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.

scholarly journals Viscoelastic Fluid over a Stretching Sheet with Electromagnetic Effects and Nonuniform Heat Source/Sink

2010 ◽  
Vol 2010 ◽  
pp. 1-14 ◽  
Author(s):  
Kai-Long Hsiao
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Viscoelastic Fluid ◽  
Stretching Sheet ◽  
Numerical Solutions ◽  
Transfer Effects ◽  
Gauss Elimination ◽  
Heat Transfer Effects ◽  
Source Sink ◽  
Gauss Elimination Method

A magnetic hydrodynamic (MHD) of an incompressible viscoelastic fluid over a stretching sheet with electric and magnetic dissipation and nonuniform heat source/sink has been studied. The buoyant effect and the electric numberE1couple with magnetic parameterMto represent the dominance of the electric and magnetic effects, and adding the specific item of nonuniform heat source/sink is presented in governing equations which are the main contribution of this study. The similarity transformation, the finite-difference method, Newton method, and Gauss elimination method have been used to analyze the present problem. The numerical solutions of the flow velocity distributions, temperature profiles, and the important wall unknown values off''(0)andθ'(0)have been carried out. The parameter Pr,E1, orEccan increase the heat transfer effects, but the parameterMorA*may decrease the heat transfer effects.

scholarly journals Analysis of the Thermal Characteristics of a Composite Ceramic Product Filled with Phase Change Material

Buildings ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 217 ◽  
Author(s):  
Joanna Krasoń ◽  
Przemysław Miąsik ◽  
Lech Lichołai ◽  
Bernardeta Dębska ◽  
Aleksander Starakiewicz
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Transfer Coefficient ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Phase Change Material ◽  
Thermal Characteristics ◽  
Ceramic Product ◽  
Change Material ◽  
The Heat Transfer Coefficient

The article presents a comparative analysis carried out using three methods, determining the heat transfer coefficient U for a ceramic product modified with a phase change material (PCM). The purpose of the article is to determine the convergence of the resulting thermal characteristics, obtained using the experimental method, numerical simulation, and standard calculation method according to the requirements of PN-EN ISO 6946. The heat transfer coefficient is one of the basic parameters characterizing the thermal insulation of a building partition. Most often, for the thermal characteristics of the partition, we obtain from the manufacturer the value of the thermal conductivity coefficient λ for individual homogeneous materials or the heat transfer coefficient U for the finished (prefabricated) partition. In the case of a designed composite element modified with a phase change material or other material, it is not possible to obtain direct information on the above parameter. In such a case, one of the methods presented in this article should be used to determine the U factor. The U factor in all analyses was determined in stationary conditions. Research has shown a significant convergence of the resulting value of the heat transfer coefficient obtained by the assumed methods. Thanks to obtaining similar values, it is possible to continue tests of thermal characteristics of partitions by means of numerical simulation, limiting the number of experimental tests (due to the longer test time required) in assumed different partition configurations, in stationary and dynamic conditions.

Role of Taylor Instability on Sublimation of a Horizontal Slab of Dry Ice

1977 ◽  
Vol 99 (3) ◽  
pp. 411-418 ◽  
Author(s):  
V. K. Dhir ◽  
J. N. Castle ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Boiling ◽  
Dry Ice ◽  
Ice Surface ◽  
Hypothetical Accident ◽  
Square Array ◽  
The Heat Transfer Coefficient

Sublimation of a horizontal slab of dry ice (≃ 190 K) placed beneath a pool of warm water or benzene (278–340 K) has been observed experimentally. Data for the heat transfer coefficient have been obtained in both steady and quasi-static states. The heat transfer coefficient for this pseudo film boiling process is found to be strongly dependent on the pool temperature. In the temperature range of stable film boiling, the heat transfer coefficient depends on the laminar or turbulent nature of the gas film. However, when the pool temperatures are such that a stable film can no longer be maintained, and the overlying liquid starts to freeze at the interface, the heat transfer coefficient data are correlated with the parameter cpΔTf/hsf for the liquid. Post-experiment visual observations of the dry ice surface show the presence of valleys and ridges arranged in a nearly square array spaced about one Taylor wavelength apart. An application of the present study to the fast reactor hypothetical accident situations in which a pool of molten fuel may be formed on horizontal steel surfaces is discussed.

Numerical Simulation of Melting in Metal Foam/Paraffin Composite Phase Change Material Using a Physically More Reasonable Macroscale Model

2019 ◽  
Author(s):  
Yuanpeng Yao ◽  
Huiying Wu
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Phase Change Material ◽  
Metal Foam ◽  
Phase Interface ◽  
Change Model ◽  
Composite Phase Change Material ◽  
Convection Dominated ◽  
Change Material ◽  
Change Problem

Abstract In this work, a macroscale model for melting phase change of metal foam/paraffin composite phase change material (MFPC) is developed by employing the enthalpy-porosity method and volume averaging technique. Both cases of varied and unvaried paraffin density during phase change are investigated in the model, and diffusion dominated interstitial heat exchange between paraffin and metal foam is considered along with the convection dominated interstitial heat transfer. The visualization experiments on melting phase change of copper foam/paraffin composite are carried out to validate the developed phase change model. It is found that with consideration of varied density of paraffin, the developed model can effectively solve the real melting problem of MFPC when metal foam is initially filled with solid paraffin. If the Boussinesq approximation is employed (i.e., unvaried paraffin density is considered during phase change), the model is more appropriate for the phase change problem on condition that metal foam can just be filled with liquid paraffin in the end of the melting process. Hence according to different treatments of paraffin density, the application of the phase change model needs to consider the influence of real paraffin filling condition of MFPC. The phase change model considering diffusion dominated interstitial heat transfer between stationary paraffin and metal foam can more accurately capture the solid-liquid phase interface positions as compared with the model only considering the convection dominated interstitial heat transfer. The present study can provide guidance for physically more reasonable simulation of the practical phase change problem of MFPC.

Analysis of heat transfer between solids at low temperatures

1976 ◽  
Vol 54 (17) ◽  
pp. 1749-1771 ◽  
Author(s):  
J. D. N. Cheeke ◽  
H. Ettinger ◽  
B. Hebral
Keyword(s):  
Heat Transfer ◽  
Thermal Contact ◽  
Impedance Matching ◽  
Debye Model ◽  
Phonon Transport ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Critical Cone ◽  
Acoustic Mismatch ◽  
The Heat Transfer Coefficient

A detailed analysis is given of the acoustic mismatch formulation first given by Little for the thermal contact resistance between solids for the case of phonon transport in a Debye model. Extrema in the heat transfer coefficients as a function of the refractive index of the interface are shown to be due to either impedance matching conditions or to the presence of the critical cone. Detailed numerical tables are presented which permit rapid evaluation of the heat transfer coefficient to an accuracy of 5% or better.

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

1981 ◽  
Vol 103 (4) ◽  
pp. 720-726 ◽  
Author(s):  
A. G. Bathelt ◽  
R. Viskanta
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Source ◽  
Phase Change ◽  
Source Surface ◽  
Transfer Coefficients ◽  
Interface Motion ◽  
Source Sink ◽  
Phase Change Heat Transfer ◽  
Solid Liquid

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.

Influence of the Surface Treatment of Tubes on the Heat Transfer in Low Pressure Atmosphere

2013 ◽  
Vol 592-593 ◽  
pp. 525-528
Author(s):  
Ladislav Šnajdárek ◽  
Petr Kracík ◽  
Jiří Pospíšil
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Surface Treatment ◽  
Liquid Flow ◽  
Thermal Gradient ◽  
Tube Bundle ◽  
Low Pressure ◽  
Vacuum Pump ◽  
The Heat Transfer Coefficient

This paper presents the current research on heat transfer at a sprinkled tube bundle consisting of smooth tubes and located in a chamber inside of which a low pressure is created by a liquid vacuum pump. It also monitors the changes of the heat transfer coefficient in relation to the speed of sprinkled and sprinkling liquid flow, thermal gradient.

Effect of Liquid Properties on Phase-Change Heat Transfer in Porous Wick Structures

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Steve Q. Cai ◽  
Avijit Bhunia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Mode Transition ◽  
Maximum Heat ◽  
Maximum Heat Flux ◽  
Phase Change Heat Transfer ◽  
The Heat Transfer Coefficient

In a heat pipe, operating fluid saturates wick structures system and establishes a capillary-driven circulation loop for heat transfer. Thus, the thermophysical properties of the operating fluid inevitably impact the transitions of phase-change mode and the capability of heat transfer, which determine both the design and development of the associated heat pipe systems. This article investigates the effect of liquid properties on phase-change heat transfer. Two different copper wick structures, cubic and cylindrical in cross section, 340 μm in height and 150 μm in diameter or width, are fabricated using an electroplating technique. The phase-change phenomena inside these wick structures are observed at various heat fluxes. The corresponding heat transfer characteristics are measured for three different working liquids: water, ethanol, and Novec 7200. Three distinct modes of the phase-change process are identified: (1) evaporation on liquid–vapor interface, (2) nucleate boiling with interfacial evaporation, and (3) boiling enhanced interface evaporation. Transitions between the three modes depend on heat flux and liquid properties. In addition to the mode transition, liquid properties also dictate the maximum heat flux and the heat transfer coefficient. A quantitative characterization shows that the maximum heat flux scales with Merit number, a dimensionless number connecting liquid density, surface tension, latent heat of vaporization, and viscosity. The heat transfer coefficient, on the other hand, is dictated by the thermal conductivity of the liquid. A complex interaction between the mode transition and liquid properties is reflected in Novec 7200. In spite of having the lowest thermal conductivity among the three liquids, an early transition to the mode of the boiling enhanced interface evaporation leads to a higher heat transfer coefficient at low heat flux.

Sign in / Sign up

Export Citation Format

Share Document