Solid-liquid Phase Change Heat Transfer Research Articles

Enthalpy-based multiple-relaxation-time lattice Boltzmann method for solid-liquid phase-change heat transfer in metal foams.

In this paper, an enthalpy-based multiple-relaxation-time (MRT) lattice Boltzmann (LB) method is developed for solid-liquid phase-change heat transfer in metal foams under the local thermal nonequilibrium (LTNE) condition. The enthalpy-based MRT-LB method consists of three different MRT-LB models: one for flow field based on the generalized non-Darcy model, and the other two for phase-change material (PCM) and metal-foam temperature fields described by the LTNE model. The moving solid-liquid phase interface is implicitly tracked through the liquid fraction, which is simultaneously obtained when the energy equations of PCM and metal foam are solved. The present method has several distinctive features. First, as compared with previous studies, the present method avoids the iteration procedure; thus it retains the inherent merits of the standard LB method and is superior to the iteration method in terms of accuracy and computational efficiency. Second, a volumetric LB scheme instead of the bounce-back scheme is employed to realize the no-slip velocity condition in the interface and solid phase regions, which is consistent with the actual situation. Last but not least, the MRT collision model is employed, and with additional degrees of freedom, it has the ability to reduce the numerical diffusion across the phase interface induced by solid-liquid phase change. Numerical tests demonstrate that the present method can serve as an accurate and efficient numerical tool for studying metal-foam enhanced solid-liquid phase-change heat transfer in latent heat storage. Finally, comparisons and discussions are made to offer useful information for practical applications of the present method.

Numerical investigation of transient thermal behavior of a wall incorporating a phase change material via a hybrid scheme

This article deals with the numerical simulation of transient thermal behavior of a mortar wall containing a microencapsulated phase change material (PCM) using a hybrid finite volume/enthalpy method. Unlike explicit algorithms, the latent heat source term has been handled implicitly in the enthalpy equation. The current approach has been implemented considering a one-dimensional transient phase change problem with conduction. The numerical results agree well with available experimental results qualitatively. Subsequently, the model has been used to investigate the effect of the speed of heating or cooling on the performance of the thermal storage of PCM-Mortar during the phase-change process. The Micronal®DS5001X microcapsules containing a paraffin mixture with a melting point of 26°C has been used to improve the heat storage capacity of a cement-mortar. Simulation results indicated that the PCM is able to enhance the solid–liquid phase change heat transfer mainly because of thermal conduction, and that rate of heating/cooling has no influence on the profile of heat flux. They also showed that the model presented here is well-suited to the thermal behavior of an encapsulated PCM embedded in a mortar wall, and it is indicated to address similar problems.

Experimental Study and Numerical Simulation on Thermal Energy Storage Characteristics of Composite Phase Change Materials in Annular Space of Vertical Double-Pipe Heat Exchanger

Experimental system on thermal energy storage characteristics of phase change materials (PCMs) in annular space of a vertical double-pipe heat exchanger was set up. The thermal storage performance of paraffin and paraffin/expanded graphite composite PCM with the mass fraction of 70% paraffin was compared. The Fluent software was used to simulate the temperature field of the composite PCM during the thermal storage process. The results show that, for the paraffin, in the sensible heat storage phase, because the heat transfer process is controlled by the heat conduction, the temperature in paraffin gradually reduces from the inside to the outside of the annular space. But for the phase change thermal storage phase, solid-liquid phase change heat transfer is controlled by natural convection and the effect of buoyancy, the temperature in paraffin reduces from top to bottom, from the inside to the outside of the annular space. For the composite PCM, heat transfer is controlled only by the heat conduction process, both the sensible and latent heat storage process, the temperature in the composite PCM decreases from bottom to top, from inside to outside of the annular space. As the thermal conductivity of composite PCM is 15.65 times of paraffin, the thermal energy storage time is shortened by 86.6% than paraffin. The temperature fields of composite PCM in different time are obtained by numerical simulation method, the measured temperatures and simulation results are in good agreement.

Numerical analysis on performance of naphthalene phase change thermal storage system in aluminum plate-fin unit

This paper presents a numerical simulation for the prediction of time, temperature and liquid fraction during the melting and solidification process in the latent heat storage of phase changed materials (PCM). The mathematical model, regarding the solid–liquid phase change heat transfer based on the enthalpy formulation, has been proposed. Naphthalene was used as the PCM which is contained in up layer of plate-fin thermal storage. Transient simulations were performed using a commercial computational fluid dynamics package, Fluent, based on the finite volume method. This computational model endeavored to describe both the melting and solidification processes of the PCM. A series of numerical calculations have been done in order to analyses the influence of several heat transfer fluid operating conditions and several fin geometric parameters on the thermal storage unit. Numerical results, which could be used for operating conditions and geometry optimization, provide guideline for the design of the latent thermal energy storage system.

Experimental and numerical study on melting of phase change materials in metal foams at pore scale

An experimental study on the melting behavior of phase change material (PCM) in metal foams has been carried out at the pore scale. Paraffin wax was used as phase change material, in which aluminum foams were embedded to enhance the heat transfer. The temperature field and the melting evolution of the PCM at the pore scale were studied using an infrared camera and an optical microscope, respectively. The experimental results indicated that the metal foam is capable of enhancing the solid–liquid phase-change heat transfer, mainly because of the thermal conduction in the metal matrix. It was observed that the effect of the metal structure on the heat transfer is significant during the melting of PCM. A thermal lattice Boltzmann model with doubled populations was implemented to simulate the two-dimensional melting of the phase change material in metal foams. The numerical results agree well with the experimental observations qualitatively.

A numerical analysis of solid–liquid phase change heat transfer around a horizontal cylinder

A numerical study is conducted to analyze the melting process around a horizontal circular cylinder in the presence of the natural convection in the melt phase. Two boundary conditions are investigated one of constant wall temperature over the surface of the cylinder and the other of constant heat flux. A numerical code is developed using an unstructured finite-volume method and an enthalpy porosity technique to solve for natural convection coupled to solid–liquid phase change. The validity of the numerical code used is ascertained by comparing our results with previously published results.

Numerical Analysis on Solid-Liquid Phase Change Heat Transfer Process between PCM and FCPCM

Due to enthalpy-porosity technique, mathematical models of phase change material (PCM) and foam composite phase change material (FCPCM) in two-dimensional rectangular canister were established in the conditions of gravity and natural convection. It solved phase change problems by the enthalpy method coming from computational fluid dynamics. The numerical results show good agreement with reference findings. The numerical comparison between PCM and FCPCM verifies that metal foam can not only enhance the thermal conductivity of the PCMs but also improve the thermal performance of the heat storage system.

Experimental and numerical study of heat transfer in horizontal concentric annulus containing phase change material

AbstractIn the present research work, solid–liquid phase change heat transfer was studied experimentally as well as numerically for paraffin wax encapsulated in the annulus of two coaxial circular cylinders with variable heat flux. Two‐dimensional mathematical model (Navier–Stokes equation) in terms of primitive variables has been formulated to study the melting characteristics of the phase change material (PCM). The finite volume method (FVM) and semi‐implicit, that is, SIMPLE scheme are applied to discretise the governing equations and track the solid–liquid moving front. From the comparison of experimental data and numerical simulation, it is evident that the convective heat transfer is dominant in melting phase. From the computational results it is also observed that both eccentricity and the variation in the angle of inclination of the eccentricity plays an important role for the net circulation of the molten phase as well as the thermal flux at the inner surface of the annulus.

Analysis of the influence of operating conditions and geometric parameters on heat transfer in water-paraffin shell-and-tube latent thermal energy storage unit

A transient heat transfer phenomenon during charging and discharging of the shell-and-tube latent thermal energy storage system has been analysed in this paper. The mathematical model, regarding the conjugate problem of transient forced convection and solid–liquid phase change heat transfer based on the enthalpy formulation, has been presented. A fully implicit two-dimensional control volume FORTRAN computer code has been developed for solving governing equations with initial and boundary conditions. The numerical model is validated with experimental data obtained by experimental investigations that have been performed on the test unit with technical grade paraffin as the phase change material (PCM) and water as the heat transfer fluid (HTF). Numerical predictions match the experimental results. This pointed out that the presented numerical procedure could be accurately used for transient heat transfer simulation. A series of numerical calculations have been done in order to analyse the influence of several HTF operating conditions and several geometric parameters on the heat transfer process inside the water-paraffin shell-and-tube latent thermal energy storage (LTES) unit. Numerical results, which could be used for operating conditions and geometry optimization, provide guidelines for the design of the latent thermal energy storage system.

Numerical Study on the Thawing Process of Biological Tissue Induced by Laser Irradiation

Most of the laser applications in medicine and biology involve thermal effects. The laser-tissue thermal interaction has therefore received more and more attentions in recent years. However, previous works were mainly focused on the case of laser heating on normal tissues (37 degrees C or above). To date, little is known on the mechanisms of laser heating on the frozen biological tissues. Several latest experimental investigations have demonstrated that lasers have great potentials in tissue cryopreservation. But the lack of theoretical interpretation limits its further application in this area. The present paper proposes a numerical model for the thawing of biological tissues caused by laser irradiation. The Monte Carlo approach and the effective heat capacity method are, respectively, employed to simulate the light propagation and solid-liquid phase change heat transfer. The proposed model has four important features: (1) the tissue is considered as a nonideal material, in which phase transition occurs over a wide temperature range; (2) the solid phase, transition phase, and the liquid phase have different thermophysical properties; (3) the variations in optical properties due to phase-change are also taken into consideration; and (4) the light distribution is changing continually with the advancement of the thawing fronts. To this end, 15 thawing-front geometric configurations are presented for the Monte Carlo simulation. The least-squares parabola fitting technique is applied to approximate the shape of the thawing front. And then, a detailed algorithm of calculating the photon reflection/refraction behaviors at the thawing front is described. Finally, we develop a coupled light/heat transport solution procedure for the laser-induced thawing of frozen tissues. The proposed model is compared with three test problems and good agreement is obtained. The calculated results show that the light reflectance/transmittance at the tissue surface are continually changing with the progression of the thawing fronts and that lasers provide a new heating method superior to conventional heating through surface conduction because it can achieve a uniform volumetric heating. Parametric studies are performed to test the influences of the optical properties of tissue on the thawing process. The proposed model is rather general in nature and therefore can be applied to other nonbiological problems as long as the materials are absorbing and scattering media.

Solid-Liquid Phase Change Heat Transfer Enhancement Analysis in Cylindrical and Spherical Walls

This paper presents a novel insight into the mechanisms of heat transfer enhancement in cylindrical and spherical walls induced by solid-liquid phase change based on the analogy between heat conduction with an internal heat source and phase change heat transfer. Two kinds of interface heat transfer enhancement with phase change heat transfer in cylindrical and spherical walls are described. The factors influencing the degree of heat transfer enhancement on the interface are clarified and their effects are quantitatively analyzed. Both the novel insight and analysis contribute to effective application of phase change heat transfer enhancement techniques.

A numerical analysis of solid-liquid phase change heat transfer around a single and two horizontal, vertically spaced cylinders in a rectangular cavity

In the present study, a new numerical model is proposed to analyze solid-liquid phase change heat transfer in a complicated geometry. The present model can treat the solid/liquid phase change heat transfer with/without porous media, as well as conventional transient natural convection with/without porous media. Solidification calculations of pure water (without porous media) around a single cylinder and two cylinders were performed to check the validity of the model. The interaction of two solidification layers were examined, and the effects of natural convection in the melt on the solidification process were also studied. The numerical results were found to be in excellent agreement with experimental data. It was also shown that for the initial water-temperature, Ti, of 0°C the solidification progresses more rapidly for the single cylinder than that for the two cylinders, but the reverse is true for Ti ⩾ 4°C.

The penetration rate of solid-liquid phase-change heat transfer interface with different kinds of boundary conditions

The penetration rate of solid-liquid phase-change heat transfer interface with different kinds of boundary conditions

The penetration rate of solid-liquid phase-change heat transfer interface with different kinds of boundary conditions

The penetration rate of solid-liquid phase-change heat transfer interface with different kinds of boundary conditions

Exact solutions of solid-liquid phase-change heat transfer when subjected to convective boundary conditions

Exact solutions of solid-liquid phase-change heat transfer when subjected to convective boundary conditions

Inward solid-liquid phase-change heat transfer in a rectangular cavity with conducting vertical walls

This paper reports basic solid-liquid interface and heat transfer data obtained during solid-liquid phase change (melting and solidification) of n-octadecane in a two-dimensional rectangular cavity with conducting vertical walls. The shadowgraph technique was used to measure local heat transfer coefficients at the heat source surface. The solid-liquid interface motion during phase change was recorded photo-graphically. During melting, a development of vortex motion at the bottom melt zone was observed to be quite similar to that in a rectangular cavity with isothermal walls. In both melting and solidification experiments the conducting walls acted as isothermal walls at the late times during the processes. Natural convection was found to control the melt shape, the melting rate and heat transfer during melting. The effect of the initial subcooling of the solid was also investigated and the results clearly showed that heat conduction was the dominant mode of energy transport during the inward solidification. For solid-liquid phase-change heat transfer short extended surfaces are more effective than longer ones.

Flow visualization during solid-liquid phase change heat transfer II. Melting in a rectangular cavity

The results of flow visualization in a rectangular test cell during the melting of n-octadecane are reported. The experiments provide information on buoyancy-induced fluid motion and its effect on the shape of the solid-liquid interface.

Flow visualization during solid-liquid phase change heat transfer I. Freezing in a rectangular cavity

The results of flow visualization experiments in a rectangular test cell during the solidification of n-octadecane from above are reported. The experiments provide information on buoyancy-induced fluid motion and its effect on the shape and motion of the solid-liquid interface.

Heat Transfer and Interface Motion During Melting and Solidification around a Finned Heat Source/Sink

The effectiveness of extended surfaces on a horizontal, cylindrical heat source/sink was studied experimentally during solid-liquid phase change heat transfer. Melting and freezing experiments were performed in a test cell suitable for photographic and shadowgraphic observations using a circular cylinder with three rectangular fins parallel to the axis and evenly distributed around the circumference of the heat exchanger. Results are reported for n-heptadecane as the phase change material. Orientation of fins on the heat exchanger with respect to the gravitational field are found to have more influence on the melting than on the freezing processes. The use of fins was found to be more effective for melting than for freezing. The instantaneous local and circumferentially averaged heat transfer coefficients at the heat source surface for melting from a cylinder with fins were usually within ±20 percent of those for melting from a bare cylinder. During solidification the degree of heat transfer enhancement due to finning is greatest when the frozen layer is thin and decreases as the layer grows thicker.

Solid-liquid phase-change heat transfer and interface motion in materials cooled or heated from above or below

Solid-liquid phase-change heat transfer has been studied experimentally and analytically in several different materials (e.g. stearic acid, sodium phosphate dodecahydrate, sodium sulfate decahydrate and n-octadecane which have been suggested as candidates for latent-heat-of-fusion thermal energy storage materials. Solid-liquid interface motion during freezing and melting from above as well as below has been determined in a rectangular test cell suitable for photographic observations. Comparison of experimental data for n-octadecane with predictions based on Neumann and other analyses which account for natural convection heat transfer at the solid-liquid interface show that natural convection in the liquid must be accounted in the prediction of phase-change boundary motion for unstable situations which arise during melting from below and solidification from above.