Nanoencapsulated Phase Change Materials Research Articles

Thermal and irreversibility analyses of a suspension embodying nano-encapsulated phase change materials using power-law and Darcy-Brinkman-Forchheimer models

The study of natural convection and heat transfer in a trapezoidal cavity finds a wide range of technological applications including thermal energy storage systems, building ventilation/insulation, waste heat recovery, electronic device cooling, controlling PV panel temperature, energy conservation, exchangers, nuclear reactors, furnaces, glass production, food processing, and drying technologies. The purpose of the current study is to explore the entropy and natural convection of non-Newtonian nano-encapsulated phase change material (NEPCM) suspension in a saturated porous medium enshrouded in a trapezoid-shaped domain with three heated blocks fitted with the bottom surface. The novelty of the present work is the introduction of power-law (Ostwald-de Waele) model subject to NEPCM suspension in trapezoidal enclosure emplacing three heated fins at its bottom surface embedded in Brinkman-Forchheimer extended Darcy medium with variant porosity. The finite element method is implemented to solve the governing equations numerically. The important findings of the present study include streamlines, isotherms, velocities, and apparent viscosity enhance while entropy generation whittles down with rise in Darcy number. Entropy generation ameliorates by 519.16 % for low to high porosity of Brinkman-Forchheimer extended Darcy medium. The maximum apparent viscosity augments by 1441.24 % when power law index ameliorates.

Heat transfer investigation of nano – Encapsulated phase change materials (NEPCMs) in a thermal energy storage device

Phase change natural convection heat transport and flow features of a variety and new types of hybrid nanoliquids, suspension of Nano – encapsulated phase change materials (NEPCMs), within a square cavity is inspected theoretically in this analysis. The capsules are arranged with a shell and a PCM as a core. The shell of this NEPCM prevents the phase change material from the direct interaction of hot fluid and from the leakage. The heat capacity of the suspension contains latent heat generated at the time of phase change. The modeled equations are numerically scrutinized with Finite element method. Variable thermal conductivity parameter 1≤Nc≤5, variable viscosity parameter 1≤Nv≤5, radiation number 0.5≥R≥0.1, Rayleigh parameter 102≤Ra≤103, volume fraction of NEPCMs1%≤ϕ≤5% and fusion temperature (0.2≤θf≤1.0) impact on the patterns of heat capacity ratio, isotherms and velocity lines are examined in detail. The results indicates that, as the volume fraction values of NEPCMs amplifies from 1% to 5% the rates of heat transfer of the nanoliquid magnifies 42% compared to the host fluid. Non – dimensional rates of heat transport magnifies with growing (Ste) values.

Synthesis of silica-encapsulated myristic acid phase-change-assisted nanocapsules for thermal management applications

AbstractMyristic acid-based silica (MA/SiO2) nano-encapsulated phase change materials (NePCMs) were synthesized by the sol–gel process. Five different samples of the MA/SiO2 nanocapsules were prepared by varying the mass of the myristic acid. The nanocapsules were characterized by Fourier transform infrared spectrophotometer (FTIR), X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), energy dispersive X-ray (EDX), and dynamic light scattering (DLS). These characterization techniques confirmed the successful encapsulation of the myristic acid inside the silica shell. The maximum latent heat was found to be 114.46 J/g for the sample which was prepared with 25 g myristic acid and 20 ml tetraethyl orthosilicate precursor material. The highest encapsulation ratio of approximately 62% was obtained in the same sample and the mean size of the nanocapsules was 597 nm. The thermal stability of these nanocapsules was assessed using the thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC) results exhibited that the thermophysical properties remained consistent after 50 heating/cooling thermal cycles indicating excellent durability of the NePCMs.

Studying the Improvement of Solar Collector Mechanism with Phase Change Materials

This study delves into the integration of phase change materials (PCM) in solar thermal collector systems to address this challenge. By incorporating nano encapsulated PCMs, researchers have mitigated concerns surrounding PCM leakage, revolutionizing the potential of solar collector systems to elevate energy efficiency, diminish carbon emissions, and yield manifold benefits. This article comprehensively investigates the design and utilization of solar phase change energy storage devices and examines the transformative impact of employing nano-coated phase change materials (Nano capsules) to augment solar collector performance. The integration of paraffin-based PCM and the insulation of the collector system have been crucial in optimizing heat retention and operational efficacy. The composition of the PCM involves a balanced blend of octadecane phase-change particles and water as the base fluid, designed to maximize thermal performance. Analysis of the experimental findings demonstrates the dynamic thermal behavior of the nano encapsulated phase change material, revealing distinctive temperature profiles about fluid dynamics and absorbent characteristics. Notably, the study emphasizes the nuanced trade-offs associated with the conductivity and melting temperature of the Nano encapsulated PCM, yielding valuable insights into energy storage capacity limitations and thermal performance variations throughout diurnal cycles. Central to the investigation, the optimal nanoparticle proportion is elucidated, shedding light on its pivotal role in modulating PCM performance. Furthermore, findings underscore the complex interplay between nanoparticle volume fraction and thermal fluid temperature, providing critical perspectives on optimizing PCM-enhanced solar collector systems.

Convection flow of nano-encapsulated phase change material in wavy chamber with double sliding walls, flame-shaped heating source, and magnetic force

This article aims to improve the convection flow within a two-dimensional chamber by utilizing nano-encapsulated phase change material (NEPCM). The chamber center contains a flame-shaped heating source, and the bottom wall is wavy. Forced convection occurs due to the motion of the chamber's side walls, while natural convection arises from the thermal gradient across the side walls. The Galerkin-finite element (GFEM) approach was employed to analyze the system's governing equations. The study investigates the impact of the following factors on heat transfer: wall velocity (Re = 10–1000), wall movement directions (both walls moving in a positive direction, both walls moving in a negative direction, and one wall negative and the other positive), intensity of the magnetic field (Ha = 0–100), and cavity porosity (Da = 10−5 – 10−2). The results demonstrate that increasing Re and Da improves the average Nusselt number (NuAvg). Conversely, raising the intensity of the magnetic field and moving the side walls in the opposite direction reduces NuAvg. At Re = 1000, increasing Da (10−2 instead of 10−5) leads to a 139% increase in NuAvg, and decreasing Ha and moving walls in the same directions increase NuAvg by 11.5% and 640%, respectively.

Optimization of temperature distribution in building envelopes of Ahmedabad region using nano-encapsulated phase change material

The incorporation of Phase Change Materials (PCM) into the building envelopes helps to increase indoor thermal comfort while lowering energy usage. The selection of PCM is directly related to its performance and might be viewed as an optimization challenge. The manuscript highlights the optimization of temperature distribution in building envelopes (walls and roofs) of Ahmedabad by choosing the suitable PCM and Nano-particle. Three different PCMs (RT31, RT 35, and RT42) and Nano-particles (Al2O3, CuO, and ZnO) with different concentrations (12 %, 16 %, and 20 %) are considered for the optimization. The PCMs are encapsulated into the building layer thickness to examine their characteristics like effective thermal conductivity, concentration, melting point, etc. These parameters are evaluated in a room that measures 5 m x 4 m x 3.5 m (L x W x H). The design-builder software (Version 7.0.2.006) is used to carry out the steady-state numerical simulations for this building envelope. The results suggest that the integration of PCM reduces the building's overall energy consumption by 7.92 kWh/m2 per year. The optimal design is proposed by establishing a temperature difference (ΔT) in building envelopes and utilizing a hybrid optimization technique (a combination of Artificial neural network (ANN) and Genetic algorithm (GA)). This temperature difference of the building envelope is confirmed to be dependent on their PCM melting point, effective thermal conductivity, concentration (in%), and PCM layer thickness. Hybrid optimization is found to be the most stable strategy for predicting temperature dilation and energy storage in building envelopes. Thus this paper gives a systematic understanding of the selection of PCM and Nano-particles and identifies the suitable PCM layer thickness for encapsulation.

Bioconvection flow of NEPCM and oxytactic microorganisms within a porous circular cylinder containing a circular cylinder fin using an artificial neural network in conjunction with the ISPH method

This article investigates the bioconvection flow within a porous circular cylinder filled with oxytactic microorganisms and incorporating nano-encapsulated phase change materials (NEPCMs). The circular cylinder, equipped with T-fins, is situated within the cylinder’s domain. The governing equations are solved using the ISPH method based on a time-fractional derivative. An ISPH simulation, coupled with an artificial neural networks (ANN) model, is employed to predict the values of the average Nusselt number ( Nu ¯ ). Utilizing bioconvection flow within a porous circular cylinder containing oxytactic microorganisms and integrating NEPCMs presents opportunities for progress in thermal management, environmental engineering, energy storage, and materials science. During the conducted simulations, we have investigated the impacts of Darcy, Lewis, Peclet, Rayleigh, and bioconvection Rayleigh numbers on a range of parameters, encompassing isotherms, heat capacity ratio, concentration profiles of oxygen and microorganisms, velocity field, and Nu ¯ . The results obtained highlight the significant influence of changes in the inner cylinder’s radius and fin length on regulating the intensity of bioconvection flow and improving heat transfer within a cavity. Additionally, the fusion temperature causes a shift in the heat capacity ratio toward the heat sources located within the cavity. The velocity field decreases by 97.39 % as the Darcy number decreases from 10 − 2 to 10 − 5 due to the challenges posed by porous media. Increasing the length of the T-fin enhances the cooling area, causing the isotherms to contract and altering the heat capacity ratio. In comparison to the target values, the ANN model demonstrates accurate prediction of Nu ¯ , bolstering confidence in its predictions.

Thermal performance of forced convection of water- NEPCM nanofluid over a semi-cylinder heat source

1) BackgroundPhase change materials (PCMs) have been used statically, which has caused the use of these materials to face challenges. Encapsulating PCMs and combining them with the base fluid can significantly solve the problem of using PCMs in BTM systems. In the present study, based on computational fluid dynamics, forced convection heat transfer of nano-encapsulated phase change materials (NEPCM) in a BTM system are simulated. The main aim of the present research is to reduce the temperature at the surface of the hot cylinder. 2) MethodsIn this research, we simulated lithium battery thermal management systems in both steady and transient states. The effects of using NEPCM particles to water were investigated. Modeling is implemented using the finite volume method and the PIMPLE and SIMPLE algorithms in OpenFoam. Furthermore, the effects of battery heat flux, Reynolds number, and the presence of nanoparticles (NPs) were analyzed. We intend to evaluate the optimal state of the system by studying the mentioned parameters. 3) Significant FindingsOur study shows that adding 3.5% NEPCM to water can reduce the length of the vortex by 22% and in unsteady-state simulation, it is observed that the presence of NEPCM particles in water reduces battery temperature up to 0.66 K.

Large eddy simulation of mixed convection of hybrid nanofluid containing nano-encapsulated phase change material in a vertical channel

Large eddy simulation of mixed convection of hybrid nanofluid containing nano-encapsulated phase change material in a vertical channel

Investigation of MHD oxytactic microorganisms with NEPCMs in rectotrapezoidal enclosure with FEM: Applications to energy storage technologies

Nanoparticle-enhanced phase change materials (NEPCMs) have gained significant attention in recent years due to their unique ability to enhance the thermal properties and overall performance of phase change materials (PCMs). The present work investigates the bioconvection flow of nano-encapsulated phase change material within a rectotrapezoidal cavity. The left wall of the is fixed at the constant high temperature whereas the right vertical wall is kept at cold temperature. The higher order Galerkin finite element method (GFEM) has been employed to simulate the proposed problem. The discrete systems of nonlinear equations are linearized by implementing the adaptive Newtons method. Influence of various pertinent parameters such as inclined magnetic field, oxytactic bacteria, radiation and Lewis number has been analyzed. It is observed that the average Sherwood and Nusselt number exhibit a positive correlation with the Hartmann and radiation parameter. Moreover, the average heat transfer exhibits a decreasing trend as the Hartmann, bioconvection Rayleigh and Peclet increase.

Magnetohydrodynamic free convection of nano-encapsulated phase change materials between two square cylinders: Mapping the thermal behavior using neural networks

The study focused on investigating the convective heat transfer of nano-encapsulated phase change suspensions in the presence of a non-uniform magnetic field within an annuli space between two square cylinders. The principal equations for the fluid flow and phase change heat transfer were formulated as partial differential equations and then represented into dimensionless format. The finite element method was used to solve these equations and simulate the free convection heat transfer. The effect of various factors, including Hartmann, Rayleigh, Eckert and Stefan numbers, geometry aspect ratio, nanoparticles’ concentration, and fusion temperature, on the heat transfer rate was examined. A neural network was also introduced and trained to establish the connection between the control parameters (inputs) and the heat transfer rate (output). The outcomes were presented in the form of the modified Nusselt number, along with isotherms, heat capacity ratio (phase change) contours, and streamlines. The results demonstrated that the neural network could accurately predict the heat transfer rate and provide a comprehensive map of heat transfer with respect to the control parameters. Nano-Encapsulated Phase Change Materials (NEPCMs) can be considered as a new type of nanofluids, in which the nanoparticle consists of a core and a shell. The core part is made of a Phase Change Material (PCM) which can undergo solid-liquid phase change at a certain fusion temperature, and absorb/release a significant amount of energy due to latent heat of the phase change.

Turbulent Heat Transfer of Hybrid Nanofluid with Nano-Encapsulated Phase Change Material in a Square Channel

Investigation of turbulent mixed convection of different working fluids, namely, pure water, CuO/water nanofluid, n-octadecane/water nanofluid (or slurry), and a hybrid water-based suspension of CuO and n-octadecane nanoparticles in a uniformly heated vertical square channel is carried out. The shear stress transport/kappa-omega model is applied to simulate the turbulent flow. Eulerian–Lagrangian two phase model and homogeneous model are employed to simulate the nanofluid flow. It is shown that Eulerian–Lagrangian two-phase model predicts higher Nusselt number and friction factor than single-phase model and the results of two-phase model are closer to experimental data. It is found that a new hybrid nanofluid with dispersed nano-encapsulated phase change material particles provides better thermal and hydrodynamic performances compared to other nanofluids. Slurry containing 5% n-octadecane provides an improvement of nearly 37.2%, while hybrid nanofluid (1% CuO + 5% n-octadecane) offers added convective heat transfer enhancement of almost 60%. With increasing volume fraction, friction factor becomes slightly larger than that of pure water. For 5% n-octadecane/water and 1% CuO + 5% n-octadecane/water nanofluids, friction factor increases by 2.5% and 1.7%, respectively. Due to dominance of thermal entropy generation, total entropy generation reduces by increasing Reynolds number and volume fraction.

Investigation of forced convection of a novel hybrid nanofluid containing NEPCM in a square microchannel: Application of single-phase and Eulerian-Eulerian two-phase models

In the present study, laminar forced convection flow and heat transfer of novel hybrid nanofluid of Al 2 O 3 -n-octadecane/water through a horizontal microchannel under a constant wall heat flux condition are investigated. N-octadecane is regarded as a nano-encapsulated phase change material (NEPCM). Simulations are performed utilizing single-phase and Eulerian-Eulerian two-phase models. Governing equations are discretized by finite volume method and then solved using SIMPLE algorithm. Effects of nanoparticles volume fraction ( φ ), Reynolds number ( Re ), and melting range ( T mr ) on thermal and hydrodynamic parameters of hybrid nanofluid are evaluated. It is shown that predictions by Eulerian-Eulerian approach are more accurate than those by single-phase approach when compared to available experimental data. Addition of Al 2 O 3 and n-octadecane nanoparticles to water-based fluid leads to a reduction in fluid and wall temperatures, which is intensified at higher φ and Re . Also, these nanoparticles do not have a significant effect on hydrodynamic development of flow, while they delay its thermal development. NEPCM with a higher T mr only slightly improves thermal performance of hybrid nanofluid, which is more noticeable in single-phase procedure. Total efficiency of hybrid nanofluid ( η hnf ) is amplified by raising φ for both approaches. This augmentation is more evident in Eulerian-Eulerian model due to better thermal and hydrodynamic performances. Maximum increases in η hnf concerning single-phase and Eulerian-Eulerian models are 27% and 60%, respectively, occurring at φ Al 2 O 3 = 1 % and φ n ‐ octadecane = 10 % . Therefore, this type of hybrid nanofluids, because of its enhanced thermo-physical properties, can be considered as a suitable candidate for thermal energy storage, heat transfer, and renewable energy applications.

Optimizing heat flow: Nano-encapsulated phase change materials in vibration-enhanced gravity-driven thermal convection

In cavities differentially heated at the sides and subjected to mechanical vibration, the natural convection incoming from buoyancy effects is not the only factor affecting the flow dynamic and heat transfer. The current work aims to address vibrational convection in a square chamber filled with a Nano-Encapsulated Phase Change Material (NEPCM) suspension. The non-dimensional equations of fluid and heat flows in the cavity are developed and solved numerically. The gravity term in the momentum equation is modified to include the effect of vibration. It is shown that the vibrational Rayleigh number has the most effect on the convective heat transfer, followed by the conductivity of the NEPCM suspension. Increasing the vibrational Rayleigh number from 103 to 107 leads to up to 3 times rise in the time-averaged Nusselt number. The NEPCM concentration has a moderate influence, as around 12% increase in the time-averaged Nusselt number is found when a 5% volume fraction of particles is employed. An increase in the Stefan number from 0.2 to 0.8 is associated with a 6.1% reduction in the time-averaged Nusselt number. Additionally, the peak heat transfer is achieved at the melting point of 0.5, with a 6.5% increase compared to the melting temperature of 0.1.

Enhanced heat transmission in a triangular enclosure with a rotating cooled wall using Nano-Encapsulated Phase Change Material nanofluid under mixed convection

Maximizing heat transfer rates within enclosed cavities is of paramount importance in various engineering applications. This study focuses on enhancing heat transmission efficiency through forced convection within a triangular cavity containing a rotating cylinder. The approach involves incorporating Nano-Encapsulated Phase Change Material (NEPCM), applying a uniform magnetic field, and introducing a cold, dynamically rotating cylinder. The cavity's configuration maintains an elevated temperature on the upper wall while the inclined side walls remain cold. The investigation also explores the impact of varying the position of the rotating cylinder within the cavity. Mathematical modeling is undertaken using the Galerkin finite element methodology. Numerical results reveal a direct proportionality between the Nusselt number (Nu) and the Darcy number (Da), as well as an inverse proportionality between Nu and the Hartmann number (Ha). Elevating the Darcy number from 10−5 to 10−2 leads to a 54% increase in the Nusselt number, while increasing the Hartmann number from 0 to 100 results in a 12.5% decrease in Nu. Intriguingly, positioning the cold rotating cylinder in the upper enclosure leads to a 240% enhancement in Nu. This study highlights the intricate interplay of geometry and external fields in optimizing heat transfer within complex cavities.

Integrating ISPH simulations with machine learning for thermal radiation and exothermic chemical reaction on heat and mass transfer in spline/triangle star annulus

This work integrates incompressible smoothed particle hydrodynamics (ISPH) with machine learning (ML) to examine the uses of two different domain shapes, spline star-domain, and triangle star-domain, on double diffusion of nano-encapsulated phase change material (NEPCM). The effects of thermal radiation and exothermic chemical reactions are conducted in this work. The hexagonal-shaped is located inside the center of the star-shape carrying (Th&Ch). The left/right walls of the star shape are kept at (Tc&Cc) and the other walls have an adiabatic condition. It is recommended to examine the smoothness of closed curves in the heat and mass transfer by changing the triangle to spline curves. The present investigations of transmission of heat and mass of NEPCM within a complicated star shape can be employed in cooling systems of electronic/battery, heat exchangers, food processing, and chemical engineering. The ISPH simulations are executed for the pertinent parameters, Darcy number, Frank-Kamenetskii number, Rayleigh number, Dufour number, Soret number, and thermal radiation parameter. The performed simulations showed the significance of the spline star domain compared to the triangle star domain in smoothening the nanofluid flow and double-diffusive convection in an annulus. Frank-Kamenetskii number is a promising factor in the enhancement of heat transfer and controlling the phase change zone within an annulus. At a spline-star cavity, the maximum velocity rises by 32.32 % and 54.95 % when the Frank-Kamenetskii number grows from 0 to 5, and thermal radiation increases from 0 to 5. Soret number works effectively in enhancing the distribution of concentration at large temperature differences. Machine learning plays a vital role in many engineering applications. Hence, ML's powerful capabilities to predict the average Nu‾ and Sh‾. In the proposed ML model, the dimensionless time and thermal radiation parameter are used as input to the ML model, while their corresponding numeral estimated values of Nu‾ and Sh‾ are used as output targets for the ML model. The values of Nu‾ and Sh‾ are predicted by the suggested ML model with a comparatively small error less than 1 %.

A ROTATING WAVY CYLINDER ON BIOCONVECTION FLOW OF NANOENCAPSULATED PHASE CHANGE MATERIALS IN A FINNED CIRCULAR CYLINDER: ISPH SIMULATIONS

The originality of this study is the introduction of numerical investigations on the bioconvection flow of nano-encapsulated phase change materials (NEPCMs) with oxytactic microorganisms in a new configuration of a circular annulus with a rotating wavy inner cylinder. The incompressible smoothed particle hydrodynamics (ISPH) method was applied to solve the governing partial differential equations for the velocity, temperature, concentration, and density of motile microorganisms. Compared with the conventional mesh-based method, this mesh-free, particle-based approach offers strong advantages in the simulation of complex problems with free surfaces and moving boundaries with large displacements. The pertinent parameters are the undulation number (<i>N<sub>und</sub></i> = 2-36), bioconvection Rayleigh number (<i>Ra<sub>b</sub></i> = 1-1000), Darcy parameter (Da = 10<sup>-5</sup>-10<sup>-2</sup>), length of the inner fin (<i>L<sub>Fin</sub></i> = 0.05-0.15), radius of the inner wavy cylinder (<i>R<sub>c</sub></i> = 0.05-0.25), Rayleigh number (Ra = 10<sup>3</sup>-10<sup>5</sup>), undulation amplitude of the inner wavy cylinder surface (<i>A</i> = 0.1-0.4), and frequency parameter (<i>ω </i>= 1-5). The undulation number of the inner wavy cylinder enhanced the flow of the oxytactic microorganisms and isotherms, whereas it had the reverse effect on the velocity, decreasing the maximum velocity by 26.56%. In addition, the comparatively high undulation amplitude and frequency increased the average Nusselt and Sherwood numbers. It was found that the embedded wavy cylinder interacting with fins plays an important role in enhancing heat transfer and the bioconvection flow within a closed domain.

Heat and mass transport of nano-encapsulated phase change materials in a complex cavity: An artificial neural network coupled with incompressible smoothed particle hydrodynamics simulations

<abstract> <p>This work simulates thermo-diffusion and diffusion-thermo on heat, mass transfer, and fluid flow of nano-encapsulated phase change materials (NEPCM) within a complex cavity. It is a novel study in handling the heat/mass transfer inside a highly complicated shape saturated by a partial layer porous medium. In addition, an artificial neural network (ANN) model is used in conjunction with the incompressible smoothed particle hydrodynamics (ISPH) simulation to forecast the mean Nusselt and Sherwood numbers ($ \stackrel{-}{Nu} $ and $ \stackrel{-}{Sh} $). Heat and mass transfer, as well as thermo-diffusion effects, are useful in a variety of applications, including chemical engineering, material processing, and multifunctional heat exchangers. The ISPH method is used to solve the system of governing equations for the heat and mass transfer inside a complex cavity. The scales of pertinent parameters are fusion temperature $ {\theta }_{f} = 0.05-0.95 $, Rayleigh number $ Ra = {10}^{3}-{10}^{6} $, buoyancy ratio parameter $ N = -2-1 $, Darcy number $ Da = {10}^{-2}-{10}^{-5} $, Lewis number $ Le = 1-20 $, Dufour number $ Du = 0-0.25 $, and Soret number $ Sr = 0-0.8 $. Alterations of Rayleigh number are effective in enhancing the intensity of heat and mass transfer and velocity field of NEPCM within a complex cavity. The high complexity of a closed domain reduced the influences of Soret-Dufour numbers on heat and mass transfer especially at the steady state. The fusion temperature works well in adjusting the intensity and location of a heat capacity ratio inside a complex cavity. The presence of a porous layer in a cavity's center decreases the velocity field within a complex cavity at a reduction in Darcy number. The goal values of $ \stackrel{-}{Nu} $ and $ \stackrel{-}{Sh} $ for each data point are compared to those estimated by the ANN model. It is discovered that the ANN model's $ \stackrel{-}{Nu} $ and $ \stackrel{-}{Sh} $ values correspond completely with the target values. The exact harmony of the ANN model prediction values with the target values demonstrates that the developed ANN model can forecast the $ \stackrel{-}{Nu} $ and $ \stackrel{-}{Sh} $ values precisely.</p> </abstract>

Highly stable and nonflammable hydrated salt nanocapsules with inorganic-organic composite shell for sustainable building technology

Inorganic hydrated salts show great potential for use in low-temperature energy storage. Nevertheless, drawbacks, such as phase separation, liquid leakage, and inherent supercooling, restrict their application in sustainable building technology. Here, nanoencapsulated phase change materials (NePCMs) was designed by combination of hydrated salt and inorganic-organic composite shell to enhance the thermal energy storage of buildings. Using a two-step method, PMMA and TiO2, considered excellent shell materials, were harmoniously combined on the surface of Na2HPO4·12H2O core. The latent heat of the nanocapsules was approximately 139.6 kJ/kg. After undergoing 500 heating and cooling cycles, the latent heat of nanocapsules only degraded by approximately 5 %. Leakage of water was not observed following heating of the NePCMs to 60 °C for 1 h. The supercooling degree of the nanocapsules decreased to around 0.7 °C. The hybrid PMMA-TiO2 shell was designed to improve shape stability, reduce water loss, and enhance mechanical properties. Through burning experiments, it was confirmed that NePCMs had good flame-retardant properties. Thus, hydrated salt nanocapsules with inorganic-organic composite shell are an ideal candidate for use as building materials for effective thermal management and fire protection.

Synthesis, characterization and application of a magnetic nanoencapsulated PCM in enhancing the natural convection in a cube cavity

Encapsulation of phase change materials (PCMs) is an intelligently effective way to overcome the challenges of PCMs usage in heat storage and transfer applications. At the first stage of the current study, a novel magnetic nanoencapsulated PCM (M−NEnPCM) consisting of n-Octadecane (n-C18) coated with a poly methyl methacrylate (PMMA) shell was synthesized through the miniemulsion ultrasonic-assistant polymerization technique. The magnetic property was introduced to the nanocapsules by adding surface-modified Fe3O4 nanoparticles into the core during the formation step. The dynamic light scattering (DLS) results showed an average nanocapsule size of 78 nm. The scanning electron microscope (SEM) along with transmission electron microscope (TEM) images confirmed the spherical shape with a core/shell structure of the M−NEnPCM. According to the differential scanning calorimetry (DSC), M−NEnPCM had melting and crystallization latent heats of 116.47 and 124.71 J/g, respectively. Moreover, based on vibrating sample magnetometry (VSM) results, the superparamagnetic property of M−NEnPCM is proved. At the second stage, the performance of water suspensions containing different amounts of the as-prepared nanocapsules in enhancing the natural convection in a cube cavity was investigated under various heat fluxes and magnetic field flux densities. The results illustrated that the use of nanocapsules leads to enhance the natural convection up to 2 times higher than that of pure water; while there are optimum levels of M−NEnPCM concentration and magnetic field flux density at which the heat transfer coefficient is maximized.