Encapsulated PCM Research Articles

Numerical investigation of phase change material integration in structured thermocline systems for concentrated solar power

The integration of encapsulated PCM in a structured thermal energy storage system is studied. The fluid and filler material are discretized using a one-dimensional approach, while the PCM is discretized two-dimensionally. The accumulated energy for the height percentage of PCM and cutoff temperature differences are obtained for three PCMs, NaNO3, KOH and H380, to obtain the best options to enhance the accumulated energy using encapsulated PCM.

An efficient method for modelling thermal energy storage in packed beds of spherically encapsulated phase change material

An approach for modelling melting (and solidification) in packed beds of encapsulated spherical PCM is presented. The approach includes a calibration step based on comparisons of simulations with experimental results of PCM melting in a cylindrical geometry, followed by detailed simulations of melting in an isolated encapsulated PCM sphere and a PCM sphere in a representative elemental volume of packed PCM spheres to study the impact of external flow conditions on PCM heating and melting. The detailed simulations show that the enthalpy-porosity model provides a reasonable estimate of the overall melting time and a good approximation of the evolution of the liquid/solid melt front during the melting process. The simulations also confirm the dominance of convection during most of the melting process. The temporal integral results of overall heat transfer coefficient and overall energy fraction from the detailed simulations are combined to yield a relationship between overall heat transfer coefficient and overall energy fraction such that the process can be modelled in terms of the condition inside the encapsulated PCM sphere, wherein the condition can also be obtained from the fraction of heat absorbed compared to the energy capacity of the PCM sphere. This relationship is then used as an input to a finite-volume model for packed beds which can be used to predict the charging time of entire packed beds of encapsulated spherical PCM. Results from the simple model show correct trends for the temporal evolution of liquid fraction and PCM temperature, and for overall charging times for the cases considered. This simple approach can substantially reduce the simulation time required to model beds of different shaped encapsulated PCMs and different dimensions.

Performance augmentation of solar air heater using absorber with multi-functional encapsulated PCM tubes

Performance augmentation of solar air heater using absorber with multi-functional encapsulated PCM tubes

Direct and non-contact measurement of liquid fraction in unconstrained encapsulated PCM melting

Almost all of the experiments on PCM melting rely on temperature measurement. However, based on the experimental evidence, the presence of a thermometer in the solid PCM affects the results. Because the solid phase covers the probe and in fact, the solid phase temperature is measured instead of the liquid phase. On the other hand, since the PCM sticks to the probe, the regime of melting can change from unconstrained to constrained melting. In this study, a new method is proposed to measure directly the liquid mass fraction of PCM during melting. This method can be categorized as a non-contact measurement method and is based on the image processing technique.In this method, images of the melting process are prepared under controlled conditions at successive times. By performing image processing techniques, the solid core boundary is determined and the enclosed area is calculated and divided by the solid phase initial surface area. The method was applied to PCM melting inside a cylinder. Meanwhile, the problem was also simulated numerically by the multi-phase method (VOF). The multi-phase method allows considering the change in the total volume of PCM (summation of volumes of both solid and liquid phases) due to the difference between solid and liquid densities. Good agreement was observed between numerical and experimental results. The RMSE was 1.8 %. Moreover, it was observed that the shapes and sizes of the solid core in experimental images and numerical results at different times match well. But for lower solid volume fractions, the solid core sinks deeper in experimental images in comparison with numerical results.

Finned-encapsulated PCM pyramid solar still – Experimental study with economic analysis

This paper presents a novel experimental work to enhance the performance of pyramid solar stills using PCM-encapsulated cylindrical fins with different heights. To optimise the fin's height as well as the water depth, the study was carried out in three phases using three identical pyramid solar stills with a basin area of 1m2. The first phase aimed to investigate the effect of using cylindrical fins of 40 mm height and comparing it with conventional stills at water levels from (10 to 40 mm). The second phase targeted studying the effect of fins heights of 20 mm, 40 mm, and 60 mm on the performance of the solar still. The third phase investigates the effect of paraffin wax embedded inside fin heights of 40 mm and 60 mm on solar still productivity. Results from phase 1 showed that using fins can improve the performance while 10 mm water depth was optimised. Phase two results showed that using a 40 mm fin's height can increase the overall efficiency up to 43.4 % compared with 38.5 % and 35.7 % using the 20 and 60 mm fins due to the shading effect. Based on phase 3 results, when using encapsulated PCM, the overall efficiency of 49.9 % was achieved using 40 mm encapsulated PCM fins compared with 34.6 % when using the conventional still. This increased water productivity by around 44.4 % compared with conventional stills. The cost of one litre produced from conventional, 40 mm finned absorber, and 40 mm finned absorber with PCM pyramid solar stills are 0.047, 0.045, and 0.043 $/l respectively.

Chitosan incorporation for improving the dimensional stability of PLA aerogel encapsulated phase change materials

Chitosan (CH) was utilized to improve the shape stability and load resistance of Polylactic acid (PLA) aerogel encapsulated PCM during phase change. Specifically, PLA aerogel with high porosity (>90 %) was prepared first, and then soaked in ethanol and subsequently CH solution, to functionalize PLA aerogel. The aerogel is used to encapsulate paraffin to obtain a shape-stable bio-based PCM. We conduct a comprehensive analysis of its anti-leakage, shape stability, and phase transition properties. The results showed that the CH-modified PCM kept a high latent heat (169.5 J/g), maintained excellent anti-leakage performance, had stronger resistance to deformation in molten state, and improved anti-leakage performance under load. Combining the convenience and environmental protection of material preparation and modification, and the excellent performance of final PCM, this material is expected to be practically applied in building temperature regulation and solar energy capture.

Synthesis of hybrid dual-MOF encapsulated phase-changing material for improved broadband light absorption and photothermal conversion enabling efficient solar energy storage

To improve the overall solar-thermal energy harvesting efficiency of encapsulated phase change materials (EPCM), a novel hierarchic SiO 2 /PCN-224/PB (ES-PCN-PB) composite shell was developed and synthesized through in-situ growth of PCN-224 decorated with PB particles onto SiO 2 encapsulated PCM. The corresponding topologies, chemical characteristics, crystallinity, optical properties, and thermal induction capacity of the ES-PCN-PB capsules were thoroughly evaluated. The articulated strategy attained phase-change enthalpies of about 124.15 J/g, with a differential temperature of 28.88 ± 0.22 °C achieving a magnified photothermal energy conversion efficiency of 96.20% due to the broadband solar spectrum absorbance and effective light to heat conversion through the electron-hole generation and non-radiative relaxation. The combination of PCN-224 and PB decorated shell was realized to be a practical approach to improve structural stability, durability, and light-harvesting ability. The coupling of the two MOFs insinuates broad spectral absorption and photothermal conversion improvement which augments a considerable contribution to straightforward solar energy harvesting in numerous PCM applications such as temperature management of greenhouses, solar water heating systems, solar cookers, and solar-thermal electricity generating systems. • A dual-MOF PCN-224/PB shell for PCM was fabricated for the first time. • Broadband solar spectrum absorption on Uv–Vis–NIR range. • Efficient light to heat conversion through the electron-hole generation and non-radiative relaxation. • This work provides a new insight for the integration of MOF on PCM shell design for an effective solar-thermal conversion. • Presented a new shell design for efficient light to thermal conversion of EPCM.

Effect of porous carbon on thermal and physical properties of composite pure alkane/expanded vermiculite phase change energy storage materials

Nine kinds of mixed N-alkanes with different proportions were prepared by mixed eutectic method. A set of ratios with enthalpy values up to 289.8 J/g were selected for encapsulated PCM. Using potato starch solution with a concentration of 30 % as porous carbon source, the heat transfer capacity of expanded vermiculite was enhanced by modification between expanded vermiculite channels, and matrix coated phase change material was prepared. SEM images show that the PCM are successfully adsorbed in the pores. The latent heat and temperature of phase change in the melting and solidification process are 208.1 J/g and 21.2 °C, 203.11 J/g and −3.4 °C, respectively. FT-IR, XRD, TGA and thermal cycling test results show that phase change energy storage particles have good thermal performance. Therefore, the prepared materials have excellent properties.

Design and performance characteristics of a solar box cooker with phase change material: A feasibility study for Uttarakhand region, India

• A low-cost ($55.01) box cooker is especially designed for the people of Uttarakhand region of India. • Thermal performance enhancement is achieved by using aluminum made hollow capsules and encapsulated PCM over the cooking plate. • Encapsulated PCM enhanced the heat transfer rate about 301 W/m°C between cooking plate and cooking stuff. • Cooking power and thermal efficiency are obtained about 53.21 W and 52.10%, respectively. • Feasibility analysis shows the possibility of fair adoption of the tested box cooker in India. In the present work, the thermal performance of a low-cost solar box cooker (SBC) has been improved through the concept of extended fins and heat storage medium. To achieve the goal, about 144 aluminium made small capsule shaped containers have been filled with PCM and placed horizontally over the absorber. Experiments have been conducted on the three different configurations such as, SBC without any modification, SBC with hollow capsules and SBC with an encapsulated PCM. Experimental study mainly emphasizes on a high heat transfer rate and reduced cooking times through the applied modifications. Thermal performance has been found improved by using encapsulated PCM during the cooking trials. Results showed that the last configuration is the best among the three different configurations developed for cooking experiments. Thermal efficiency has been found improved by 52.2%, heat transfer coefficient improved by 301 W/m o C, cooking power enhanced about 53.21 W, and the overall heat loss coefficient reduced about 4.11 W/m o C on the third configuration. The modified SBC purposely designed for the people from hilly regions who are unable to access the clean cooking fuels. Present design is economic ($55.01) and feasible for cooking of common edibles available in Uttarakhand and nearby regions in India. The payback period ranges from 0.80 years to 4.01 years for different fuels. Notified that the modified cooker also meets the Bureau of Indian standards (BIS) developed for solar cookers.

Effects of Surface Rotation on the Phase Change Process in a 3D Complex-Shaped Cylindrical Cavity with Ventilation Ports and Installed PCM Packed Bed System during Hybrid Nanofluid Convection

The combined effects of surface rotation and using binary nanoparticles on the phase change process in a 3D complex-shaped vented cavity with ventilation ports were studied during nanofluid convection. The geometry was a double T-shaped rotating vented cavity, while hybrid nanofluid contained binary Ag–MgO nano-sized particles. One of the novelties of the study was that a vented cavity was first used with the phase change–packed bed (PC–PB) system during nanofluid convection. The PC–PB system contained a spherical-shaped, encapsulated PCM paraffin wax. The Galerkin weighted residual finite element method was used as the solution method. The computations were carried out for varying values of the Reynolds numbers (100≤Re≤500), rotational Reynolds numbers (100≤Rew≤500), size of the ports (0.1L1≤di≤0.5L1), length of the PC–PB system (0.4L1≤L0≤L1), and location of the PC–PB (0≤yp≤0.25H). In the heat transfer fluid, the nanoparticle solid volume fraction amount was taken between 0 and 0.02%. When the fluid stream (Re) and surface rotational speed increased, the phase change process became fast. Effects of surface rotation became effective for lower values of Re while at Re = 100 and Re = 500; full phase transition time (tp) was reduced by about 39.8% and 24.5%. The port size and nanoparticle addition in the base fluid had positive impacts on the phase transition, while 34.8% reduction in tp was obtained at the largest port size, though this amount was only 9.5%, with the highest nanoparticle volume fraction. The length and vertical location of the PC–PB system have impacts on the phase transition dynamics. The reduction and increment amount in the value of tp with varying location and length of the PC–PB zone became 20% and 58%. As convection in cavities with ventilation ports are relevant in many thermal energy systems, the outcomes of this study will be helpful for the initial design and optimization of many PCM-embedded systems encountered in solar power, thermal management, refrigeration, and many other systems.

Analysis of hybrid nanofluid and surface corrugation in the laminar convective flow through an encapsulated PCM filled vertical cylinder and POD-based modeling

In the present work, performance assessment of a PCM filled three dimensional vertical cylinder is conducted under the combined effects of surface corrugation and presence of binary nanoparticles in the heat transfer fluid. The numerical simulation is performed by using finite element method with varying values of Reynolds number (100≤Re≤750), number (1≤N≤8) and height (H/10≤h≤H/2) of rectangular type corrugation form and volume fraction of particles (0≤ϕ≤0.02) in unsteady configuration. Thermal transport features are enhanced while charging time is reduced for higher values of Reynolds number, solid volume fraction of the binary mixture in the heat transfer fluid. Complete charging time is reduced by 57% with increase of Reynolds number from 100 to 750 while it is reduced by 23% when nanofluid at the highest solid volume fraction is used instead of water. However, the corrugation parameters have reverse effects on the charging process. A computational framework for reconstruction of heat transfer fluid and PCM temperatures for the unsteady parametric configuration in the computational domain is offered by utilizing proper orthogonal decomposition (POD) technique with 25 modes for heat transfer fluid and 75 modes for PCM.

Simplified mathematical model and experimental analysis of latent thermal energy storage for concentrated solar power plants

Depletion of fossil reserves and environmental concerns arising from their use has led to the development of renewable energy technologies. Concentrated solar power (CSP) is one of the promising alternative energy solutions that can be built in higher capacity (hundreds of megawatts) and provide higher thermal efficiencies compared to other technologies. However, almost all CSP systems require thermal energy storage (TES) to improve the capacity factor and bridge the gap between supply and demand. In the current work, a reduced-order one-dimensional mathematical model of a phase change material (PCM) based TES is proposed and experimentally validated on different sets of data including different PCM, operating ranges and storage size per geometrical unit of the CSP. The model considers single EPCM as a lumped thermal mass without much compromise on the accuracy having less than 9% overall error in terms of predicting energy storage capacity when compared to experimental data. Additionally, an experimental setup for encapsulated-PCM (EPCM) is developed using NaNO3-KNO3 as the PCM. This system has a storage capacity of 9.7 MJ and a storage time of 6 hours is required to completely charge the system at selected conditions. An analysis of the system performance is presented under different experimental conditions. The model development, experimental analysis and validation shall provide reliable design estimates while designing EPCM-TES for large-scale applications. Therefore, the current simplified mathematical model best fits such applications where a design engineer needs to make quick decisions regarding the selection of an EPCM-TES system or where a reduced-order model of entire CSP plant is required.

Numerical Design and Laboratory Testing of Encapsulated PCM Panels for PCM-Air Heat Exchangers

Heat transfer between encapsulated PCM panels and air plays an important role in PCM-Air heat exchangers. A new design for the encapsulation panel was developed considering practical aspects such as the cost of production and ease of manufacturing, in addition to heat transfer and pressure drop. A number of encapsulated panel surfaces were first investigated via 3D CFD simulations and compared with an existing panel in use by a commercial PCM-Air heat exchanger manufacturer. After validation, 2D CFD simulations were carried out for 32 different geometries to select the most effective design, which was fabricated and tested in the laboratory. Laboratory parameters tested included heat transfer, pressure drop and melting/solidifying. The laboratory results confirmed the improvements of the new panel in comparison with the existing panel and a flat panel. It was found that the proposed design doubled the heat transfer, holds 13.7% more material and the fan can overcome the increased pressure drop.

Effect of surfactants on solidification characteristics of DI water based PCM for Cold Thermal Energy Storage

Cold Thermal Energy Storage is an upcoming need for sustainable energy consumption and storage. It finds application in wide variety of energy need in the sub-zero temperature zone. This work aims to study the effect of various surfactants on solidification characteristics of spherically encapsulated DI water with different surfactants. A constant temperature bath at -7°C is used to charge spherical encapsulated PCM using VCR system. Tween 80, Gum Arabic (also known as Gum Acacia) and PVP K30 are selected as surfactants and samples are prepared at various concentrations. To check the feasibility of the sample for thermal energy storage application its thermal properties are determined. Tween 80 and Gum Arabic showed no super cooling and subsequent reduction in super cooling was observed in case of PVP.

Numerical analysis of solidification of PCM in a closed vertical cylinder for thermal energy storage applications

The solidification dynamics of cylindrical encapsulated PCM have been analyzed under convective boundary conditions that relate to thermal energy storage systems. A three dimensional, transient CFD model has been solved for examinations. Besides the widely used conduction model of solidification, in this study, the effect of natural convection within the liquid layer has been considered in the numerical model. The effects of parameters such as the initial superheating temperature, the encapsulation size, and the heat transfer coefficient at the outer surface of the capsule have been examined in terms of solidification dynamics and extracted energy during the phase change process. It was found that while the diameter of encapsulation significantly affects the solidification and the energy extraction times, the effect of encapsulation height on the solidification and the energy extraction times are not notable.

Latent heat storage for hot beverages

Latent heat storage has shown a great potential in many engineering applications. The utilization of latent heat storage has been extended from small scales to large scales of thermal engineering applications. In food industry, latent heat has been applied in food storage. Another potential application of latent heat storage is to maintain hot beverages at a reasonable drinking temperature for longer periods. In the present work, a numerical calculation was performed to investigate the impact of utilizing encapsulated phase change material PCM on the temperature of hot beverage. The PCM was encapsulated in rings inside the cup. The results showed that the encapsulated PCM reduced the coffee temperature to an acceptable temperature in shorter time. In addition, the PCM maintained the hot beverage temperature at an acceptable drinking temperature for rational time.

Dynamic thermal performance of four encapsulated PCM spheres for domestic medium temperature applications

Charging and discharging experiments are performed with four phase change materials, each encapsulated in aluminum spheres and suspended in a Sunflower Oil thermal energy storage tank. The PCMs used are erythritol, adipic acid, high density polyethylene (HDPE) and an eutectic solder (Sn63/Pb37). The PCMs possess different melting temperatures and are potential material candidates for a PCM packed bed thermal energy storage for medium temperature applications (100 oC to 250 oC). Sunflower Oil, as the heat transfer fluid, is heated electrically to melt the PCMs during charging cycles, while heat is extracted from the storage tank to solidify the PCMs during discharging cycles. Three charging and discharging flow-rates (4 ml/s, 6 ml/s and 8 ml/s) are used in the experiments. The eutectic solder showed the best phase change transition characteristics during both charging and discharging cycles. Adipc acid performed better than both erythritol and HDPE during the charging and discharging heat transfer cycles. HDPE showed the worst performance since no clear phase change transition characteristics was evident during charging and discharging cycles. Results obtained suggest that the addition of nucleating agents to both erythritol and adipic acid could enhance their phase change transition characteristics.

Numerical investigation on the phase change process of different shaped macro encapsulated PCM

Latent heat energy storage using macro encapsulated phase change material is an emerging technique for thermal energy storage applica- tions. The main aim of the present investigation is to investigate the melting process of phase change material filled in different shaped configurations. The selected different cavities are square, circular and triangular. A mathematical model based on convection dominated melting is required to be developed, especially in view of the complex flow geometries encountered in such problems. Thus, an attempt has been made to develop a model using ANSYS Fluent 16.2 to investigate the heat transfer rate and solid-liquid interface visualization of PCM filled in different shapes of cavity. It is found that triangular shaped macro encapsulated PCM melts faster than square and circu- lar shaped encapsulated PCM.

Influence of wall material on solidification characteristic of water based encapsulated PCM capsule

The experimental study is performed to investigate the solidification behaviour of water-based PCM in different capsule materials filled with 90% of its volume. The experiments are conducted with two stainless steel material and high-density polyethylene (HDPE) spherical capsules are maintained at different surrounding temperatures of -9°C and -12°C filled with 90% of PCM in its total fill volume. From the experimental results observed that the capsule material gives considerable effect on subcooling at lower temperature driving potential. Considering the experimental study which is concluded that solidification process time of encapsulated PCM of stainless steel material requires less time comparing to HDPE material.

Numerical modelling of melting and settling of an encapsulated PCM using variable viscosity

Thermal energy storage units using macro-encapsulated PCM in industrial and residential applications are contemporary due to better efficiency during charging and discharging. This article focuses on numerical modelling of the melting process in a macro-encapsulated PCM. Accounting the non-linear enthalpy–temperature relation and ramping down the velocity in solid phase is therefore fundamental. In the present article the variable viscosity method is implemented to ramp down the solid velocity and allow settling of the solid phase. This complete numerical model of melting and settling of PCM in a capsule is implemented in OpenFOAM. The numerical results for different solid viscosities are validated with experiments and show good agreement. The influence of the solid viscosity value and the pressure–velocity convergence is studied. It is observed that the pressure–velocity convergence only plays a greater role in the case where the computation of the exact solid velocity is required.