent heat storage is particularly attractive, since it can store the energy as the latent heat of fusion at a constant temperature, thus providing a high energy storage density. The low temperature encapsulated phase change materials (PCM) in buildings have been extensively investigated mostly in rigid cells. The present paper studied the encapsulation of salts PCM material within elastic shells. The mechanical feasibility of such a spherical shell coating of a melting material is first investigated. The influence of encapsulation on the melting process of PCMs is thereafter studied for this particular geometrical case, including the complicated interactions with melting temperature of PCMs. The stored energy and pressure variation due to the volume change during the melting process are examined. It is shown that the encapsulated PCM particles can melt without cracking the coating shell only under specific conditions.