Latent Heat Of Phase Change Material Research Articles

A novel solar-geothermal system integrated with earth–to–air heat exchanger and solar air heater with phase change material—numerical modelling, experimental calibration and parametrical analysis

In order to compensate drawbacks of traditional earth–to–air heat exchanger (EAHE) system, such as the unstable outlet air temperature, the overheating and the limited operation period, a novel coupled system systematically integrating an EAHE and a solar air heater (SAH) with phase change material (PCM), was proposed in this study. The complementary between geothermal and solar energy is exploited and served for building energy savings. On-site experimental testing and enthalpy-based numerical modelling using the control volume method were conducted for thermal and energy performances prediction. Systematic and parametrical analyses have been conducted using the developed mathematical model to investigate the effects of critical parameters on the thermal and energy performances. Our findings illustrate that the implementation of PCM can effectively stabilize the outlet air temperature for nearly 4.5 h and prolong the working period to 24 h. Due to the heat transfer enhancement, the increase of the airflow rate can significantly increase the system heating capacity, whereas the outlet air temperature is decreased with a maximum magnitude of 5.3 °C. Furthermore, the diurnal thermal performance of the system is highly dependent on the phase change temperature, whereas the time-duration of the effective operation is highly dependent on the PCM latent heat. Moreover, the system nocturnal thermal behavior can be improved with the increase of the PCM thermal conductivity, whereas a saturated improvement can be noticed when the PCM thermal conductivity is 1.0 W/(m·K). This study proposes a complementary geothermal and solar energy system, together with phase change material for the performance stability improvement, which are important for the promotion of green buildings with energy-efficient utilization of geothermal and solar energy.

Feasibility study on temperature control with phase change material in intensive heat-releasing space during emergency power failure: A case analysis of information system room

Phase change material (PCM) is widely used to control temperature because of its easy control, and independent work even without external power supply. However, few studies focus on temperature control via a PCM cooling system without auxiliary facilities, in an intensive heat-releasing space during emergency power failure. This study takes an information system room with an emergency power failure as the research object. A cooling system implementing PCM plates is proposed and its feasibility is analyzed. A mathematical heat transfer model, which considers the air, heat source, phase change cooling devices, and the enclosure structure of room, is established. The performance of the PCM and air temperature are analyzed, and the effects of the melting temperature, latent heat, thermal conductivity, and size of the PCM plates are systematically investigated. Analysis results indicate that: (i) Under the condition of parameter optimization, the air temperature is 32.10 °C at 9 h. Therefore, the cooling system utilizing the PCM plates can effectively maintain the air temperature of the information system room below 35 °C within 9 h. Until 16 h, the air temperature remains below 35 °C. (ii) Increasing the aspect ratio of PCM plates and decreasing PCM latent heat have the similar effect on the air temperature control. Additionally, the two parameters are related to the surface area of the PCM plates. (iii) The lower the melting temperature of the PCM, the better the air temperature can be controlled. For the conditions considered in this study, the appropriate melting temperature is approximately 25 °C. (iv) As thermal conductivity increases, air temperature reduces, and fluctuation of the PCM heat flow significantly decreases. However, as the thermal conductivity approaches 1 W/(m·K), further increases in the thermal conductivity have no marked impact on air temperature control.

Experimental investigation and two-level model-based optimisation of a solar photovoltaic thermal collector coupled with phase change material thermal energy storage

This paper presents an experimental investigation of an air-based solar photovoltaic thermal (PVT) collector coupled with a centralised phase change material (PCM) thermal energy storage (TES) system, and the development of a model-based strategy to facilitate optimisation of the PVT-PCM systems. The originality of this study includes using statistical analysis to reveal the practical deficiencies of PVT-PCM systems, and orientating the system optimisation using a two-level model-based strategy. A set of experiments were designed and performed based on a lab-scale experimental facility to examine both electrical and thermal performance of the PVT-PCM system with various air flow rates, and different slopes and orientations of the PVT collector. The optimisation strategy was developed to identify the optimal design and at the same time to generate a performance map that can be used for control optimisation. The experimental results showed that there existed an optimal air flow rate for the PVT-PCM system under a given solar radiation for maximal overall system efficiency. To better utilise the PCM latent heat storage capacity, both the useful thermal energy generated from the PVT collector and the heat transfer within the TES unit need to be optimised. Compared to a baseline case without optimisation, the average overall system efficiency increased from 37.6% to 40.2%, and the average daily utilisation ratio of the latent TES capacity improved from 13.3% to 79.5%.

Conjugate heat transfer analysis of PCM suspensions in a circular pipe subjected to external cooling convection: Parameter effects

In this paper, a numerical method was used to investigate the conjugate heat transfer of phase change material (PCM) suspensions in a circular pipe under external cooling convection. The parameters considered in this study and their ranges were the volumetric fraction of PCM particles (cv) = 0–0.2, the Biot number (Bio) = 0.1–100, the Stefan number (Ste) = 0.01–0.2, and the Peclet number (Pe) = 100–1000. The results showed that the PCM concentration, Bio, and Ste had significant effects on the fluid temperature, inner/outer wall temperature, and inner/outer wall heat flux, while Pe only had a significant effect on the axial heat transfer of the wall. When a PCM-containing working fluid was used for cooling, the PCM latent heat could directly affect the fluid outlet temperature and the cooling effect. If the latent heat is changed, other thermal system parameters should be adjusted accordingly.

Energy and exergy model with parametric study of a hot water storage tank with PCM for domestic applications and experimental validation for multiple operational scenarios

Latent heat thermal energy storage (TES) with phase change materials (PCM) has been incorporated in domestic hot water (DHW) systems, frequently inside the water storage tank, as a way to improve its efficiency. The main challenge for further studies about optimization and design relies on finding accurate energy and exergy models capable of predicting diverse operating cycles with reduced computational resources. This paper describes the simulation and experimental validation of a PCM storage tank under multiple operational scenarios required in practice. Paraffin wax is used as PCM, contained in cylindrical bottles, to store and release energy during solid–liquid phase transformation. Simulation is addressed by using an integrated approach with both analytical and numerical methods, in which classic thermodynamic and heat transfer techniques are used to model the tank and the working fluid, and a finite difference formulation of the two-dimensional enthalpy method is implemented for the PCM. Experimental results were obtained by testing the system in laboratory conditions with different full 24-hour typical operating cycles, considering constant or variable inlet conditions during the thermal charging process along with constant flow rate discharge or batch-wise discharge. Predictions are in good agreement with experimental data. Lastly, the effects of key design parameters on the energy and exergy efficiencies of the PCM storage tank are also evaluated under different scenarios via parametric analysis of the model. Parameters considered in this study include the properties of PCM (mean melting temperature and latent heat of fusion), water flow rate, aspect ratio of the tank, and percentage of PCM inside the tank.

Multi-scale analysis on thermal properties of cement-based materials containing micro-encapsulated phase change materials

The incorporation of phase change materials (PCMs) in building envelopes for passive thermal storage can enhance the thermal mass effect and thereby reduce energy consumption. In this investigation, multi-scale analysis of cementitious mortar and concrete containing microencapsulated PCM (MPCM) was performed experimentally and using numerical simulations. A three-dimensional two phase random composite model, which can be integrated with finite element method, was developed to predict the effective thermal properties of cementitious mortar and concrete with MPCM. MPCM was considered as inclusions in a continuous mortar matrix and the latent heat of PCM was incorporated into the simulations. The results showed that the effective thermal conductivity is strongly correlated with the volume fraction of PCM and is independent of the spatial distribution of the inclusions. These predictions were within the upper and lower bounds of parallel and series analytical models and agreed well with the experimental data (correlation coefficient 0.96 for concrete and 0.98 for mortar). Numerical simulations of the macro-scale behaviour of mortar and concrete with PCM for passive thermal storage showed a reduction in the maximum heat flux and time lag effect subjected to diurnal temperature variations. However, an optimum amount of PCM should be selected to fully exploit these passive systems. The developed models can be applied for optimising the design of composites to achieve the best thermal performance.

A cycling study for reliability, chemical stability and thermal durability of polyethylene glycols of molecular weight 2000 and 10000 as organic latent heat thermal energy storage materials

In this experimental study, thermal aging test for investigating the variations in thermal and chemical properties of two selected organic phase change materials (PCMs) has been carried out. Polyethylene glycols (PEGs) of molecular weight of 2000 and 10 000 have been considered as potential latent heat thermal energy storage (LHTES) materials for investigation. The aim of this study is to identify the probable variations in thermal properties and chemical structures of PEGs after melting/freezing cycles repeated for 1500 times. The differential scanning calorimetry (DSC) technique was adopted for measuring the thermal properties such as melting point and latent heat of PCMs. In order to study the variations in PCM's chemical functional groups, Fourier transform infrared (FT-IR) spectroscopy was used. Thermal durability property after the cycling test was investigated using thermogravimetric analysis. The DSC measurements indicated that PEG2000 experienced a maximum variation of about 4°C in melting point while the latent heat of fusion reduces by 16% after the cycle test. PEG10000 shows a variation of about 0.3°C in melting point and 15% of the latent heat of melting after the entire cycle test. The spectral investigation confirms that there are no variations in the functional groups of selected materials after cycle test, which can be inferred as chemical stability of them. The thermal gravimetric analysis curves show that both PEGs are thermally quite durable as well after such large number of melt/freeze cycles. Thermal cycling results and economic analysis confirm that both PEGs are potential PCMs for passive solar thermal management purposes. Highlights Synthesis of polyethylene glycol-based binary eutectic mixtures. Accelerated thermal cycle test of eutectic mixtures. Binary mixtures were found chemically stable. Charging/discharging rates of PEG are controlled. Novelty Statement This paper presents the thermal performance of two polyethylene glycols, viz., PEG2000 and PEG10000. These materials were melted and solidified 1500 times for testing their suitability as thermal energy storage materials, and it was found that these materials are stable enough to store solar energy for five years. They found to be suitable for many solar energy storage applications.

Latent heat storage for centralized heating system in a ZEB living laboratory: integration and design

The ZEB Lab project, coordinated by SINTEF and NTNU, aims at building a ZEB (Zero Emission Building) in Trondheim (Norway) in 2019, to be used both as office building and living laboratory. An innovative latent heat storage (LHS) unit using phase change material (PCM) will be integrated in the centralized heating system. The LHS unit will be able to store excess heat from various heat sources connected to the heating system, when they are not required for space heating. One challenge is to make use of the full potential of the PCM latent heat to have a compact and effective unit, while the unit itself should have a low associated CO2-footprint. The LHS system consists of two units designed for a total heat storage capacity of 0.6 MWh, corresponding to the heat needed on top of the heat pump to cover for up to 3 consecutive days in the coldest period of the year, with a maximum combined effect of 26 kW. A bio-based wax is used as PCM with melting temperature 37 °C and measured latent heat 198 kJ/kg. Dynamic system modelling is used to support the design of the LHS unit and ensure sufficiently high heat transfer rates.

Analysis of a phase change material-based unit and of an aluminum foam/phase change material composite-based unit for cold thermal energy storage by numerical simulation

Thermal energy storage systems have increasingly attracted researchers and engineers in the last decades, not only because they permit to overcome the mismatch between thermal energy supply and demand in solar thermal systems, but also because they have the potential to improve the power grid reliability and flexibility, as they allow, for example, to store the heat or the cooling energy produced by residential electric heat pumps for a later use. In this context, this work analyses the cooling energy charging and discharging of two different cold thermal energy storage units, based on the use of a phase change material (PCM), by numerical simulation. One unit consists of an aluminum cylindrical container partially filled with a biological PCM. The other one is similar, with the only difference that it also includes an aluminum metal foam immersed in the PCM. Two different 2D axisymmetric models have been developed, both based on the effective heat capacity method in order to account for the PCM latent heat, for the numerical simulation of the two different units, and the numerical results are compared with experimental ones, obtained by means of a climatic chamber, in order to assess, in each case, the best set of the model arbitrary parameters among the considered ones. Moreover, for each simulation model, a sensitivity analysis is performed to show the effects of two arbitrary model parameters on the numerical results. Simulation results relative to the unit with only the PCM indicate that the cooling energy charging is most affected by conductive heat transfer, and in particular by the thermally resistive layer of solid PCM that forms at the lateral wall of the aluminum container, and that heat transfer by free convection plays a crucial role in the cooling energy discharging process. As concerns the unit with the PCM and the aluminum foam, numerical results show that the charging process and the discharging one are about four times and two times faster than without the foam, respectively. Furthermore, numerical results show that, with the employed aluminum foam, free convection within the PCM is negligible in both the cooling energy charging and discharging process.

Design and thermal insulation performance analysis of endothermic opacifiers doped silica aerogels

In order to reduce the thermal radiation and further deter the heat transfer in silica aerogel thermal insulation materials, the endothermic opacifier is designed with the shell of SiC and the core of phase change material (PCM) in this paper. Then the transient heat transfer characteristics of the endothermic opacifiers doped silica aerogel (EOSA) are numerically investigated and its short-term thermal insulation performance is estimated with a modified lattice Boltzmann method (LBM) model. The modified LBM scheme is established with a new source term to remedy the effect of the variation in the volumetric heat capacity of the specimen, and this scheme is fully validated based on the analytical results and available experimental data. The results demonstrate that adding the endothermic opacifier to silica aerogels results in a significant heat transfer delay and an improvement in short-term thermal insulation performance by suppressing radiation heat transfer and solid-liquid phase change heat absorption. With the same doping amount, the endothermic opacifiers doped silica aerogel exhibits more excellent short-term thermal insulation performance and a lower density than that of SiC opacifiers doped silica aerogels (SOSA). It indicates that the EOSA possesses great potential to be a candidate as the lightweight and efficient thermal insulation material at high temperature. Besides, exhaustively parametric studies based on the EOSA, including doping amount, latent heat of PCM, phase change temperature and endothermic opacifier particle size are conducted, and several design rules are established. This analysis could serve as a framework to develop and design silica aerogel composites with low-density and excellent short-term thermal insulation performance.

Preparation and thermophysical properties of graphene nanoplatelets-octadecane phase change composite materials

<sec> Latent heat storage mainly uses the latent heat of phase change material (PCM) to realize thermal energy storage and utilization, which is the most important thermal energy storage method at present. However, most of PCMs have the disadvantage of low thermal conductivity, which greatly restricts the thermal response rate and system efficiency of the thermal energy storage system. With the development of nanotechnology, it is expected to improve the thermal conductivity of traditional PCMs by adding high thermal conductivity nanoparticles. In this paper, a novel two-dimensional carbon nanomaterial, graphene is selected as an additive for PCM.</sec><sec> In this paper, graphene nanoplatelets-octadecane phase change composite materials are prepared with a two-step method and the mass fractions of graphene nanoplatelets are 0%, 0.5%, 1%, 1.5%, and 2%. Their microstructures, morphologies and thermophysical properties are characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR), differential scanning calorimetry (DSC), and thermal conductivity analysis. The effects of the addition quantity of graphene nanoplatelets on the phase transition temperature, enthalpy, specific heat capacity, thermal conductivity and thermal stability of the composite PCM are compared. The experimental results show that the dispersion stability of the graphene nanoplatelets in the composite system is greatly improved by the addition of dispersant, and the system does not produce obvious agglomeration nor sedimentation after multiple phase transformation cycles. The graphene nanoplatelets still maintain good lamellar structure and homogeneous dispersion in the n-octadecane matrix, and no chemical reaction occurs in the composite process. Comparing with the n-octadecane, the melting point of the composite phase change material decreases slightly, and the freezing point increases slightly. With the increase of graphene nanoplatelets, the latent heat value of graphene nanoplatelets-octadecane composite phase change material decreases gradually. For the composite phase change material with 2.0 wt.% graphene nanoplatelets, the melting enthalpy and solidified enthalpy are reduced by 6.01% and 7.35%, respectively. When the mass fractions of graphene nanoplatelets are 0.5%, 1%, 1.5%, and 2%, the thermal conductivity values of phase change composite materials are nearly 32.4%, 77.4%, 83.1%, and 89.4% higher than the thermal conductivity value of pure octadecane, respectively. Comparing with the significant increase in thermal conductivity, the addition of graphene nanoplatelets has little effect on the phase transition temperature and latent heat of PCM, and still exhibits the good heat storage performance. </sec>

Determination of Optimum Hot-Water Temperatures for PCM Radiant Floor-Heating Systems Based on the Wet Construction Method

Owing to use of mortar, which demonstrates low heat storage and discharge performance, conventional radiant floor-heating systems, based on the wet construction method and hot-water circulation, consume large amounts of energy. This study proposes a new type of radiant floor-heating system that is capable of reducing energy consumption via use of the latent heat of a phase change material (PCM), whereby the phase change, which occurs within, is induced by the thermal energy supplied by hot water. Simulation analyses revealed that hot-water supply temperatures, required to maintain the floor-surface and indoor-air temperatures at the set point using PCM latent heat, were in the range 40–41 °C. At supply water temperatures measuring less than 39 °C or exceeding 42 °C, the latent-heat effect of the phase change of the PCM tended to fail, and the corresponding floor-surface temperature assumed a value different from that corresponding to the set point. By contrast, supply temperatures in the range 40–41 °C resulted in return temperatures measuring approximately 27.4–27.5 °C, which in turn corresponded to an indoor air temperature of 21.6–22.6 °C that was stably maintained within ±0.6 °C of the 22 °C set-point temperature.

Numerical Thermal Characterization and Performance Metrics of Building Envelopes Containing Phase Change Materials for Energy-Efficient Buildings

Residential and commercial buildings consume nearly 40 percent of total USA energy use and account for one-third of total greenhouse gas emissions. The challenges are how to effectively promote energy efficiency in buildings to respond to the high financial burden of energy consumption, while reducing pollution. Phase change materials (PCMs) have been used as passive energy storage for building systems. Along this vein, this study aims to numerically elucidate the design parameters of building envelopes strengthened by PCM layers, and unveil their impacts on building energy efficiency. Critical design variables, such as the thickness of the PCM layer, the latent heat of PCMs, or melting temperature of PCMs were selected for a parametric study, while performance metrics were used to assess building efficiency. Results revealed that PCM-enabled building walls exhibited different levels of improvement, in terms of reduction of peak temperature and temperature swings. Among the variables, the selection of the proper melting point for a PCM was identified as the most crucial parameter for determining building energy efficiency, while the heat of fusion was also observed as a critical property of PCM for building potential. Findings also demonstrated that the placement of the PCM near the interior wall surface could achieve higher efficiency, as compared to other cases. Results also showed that the thermal conductivity of PCM has a minimum contribution to energy storage capacity.

Energy efficiency of PCM integrated in fresh air cooling systems in different climatic conditions

The study provides novel and validated explicit equations of the apparent heat capacity variation with temperature for three phase change materials (PCM): RT20, RT25 and RT27. The developed models of PCM thermal behavior were successfully applied in the energy efficiency analysis of the fresh air cooling system with PCM latent heat storage system, serving a virtual office building considered to be located in different climatic conditions. Following the study, a practical guideline for estimation of the required quantity of PCM in fresh air cooling systems was provided. Two novel specific energy indicators were also proposed, which are useful for feasibility studies. The evaluation of PCM energy efficiency in fresh air cooling systems revealed that savings in the electric energy consumption of (7–41) % can be achieved, depending on the particular local conditions. Limits of the use of PCM in fresh air cooling systems were also provided.

Recent Investigations of Phase Change Materials Use in Solar Thermal Energy Storage System

Solar thermal energy storage (TES) is an efficient way to solve the conflict between unsteady input energy and steady output energy in concentrating solar power plant. The latent heat thermal energy storage (LHTES) system is a main method of storing thermal energy using phase change materials (PCMs). Thermal properties, that is, melting points and latent heat, are the key parameters of PCMs for the TES system. In this paper, the PCMs are classified into inorganic and organic by the chemical composition, and according to the melting point, the inorganic PCMs can be divided into three contributions: low‐temperature heat storage (less than 120°C), medium‐temperature heat storage (120–300°C), and high‐temperature heat storage (more than 300°C). The present article focuses mainly on the recent investigations on the melting point and latent heat of PCMs via DSC setup in the solar TES systems. The results can provide a good reference for the selection and utilization of PCMs in the solar TES systems.

Reduced-scale experiments to evaluate performance of composite building envelopes containing phase change materials

This study presents a convenient approach to rapidly assess the thermal performance of building envelopes containing phase change materials (PCMs) or other building materials. It establishes that the transient thermal behavior of full-scale building test structures featuring envelopes with PCMs can be represented by a reduced-scale test cell conveniently placed inside an environmental chamber. Indeed, PCM-composite envelopes have been considered for reducing and time-shifting the thermal load on buildings thanks to the latent heat associated with reversible transition between liquid and solid phases. First, a thermal model coupling outdoor, wall, and indoor temperatures and accounting for PCM latent heat was developed. It was validated against experimental temperature measurements within a reduced-scale test cell enclosure placed in an environmental chamber and subjected to a series of sinusoidal temperature cycles. Then, scaling analysis of the experimentally-validated thermal model was performed. It identified eight dimensionless numbers governing the transient thermal behavior of building structures with envelopes containing PCMs. The scaling analysis was validated using detailed numerical simulations for different enclosure geometries and outside diurnal climate conditions. Finally, the method was demonstrated on full-scale experiments reported in the literature. It can be used to assess building envelope thermal performance by designing representative reduced-scale experiments without requiring a significant amount of material, time, or space.

Enhanced thermal management with microencapsulated phase change material particles infiltrated in cellular metal foam

Infiltrating phase change material (PCM) in porous material is an effective method to improve the thermal conductivity of PCM. However, this technique inevitably causes PCM/matrices compatibility issue and volume variation of PCM in phase change. To address these problems, a new strategy for passive thermal management with microencapsulated phase change material (MEPCM) particles embedded into cellular metal foam was proposed in this study. We experimentally evaluated the thermal performance of MEPCM/foam composite. Also, the pure MEPCM control groups heated in three angles (0°, 90°, 180°) were employed to quantify the enhancement of foam and natural convection of core PCM. Results indicated that the pure MEPCM leaded to significant surface temperature increase and huge inner temperature difference near the wall due to the low thermal conductivity and absence of natural convection of core PCM. Comparatively, the addition of metal foam had lowered the surface temperature by maximum 47% and unified the internal temperatures in MEPCM/foam composite ascribed to the enhancement of thermal conductivity by metal foam and the fully use of PCM latent heat. Moreover, the lower porosity composite provided better thermal performance at the cost of less thermal management time.

Modelling and simulation of phase change material latent heat storages applied to a solar-powered Organic Rankine Cycle

Solar energy is one of the most promising renewable energy sources, but is intermittent by its nature. The study of efficient thermal heat storage technologies is of fundamental importance for the development of solar power systems. This work focuses on a robust mathematical model of a Latent Heat Storage (LHS) system constituted by a storage tank containing Phase Change Material spheres. The model, developed in EES environment, provides the time-dependent temperature profiles for the PCM and the heat transfer fluid flowing in the storage tank, and the energy and exergy stored as well.A case study on the application of the LHS technology is also presented. The operation of a solar power plant associated with a latent heat thermal storage and an ORC unit is simulated under dynamic (time-varying) solar radiation conditions with the software TRNSYS. The performance of the proposed plant is simulated over a one week period, and the results show that the system is able to provide power in 78.5% of the time, with weekly averaged efficiencies of 13.4% for the ORC unit, and of 3.9% for the whole plant (from solar radiation to net power delivered by the ORC expander).

Thermal characterization of phase change materials based on linear low-density polyethylene, paraffin wax and expanded graphite

Thermal characterization of Phase Change Materials (PCMs) based on linear low-density polyethylene (LLDPE), paraffin wax (W) and expanded graphite (EG) is reported in this paper. Investigated PCMs showed high potential for application in energy storage systems.The latent heat, Lm, sensible heat Qsens, and the ability of the prepared PCMs to store and release thermal energy were investigated using specific home-made equipment based on the transient guarded hot plane method (TGHPT). The sensible heat of PCM containing 40 wt.% of paraffin wax was investigated in the temperature range 25–35 °C, they exhibited a drop in Qsens from 31 to 24 J/g depending on the concentration of EG. A similar decrease in sensible heat with increased loading of EG was observed for PCMs containing 50 wt.% of EG.The storage and release of thermal energy during phase change which is associated with the latent heat of the materials were investigated within the temperature range 20–50 °C. PCMs containing 40 wt.% of paraffin wax exhibited latent heat of 36 J/g, whereas the latent heat of PCMs containing 50 wt.% of paraffin wax was 49 J/g. The addition of EG decreased the time needed to melt and solidify PCMs due to increase in thermal conductivity of PCMs with increase in EG content. This behavior was confirmed by the thermal conductivity measurements, where thermal conductivity increased from 0.252 for sample without EG to 1.329 W/m × °C for PCM containing 15 wt.% of EG.The reproducibility of storage and release of thermal energy by PCMs was demonstrated by subjecting them to repeated heating and cooling cycles (over 150 cycles).

Figure of merit for the thermal performance of cementitious composites containing phase change materials

This paper presents a novel method to quantitatively characterize the thermal performance of composite materials containing phase change materials (PCM) based on a figure of merit we termed the energy indicator. The method features (i) commonly used specimen geometry, (ii) straightforward experimental implementation, and (iii) sensitivity to relevant design parameters including PCM volume fraction, enthalpy of phase change, composite effective thermal conductivity, and specimen dimensions. The experimental method and the concept of energy indicator were demonstrated on PCM-mortar composites using various volume fractions of two commercial microencapsulated PCMs. This was supported by transient two-dimensional heat transfer simulations. The energy indicator was shown to increase linearly with increasing microencapsulated PCM volume fraction and latent heat of fusion and quadratically with the specimen radius. This figure of merit can be used to rapidly screen and select microencapsulated PCM composite materials for energy efficient buildings or crack-resistant concretes.