Convection Of Phase Change Material Research Articles

Simulation of heat transfer in a nanoparticle enhanced phase change material to design battery thermal management systems: A lattice Boltzmann method study

BackgroundIn the present paper, the natural convection of phase change material (PCM) in a T-shaped cavity is investigated by the lattice Boltzmann method (LBM). In recent years, LBM has become a powerful method for computational modeling of a broad variety of complex fluid flow concerns, including the simulation of the melting process in PCMs. MethodsThe enclosure contains CuO nanoparticles and two constant temperature heat sources on the sidewalls of the cavity. The obtained results are presented in different Rayleigh numbers (Ra=103–105), cavity angles (θ = 0 − 90), the volume fraction of nanoparticles (ϕ = 0 − 0.03), and aspect ratios. Results show that the PCM melting speed is lower for low Rayleigh numbers compared to when the number is equal to 105 by 50%. To alter melting time in a specific Ra number, adding nanoparticles, changing cavity slope, and aspect ratio are investigated. Results show that the melting rate is little affected by the addition of nanoparticles but, generally adding nanoparticles delays PCM melting. Significant findingsRaising the distance between the battery and the top of the cavity is known to delay melting by 70% when the distance ratio increase from H1/H = 0.25 to 075, whereas increasing or lowering the distance between the batteries does not affect the melting time. Such a study can be used to design battery thermal management systems (BTMS).

Natural convection of rectangular cavity enhanced by obstacle and fin to simulate phase change material melting process using Lattice Boltzmann method

In recent years, the lattice Boltzmann method has become a powerful method for computational modeling of various complex fluid flow concerns, including the simulation of the melting process in phase change materials. In the present paper, the natural convection of phase change materials in a cavity is simulated, and the effect of adiabatic obstacle and fin is investigated by the lattice Boltzmann method. The obtained results are presented in different Rayleigh numbers (Ra = 103-105), and cavity angles (θ=-90to90) in three scenarios (without adiabatic fin and obstacle, with an adiabatic obstacle, and with adiabatic fin). The investigation across various cavity angles, with adiabatic obstacles and fins, demonstrates a consistent trend of effective melting process delay by up to 50%, underscoring the significant impact of these adiabatic features on PCM behavior. Adiabatic obstacles induce localized melting delays due to unmelted zones around them. Streamlines highlight vortices formed by obstacles, and elevated Nusselt numbers correlate with accelerated melting facilitated by adiabatic fins. Modifying the adiabatic fin height from Yf = 0.1 to Yf = 0.7 leads to a doubling of melting time at around 80% PCM melting. Conversely, decreasing fin height from 0.5 to 0.7 extends the complete melting time by approximately 10%, showcasing the influential role of fin height in shaping PCM melting behaviour.

Asymmetric PCM melting and thermal convection in a rectangular enclosure with straight and wavy heat transfer passages

Experimental and numerical investigations of thermal convection in the vicinity of a straight and wavy horizontal heat transfer fluid passage (HTF)s placed in a rectangular enclosure filled with phase change material (PCM) are presented. The enthalpy-porosity-based finite volume solver is used to simulate the spatiotemporal evolution of the thermal convection, which is well-complemented by experimental visualization and thermocouple measurements. Heat transfer from the horizontal HTF exhibits asymmetrical melting. Heat diffusion is the dominating energy transfer mechanism on the bottom part of the HTF passage and is compared with the Stefan problem. The temporal evolution of thermal convection on the top part of HTF passage involves three distinct phases of melting, viz. initial conduction phase, Rayleigh–Bénard (R-B) convection with linear convection, and vortex coalescence effects. The final stage of the melting process is influenced by the topography of a peninsula of unmelt PCM, which is influenced by specific top-boundary conditions. Thermal convection in PCM above the wavy HTF passage exhibits restricted plume development leading to an improved melting rate and a higher average melt height. Augmentation of internal convection characteristics of HTF with the evolution of melting is also explored. A systematic investigation of the convection plume development and heat transfer characteristics in PCM by varying the HTF Reynolds (1700<Re<2750) and Stefan numbers (0.4<Ste<0.6) has been carried out, and analyzed the nature of thermal plumes, melt fraction, and average penetration length with the Fourier number. Additionally, novel correlations are proposed between Nusselt and Rayleigh numbers for straight and wavy tubes in the intermediate melting stage (1.3×104<Ra<4.7×107).

Natural Convection in the Melting of Phase Change Materials in a Cylindrical Thermal Energy Storage System: Effects of Flow Arrangements of Heat Transfer Fluid and Associated Thermal Boundary Conditions

Abstract Latent thermal energy storage systems (LTESS) have received widespread attention due to their high energy density to store a significant amount of thermal energy in the form of latent heat into phase change materials (PCM) at a nearly constant melting temperature. The thermal efficiency of LTESS is usually limited by poor heat conduction in PCM but enhanced by the natural convection of molten PCM. The natural convection increases the uniformity of temperature by mixing in a PCM enclosure and therefore increases the heat transfer rates and accelerates the melting. While there is negligible natural convection, periodic reciprocation of heat transfer fluid (HTF) through the PCM enclosure has been demonstrated to increase the heat transfer rates to PCM by increasing the melt interface area and reducing temperature gradients across PCM compared to fixed-directional flow arrangements. The current study examines the effects of HTF flow direction on the strength and duration of natural convection in PCM in a vertical cylindrical shell-and-tube container. Gallium is used as the PCM because of its low melting temperature and high thermal conductivity, and water is used as the HTF. A 2-D axisymmetric numerical model developed in ANSYS Fluent was used for the study of the cylindrical LTESS. The aspect ratio of the cylindrical container is nearly 1, which allows the generation of natural convection currents of strong magnitude in molten PCM in the vertical orientation. The irregular melting front in the PCM is caused by both natural convection in molten PCM and thermal boundary conditions for different HTF flow arrangements. The temperature and melting front profiles of PCM with the reciprocating flow arrangement are compared to unidirectional flows in upward and downward directions. The influence of HTF operating parameters such as temperature, velocity, and reciprocation period on PCM melting is studied. Scale analysis is also applied to characterize the different melting regimes of PCM under different flow arrangements.

Natural convection in phase change material: Experimental study

Natural convection in a melting material (hexadecane) is studied experimentally using Magnetic Resonance Imaging. This imaging technique allows to discriminate solid and liquid phases and to measure velocity vectors in the volume sample, even through/in opaque phases. Within our experimental conditions, the convection occurs above Ra≈1430. The thermo-convective flow affects the melting interface leading to higher liquid height in uprising flow and lower liquid height in downward flow regions. Our experiments show that (i) the transient evolution of the mean liquid height h¯ is enhanced with convection since h¯∝t0.8 (h¯∝t12−3β with β=1/4), while h¯∝t0.5 in the conductive regime similarly to the Stefan’s problem; (ii) the steady averaged liquid height h¯ increases 4 times larger in the convective regime than in the conductive regime. In our experiments the range of A, ratio between the solid and liquid heights, is such as A>1.5. Within this range of values we obtain convective pattern under the form of hexagons / polygons. As the melting boundary grows, we observe a decrease in the polygon number. The polygonal pattern is characterized by a constant dimensionless wavelength, i.e. λ/h¯≈2, and thus a constant wavenumber around 3.1 similarly to the primary bifurcation in the classical Rayleigh–Bénard Convection (RBC). Heat transfer is evaluated via the Nusselt number Nu. Close to the onset of convection and above, our results highlight a scaling law Nu∝Raβ with β=1/4 similarly to the classical RBC. The kinetic energy Ec is also evaluated via velocity measurements leading to Ec/E0∝Nu4 and therefore to Re∝Ra2β∝Ra1/2. Within the frame of our experiments, all scaling laws are converging to β=1/4. They reflect clearly an increase in the convective intensity from both thermal and dynamical points of view.

Characteristics of natural convection in n-eicosane in a square cavity with discrete heat source

The natural convection of phase change material (PCM) in a two-dimensional square cavity is numerically analyzed. The cavity consists of heat surface with a constant total heated area and adiabatic wall. The Grashof and Prandtl numbers for the PCM (n-eicosane with the melting temperature, Tmelt=36°C) in basic LHS system are 9 × 10^5 and 62.7, respectively, at 350.15K. The mass, momentum and energy balance equations of the system were considered. Three basic heating surface strategies were considered (discrete heat sources): single, side-side and side-bottom heating surface. The results show that the transient Nusselt number, mean kinetic energy at the surface and energy storage rate of the fluid are effectively enhanced by proper arrangement of the discrete heat source location and heating from the bottom half of the left and right sides requires the least time for 300 kJ energy storage. The results indicate that optimally placed discrete heat sources in PCM could be a promising alternative for high-efficient thermal energy storage.

Modeling and identification of combined effects of pulsating inlet temperature and use of hybrid nanofluid on the forced convection in phase change material filled cylinder

Effects of pulsating heat transfer fluid temperature and hybrid nano-additive inclusion in the base fluid are numerically studied for laminar forced convection through a phase change material embedded thermo-fluid system with finite element method. Effects of different values of Reynolds number (between 250 and 1000), amplitude (between 0 and 0.05) and frequency (Strouhal number between 0.01 and 0.5) of pulsating inlet temperature, nanoparticle volume fraction of hybrid particles (between 0 and 0.02) on the dynamic features of the system with performance characteristics are analyzed. It is observed that the phase change material onset temperature becomes oscillating with drastically reduction of full completion time as the Reynolds number and amplitude of pulsation are increased. The amount of reduction in the full phase transition is 63% when cases at Re=100 to Re=400 are compared. When lowest and highest amplitude configurations are compared, 62% reduction in the complete phase transition time is observed while the impact of frequency is marginal at higher frequencies. When the hybrid nanoparticles are introduced in the base fluid, transition time and dynamic features of onset temperatures are affected. Successful results that capture the dynamic behavior of the phase change embedded thermal system is achieved with a nonlinear dynamic system modeling approach.

Numerical simulation and parametric analysis of latent heat thermal energy storage system

This paper presents the numerical analysis of the transient performance of the latent heat thermal energy storage unit established on finite difference method. The storage unit consists of a shell and tube arrangement with phase change material (PCM) filled in the shell space and the heat transfer fluid (HTF) flowing in the inner tube. The heat exchange between the HTF, wall and PCM has been investigated by developing a 2-D fully implicit numerical model for the storage module and solving the complete module as a conjugate problem using enthalpy transforming method. A comparative investigation of the total melting time of the PCM has been performed based on natural convection in liquid PCM during the charging process. The novelty of this paper lies in the fact it includes convection in PCM and this investigation includes a detailed parametric study which can be used as a reference to design latent heat storage. The results indicate that natural convection accelerates the melting process by a significant amount of time. In order to optimize the design of the thermal storage unit, parametric study has been accompanied to analyze the influence of various HTF working conditions and geometric dimensions on the total melting time of the PCM. Another important feature considered in this work is the influence of the inner wall of the tube carrying the HTF on the entire melting time of the PCM. An error of around 7.2% is reported when inner wall of the tube is ignored in the analysis.

Towards the simulation of supercooling and convection in phase change materials using a thermal lattice Boltzmann method

Towards the simulation of supercooling and convection in phase change materials using a thermal lattice Boltzmann method

Numerical study of convection in phase change material based on Lattice-Boltzmann method

In this paper, the lattice Boltzmann method was studied for the phase change process with convective heat transfer in phase change energy storage materials. Firstly, the macroscopic heat transfer equations for the phase change process with convective heat transfer was given, by which we built the lattice Boltzmann equations for solving the problems. In the model, the speed model of D2Q9 was selected, and the boundary conditions including of non-equilibrium extrapolation and bounce back scheme were selected. Then, the effects of different Rayleigh number on the temperature field and velocity field were analyzed. Further research in a square cavity heat transfer processes with high temperature object and low temperature object were studied, in order to observe the effects of different temperature objects in the phase change process using the changes of phase field.

Towards the simulation of supercooling and convection in Phase change materials using a thermal lattice Boltzmann method

The use of phase-change materials (PCM) in building materials is becoming increasingly used in the building sector. However, the presence of certain phenomena such as convection and supercooling may affect the fusion times and, consequently, the design of PCMs. Supercooling can have a noteworthy impact on the system performance. Moreover, convection alters the shape of the phase-front and should also be taken into account. Thereby, we propose here a thermal lattice Boltzmann model (TLBM) to simulate the phase-change problem with convection and supercooling. The numerical findings show that convection and supercooling phenomena are successfully taken into consideration. In addition, where appropriate, supercooling results exhibit a delay for the propagation of the solid-liquid interface. This proves that consideration of such a phenomenon in numerical modelling remains paramount for better design of PCM design.

Effective thermal conductivity for melting in PCM encapsulated in a sphere

Heat transfer in phase change materials (PCMs) contained in spherical encapsulations can be modelled more simply if an effective thermal conductivity can be determined to represent the natural convection occurring within the PCMs. Previous research has shown that natural convection in PCM can be characterised by a constant effective thermal conductivity during the melting process. However, this research did not consider the impact of the increased buoyancy forces with increased temperature difference between the heat transfer fluid flowing around the encapsulation and the PCM. An experimental study was conducted on the heat transfer through a single sphere subject to varying temperature differences. A computational fluid dynamics (CFD) model which ignored buoyancy of the PCM in a sphere was developed. Using this CFD model, the effective thermal conductivity of the liquid portion of the PCM was determined by correlating data from the model against experimental data at various temperature differences with water as the PCM. A suitable relationship for the effective thermal conductivity was developed as a function of the Rayleigh number. This empirical correlation applies to the geometry and PCM used in this study. The study demonstrates the applicability of determining effective thermal conductivity relationships to represent natural convection in PCM thermal storage systems. This correlation can be directly applied to numerical models of PCM storage systems with spheres.