Melting Heat Transfer Characteristics Research Articles

Experimental study on the melting heat transfer characteristics of a phase change material under mechanical agitation

Phase change materials (PCMs) are extensively employed for the thermal management of electronic devices, but their low thermal conductivity often results in slow heat absorption and release in practical applications. Existing improvement measures primarily focus on enhancing heat conduction, while research from the perspective of convection is scarce. Therefore, an experimental study on the melting heat transfer characteristics of n-docosane under mechanical agitation (0–1600 RPM) was conducted at 4.7–34 kW/m2. Upon agitation, the heating wall temperature (Tw) rapidly decreases, while the PCM temperature, heat transfer coefficient and Nusselt number significantly increase, and their variation amplitude is positively correlated with the rotation speed. This can be attributed to enhanced liquid PCM convection and accelerated solid PCM melting. At 8.5 kW/m2, the Tw at 1600 RPM is approximately 27 °C lower than that at 0 RPM, leading to a fourfold increase in the Nusselt number. Tw decreases with increasing rotation diameter, especially at lower rotation speeds. From 30 to 50 mm, the temperature decreases by approximately 13 and 10 °C at 800 and 1600 RPM, respectively. Tw changes slightly with increasing rotation height. Agitation can reduce the increase in Tw caused by a higher heat flux. Agitation can quadruple the upper limit of heat flux from 8.5 to 34 kW/m2 while maintaining consistent thermal control requirements. The power consumption of agitation increases as the rotation speed and diameter increase, peaking at 10.1 W. Moreover, after considering the minimum start-up time, Tw, and power consumption, the optimal configuration is determined: a rotation height of 10 mm and a rotation diameter of 40 mm for 1600 RPM and 50 mm for 800 RPM. These findings hold significant implications for PCM-based thermal management, particularly in terms of incorporating active convection enhancement.

Influence of rotation on heat absorption performance of solid–liquid phase change tank

The abundant and environment friendly solar energy is considered as the promising way to instead of traditional fusil energy for reducing carbon emission. Phase change tank (PCT) has been widely implemented in photo-thermal utilization of solar energy system, since PCT solves the imbalance of solar energy in time and space. Rotation application is arisen as an innovative way to improving heat absorption performance of the PCT. In this work, the effects of rotation velocity on the melting performance, heat transfer, and heat absorption characteristics in the PCT were investigated. Particular attentions were paid to the coupled influence of active (rotation) and passive enhancement (addition of metallic fins) upon the melting process. The Boussinesq approximation and an enthalpy-porosity model were applied for simulation. It was followed by assessing the performance of 10 rotation angular velocities from 0 to 2 rad·s−1. Results manifested that the best enhancement on melting performance was not achieved by the fastest rotation. The shortest melting time was achieved with the reduction of 55.02% at a rotational speed of 1.1 rad·s−1. The enhanced natural convection due to the optimized rotation resulted in a 47.79% increase in the Grashof number in comparison to stationary. Additionally, rotation was found to be effective in preventing local thermal overcrowding, which can impede heat transfer.

Stagewise melting heat transfer characteristics of phase change material in a vertically placed rectangular enclosure

In this work, the stagewise melting heat transfer properties of lauric acid in a side-heated rectangular enclosure are investigated by using a numerical model validated by a published experimental study. During the discussion, the conduction process is treated as stage I, the processes of mixed convection–conduction and convection are collectively treated as stage II, and the shrinking solid process is treated as stage III. The effects of the enclosure geometry and the thermal conditions encountered by the lauric acid on heat transfer are discussed, particularly the transition points between different adjacent stages and the heat transfer characteristics during each stage. Increasing the height delays the transition point between stages I and II, but advances it between stages II and III. Increasing the width has no effect on the transition point between stages I and II, whereas it delays the transition point between stages II and III. Increasing the wall temperature and the initial temperature leads to an advancement of the two transition points. Dimensionless correlations are summarized for the transition points between adjacent stages, the melting completion times for the whole process, and the transient heat transfer coefficients and liquid fractions for each phase.

Impact of Melting Heat Transfer and Variable Characteristics on an MHD Non-Newtonian Shear-Thinning Fluid Flow with Gyrotactic Microorganisms over a Nonlinear Stretched Surface

Impact of Melting Heat Transfer and Variable Characteristics on an MHD Non-Newtonian Shear-Thinning Fluid Flow with Gyrotactic Microorganisms over a Nonlinear Stretched Surface

Regulation mechanism of magnetic field on non-Newtonian melting and energy storage performance of metal foam composite nano-enhanced phase change materials

A numerical study is conduced to explore regulation mechanism of magnetic field on melting heat transfer and energy storage performance of nano-enhanced phase change material (NEPCM) composited with metal foam. The enthalpy-porosity method, Darcy-Forchheimer model and local thermal non-equilibrium model are used to describe melting process, flow in porous media and coupling heat transfer, respectively. The proposed model is then verified by experiments using thermochromic liquid crystal thermometry. Effects of nanoparticles mass fraction (0%≤Φwt≤5%), magnetic number (0≤Mn≤7×106), and Rayleigh number (104≤Ra≤106) on the non-Newtonian fluids flow, melting heat transfer and energy storage characteristics are illustrated and discussed. Results show that the addition of Fe3O4 nanoparticles can effectively promote melting and induce non-Newtonian effect of molten NEPCM, but Φwt has no significant influence on the heat transfer. With the increase of Mn, the suppression effect of magnetic field on the whole melting process of NEPCM enhances at moderate Ra = 105, and natural convection is fully developed with a “force bridge” phenomenon of Kelvin force. For lower Ra (=104), natural convection becomes weaker and magnetic field presents a “force loop” phenomenon. For larger Ra (=106), natural convective heat transfer has absolute predominance and the suppression effect of magnetic field can be ignored. Moreover, the increase of Φwt and Ra have obvious positive contributions to heat storage and heat storage efficiency. At low Ra, the suppression effect of magnetic field on heat storage and total melting time leads to decrease in energy storage efficiency.

Melting behavior and heat transfer performance in a modified PCM-filled enclosure with fins under hypergravity conditions

The latent heat energy storage (LHTES) system has been suggested for the thermal management of airborne equipment due to its superior thermal energy storage capability. The enthalpy-porosity method is used to investigate the melting heat transfer characteristics of phase change material (PCM) in embedded fin enclosures under hypergravity. The effects of different hypergravity values and directions on the melting process are analyzed. The results indicate that the melting is greatly accelerated by the fin due to its high thermal conductivity. Compared with the enclosure without fins, the addition of fins reduced the melting time by a maximum of 46.0%. Under the hypergravitational environment, natural convection is significantly enhanced, which leads to a more than 5 times increase in the maximum velocity of the liquid PCM as the gravity value increases from 1 g to 9 g. The direction of hypergravity also affects the heat transfer performance. Under hypergravity values of 5 g, the total melting time at θ = 0° is reduced by 60.24% compared to the case of θ = 90°. The findings of this study may contribute to the design of the LHTES system in aerospace applications.

Outlining the Impact of Melting on Mhd Casson Fluid Flow Past a Stretching Sheet in a Porous Medium with Radiation

This article focused on framing the characteristics of melting heat transfer in a porous medium induced by thermal radiation on (MHD) Casson fluid flow. The current model is used to predict the porous regime's viscoelastic action of water. First, the governing PDE is converted to ODE through an effective similarity transformation, and then the formed nonlinear equations are solved using the Runge-Kutta Fehlberg-45 order method. It illustrates and examines a detailed analysis of certain parameters on the velocity, temperature, coefficient of skin friction, and reduced number of Nusselt. The results indicate that velocity profile decreases in M and around but an opposite temperature pattern. In addition, an improvement in R and Me results in the amount of Nusselt number. The present analysis results are compared with the available works in particular situations, and more agreement has been observed.

Numerical study on enhanced melting heat transfer of PCM by the combined fractal fins

The melting heat transfer characteristics of PCM were studied in different combined types of heat exchangers. The effect of combining two different bifurcation level fractal fins was considered for PCM melting heat transfer in a phase change heat exchanger. Based on fractal theory and enthalpy-porosity method, a PCM melting model of two-dimensional unsteady heat transfer was established in a combined fractal fin heat exchanger. The influences of some factors, such as combined types of fractal fins, bifurcation level, heat transfer area of the fins and the spacing of the fins, were discussed for the melting heat transfer process. The results show that the complete melting time of PCM in a combined fractal fin heat exchanger is reduced by 68% compared with the traditional fractal fin heat exchanger. The melting time shows decreasing first and then gradually stabilizing as the bifurcation level number and heat transfer area of the combined fractal fins increase. The melting rate of PCM is the fastest in the Case 4 heat exchanger, and the complete melting time of PCM is the shortest in the Case 3 heat exchanger. Fin spacing and heat transfer area have a significant impact on the complete melting time. On this basis, the thermal performance coefficients between the fins zone and PCM zone are defined. The complete melting time of PCM is found to be exponentially negatively correlated with the thermal performance coefficient by curve fitting. The temperature distribution uniformity coefficient is proposed to evaluate the temperature distribution uniformity during the melting process of PCM. It is found that the temperature distribution uniformity of Case 2 has the best at the end of melting. The above results provide a theoretical basis for structural design of the heat exchanger with combined fractal fins to enhance PCM melting heat transfer.

Experimental investigation on melting heat transfer characteristics of a phase change material under hypergravity

Phase change material (PCM) has great application potential in airborne equipment cooling. However, aircraft are exposed to hypergravity during maneuvering flight, and the corresponding melting heat transfer characteristics remain unknown, urgently necessitating the present research. First, an experimental system on melting heat transfer of n-docosane (C22H46) under hypergravity is established. Then, the melting characteristics under different hypergravities (0–6g) are studied, revealing a significant effect. When the heat flux is constant, an increase in hypergravity yields accelerated melting and a decrease in the heating wall temperature because hypergravity enhances the heat convection inside the liquid PCM. The maximum differences of the time required for complete melting and the corresponding heating wall temperature under hypergravity to those under normal gravity are –20.6% and –21.0%, respectively. However, with increasing hypergravity, the strengthening effect gradually weakens, indicating a limit to the influence of hypergravity on the melting characteristics. Furthermore, the melting characteristics at different heat fluxes (2.5–7.5 kW/m2) under hypergravity are investigated. Under constant hypergravity, increasing heat flux accelerates the melting rate and increases the heating wall temperature, but this effect is suppressed by the hypergravity-enhanced heat convection and weakens with increasing heat flux. Finally, the theoretical liquid level positions of the PCM in the ground and body coordinate systems are analyzed and compared with the experimental results, yielding good agreement. In addition, due to the change in liquid level position caused by hypergravity, the PCM incompletely contacts the heating wall, leading to area overheating, which should be avoided in practical applications.

Semi-theoretical correlations of melting process driven by Rayleigh–Bénard convection suitable for low melting point metal

This paper studies the melting process of low melting point metal (LMPM) in a square cavity heated from bottom in the presence of Rayleigh–Bénard convection. Existing research focuses on high–Pr PCM melting process, and the difference between low and high-Pr PCM melting process needs to study. Scale analysis and numerical investigation are applied to analyze low-Pr LMPM melting process. Scale analysis tries to research the LMPM melting rate and obtain basic theoretical relationships of liquid fraction and Nu with Fo, Pr, Ras and Ste. A numerical model is established to elaborate dynamic melting heat transfer characteristics of low–Pr LMPM. The numerical results show that different from high-Pr PCM, the flow cell morphology presents obvious changes for low-Pr LMPM, and the time needed to completely melt is much shorter and the average heat flux is higher. The Rayleigh–Bénard convection causes oscillation of Nu in the convection dominated regime, and the average Nu for LMPM increases from 5.11 to 13.77 with the Ra from 5.0×105 to 1.25×107. Finally, the semi-theoretical correlations for liquid fraction and Nu are developed by scale analysis and numerical investigation, and the accuracy is numerically validated.

A review on the use of coconut oil as an organic phase change material with its melting process, heat transfer, and energy storage characteristics

A review on the use of coconut oil as an organic phase change material with its melting process, heat transfer, and energy storage characteristics

A numerical investigation of heat transfer process in paraffin/ethylene-vinyl acetate/graphene aerogel ternary composite

• The heat transfer process of Pa/EVA/GA were predicted by VAM. • The two-temperature model was adopted. • GA significantly improved heat transfer performance of Pa. • EVA increased the viscosity of paraffin and accelerated heat transfer. Melting and solidification heat transfer characteristics of different paraffin/ethylene-vinyl acetate/graphene aerogel (Pa/EVA/GA) composites were predicted by the volume-averaged method (VAM). In parameter settings, Pa/EVA was treated as fluid, and GA was set to solid. The two-temperature model based on the assumption of local thermal nonequilibrium was adopted to solve the large difference in thermal conductivity between GA and Pa/EVA. The simulation results were validated by experimental data. The numerical results denoted that GA and EVA significantly improved heat transfer performance of Pa and reduced the melting/solidification time. The heat transfer of the composites was dominated by heat conduction, as the three-dimensional skeleton of GA and the high viscosity of EVA inhibited the natural convection of paraffin. Compared with Pa/EVA 0 /GA, Pa/EVA 5 /GA and Pa/EVA 10 /GA had a higher surface heat flux, decreased the velocity of paraffin, and had a more even temperature distribution.

Melting and solidification performance in two horizontal shell‐and‐tube heat exchangers with different structures

Recently, a critical problem of latent heat thermal energy storage remains the low thermal conductivity of phase change materials (PCMs), which can lead to low heat transfer rate. Structural optimization design is an effective solution for this problem. In this work, two horizontal shell-and-tube heat exchangers (HEs) with one inner tube (n = 1) and four inner tubes (n = 4) are designed keeping the same amount of PCM and water flow rate, and their melting and solidification thermal performance and heat transfer characteristics are compared. The results show that in comparison with one-inner-tube HE, the temperature of detected points are affected by both upper and lower inner tubes for four-inner-tube HE, thus the differences in phase change process appear. In addition, the phase change time reduction rates are 34.1%, 33.39%, 28.82% at Tin (inlet water temperature) = 75°C, 80°C, 85°C during charging process, and 17.2%, 27.69%, 36.67% at Tin = 10°C, 15°C, 20°C during discharging process, respectively. In comparison with the one-inner-tube HE, the theoretical efficiency of four-inner-tube HE is increased from 75.88% to 90.34%. Although more friction loss should be paid by four-inner-tube HE, a lower energy consumption and a higher heat-energy ratio are achieved. Based on the results of this study, the amount of cumulative heat per energy consumption is 1.52 × 108 and 2.88 × 108 for one-inner-tube and four-inner-tube HE, respectively.

Experimental and numerical investigation of the melting process and heat transfer characteristics of multiple phase change materials

Experimental and numerical investigation of the melting process and heat transfer characteristics of multiple phase change materials

Numerical Investigation on Melting Process of a Phase Change Material Under Supergravity

AbstractA numerical investigation on the melting process of paraffin wax RT44 under supergravity (5–20 g) was conducted to evaluate the effect of supergravity on the melting heat transfer characteristics. The simulations were conducted in a horizontally placed container with a constant heat flux of 5–50 kW/m2 maintained on the bottom wall under both supergravity and the earth gravity (1 g). The numerical data under supergravity are compared with those under the Earth gravity for all circumstances. The results indicate that the melting heat transfer characteristics of the phase change material (PCM) are affected by supergravity significantly (around 30%) within 20 g. With the increase of supergravity, the heating wall temperature decreases, and the liquid fraction as well as the melting rate increases. Meanwhile, the variation amplitudes of these melting characteristics decrease gradually until less than 2% at 20 g. The effect of supergravity can be attributed to the intensification of the natural convection due to buoyancy, yielding vortexes in internal flow and fluctuations of solid–liquid interface and temperature field.

A numerical investigation of the melting heat transfer characteristics of phase change materials in different plate heat exchanger (latent heat thermal energy storage) systems

In this study, the melting heat transfer in plate heat exchanger LHTES(Latent Heat Thermal Energy Storage) systems was numerically investigated. In the numerical analyses, using the Finite Volume Method (FVM), the phase change process was examined for different heat exchanger geometries (Geometry a, b and c), different heat transfer fluid (HTF) inlet temperatures (52 °C, 57 °C and 62 °C), different steel plate thicknesses (0.4 mm, 0.6 mm and 0.8 mm) and different PCMs(Phase Change Materials) (RT-35 and n-octadecane). The numerical analyses were performed by simplifying the problem down to two dimensions. From the results, time-dependent average PCM temperatures, and liquid fraction contours and graphs were produced. The results showed that for the same PCM, boundary conditions and geometrical characteristics, the complete melting time of the PCM in a plate heat exchanger LHTES system with different geometries could be decreased by 75% in comparison to a cylindrical LHTES system of the same PCM volume. The maximum thermal performance achieved was recorded for the following conditions: Geometry a, a HTF inlet temperature of 62 °C, a steel plate thickness of 0.6 mm and n-octadecane as the PCM.

A series solution for melting heat transfer characteristics of hybrid Casson fluid under thermal radiation

A series solution for melting heat transfer characteristics of hybrid Casson fluid under thermal radiation

Investigation of enclosure aspect ratio effects on melting heat transfer characteristics of metal foam/phase change material composites

PurposeThe purpose of this paper is to study thermal performance of metal foam/phase change materials composite under the influence of the enclosure aspect ratios (ratio of enclosure height: length). In this study, a compound metal foam/phase change material (PCM), which has been proved to be one of the most promising approaches for thermal conductivity promotion on PCMs, was used.Design/methodology/approachThe PCM is considered initially at its melting temperature. The enclosure for all the cases has a constant volume with various aspect ratios. The left side of the enclosure is suddenly exposed to a thermal source having a constant heat flux, while the other three surfaces are kept thermally insulated. A two-dimensional numerical model considering the non-equilibrium thermal factor, non-Darcy effect and local natural convection was proposed. The coupling between velocity and pressure is solved using the SIMPLEC, and the Rhie and Chow interpolation is used to avoid the checker-board solutions for the pressure.FindingsThe effects of foam porosity and aspect ratio of the enclosure on the PCM’s melting time were investigated. The results indicated that enclosure aspect ratio plays a fundamental role in phase change of copper foam/PCM composites. For higher porosities, enclosures with bigger aspect ratios proved to led to optimal melting time. Besides, the best enclosure aspect ratio and foam porosity for a fixed-volume enclosure to have the shortest melting time are 2.1 and 91.66 per cent, respectively. However, for a specific amount of PCM inside a variable volume enclosure, the optimal melting time was for foam with ε = 95 per cent. The achieved results prove the great importance of selection of aspect ratio to benefit both conduction and convection heat transfer simultaneously.Originality/valueThe area of energy storage systems is original.

Melting Heat Transfer Characteristics of Liquid Metal as Phase Change Material under Microgravity

相变蓄热适用于周期性热流作用下航天器内部工作单元的温度控制，但是需解决微重力环境下相变材料融化速率低的问题.鉴于液态金属高导热系数和高单位体积潜热的特点，在微重力下将液态金属作为相变材料有望提高融化速率.通过对微重力下液态金属镓融化过程的相界面演化、流线和温度分布特征进行数值研究，分析了腔体尺寸和过热度对融化过程的影响.结果表明：微重力下镓的融化过程中，热传导起主导作用；镓的融化时间比冰和正十八烷分别减少了88.3%和96.4%，储热量分别为冰和正十八烷的1.2倍和2.2倍；融化时间随过热度增加而减小，随腔体半径增大而增大.此外推导出了液相分数随无量纲时间变化的关系.

Melting of nano-PCM inside a cylindrical thermal energy storage system: Numerical study with experimental verification

In the current work, the melting process, heat transfer, and energy storage characteristics of a bio-based nano-PCM in a vertical Cylindrical Thermal Energy Storage (C-TES) system are numerically investigated and verified with experimental work. Mathematical models based on non-linear differential equations are developed to study the mass, momentum, and energy transport processes inside the C-TES system. The effects of nanoparticles volume fraction (i.e. ϕ = 0%, 3%, and 5%) and Rayleigh number (i.e. Ranl = 106, 107, and 108) on the melting process are investigated. To compare the numerical results, an experimental setup is developed and transient images are captured to identify the location and shape of solid-liquid interface. To prepare nano-PCM, the copper oxide (CuO) nanoparticles are dispersed into the bio-based coconut oil PCM. The C-TES system is insulated from the bottom, isothermally heated from its lateral walls and the top. Numerically obtained solid-liquid interface locations and melt fractions for base PCM and nano-PCM are compared with experimental analysis and a very good agreement is obtained. The numerical results are further compared with existing numerical and experimental results available in the literature. The work then explains the effects of Rayleigh number and volume fraction of nanoparticles on melt fraction, Nusselt number, and stored energy. The results indicate that adding nanoparticles do not change the patterns of melt fraction, Nusselt number, and energy storage capacity with time compared to the base PCM case. The effects of specific heat capacity of solid nano-PCM, liquid nano-PCM, and latent heat capacity of nano-PCM on energy stored are discussed. The results show that the difference in energy stored with Rayleigh number is less during the beginning of the melting; as melting reaches in the convection dominated regime, a larger difference is observed due to increased melting at larger Rayleigh number.