Phase Change Material Capsules Research Articles

Energetic and thermal comfort assessment of phase change material passively incorporated building envelope in severe hot Climate: An experimental study

Phase change materials (PCMs) can beneficially work as a successful thermal energy storage medium in different applications. PCMs have shown a remarkable enhancement in building energy-saving and thermal comfort in hot locations. In this paper, the thermal behaviour of a PCM-enhanced thermally-poor building envelope is studied experimentally. To this aim, two identical rooms, one loaded with PCM (PCM room) and the other without (reference room), are built and tested under a severe hot climate of Al Amarah city, Iraq. Previously examined parameters, such as the optimal position and thickness of the PCM layer in the roof and the best-thermally performed PCM capsules integrated concrete bricks, are considered to build the PCM room. Several energetic and thermal comfort indicators such as maximum temperature reduction (MTR), average temperature fluctuation reduction (ATFR), decrement factor (DF), time lag (TL), operative temperature difference (OTD), discomfort hours reduction (DHR) and maximum heat gain reduction (MHGR) are determined and discussed to show the potential of PCM. The experimental results revealed that the incorporated PCM could remarkably improve the thermal performance of building envelope exposed to high outdoor temperatures. Amongst envelope elements and compared with the reference room, the roof and east wall of the PCM room recorded the best thermal behaviour, where the MTR difference, ATFR, DF, and TL difference reached 3.75 °C, 6.5 °C, 25.6%, 70 min for the roof, and 2.75 °C, 2.4 °C, 12.8% and 40 min for the east wall, respectively. Moreover, the PCM room shows a thermal comfort enhancement by 11.2% and 34.8%, considering the DHR and MHGR, respectively, compared with the reference one. The study highlighted that suitable ventilation means are necessary to improve the building performance and reach acceptable thermal comfort when the PCM is incorporated passively.

Properties of PCM-based composites developed for the exterior finishes of building walls

Phase change materials (PCM) are widely known for their high thermal storage capabilities. They are generally utilized to increase the thermal mass of buildings’ lightweight materials, which improves their thermal performance and reduces the need for air-conditioning systems. PCM layers are commonly applied to the buildings’ interior parts, close to the indoor environment, which helps regulate the indoor temperature. However, few studies reported that PCM application on the exterior of the envelopes increases their thermal insulation, which can reduce the outdoor heat gain. Therefore, this study aims to develop PCM-based composites for the exterior finishes of building walls. To this end, microencapsulated PCM was integrated into the cement render and foamed concrete with different fractions. The developed composites were tested, evaluated, and compared to the composites without PCM integration. The results showed that PCM integration into foamed concrete reduced the density and thermal conductivity to 896 kg/m³ and 0.18 W/mK, respectively, i.e., lower by 50% and 86% compared to the conventional cement render. Besides, PCM integration added thermal energy storage of 38 J/g to the composite, which can improve its thermal mass. Although the compressive strength decreased by 53% with PCM integration into the cement render, it increased by 28–49.7% with PCM integration into foamed concrete due to PCM capsules substituting some of the air gaps. The findings of this study demonstrate a high potential of using PCM-based foamed concrete to produce lightweight cladding panels for building exteriors with improved thermal insulation and thermal mass to reduce external heat gain.

Investigation on a Solar Thermal Power Plant With a Packed Bed Heat Storage Unit

Abstract The objective of the present work is to research the dynamic thermal performance of the solar power plant during the phase change material (PCM) capsule heat storage tank discharging process. Therefore, a transient, one-dimensional two-phase model for a packed bed latent heat storage unit and a comprehensive concentrating solar power generation system that combines a CO2 Brayton cycle and organic Rankine cycle were integrated. The influences of the key parameters of the packed bed PCM capsule heat storage tank on the overall power output and thermal efficiency of the system during discharge have been investigated, including the heat transfer fluid (HTF) velocity, the diameter of the PCM capsule, and the height of heat storage tank. The orthogonal analysis method is selected in this article, and the results showed that the maximal transient power output and overall power output of the actual combined cycle mode are decreased about 22% and 25%, respectively, in this research, compared with the idea Carnot cycle mode. That the HTF velocity in the thermal energy storage tank can be used to control the transient power output of the solar thermal power system. Using the small-sized filler capsule is an effective method to increase the thermal performance of the concentrated solar power (CSP) combined cycle system. Moreover, the corresponding discharging time is increased obviously, and the CSP with a high packed bed height can generate a more stable power output value during thermal energy discharging.

A numerical study on the thermal storage properties of packer bed under different arrangements of phase change material capsules

To evaluate the thermal storage properties of packer bed under different arrangements o phase change material capsules, three packing models (strip packing model, in-line packing model and disordered packing model) are developed. The index of thermal storage properties for packer bed such as exergy efficiency, energy efficiency, pressure drop, charging time, temperature uniformity, and thermal storage capacity is studied. The results show that the uniformity of the temperature field of the orderly packing model is obviously better than that of the disorderly ones. In addition, the in-line packing model has obvious advantages on the energy efficiency and the thermal storage capacity compared with the strip packing model. The strip packing model has the highest exergy efficiency, but it has a high pressure drop.

Experimental investigation and modelling of a laboratory-scale latent heat storage with cylindrical PCM capsules

Heat storage efficiency is required to maximize the potential of combined heat and power generation or renewable energy sources for heating. Using a phase change material (PCM) could be an attractive choice in several instances. Commercially available paraffin-based PCM was investigated using T-history method with sufficient agreement with the data from the manufacturer. The introduced LHTES with cylindrical capsules is simple and scalable in capacity, charging/discharging time, and temperature level. The overall stored energy density is 9% higher than the previously proposed design of similar design complexity. The discharging process of the designed latent heat thermal energy storage (LHTES) was evaluated for two different flow rates. The PCM inside the capsules and heat transfer fluid (HTF) temperature, as well as the HTF flow rate, were measured. The lumped parameter numerical model was developed and validated successfully. The advantage of the proposed model is its computational simplicity, and thus the possibility to use it in simulations of a whole heat distribution network. The so-called state of charge (SoC), which plays a crucial role in successful heat storage management, is a part of the evaluation of both experimental and computational data.

Numerical Study to Investigate the Thickness of the PCM Layer for the Three Layers Tank for the CSP Plants

In the present study, the phase change material (PCM) layer thickness of the top and bottom PCMs change gradually with constant the middle PCM layer thickness for the three-layers thermocline thermal energy storage (TES) tank. It has been studied using spherical capsules packed with three types of PCMs with different thermophysical properties. A transient two-phase dispersion-concentric (D-C) model is used to calculate the process of phase change inside pellets to identify the temperature allocation. The method of heat transfer among molten salt and PCMs capsules is extensively discussed, with multiple numerical results shown. The results show that the thickness of the PCM layer has a high impact on the thermal performance of the TES tank. As the layer thickness of the top PCM increases, the time required to discharge the thermocline TES tank increases. The (80 % high phase change material (HPCM) -10 % intermediate phase change material (IPCM) - 10 % low phase change material (LPCM)) configuration has 14.6 %, 27.2 %, and 46.8 % higher overall efficiency than (33.3 % HPCM - 33.3 % IPCM -33.3 % LPCM) configuration, (70 % HPCM - 10 % IPCM - 20 % LPCM) configuration, and (10 % HPCM -10 % IPCM - 80 % LPCM) configuration. In contrast, the (80 % HPCM - 10 % IPCM - 10 % LPCM) configuration shows the highest capacity and utilization ratio.

Numerical Study on the Dynamic Performance of Combined Sensible-Latent Heat Packed-Bed Thermocline Tank

Abstract Thermal energy storage (TES) using thermocline technology with phase change materials (PCM) is a promising technique for peak-shaving operation in cogeneration units. One of the disadvantages of this connotation is the use of the highly cost PCM capsules in a water tank. To circumvent this issue, a new thermocline tank connotation is proposed. The tank is packed with a mixture of solid filler pills and PCMs capsules, forming a multi-layered packed-bed system. A transient concentric-dispersion model is developed to assess the dynamic performance of a solid-PCM multi-layered packed-bed (SPMLPB) tank. The influences of the PCMs volume fraction (VF) and the charge and discharge dimensionless cutoff temperatures criterion on the dynamic performance have been investigated. The results show that the VF of PCMs influences the system's behavior, in terms of both energy storage and release. As the PCMs volume fraction increases from 10% to 40%, the amount of energy storage, energy release, and latent utilization ratio increased by 82.65%, 73.94%, and 55%, respectively, while the overall exergy efficiency drops by 6.3%. Besides, increasing both the charge and discharge cutoff temperatures criterion (STch*/STdisch*) enhances the total utilization ratio and energy recovered. When STch* increases from 0.27 to 0.7, the total utilization ratio and energy recovered increased by 63.63% and 28.67%, respectively, by maintains STdisch*=0.26.

Experimental investigation of modified solar still coupled with high-frequency ultrasonic vaporizer and phase change material capsules

In present study, the effect of combining single-slope solar still unit with high-frequency ultrasonic vaporizer, PCM capsules, and external solar water heater on improving its performance was experimentally investigated. A single-slop solar still was developed and examined under the harsh climate of Baghdad city in middle Iraq territory. Compared with the conventional solar still, the results indicated that using PCM cylindrical capsules increases the water productivity of the still about 30.6%. High water productivity was achieved by using an external solar water heater and high-frequency ultrasonic vaporizer was about 415% respectively. Results also illustrate that increasing the operation time of ultrasonic vaporizer has a negative effect on water productivity and thermal efficiency. The maximum thermal efficiency reached 39.3% for the modified solar still with ultrasonic vaporizer with 30 min operation time, while its value is reported to be about 34.2% for 60 min operation time. According to the economic analysis, such units are reliable in remote regions with an estimated cost equal 0.037 and 0.028 $/L for conventional and modified solar still with ultrasonic vaporizer respectively.

Effect of encapsulation area on the thermal performance of PCM incorporated concrete bricks: A case study under Iraq summer conditions

In this paper, the thermal performance of phase change material (PCM) incorporated concrete bricks is studied experimentally. Four concrete bricks (three with macroencapsulated PCM and one without PCM represented the reference) are fabricated, and their thermal performance is tested under hot climate conditions. The study considered the effect of PCM encapsulation heat transfer area on brick's thermal performance at the same PCM quantity. PCM bricks included three different PCM capsule arrangements in which the first brick involved one bulky capsule (Brick-B, 4*4*10 cm3), the second brick had two capsules (Brick-C, 4*4*5 cm3), and the third brick involved five PCM capsules (Brick-D, 4*4*2 cm3). The peak temperature reduction (PTR), the conductive heat transfer reduction (HTRc), and the time delay (TD) were presented and calculated, taking into account the inner and outer brick surface temperatures of PCM bricks compared with the reference brick. Results showed that concrete bricks' thermal performance could be remarkably improved using PCM even under maximum outdoor temperatures. Moreover, the best thermal performance is reported for Brick-D, in which the maximum PTR, HTRc, and TD are reached 156.5 %, ∼61 %, and ∼133 %, respectively, compared with the reference brick under maximum outdoor temperatures.

Prediction of melting characteristics of encapsulated phase change material energy storage systems

This paper presents a numerical study of encapsulated phase change material (PCM) energy storage systems consisting of a single capsule or multiple capsules with different arrangements. A numerical model is developed for predicting the melting characteristics of encapsulated PCM with circular geometry, subjected to the flow of heat transfer fluid (HTF) over the capsules. The model also incorporates the effect of natural convection inside the PCM capsules. The single capsule system is analyzed to capture the effect of different parameters such as capsule size, fluid temperature, fluid velocity, and direction of flow. The model is applied to investigate multiple capsule systems to enhance the melting rate by the effective distribution of PCM capsules. Straight and alternate arrangements are compared for a varying number of capsules by maintaining the same latent energy storage capacity. Parametric studies are also performed for multiple capsule systems. Subsequently, a novel design of graded systems is proposed for improving the multi-capsule system by reducing the total duration of melting. The capsules are arranged with a percentage reduction in size along the flow direction, keeping the overall energy storage capacity constant. Simulation results show that there exists an optimum value of the reduction percentage for which the melting time is lowest.

Experimental and numerical study on flow characteristic and thermal performance of macro-capsules phase change material with biomimetic oval structure

The emergence of bionics provides new ideas for the innovation of engineering technology, which has been widely used in energy storage, heat transfer enhancement, and solar thermochemical reactions. To improve the flow characteristic and thermal performance of phase change material (PCM) capsules, the idea of heat storage unit with biomimetic oval structure is proposed. An experimental system is developed, and PCM capsules with different structures (bionic-oval, sphere, and ellipse) are prepared by 3D printing. The experimental and numerical analyses show that the unconstrained melting time of oval-shaped capsule is 12% shorter than that of sphere capsule, and the average Nusselt number of oval-shaped capsule is 20% higher than that of sphere capsule. The optimization results show that the oval-shaped capsule can provide a lower resistance coefficient when the long-short ratio and long-symmetry ratio are 1.25 and 1.67, respectively. The research results can provide guidance and new ideas for the application of bionics in the field of energy storage.

Preparation and Evaluation of PCMs by Macro Encapsulation for Solar Energy Storage

Background: Phase Change Materials (PCMs) are used in a latent heat storage system for storing thermal energy. The thermal conductivity of PCMs is enhanced by macro encapsulation for large-scale use. Objective: This technique not only provides a self-supporting structure of PCM but also separates the PCM from thermal fluids and enhances the heat transfer rate. Methods: The current work involves the study of encapsulation of low-cost inorganic PCMs, such as sodium nitrate (NaNO3), in a temperature range of 300 - 500°C. Silicate coating is also applied to PCM capsules. A solar water heater is then designed using the macro encapsulated PCM. Result and Conclusion: The water heater consists of cylindrical copper pipes filled with phase change material. The efficiency of the solar water heater is found to be 22.5%

Thermal performance of concrete bricks based phase change material encapsulated by various aluminium containers: An experimental study under Iraqi hot climate conditions

This study presents the experimental results of concrete bricks based macroencapsulated phase change material (PCM) in different capsule designs (circular, square and rectangular cross-sections). Eight concrete bricks (including a reference brick without PCM) are fabricated, and their thermal performance is tested under hot summer conditions of Al Amarah city, Iraq. The study considered several indicators such as the interior maximum temperature reduction (MTR), decrement factor (DF) and time lag (TL) to compared among tested bricks in addition to the thermal behaviour during melting and solidification of PCM. Results indicated that all PCM based bricks are performed better than the reference brick in which the maximum interior temperature is shaved and shifted. Moreover, the best thermal performance is reported for bricks of large PCM capsules number. Amongst others, the brick-based square cross-section PCM capsules showed the best thermal contribution where the average MTR of 1.88°C, average DF of 0.901 and average TL of 42.5 min were obtained compared with the reference brick. The study concluded that PCM capsules' heat transfer area is the main parameter that controls PCM's thermal behaviour as long as all PCM capsules have the same PCM quantity and position. Therefore, excessive encapsulation area might influence the thermal performance of concrete brick and should be specified for the efficient use of PCM storage capacity.

Thermal performance analysis of packed-bed thermal energy storage with radial gradient arrangement for phase change materials

The current paper investigates the radial gradient arrangement of phase change material capsules effect on the thermal behavior of a packed-bed latent thermal energy storage system. A transient two-dimensional dispersion-concentric model is developed to analyze the phase transition of phase change materials. Moreover, the heat transfer characteristics between air and phase change material capsules in four different packed bed systems are discussed in detailed. The results indicate that the use of radial gradient arrangement in the phase change material capsules significantly enhances the heat transfer performance of the system. The system pressure drop is apparently decreased when the radial gradient arrangement is taken into consideration. From case 1 to case 4, the overall energy efficiency is 84.16%, 80.43%, 83.55%, and 82.46%, respectively. The capacity ratio of case 1 is higher than all studied cases by 5.03%, 1.11%, and 3.74%, respectively. The utilization ratio of case 1 is higher than all studied cases by 5.15%, 1.45%, and 3.43%, respectively. Furthermore, considering the loss of pressure drop, it is found that case 3 is the most viable option of all the studied cases. This study provides a numerical basis for the thermal stability output and the structure optimization of packed bed system.

Heat-Storage Performance Optimization for Packed Bed Using Cascaded PCMs Capsules

The design, in which the capsules are packed in the bed at different sections based on the Phase Change Material (PCM) melting temperature, is an effective method to improve the heat-storage performance of the latent heat energy storage system. A latent heat storage system was established in the present study in order to optimize the arrangement of cascaded PCM capsules. Four kinds of paraffin with different melting temperatures were selected as the PCM for the experiment. The effects of stage number, cascade ratio and melting temperature on the heat-storage performance of the latent heat storage system were investigated during the charging and discharging operations. The complete time of charge and discharge, heat storage-release capacity, energy efficiency, exergy efficiency and entransy dissipation (based on a new entransy theory) were computed for different arrangement cases, in order to analyze and evaluate the heat-storage performance of the system under different stage numbers and cascade ratios of PCMs. The results revealed that the arrangement of cascaded PCM capsules has an obvious effect on the heat-storage performance of the system. When more high melting PCMs are adopted, the heat storage-release capacity, energy efficiency and exergy efficiency increases, while the entransy dissipation decreases. However, the temperature increase becomes slow, and the charging or discharging process becomes long.

Virtual and physical experiments of encapsulated phase change material embedded in building envelopes

This paper investigates the temperature and heat flux fields of composite materials containing phase change materials (PCM) for energy efficient buildings. A novel numerical method validated by accurately controlled laboratory experiments is presented for virtual experiments of more complex applications. Considering a finite bounded domain containing one inclusion, the Green’s function technique has been applied to obtain the transient heat transfer response caused by sources on inclusion domains and prescribed boundaries. Based on the Eshelby’s equivalent inclusion method (EIM), the thermal property mismatch between the PCM particle and matrix phases is simulated with a uniformly distributed eigen-temperature gradient field and a fictitious heat source on the particle. Through the combination of EIM and boundary element method, namely the iBEM, the temperature field can be written in terms of the temperature and heat flux on the boundary and the distributed eigen-temperature gradient and heat source on the particle. By using the equivalent heat flux conditions and the specific heat-temperature relationship, the eigen-temperature gradient and fictitious heat source can be solved and the temperature field of the bounded domain can be calculated. This new numerical method has been verified by the finite element simulation and validated with the laboratory measurements of the transient heat transfer within a building block containing a PCM capsule. Parametric studies have also been conducted to study the influences of the PCM location and volume fraction on the temperature field of composites with multiple particles. The virtual experiments demonstrate the energy saving and phase delay by using the PCM-concrete wall panel. This method will be very useful for the design and thermal analysis of building envelopes.

High-performance phase change material capsule by Janus particle

A new method is proposed to fabricate high-performance phase change material capsules with high thermal storage capacity and increased thermal conductivity. The capsules are achieved by free radical polymerization against the example paraffin/water emulsions stabilized with Janus particles (JPs). It is key that the highly conductive Ag-contained JP adopt parallel lying at the emulsion interface, which is responsible for increasing the interfacial thermal conductivity. Thermal storage capacity can be retained over 90% with no paraffin leakage, which is stable after many cycles of heating and cooling. The high-performance phase change material capsules are promising in effective thermal management in the form of either powder or slurry.

Experimental evaluation of heat transfer performance under natural and forced convection around a phase change material encapsulated in various shapes

Cold thermal energy storage can reduce peak electricity use in electric air conditioning systems as well as improve free space cooling, through convective heat transfer between a surrounding fluid (heat transfer fluid or air) and encapsulated phase change material (PCM). In this work, heat transfer performances and phase change behaviours of six PCM capsules with equal-volumes but varying-shapes were studied experimentally, for use in cold latent heat storage. A tetra-n-butylammonium bromide-based PCM with an adjustable phase change temperature of 0–12 °C was injected into capsules of spherical, cylindrical (short and long), pyramidal, tetrahedral, and a biomimetic red blood cell shape. First, an infrared camera recorded the surface temperature variation during the melting process of each capsule in air under natural convection. Second, an experimental setup was built to investigate latent heat storage during the freezing and melting processes for each shape under forced convection, focusing on the effects of fluid temperature, flowrate and PCM capsule tilt angle on freezing and melting times. The results showed that the freezing and melting times were dependent on not only the surface area to volume ratio, but also on the distance from centroid to inner capsule surface. Importantly, the red blood cell shape was found to be the most favourable geometry because it yielded the most rapid freezing and melting process, which were further enhanced in a configuration where the freestream flow directly impinged onto its centroid. The work is a pioneering study on the effects of PCM capsule geometry, providing experimental data and recommendations for future studies on CTES and applications.

Novel rotary regenerative heat exchanger using cascaded phase change material capsules

A novel rotary regenerative heat exchanger with cascaded phase change material (PCM) capsules was proposed and proved to be a better alternative to the traditional one. The rotary regenerative air preheater used in coal-fired power plant was taken as an example to comparatively analyze the performance characteristics of the rotary regenerative heat exchanger with latent heat storage material and the one with sensible heat storage material. The latent rotary regenerative air preheater (LRAPH) can achieve more uniform outlet temperature of air at low rotating speed than the sensible one (SRAPH), which is conductive to the measurement and process control in application. PCM capsule functions as both a latent heat storage material at its phase change temperature and as a sensible heat storage material at other temperature values. At lower rotating speed, more PCM capsules in LRAPH will work at the phase change temperature resulting in small temperature swings of fluid and matrix. The heat exchanger effectiveness is comparatively analyzed for SRAPH and LRAPH with different matrix parameters. The replacement of sensible heat storage materials by the latent ones would lead to an efficiency improvement of RAPH as large as 11% especially at lower rotating speed. The LRAPH is more capable to counter the entrainment leakage and the problems induced by temperature swings than traditional SRAPH. The cascaded distribution of PCM capsules with different phase change temperatures should be reasonably set according to the specific characteristics of temperature distribution in application to make full use of advantages of cascaded PCMs.

Effect of Inlet and Geometrical Parameters on the Melting of PCM Capsules of Elliptical Cross Section.

This paper focuses on the melting of phase change material capsulated in the elliptical cross-section horizontal cylinder under convective boundary conditions. Different parameters are discussed, namely, the HTF inlet temperature and velocity and the axes ratio of the capsule cross-section. The effect of HTF inlet temperature, inlet velocity, and the capsule axes ratio was studied using the CFD software FLUENT 6.3.26. A comparison between the numerical and experimental results was made for the system. The experimental results matched well with the heat transfer model. It is shown that the inlet temperature of the heat transfer fluid (HTF) has a great effect on the process of paraffin wax melting. The increase of HTF inlet temperature increases the Phase change material( PCM) liquid fraction at constant charging time and decreases at the same time the total time of the capsulated paraffin wax melting. The geometry of the capsule cross-section represented by its axes ratio has a sensible effect on the process of paraffin wax melting. Increasing the axes ratio of the capsule, i.e. elongated the capsule in the perpendicular direction of flow increasing the PCM liquid fraction at constant charging time and decreases the total time of the capsulated paraffin wax melting. The increase of HTF inlet velocity has a weak effect on the process of paraffin wax melting in the inlet velocity range 0.003-0.012 m/s.