Inward Melting in a Vertical Tube Which Allows Free Expansion of the Phase-Change Medium

1982 ◽  
Vol 104 (2) ◽  
pp. 309-315 ◽  
Author(s):  
E. M. Sparrow ◽  
J. A. Broadbent
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Numerical Solutions ◽  
Melting Process ◽  
Vertical Tube ◽  
Conduction Model ◽  
Free Expansion ◽  
Melting Front ◽  
Quantitative Results ◽  
Change Temperature

Experiments on the melting of a phase-change medium in a vertical tube yielded quantitative results both for the heat transfer and the timewise evolution of the melting front. The upper surface of the phase-change medium was bounded by an insulated air space, which accommodated the volume changes which accompany the melting process. Numerical solutions based on a pure conduction model were also performed for comparison purposes. It was found that the rate of melting and the heat transfer are significantly affected by fluid motions in the liquid melt induced by the volume change and by natural convection, with the former being significant only at early times. For melting initiated with the solid at the phase-change temperature, the experimentally determined values of the energy transfer associated with the melting process were about 50 percent higher than those predicted by the conduction model. Furthermore, the measured values of the energy stored in the liquid melt were about twice the conduction prediction. A compact dimensionless correlation of the experimental results was achieved using the Fourier, Stefan, and Grashof numbers. Initial subcooling of the solid substantially decreased the rate of melting, with corresponding decreases in the energy transfers for melting and sensible heat storage.

Heat Transfer Enhancement of Finned Copper Foam/Paraffin Composite Phase Change Material

2021 ◽  
Vol 14 ◽  
Author(s):  
Tingting Wu ◽  
Yanxin Hu ◽  
Xianqing Liu ◽  
Changhong Wang ◽  
Zijin Zeng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Transfer Rate ◽  
Flow Resistance ◽  
Phase Change Materials ◽  
Heat Transfer Performance ◽  
Melting Process ◽  
Copper Foam ◽  
Composite Phase Change Material ◽  
Change Material

Background: The employment of Phase Change Materials (PCMs) provides a potential selection for heat dissipation and energy storage. The main reason that hinders the wide application is the low thermal conductivity of PCMs. Combining the proper metal fin and copper foam, the fin/composite phase change material (Fin-CPCM) structure with good performance could be obtained. However, the flow resistance of liquid paraffin among the porous structure has seldom been reported, which will significantly affect the thermal performance inside the metal foam. Furthermore, the presence of porous metal foam is primarily helpful for enhancing the heat transfer process from the bottom heat source. The heat transfer rate is slow due to the one-dimensional heat transfer from the bottom. It should be beneficial for improving the heat transfer performance by adding external fins. Therefore, in the present study, a modified structure by combining the metal fin and copper foam is proposed to further accelerate the melting process and improve the temperature uniformity of the composite. Objective: The purpose of this study is to research the differences in the heat transfer performance among pure paraffin, Composite Phase Change Materials (CPCM) and fin/Composite Phase Change Material (Fin-CPCM) under different heating conditions, and the flow resistance of melting paraffin in copper foam. Methods: To experimentally research the differences in the heat transfer performance among pure paraffin, CPCM and Fin-CPCM under different heating conditions, a visual experimental platform was set up, and the flow resistance of melting paraffin in copper foam was also analyzed. In order to probe into the limits of the heat transfer capability of composite phase change materials, the temperature distribution of PCMs under constant heat fluxes and constant temperature conditions was studied. In addition, the evolution of the temperature distributions was visualized by using the infrared thermal imager at specific points during the melting process. Results: The experimental results showed that the maximum temperature of Fin-CPCM decreased by 21°C under the heat flux of 1500W/m2 compared with pure paraffin. At constant temperature heating conditions, the melting time of Fin-CPCM at a temperature of 75°C is about 2600s, which is 65% less than that of pure paraffin. Due to the presence of the external fins, which brings the advantage of improving the heat transfer rate, the experimental result exhibited the most uniform temperature distribution. Conclusion: The addition of copper foam can accelerate the melting process. The addition of external fins brings the advantage of improving the heat transfer rate, and can make the temperature distribution more uniform.

Modeling and Simulation on Heat Transfer in Blood Vessels Subject to a Transient Laser Irradiation

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Xuelan Zhang ◽  
Liancun Zheng ◽  
Lin Liu ◽  
Xinxin Zhang
Keyword(s):  
Heat Transfer ◽  
Blood Vessels ◽  
Laser Irradiation ◽  
Numerical Solutions ◽  
Thermal Relaxation ◽  
Initial Time ◽  
Laser Exposure ◽  
Conduction Model ◽  
Heaviside Step Function ◽  
The Impact

Abstract This paper investigates heat transfer of blood vessels subject to transient laser irradiation, where the irradiation is extremely short times and has high power. The modified Fourier heat conduction model (Cattaneo–Christov flux) and Heaviside step function are used in describing the thermal relaxation and temperature jump characteristics in initial time. A novel auxiliary function is introduced to avoid three-level discretization and temporal–spatial mixed derivative, and the numerical solutions are obtained by Crank–Nicolson alternating direction implicit (ADI) scheme. Results indicate that the temperature distributions in blood vessels strongly depend on the blood property, the laser exposure time, the blood flowrate (Reynolds number) and the thermal relaxation parameter. The isothermal curve exhibits asymmetric characteristics due to the impact of blood flow, and the higher blood velocity leads to more asymmetric isotherm and less uniform thermal distribution. Further, the heat-flux relaxation phenomenon is also captured, and its effect on blood temperature becomes more noticeable as blood flows downstream of blood vessels.

Numerical Simulation of Core Temperature and Melting Process of IVR Core After a Severe Water Loss Accident

2017 ◽  
Author(s):  
Yiqun Liu ◽  
Xiaoying Zhang ◽  
Jingya Li ◽  
Biao Wang ◽  
Dekui Zhan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Water Level ◽  
Water Loss ◽  
Reactor Core ◽  
Melting Process ◽  
Nucleate Boiling ◽  
Maximum Temperature ◽  
Conduction Model ◽  
Fuel Rods ◽  
The Core

After the occurrence of severe water loss accident in a PWR, the water level in the reactor core would decrease gradually, leading to heat up and melted down of the core, threatening safety of the nuclear power plant and the surrounding environment. In this paper, the 1/4 core of AP1000 PWR was adopted for study, a numerical method has been established to calculate the transient change of temperature and melting process of the core and envelope structure (boarding, basket and RPV) after the severe water loss accident. A two-dimensional conduction model with cylindrical coordinate has been used to simulate heat transfer along the radius and height direction of fuel rods and control rods in fuel assemblies. Heat transfer condition on rod surface considers nucleate boiling for rod surface below the water level, while radiative heat transfer among neighboring rods and natural convection with water vapor was considered for rod surface above the water level. Heat transfer along thickness of envelope structures were modeled with the one-dimensional conduction model. The results show that the maximum temperature of the whole reactor core does not exceed 3000K and AP1000 will not meet the melting of fuel rods with the help of RPV external water chamber cooling. The temperature values of the fuel rods and the control rod show the characteristic distribution of the two regions. At 4904s, the maximum temperature of the rod rises to 2900K, and then stabilize. The temperature of the shell is up to 2000K, the maximum temperature of the basket is to 1260K, the variation of RPV wall temperature is not obvious.

Issues in Thermal Contact and Phase Change in Porosity Prediction

1993 ◽  
Vol 115 (1) ◽  
pp. 2-7 ◽  
Author(s):  
H. Huang ◽  
V. K. Suri ◽  
J. L. Hill ◽  
J. T. Berry
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Thermal Gradient ◽  
Numerical Solutions ◽  
Thermal Contact ◽  
Computational Error ◽  
Source Sink ◽  
The Heat Transfer Coefficient ◽  
Change Problem

One of the major objectives of solidification modeling is to determine, prior to pouring, whether porosity, such as massive cavities and dispersed pores, are likely to appear in the casting. The numerical solutions of solidification heat transfer alone, however, cannot provide such information. In order to predetermine the presence of porosity, various criteria functions have been proposed by a number of investigators. These criteria functions are associated with cooling rate, thermal gradient, solidus velocity and local solidification time, etc. Since these parameters can be derived from numerical solutions, the reliability of porosity prediction largely depends on the accuracy of the numerical solutions employed. Thermal contact and phase change affect the numerical solutions significantly, and hence the local values of the predicted parameters. Consequently, these phenomena must be given special attention. This paper addresses some important aspects of thermal contact and phase change in determining the values of criteria functions. The free thermal contraction method is used to describe the variation and distribution of the heat transfer coefficient at the casting/mold interface. The phase change problem is treated by the heat source/sink algorithm. The sensitivity of criteria functions and the role of computational error are also discussed.

Numerical Solution of Heat Transfer During Solidification of an Encapsulated Phase Change Material

2013 ◽  
Author(s):  
Antonio Ramos Archibold ◽  
Muhammad M. Rahman ◽  
D. Yogi Goswami ◽  
Elias L. Stefanakos
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Numerical Solution ◽  
Phase Change Material ◽  
Outer Surface ◽  
Power Plants ◽  
Thermal Power ◽  
Melting Front ◽  
Stefan Number ◽  
Change Material

Macro encapsulation techniques have gained considerable attention in latent heat storage systems for solar energy applications in order to improve the overall energy conversion efficiency in solar thermal power plants. However the heat transfer mechanisms that govern the charging and discharging processes at high operating temperatures are still under development and represent an important aspect in the thermal energy storage design process. This study presents a numerical solution of the heat transfer and phase change that occurs during the solidification process of a phase change material (PCM) encapsulated in a spherical container. A transient two-dimensional axisymmetric mathematical model was solved using the control volume discretization approach along with the enthalpy-porosity method to track the melting front. A spherical shell of thickness t, under the gravitational field is completely filled with liquid PCM. For time t>0, a constant temperature boundary condition Tw, which is lower than the phase change temperature of the PCM, is imposed at the outer surface of the shell. A comprehensive analysis is presented in order to assess the role of the capsule size, buoyancy-driven flow in the liquid phase, and shell outer surface temperature on the thermal performance of the system. Results show that with the increase of Stefan number the solidification rate is enhanced. A reduction of 39.25% in total solidification time is predicted when the Stefan number changed from 0.095 to 0.143. Finally a generalized correlation for the solid mass fraction during solidification is obtained based on a combination of Fourier and Stefan numbers and a dimensionless material parameter.

Melting of Phase Change Materials With Volume Change in Metal Foams

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Zhen Yang ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Phase Change ◽  
Volume Change ◽  
Phase Change Materials ◽  
Metal Foam ◽  
Melting Process ◽  
Metal Foams ◽  
Volume Shrinkage ◽  
Two Temperature

Melting of phase change materials (PCMs) embedded in metal foams is investigated. The two-temperature model developed accounts for volume change in the PCM upon melting. Volume-averaged mass and momentum equations are solved, with the Brinkman–Forchheimer extension to Darcy’s law employed to model the porous-medium resistance. Local thermal equilibrium does not hold due to the large difference in thermal diffusivity between the metal foam and the PCM. Therefore, a two-temperature approach is adopted, with the heat transfer between the metal foam and the PCM being coupled by means of an interstitial Nusselt number. The enthalpy method is applied to account for phase change. The governing equations are solved using a finite-volume approach. Effects of volume shrinkage/expansion are considered for different interstitial heat transfer rates between the foam and PCM. The detailed behavior of the melting region as a function of buoyancy-driven convection and interstitial Nusselt number is analyzed. For strong interstitial heat transfer, the melting region is significantly reduced in extent and the melting process is greatly enhanced as is heat transfer from the wall; the converse applies for weak interstitial heat transfer. The melting process at a low interstitial Nusselt number is significantly influenced by melt convection, while the behavior is dominated by conduction at high interstitial Nusselt numbers. Volume shrinkage/expansion due to phase change induces an added flow, which affects the PCM melting rate.

scholarly journals Effect of Inclined Magnetic Field on the Entropy Generation in an Annulus Filled with NEPCM Suspension

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Seyyed Masoud Seyyedi ◽  
M. Hashemi-Tilehnoee ◽  
M. Sharifpur
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Phase Change ◽  
Entropy Generation ◽  
Phase Change Materials ◽  
Transfer Problem ◽  
Mass Conservation ◽  
Melting Process ◽  
Industrial Applications ◽  
Inclined Magnetic Field

The encapsulation technique of phase change materials in the nanodimension is an innovative approach to improve the heat transfer capability and solve the issues of corrosion during the melting process. This new type of nanoparticle is suspended in base fluids call NEPCMs, nanoencapsulated phase change materials. The goal of this work is to analyze the impacts of pertinent parameters on the free convection and entropy generation in an elliptical-shaped enclosure filled with NEPCMs by considering the effect of an inclined magnetic field. To reach the goal, the governing equations (energy, momentum, and mass conservation) are solved numerically by CVFEM. Currently, to overcome the low heat transfer problem of phase change material, the NEPCM suspension is used for industrial applications. Validation of results shows that they are acceptable. The results reveal that the values of N u ave descend with ascending Ha while N gen has a maximum at Ha = 16 . Also, the value of N T , MF increases with ascending Ha . The values of N u ave and N gen depend on nondimensional fusion temperature where good performance is seen in the range of 0.35 < θ f < 0.6 . Also, Nu ave increases 19.9% and ECOP increases 28.8% whereas N gen descends 6.9% when ϕ ascends from 0 to 0.06 at θ f = 0.5 . Nu ave decreases 4.95% while N gen increases by 8.65% when Ste increases from 0.2 to 0.7 at θ f = 0.35 .

scholarly journals Role of honeycomb structure in improving the melting process of a phase change material inside a latent heat storage unit

2021 ◽  
Vol 19 ◽  
pp. 589-592
Author(s):  
M. Hariss ◽  
◽  
M. El Alami ◽  
A. Gounni
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Numerical Study ◽  
Melting Process ◽  
Honeycomb Structure ◽  
Melting Time ◽  
Storage Unit ◽  
Latent Heat Storage ◽  
The Impact

In this work, a numerical study is performed to analyze the impact of honeycomb structure on heat transfer within the PCM. The modeling is based on a transient calculation making it possible to analyze the phase change of the paraffin using the commercial software "Fluent" based on the enthalpy-porosity model. The results showed that the impregnation of a metal matrix in a rectangular enclosure helps to decrease the melting time and thus improve the heat transfer within the PCM.

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