Freezing Of Phase Change Material Research Articles

Enhancing solar panel cooling efficiency: a study on the influence of nanofluid inclusion and pin fin shape during melting and freezing of phase change materials

The present article presents a 3D simulation of a solar thermal panel containing phase change materials (PCMs). Two pipes are devised in the panel, and several pin fins (PFs) are applied to each pipe. Organic PCMs are encapsulated in a compartment around the PFs and pipes. The variable is PF shape, which includes four types, i.e., square, rectangular, triangular, and circular. Nanofluid (NFD) is used within the pipes. The study is carried out transiently and continued until the stabilization of outlets. Utilizing an FEM method based on a weak form, namely, Galerkin, to find a numerical solution for mathematical modeling. The artificial intelligent results indicate that using triangular, square, rectangular, and circular PFs provides the highest NFD temperature in the outlet, respectively. Circular PFs lead to a lower heat transfer coefficient (HC) compared to other PFs. The comparison between various PF shapes shows that the use of circular and triangular PFs results in the lowest and highest panel temperature, respectively. Moreover, the highest and lowest volume fraction of melting PCMs around the pipe is obtained through the use of triangular and circular PFs, respectively.

Development of novel correlations towards the freezing time estimation of phase change material inside a cylindrical capsule involving thickness and its thermal conductivity for thermal storage applications – An experimental and parametric studies

The freezing of phase change materials (PCM) is a widespread phenomenon with numerous potential applications in fields such as refrigeration, thermal storage, chemical industries, etc. Thermal energy storage (TES) is one such application where the inward freezing concept is utilised during the solidification of a PCM in cylindrical container. Literature shows various correlations to predict the inward and outward freezing duration of PCM inside a cylindrical container. However, no correlation describes the effect of container material properties on the PCM freezing time. Therefore, two new correlations are developed - one for the inward freezing time of PCM inside a cylindrical container and the other for the outward freezing time around it, taking into account the effect of container material thermal conductivity and its thickness. Subsequently, experimental research is conducted to validate the proposed correlation, which agrees with the experimental freezing time, with a maximum inaccuracy of around 7.8 %. Finally, a parametric study analysing the effect of container thermal conductivity and thickness on the inward freezing time of PCM reveals that the thickness of the container plays no role in freezing when container thermal conductivity exceeds 5 W m−1 K−1.

Thermal management of a prismatic lithium battery pack with organic phase change material

BackgroundThis article examines a T-shaped lithium-ion battery pack (BPC) consisting of six prismatic cells using the finite element method (FEM). An optimal model is introduced for batteries’ thermal management (THMT) by changing the position of the inlets and outlets. MethodsThe outlet is where the fully developed airflow leaves, and the walls use the no-slip boundary condition. The batteries are placed in an enclosure filled with phase change material (PCM) to create temperature uniformity on the batteries. The hydrodynamic and thermal modeling of airflow and the melting and freezing of PCM are performed in this study using the COMSOL program. Significant findingsThe results demonstrate that the batteries’ maximum temperature (TMX) changes by changing the location of the inlets. Changing the position of inlets also affects the melting and freezing of the PCM, and better temperature uniformity on the batteries may be achieved using some models. The M4 model, in which the inlet and outlet are on the left and right sides, and an outlet is in the center, is the most appropriate model for industrial applications.

Impact of the number of tubes containing nanofluid flow on the melting and freezing of phase change materials in the thermal management of plate lithium-ion batteries

Phase change material (PCM) and nanofluids (NFs) flow are used in three-dimensional simulations for the thermal management (TMGT) of a plate battery. On each side of the battery, there are two enclosures in which the PCM is housed. Within the PCM, there is a tube that allows alumina/water NFs to flow. The two-phase model is used to simulate the NFs flow, the number of tubes inside the PCM is varied from 1 to 4, and the NFs velocity (VNF) is changed from 10 to 30 mm/s. Also, the distance of the tubes from the battery center changes to determine the volume fraction of molten PCM (VFMPC) and the maximum temperature of the battery (T-BT). For the simulations, the finite element technique (FEM) is used. The findings show that the lowest maximum T-BT and VFMPC are caused by a 5-mm distance between the tubes, whereas the greatest maximum temperature (T-MX) and VFMPC are caused by an 8-mm gap. The use of more tubes in PCM causes the VFMPC to be decreased. Besides, the maximum T-BT is reduced with time. Enhancing the VNF causes the maximum T-BT to decrease. The maximum T-BT is decreased by 45.37% in 1200 s by adjusting the VNF from 10 to 30 mm/s.

Numerical analysis of complex heat storage unit during freezing of phase change material enhanced withTiO2 nanoparticles

Improvement of discharging process of system with inclusion of nanoparticles (TiO2) and install of new style of fins have been illustrated in this investigation. The scrutinized paraffin (n-eicosane) become solidify at 309 K and fraction of nanoparticles is less than 0.03 for all cases which is permission of using homogeneous model for estimating properties. Although the efficacy of gravity force can be neglected in freezing, in current modeling, the related term has been applied and contours for velocity have been reported. The outer wall of tank has square shape and zero gradient condition was applied for that wall. The circular wall which the fins attached to this has cold wall (296 K). Thus, appearance of fins makes the freezing faster. Number of fins (n = 1, 3, 7) and fraction of TiO2 (ϕ = 0, 0.03) were the variables of simulations. With adding nano-powders, the required time declines about 3.33 %, 2.69 % and 2.015 % when n = 1, 3 and 7, respectively. Increasing number of fins from 1 to 3 and 7, makes freezing time to decline around 23.24 % and 28.41 %.

Time-Controlling the Latent Heat Release of Fatty Acids using Static Electric Field

Latent heat released during freezing of phase change material (PCM), which occurs at a constant temperature, can be modified using an electric field, through a process called electrofreezing. To date, the effects of the electric field on the freezing of salt solutions or salt hydrates of inorganic PCM, such as reduction of the supercooling degree, increase of nucleation rate, and reduction of the induction time due to changes in the Gibbs free energy, have been the focus. In this paper, we describe the electrofreezing of stearic acid and lauric acid of fatty acid PCM. Because common organic PCM has relatively small or even zero supercooling, the effect of the DC electric field on the time of latent heat release at a constant temperature and crystallization time was more pronounced. A comparison was also done with inorganic CaCl2⋅6H2O PCM using previously published data. We propose that the two time parameters are closely related to the electrical and thermal conductivities. Different nucleation mechanisms for fatty acids and CaCl2⋅6H2O with interactions between the crystalline sample and electric field, as well as dissimilar Joule heating effects, have been proposed. Changes in the chemical structure and thermal stability due to electric field treatment are evaluated using the Fourier-transform infrared spectra, the decomposition and melting temperatures, and the calculation of the latent heat of fusion. We also discuss the potential applications of lauric and stearic acids as phase change composites in thermoresponsive devices for high electrical to thermal energy conversion efficiencies.

An optimizer using the PSO algorithm to determine thermal parameters of PCM: A case study of grey water heat harnessing

The melting and freezing of Phase Change Materials (PCMs) is categorized as a moving boundary problem. For this reason the mathematical solution to study the behaviour of practical applications is only possible via complex numerical approximations. However for a preliminary design the main concern is to select the optimum thermal characteristics of the PCM storage unit, for both melting and freezing. This is to be done before the detailed design by integrating an optimization algorithm with a numerical simulation. The application of using PCMs to harness the waste heat from non-industrial grey water is investigated as a case of study. For this purpose, the 2-phase analytical solution to the Stefan problem is coupled with the particle swarm optimizer (PSO) to find the best combination of thermal characteristics within the prescribed boundary conditions of this case study. Results show that the optimum phase change temperature lies between 20 and 22 °C, depending on various sets of input parameters. At the same time the ratio of latent to sensible heat transferred by the PCM highly influences this optimum temperature for the combination of both melting and freezing. Similarly results show melting being faster and more intensive in term of latent heat charging compared to a higher sensible heat discharging while freezing.

System-level analysis of a novel air-cooled condenser using spray freezing of phase change materials

A comprehensive system-level analysis is performed for a novel air-cooled condenser based on spray freezing of phase change materials (PCMs). This novel air-cooled condenser uses PCMs to decouple the process of steam condensation and heat rejection to air in order to significantly improve air-side heat transfer and reduce steam condensation temperature as compared to conventional air-cooled condensers (ACCs). Melting of solid PCM particles in a two-phase PCM slurry flow anchors the steam condensation temperature close to the PCM melting point regardless of the change in ambient air temperature. Spray freezing of millimeter-sized liquid PCM droplets increases the air-side heat transfer coefficient by five times compared to the finned-tubed ACCs. A multiscale model, which directly captures the melting and settling of PCM particles at the microscopic level and accounts for phase change through energy source terms at the macroscopic level, has been developed to simulate the PCM slurry flow over heated tube bundles. Using this multiscale model, the effects of particle volume fraction, Reynolds number, and particle to steam tube diameter ratio on the averaged wall Nusselt number of the steam tubes are investigated. It is found that the averaged wall Nusselt number for a PCM slurry flow of 20% solid fraction achieves a 38% enhancement over the PCM single-phase flow of same Reynolds number. On the air side, the freezing/melting of PCM droplet/particle is approximated based on a 1-D transient heat conduction model and the air-side pressure drop across the PCM droplet array is determined using a 3-D k-ε turbulence model. The performance of this spray-freezing PCM ACC is compared against a baseline ACC of a 500 MWe power plant. It is found that, for comparable footprint area and ambient conditions, the spray-freezing PCM ACC reduces the initial temperature difference to as low as 16.8 °C and provides up to 10.8 MW net power production gain compared to the baseline ACC.

Convective melting and freezing of phase change materials encapsulated within small diameter polymer tubes

This work characterizes the inward melting and freezing of phase change materials (PCMs) within small diameter polymer tubes under convective boundary conditions. Using air as the heat transfer fluid, a custom-built experimental apparatus was used to control the convective heating and cooling of vertically oriented PCM-filled tubes with an outer diameter of 3.175 mm. Various air speeds and air temperatures were investigated, as well as the effects of wall thickness and material properties, using three different polymer encapsulant tubes. Volume fraction, latent heat transfer rate, and the associated overall heat transfer coefficient have been measured experimentally during the transient melting and freezing processes. Using a commercially available paraffin-based PCM with a nominal melting temperature of 35 °C, phase change times ranging from 50 s to 180 s were recorded with air speeds and air temperatures of 4.7–15.3 m/s and 25.3–62.6 °C, respectively. Overall latent heat transfer coefficients as high as 200 W/m2 K were measured and shown to decay with time as the PCM changes phase during inward melting and freezing. For the thinnest encapsulants tested here, the results were consistent with a simplified one-dimensional quasi-steady-state thermal circuit model. Deviations from this model were observed and explained, including the importance of the wall thickness and thermal conductivity of the encapsulant.

Unidirectional freezing of phase change materials saturated in open-cell metal foams

An experimental and theoretical study of the unidirectional freezing of water as a PCM filled in metal foams has been carried out. Particular concern is placed upon determining how the contact conditions between the metal foam and the cold wall influence the freezing process, as well as exploring the local thermal equilibrium between the metal foam and the PCM. To address these questions, three contact conditions were considered, i.e., natural contact, applied pressure, and bonding with a high thermal conductivity adhesive. To explore the local thermal equilibrium, temperatures on foam ligaments and within the pores were measured individually using thermocouples. For the current copper foam/water PCM system, the three different contact conditions were found to have similar freezing rate. This indicates that in practice one can simply embed metal foam blocks into PCMs with no need of bonding them to the cold wall via sintering, thermal adhesive or other methods, thereby reducing the costs of devices in thermal energy storage systems. Effects of foam properties, including porosity and pore density on the freezing rate, were also discussed.

Numerical study of the spacecraft thermal control hardware combining solid–liquid phase change material and a heat pipe

A new spacecraft thermal control hardware composed of two parallel channels working for heat pipe (HP) and solid–liquid phase change material (PCM), respectively, is suggested for the high heat dissipating component which works intermittently with short duty. In present study the honeycomb structure radiator embedded with the device combining HP and PCM is designed, and the detailed thermal math models are developed for numerical analysis. The comparison of computational results between with and without PCM shows that the HP–PCM device redistributes temporal peak heat around a whole orbit period through alternate melting and freezing of PCM, and, as a result, the maximum and minimum temperatures are effectively alleviated. The drawback of PCM application due to low thermal conductivity can be successfully resolved by means of parallel arrangement of the HP channel. The suggested HP–PCM device can be a kind of off-the-shelf component and it does not require any case dedicated configuration. Therefore, it can be used with less impact on the program cost and schedule different from most of the PCM applications.

열관과 상변화물질을 일체형으로 병렬 배열한 위성용 열제어 부품 연구

ABSTRACT The satellite thermal control H/W composed of two parallel channels working for heat pipe (HP) and phase change material (PCM) is suggested for the high heat dissipating component which works intermittently with short duty. In a limited point of view, the HP-PCM device is a kind of off-the-shelf component that requires no dedicated configuration and thermal designs to PCM. Therefore, it can be used with less impact on the program cost and schedule different from most of the PCM applications. In present study the typical honeycomb structure radiator applying the HP-PCM device is designed and the detail thermal math model is developed for numerical analyses. The result comparison between without and with PCM shows that the HP-PCM device redistributes the peak heat around the whole mission period through the alternate melting and freezing of PCM, and, as a result, the maximum and minimum temperatures are effectively alleviated. The drawback of PCM application due to low thermal conductivity can be successfully resolved by means of parallel arrangement of HP channel.