Phase Change Heat Transfer Characteristics Research Articles

Numerical study on phase change propulsion mechanism of thermal underwater glider based on spectral method

The thermal underwater glider’s propulsion power is provided by the phase change energy storage tube. To improve the propulsion performance of the glider, it is essential to study the phase change heat transfer characteristics. This work proposes a collocation spectral method to handle the spatial derivative term and introduces a fourth-order Runge-Kutta method to handle the time derivative term. The temperature distribution and liquid volume fraction of the phase change material in the energy storage tube were numerically simulated under specific boundary conditions. The simulation results were then compared to the experimental data, and a good agreement was observed.Based on these findings, the impact of incoming free stream velocity and temperature difference intensity on phase change within the vessel was examined. The results underscored the dominance of convection in solid–liquid phase change and identified key factors influencing phase change in scenarios with Stefan numbers below 0.1342. Additionally, the study highlighted the limitations of fixed-value approximations and the nonlinear nature of phase change over time. These insights provide valuable guidance for developing phase change devices that harness volumetric potential energy aboard underwater thermal gliders.

Research on one-dimensional phase change heat transfer characteristics based on instrument compartment structure

To address the issue of electronic equipment failure inside the instrument compartment due to aerodynamic heating during high-speed flight. Combining the heat transfer characteristics of phase change materials, a new instrument compartment structure was proposed as the research subject based on phase change materials. While studying the heat transfer characteristics of this structure, one-dimensional phase change heat transfer theoretical model was constructed based on the Lightfoot integral equation method, and the corresponding analytical solution was obtained. To explore the temperature change law of the instrument compartment structure and verify the rationality of the theoretical model, the new thermal experiment was carried out for the instrument compartment structure. Compared with the aluminum alloy instrument compartment structure, the experimental results show that the instrument compartment structure design based on phase change materials could effectively reduce the temperature of the structure itself, and the experimental data are in good agreement with the theoretical calculation results, which verified the rationality of the theoretical model and provided a scientific basis for the practical application of phase change materials in instrument compartment structures.

Thermocapillary convection modes and phase change heat transfer characteristics of three-dimensional metal foam composited phase change materials with different aspect ratios under microgravity

This work aims to investigate the flow, heat transfer and phase change characteristics of porous media composite phase change materials with different aspect ratios in the thermocapillary mode under microgravity. A three-dimensional hydrodynamic model of thermocapillary-enhanced phase change heat transfer in the composite is developed. The model considers the shear stress boundary conditions on the porous free surface, employing the enthalpy-porosity method and the Darcy–Forchheimer model to describe the phase change process and fluid flow within the porous matrix, respectively, and the local thermal non-equilibrium model to describe the transient heat energy transfer between the paraffin and copper foam. The effects of different Marangoni numbers (Ma), aspect ratios (AR), Darcy numbers (Da) and porosities (ε) on the phase change heat transfer are compared. The results show that the increase of Ma from 6 × 104 to 2 × 105 accelerates the thermocapillary effect, and positively affect the thermal transport inside the cavity. The total melting time of the composite is reduced by 22.6 %, the heat storage efficiency is improved by 31.1 %, and secondary vortices appear in the convection zone. The large AR is favorable to the development of thermocapillary convection, but it also causes the reduced temperature gradient and heat transfer area of the heat source as well as the increased heat transfer distance. Compared to AR = 1, the total melting time increased by 34.4 % and 46.9 % for AR of 1.95 and 2.25 at a larger Ma, while the heat storage efficiency decreased by 26.5 % and 33.7 %, respectively. For a fixed ε, the decrease in Da hinders the development of convection, thus weakening the heat transfer and storage performance of the composite, and also causes heat conduction to dominate the phase change process in advance.

Three-dimensional numerical simulation of solid-liquid phase change in the cavity of composite structures based on TPMS

Solid skeletons will play an important role in improving the thermal properties of phase change materials. For this reason, the efforts should be dedicated to studying the heat transfer characteristics of solid-liquid phase change with different structural skeletons. In this paper, the composite structures spliced with Gyroid and Diamond skeletons in the horizontal or vertical directions were established by using the Triply Periodic Minimal Surface method. A three-dimensional dimensionless lattice Boltzmann model of the phase change material (PCM) cavity with the spliced skeleton was developed by using the two-region model for solid-liquid phase change in the mushy zone. Based on the pore scale, the phase change heat transfer characteristics under the thermal conductivity ratio of the skeleton to PCM of 100 were analyzed in depth with constant temperature heating at the left wall surface. The results showed that the skeleton spliced in different directions has different effects on the temperature field and heat transfer characteristics of the phase change process. The (G + D)H spliced skeleton which was arranged by Gyroid and Diamond skeletons in the horizontal direction led to a faster melting rate of the PCM than the (D + G)H spliced skeleton which was arranged by Diamond and Gyroid skeletons. The promotion effect of a large porosity skeleton on the melting process of PCM was less than that of a small porosity skeleton. The dimensionless complete melting time for the cavity containing skeleton with porosity ε = 0.915 was increased by 35.7 % and 19.4 % compared to the cavities containing skeletons with porosity ε = 0.826 and 0.871, respectively. This study lays the foundation for the development and application of TPMS spliced skeletons in phase change heat storage and enhanced heat transfer technologies.

Study on Phase Change Flow and Heat Transfer Characteristics of Microalgae Slurry in the Absorber Tube of a Parabolic trough Solar Collector

The study of gas–liquid two-phase flow and heat transfer in non-Newtonian fluids is of great significance for the research and development of refrigeration and energy storage. In this paper, the characteristics and influencing factors of the phase change reaction in microalgae slurry were studied by numerical simulation and experimental verification. In order to further study the rheological and heat transfer characteristics of gas–liquid two-phase flow in the collector, the effects of wall heat flux, inlet velocity and microalgae slurry concentration on the phase change reaction in microalgae slurry were studied. The results show that when the boundary conditions of microalgae slurry with the same concentration change, the phase transition of microalgae slurry is different. The higher the wall heat flux, the more forward the phase transition occurs, and the smaller the flow rate, the more forward the phase transition occurs. When the boundary conditions remain unchanged, the phase transition point of microalgae slurry with different concentrations is the same, and the concentration of microalgae slurry will not be affected. However, the deviation between the fluid temperature and the thermal conductivity of high-concentration fluid after phase change is larger than that of low-concentration fluids. The deviation in the fluid temperature reaches approximately 10 K, and the deviation in thermal conductivity reaches approximately 0.025 W/(m·K). Therefore, the change in the fluid temperature and heat transfer intensity after phase change in microalgae slurry is more intense than that of Newtonian fluids.

Experimental study on the melting heat transfer of octadecane with passively adding graphene and actively applying an electric field

The low thermal conductivity of organic phase change materials (PCMs) has seriously obstructed the performance of thermal latent-heat thermal storage (LHTS) system. For the first attempt, we experimentally studied the phase-change heat transfer characteristics of octadecane inside a horizontal cavity with the passive addition of nano graphene and the active application of an electric field. The effects of nano graphene weight ratio, direct current (DC) voltage magnitude and polarity on melting heat transfer and their corresponding mechanism are then examined. Results are reported for the real-time melting process, the liquid fraction, and the evolution of absorbed energy. The velocity fields obtained by particle image velocimetry (PIV), the temperature fields measured by fiber Bragg grating (FBG) sensors, and the current-voltage curves are reported to reveal the heat transfer enhancement mechanism. The absorbed thermal energy is increased by 33.6% when nano graphene is added alone. A single electric field promotes the energy absorption by 153.5% where electric field driven flow develops. The net charge is generated by the conduction mechanism. For composite PCMs’ melting, the absorbed energy is enhanced by 124.8% at most when the cavity's bottom wall is exposed to -10.0 kV. However, when +10.0 kV is applied to the bottom wall the electrophoretic deposition takes place, and the combined augmentation effect on absorbed thermal energy is 111.2%. The present results provide a reference for improving the LHTS system's performance through sole or synergistic heat transfer enhancement method.

Numerical investigation of phase change heat transfer in a confined micro-space by lattice Boltzmann method

Phase-change heat transfer has attracted wide attention in thermal management of electronic infrastructures, such as the data center and 5G base station antenna. It possesses the characteristics of high equivalent thermal conductivity, rapid heat diffusion and good temperature uniformity. However, the existing thermal solution to advanced high-performance devices becomes more challenging with high heat flux and small heat dissipation area. Current surface modification technology has been applied for enhancing phase-change means in energy-related fields. In this paper, the hybrid lattice Boltzmann (LB) method was utilized to explore vapor-liquid phase-change mechanism and its enhancement in a confined micro-space. Different modified surfaces’ effects on bubble growth behavior and interfacial phase-change heat transfer were respectively discussed. Based on the pseudopotential LB approach and energy equation, the boiling and condensation regimes were quantitatively evaluated with the heat transfer coefficient and transient heat flux. The numerical results indicated that the wettability possessed significant impacts on the primary characteristics of phase-change heat transfer. It was found that hydrophilic contact angle promoted the initial boiling, while hydrophobic one helped to facilitate drop-wise condensation. The hybrid surfaces possess the best performance for the boiling heat transfer enhancement. Both the modified hybrid and wettability gradient surfaces have positive contributions to the condensation heat transfer enhancement. This study is expected to provide a reference for improving phase-change heat transfer technology for sustainable energy applications.

Characteristics of phase-change flow and heat transfer in loop thermosyphon: Three-dimension CFD modeling and experimentation

Two-phase loop thermosyphon (TPLT) shows an oscillation phenomenon since the complex phase-change heat transfer and flow behaviors, decreases the system reliability in practice. A combined three-dimension CFD simulating/experimental investigation was carried out to investigate the phase-change flow inside TPLT. Results of the 3D-CFD model show good agreement with the experiments, with a maximum deviation of 2.86% and 3.98% for temperature distribution and pressure, respectively. In the vertical evaporator heating mode, the filling ratio of 23.3% produced the lowest total thermal resistance of 0.28–0.22K/W since the dominant heat transfer mechanism of phase-change in the loop. With the increasing FR, from 48.0 to 84.1%, the dominant heat transfer mechanism might be transformed to single-phase convection. Thermal performance with the horizontal evaporator heating mode is better than that with the vertical evaporator heating mode since the good flowability at high FR = 84.1%. In the horizontal evaporator heating mode, a bidirectional flow was observed in the loop with the horizontal evaporator even at low FR = 23.3%, which caused pressure fluctuation and reduced thermal performance. But the flow stability could increase by 90% with the auxiliary of a porous media in the horizontal evaporator, indicating that the porous media had a positive effect on avoiding bidirectional flow.

Thermal management and phase change heat transfer characteristics of LiFePO4 batteries by cooling phase change materials

The cycle life and thermal safety of lithium-iron-phosphate (LiFePO4) batteries are important factors restricting the popularization of new energy vehicles. The study aims to prevent battery overheating, prolong the cycle life of power batteries and improve their thermal safety by discussing the heat production of LiFePO4 batteries to solve the problem of temperature rise in the natural-convection environment and cut the energy consumption in the liquid cooling system. A numerical simulation and experiment are employed to study the heat production characteristics of LiFePO4 batteries and the heat transfer characteristics of the system, with its PCM and coupling PCM of paraffin and expanded graphite), channel liquid, and micro-channel PCM coupling cooled to control the temperature of the batteries. The results show that the temperature goes higher with the discharge rate during discharge. Since it has large internal component values, LiFePO4 produces more heat at the beginning and end of discharge. When the battery pack is discharged at 1C and 2C rates, the mass-flow rates are 1.8 ? 10?3 kg/s and 3.6 ? 10?3 kg/s, the temperature can be controlled at most 40?C, and the temperature difference less than 3?C, respectively. Paraffin is composed of expanded graphite, and the thermal conductivity of the composite heat storage PCM (phase change heat storage materials) is 24 times of that of pure paraffin. Therefore, cooling the active liquid and coupled PCM can improve the cooling efficiency and has a good effect on solving the problem of temperature rise and energy consumption reduction. The research provides a reference for the thermal energy management of LiFePO4 batteries, providing a method of cooling PCM of LiFePO4 batteries.

CFD analysis for heat transfer comparison in circular, rectangular and elliptical tube heat exchangers filled with PCM

A two-dimensional computational fluid dynamics (CFD) investigation of the melting of phase change material (PCM) and heat transfer characteristics of a heat exchanger of shell and tube type having circular, rectangular and elliptical tubes are analyzed in this study. Gallium in the rectangular shell of heat exchange is considered as the working fluid in this present study. A fixed temperature boundary condition is applied at the circumference of the tubes and a standard k-epsilon turbulence model is used for the simulation. The variation in the shape of the tubes at a fixed temperature of 60 °C has been utilized for the analysis and the effect of the shape of these tubes on melting of PCM in terms of liquid proportion and melting time has been analyzed. The melting duration of PCM is 745 s for a configuration with circular tubes, 650 s for a configuration with rectangular tubes, and 740 s for a configuration with elliptical tubes and the duration by the PCM to reach 60 °C for a configuration with circular tubes is 800 s, for a configuration with rectangular tubes is 725 s, and for a configuration with elliptical tubes is 770 s. Hence it is indicated by the results that the lowest melting time of PCM can be obtained by the heat exchanger having rectangular tubes followed by elliptical tubes and circular tubes at a temperature of 60 °C.

Visualization study on the condensation heat transfer on vertical surfaces with a wettability gradient

The functional surface is a crucial approach to enhance the condensation heat transfer. This paper designs and fabricates a functional surface with wettability gradient by the use of etching and chemical vapor deposition methods. The dynamic phase change behaviors and heat transfer characteristics of humid air condensation on vertical surfaces with wettability gradient have been experimentally investigated and compared with the corresponding hydrophilic and hydrophobic surfaces by a visualization system. The results indicate that the heat transfer performance of humid air condensation on traditional gradient surface is superior to hydrophilic case but inferior to hydrophobic case in large-scale application due to small wettability gradient. Considering this, the periodic gradient surface with periodical layout of multi-layer wettability gradient is introduced to improve the condensation heat transfer. The presence of a larger wettability gradient for the periodic gradient surface induces the efficient droplet removal and the preferable inter-layer and intra-layer actions, leading to an improvement of condensation heat transfer.

The numerical simulation of radiant floor cooling and heating system with double phase change energy storage and the thermal performance

Being dependent statistics, building energy consumption has accounted for 2/5 of the world's total energy consumption. The combination of phase change energy storage materials with floor radiant cooling and heating system has become one of the main technical means of energy-saving buildings. Based on double phase change energy storage capillary floor radiant heating system, considering the effect of natural convection, wide phase transition area and latent heat release, combining with the characteristics of phase change materials phase behavior change, a novel three phase zone heat transfer model was established, and the Finite Volume method was used to solve the numerical problem. Then the heat storage and heat release of phase change energy storage floor under different working conditions in winter and summer were simulated to decide the phase-change heat transfer characteristics, the best water supply temperature, and the change rule of the surface temperature of the floor were analyzed. The research results can provide theoretical support for to draw up intermittent cooling and heating schemes.

Investigation on Unsteady Phase-Change Heat Transfer Characteristics of Centrifugal Granulated Particles

In this paper, the flying heat transfer characteristics of slag particles are studied in the process of the dry centrifugal granulation. When the solidification time of particle surface decreased by 66.67% at the rotational speed of 800 rpm, the total solidification time on the particle surface decreased by 55.5% and the average cooling rate increases faster in the phase transition region; When the rotating speed is increased by 87.5%, the complete solidification time on the surface of particles with different particle sizes is shortened by about 6%, and the average cooling rate is increased in the transformation region. Compared with particle size, it has little effect on heat transfer; When the air outlet angle is increased from 30° to 90°, the solidification time of particle surface increases from 0.095 s to 0.1 s; The decrease of space temperature has a great influence on shortening the time of liquid phase existence and particle solidification process. The obtained results could provide a reference for the design of granulation equipment and the adjustment and control of various parameters in the operation process in the industrial application process.

Visualized experiments on phase-change heat transfer of a metal “endoscopic” two-phase closed thermosyphon

A novel metal “endoscopic” two-phase closed thermosyphon (METPCT) which could be used to intuitively investigate the phase-change heat transfer and two-phase flow characteristics were developed. The visualized experimental set-up was established by using a rigid borescope and a high-speed camera. The phase-change heat transfer characteristics of the internal working fluid inside the METPCT under various cooling water temperatures (10, 15, 20 °C) and input power (100 ~ 900 W) have been investigated. Different heat and mass transfer regimes, e.g. start-up, geyser boiling and steady-state, were analyzed. During the start-up, the heat transfer in the evaporator is mainly heat conduction, natural convection and surface evaporation. Meanwhile, the start-up time decreases as the increases with cooling water temperature. The geyser boiling includes the incubation and expulsion stage, and the wall temperature response shows slight fluctuation and sharp fluctuation during the expulsion stage. In the steady-state, from bottom to top of the liquid pool in the evaporator, the two-phase flow pattern evolves from bubbly flow to slug flow, churn flow and then dispersed flow, and its transition position is closer to the bottom with the increase of input power. In addition, the heat transfer modes at the condenser are the combination of droplet condensation, discontinuous film condensation, and uniform film condensation. This work provides a new visualized experimental method to investigate the phase-change and two-phase flow properties in a TPCT, which helps to understand the heat and mass transfer mechanism of the TPCT.

Magnetic regulating the phase change process of Fe3O4-paraffin wax nanocomposites in a square cavity

The addition of external force provides an alternative way to promote the application of phase change materials in thermal-energy storage, space heating, and cooling systems. However, the experimental investigation using external magnetic force to regulate the phase change process is still limited. Here, magnetic Fe3O4 nanoparticles were added to paraffin wax to form phase change nanocomposites with enhanced thermal properties and controllable magnetism. The thermal properties of nanocomposites were measured and the phase change processes under magnetic controlling were experimentally and numerically investigated. A two-dimensional enthalpy-based lattice Boltzmann model with considering the external magnetic force was proposed and the measured thermal properties were used in the simulation. Good agreement between the experiment and simulation was achieved. The effects of different mass fractions of Fe3O4 nanoparticles (0, 1, 2, 3 and 4 wt%), magnetic directions, magnetic field intensities (0, 20, 40, 60 mT) on the phase change characteristics are discussed. The heat transfer efficiency in a square cavity filled with the nanocomposites developed more quickly when the paraffin wax was doped with a higher Fe3O4 mass fraction. Moreover, the phase change characteristics were controlled by the intensity and direction of the magnetic field. This study presents a method to achieve magnetically regulating phase change heat transfer characteristics that have potential applications in the energy-storage industry.

Dynamic tuning of magnetic phase change composites for solar-thermal conversion and energy storage

Photo-thermal conversion and energy storage using phase change materials are now being applied in industrial processes and technologies, particularly for electronics and thermal systems. This method relies on adding high thermal conductivity fillers, such as nanoparticles, to enhance the phase change process. In the long term, dynamic tuning heat transfer provides a superior means of tuning control the heat transfer efficiency and speed. In this study, a nanofluid phase change material was prepared by adding magnetic nanoparticles, effectively combining the properties of high thermal conductivity and magnetism, in an attempt to develop a magnetically enhanced approach for dynamic tuning of photo-thermal conversion charging. Our results showed that the phase change efficiency of magnetic phase change material can be improved by magnetic field application. With the increasing magnetic strength, the photo-thermal storage efficiency was enhanced, and storage capacity was improved by more than 48%. Meanwhile the steady temperature of the magnetic phase change material increased, enhancing the open-circuit voltage in photo-thermoelectricity experiments. Thus, the proposed method demonstrated in this study achieved superior phase change heat transfer characteristics within a photo-thermal conversion process by dynamically controlling the magnetic field distribution, which should be especially useful for direct solar energy utilisation.

Preparation and characteristics evaluation of mono and hybrid nano-enhanced phase change materials (NePCMs) for thermal management of microelectronics

Efficient, clean and quiet thermal management has become a vital challenge in for cooling of electronic devices. To enhance the capability and efficiency of passive thermal management, novel composite materials have been designed by the combination of graphene nanoplatelets (GNPs), multiwall carbon nanotubes (MWCNTs), aluminium oxide (Al2O3) and copper oxide (CuO) dispersed in the RT-28HC used as a phase change material (PCM). The series of mono and hybrid nano-enhanced phase change materials (NePCMs) were synthesized using constant mass fraction of 1.0 wt% of each type of nanoparticles to establish the optimum NePCM in terms of thermal properties for deficient thermal management of microelectronics. Various material characteristic techniques such as ESEM, FT-IR, XRD, TGA, DTG, DSC, IRT and thermal conductivity apparatus were used. The microstructure, chemical composition, crystallinity, thermal and phase-change heat transfer characteristics were investigated extensively for each sample of NePCM. The results showed the good chemical and thermal stability of all NePCMs without changing the chemical structure of RT-28HC. The surface morphology and crystal formation analysis revealed the uniform dispersion of nanoparticles onto the surface of RT-28HC. In comparison of mono and hybrid NePCMs, the results showed that the hybrid NePCM of GNPs/MWCNTs at mass percentage ratio of 75%/25% had the highest thermal conductivity enhancement of 96% compared to the pure PCM having optimum value of phase-change enthalpy of 245.18 J/g. Finally, enhancement in phase transition while melting and thermal properties evidenced that hybrid NePCMs can be used as potential candidate for the thermal management of microelectronics.

Phase change heat transfer characteristics of an additively manufactured wick for heat pipe applications

This study presents the phase change heat transfer characteristics of an additively manufactured wick for heat pipe applications. For this study, a flat heat pipe is considered that is made of stainless steel 316L utilizing a fabrication process that yields a wick structure with multi-scale features. Using laser powder bed fusion, relatively large pore structures, similar to screen-mesh structures, are laser molten with micro-scale laser-sintered features on top of this – we refer to these as multi-scale features in this paper. To characterize the phase change processes at heat pipe operating conditions, an experimental facility was developed. For this aim, a test cell with an internal volume of 40 × 20 × 6 mm3 was fabricated. Different filling ratios with water as working fluid and heat inputs ranging from 0.75 to 82.5 kW/m2 were tested. Additionally, a thermal network model to predict the overall heat transfer performance of an additively manufactured flat heat pipe is presented. The model is based on the heat conduction through the wick and wall in both axial and radial directions. Validation by comparison to experimental data shows an excellent agreement for the operating temperature (adiabatic or vapour temperature). The fabricated wick structure exploits enhanced evaporation heat transfer; thin film evaporation occurs due to the multi-scale sintered powder features on top of the fabricated wick surface. Additionally, the optimal filling ratio for which the device has maximal thermal performance is determined. The evaporation superheat is determined and discussed for different filling ratios. Experimental results show the optimum thermal performance of the flat heat pipe for a filling ratio of 110%. Compared to conventional wick structures, additively manufactured wick design exhibits improved thermal performance at higher heat fluxes. The experimental results suggest that additive manufacturing is a promising technology to fabricate freeform porous structures for heat pipes in general.

Flow and heat transfer characteristics of microchannel flow boiling enhancement with channel configurations

The heat dissipation problem encountered in the process of the development of new electronic equipment and mechanical components towards miniaturization has become the bottleneck of continuous progress in the field of mechanical and electronic control engineering, and the flow boiling heat transfer technology in microchannel may provide the effective cooling guarantee for this purpose. Given the reasonable operating temperature ranges of devices and the diversity of coolant evaporation temperature and pressure choices, refrigerants have become an important option, especially for zeotropic mixtures, which can not only modulate the properties of pure components, but also present the unique phase change heat transfer characteristics with great application prospects. In the present study, the flow boiling heat transfer research of R134a/R245fa zeotropic mixtures as well as their pure compartments in parallel multi-microchannel with continuous and segmented channel configurations were experimentally studied. Each microchannel test section consisted of seven parallel channel passages with the same total length of 110 mm. The cross-sectional area of each channel passage was 2 mm × 1mm (width×height) with the slab width of 0.5 mm. What difference from continuous microchannel was that 10 mm-long interconnected area was arranged every 30 mm along the channel length in segmented one. The experiments were carried out at the same inlet saturation temperature of 26 °C under the conditions comprising the heat flux range of 20− 350 kW/m2 and mass flux range of 300− 400 kg/(m2 s), respectively. In order to obtain more accurate data matching relationship, the analysis of heat transfer performance focused on the region near the outlet of the test sections. It’s worth noting that the multi-microchannel should be treated as fin effects during the heat transfer data reduction. The ribbed slabs could be considered as the rectangular straight fins either for continuous or segmented multi-microchannel. The results showed that compared with continuous microchannel, the heat transfer performance was slightly enhanced for pure components while slightly suppressed for zeotropic mixtures in segmented microchannel at lower effective heat flux. With the increase of effective heat flux, the heat transfer suppression effect of zeotropic mixtures was gradually weakened. The interconnected area was helpful to delay the occurrence of the transfer deterioration and improve the flow boiling CHF regardless of pure or zeotropic refrigerants. Besides, the flow boiling pressure drop in segmented microchannel was obviously reduced for zeotropic mixtures and their pure components. The smaller the liquid-vapor density ratio of test refrigerants, the higher the reduction of pressure drop with the help of interconnected area. For zeotropic mixtures, the flow boiling pressure drop was smaller at lower effective heat flux and the increasing trend of pressure drop on heat flow is slower.

Numerical investigation of the influence of mushy zone parameter Amush on heat transfer characteristics in vertically and horizontally oriented thermal energy storage systems

The effect of the value used for the mushy zone parameter (Amush) on predicted heat transfer and melting characteristics of a phase change material (PCM) Lauric acid, in both vertical and horizontal enclosures was studied. There is a lack of clarity regarding which value of this parameter should be used for accurate simulations of phase change heat transfer, addressing this will aid in accurate simulation and design of systems for LHTES (Latent heat thermal energy storage). The numerical analysis undertaken used a commercial CFD code ANSYS FLUENT 18.2 and the enthalpy-porosity formulation. The range of mushy zone parameter used was from 105 to107.The predicted locations of the melt front were compared to published experimental data available in the literature. The simulations provided quantitative information about the amount of energy stored and the melt fraction and providing improved understanding of the heat transfer process. Comparison between predictions using different values of Amush, and experimental data showed that correct selection of the value of Amush to be used in the momentum equations is an important parameter for accurate modelling of LHTES and has a significant influence on the solid-liquid interface shape and progression. The study reveals that increasing the value of Amush leads to a decrease in fluid velocity, decreasing convection and the rate of heat transfer, therefore, proper selection of the mushy zone parameter is necessary to accurately simulate LHTES systems and provide a better understanding of the phase change behaviour and heat transfer characteristics.