scholarly journals Modeling the Influence of Temperature-dependent Thermal Properties on the Freezing Front

2019 ◽  
Vol 8 (6) ◽  
pp. 129
Author(s):  
Victor M. Chavarria
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Statistical Error ◽  
Analytical Models ◽  
Parameter Estimates ◽  
Temperature Dependent ◽  
Freezing Front ◽  
Model Accuracy ◽  
Medium Temperature ◽  
Wide Range

Although numerical methods enable comprehensive analyses of food freezing, a thorough quantification is lacking the effects on the process introduced by uncertainties in variable thermal properties. Analytical models are, however, more suitable tools to perform such calculations. We aim to quantify these effects by developing a solution to the freezing front (FF) problem subject to temperature-dependent thermal properties and one-dimensional convective cooling. The heat integral balance method, Kirchhoff's transformation, and Plank's cooled-surface temperature equation (as a seed function) enabled us to obtain an approximate solution to the FF penetration time. To optimize model accuracy, two adjustable parameters were correlated with the inputs via nonlinear regression referenced to numerical simulation FF data. The mapped sensitivities, generated by perturbations in the temperature-dependent thermal conductivity and effective heat capacity, undergo rapid nonlinear changes for Biot numbers below 6. Above this level, these sensitivities stabilize depending on the cooling medium temperature and a thermal conductivity parameter. The median thermal conductivity-driven sensitivity is 0.348 and its interquartile range (IQR) is 0.220 to 0.425, whereas the median latent heat-driven sensitivity is 0.967 (IQR: 0.877 to 0.985). Statistical error measures and a ten-split K-fold validation support the model accuracy and reliability of the parameter estimates. Together, the model allows for gaining insights into the nonlinear behavior and magnitude of the influence of variable properties on the FF for a wide range of conditions. Nonlinear methods and prior information enable practical modeling of transport phenomena in foods.

scholarly journals Study of thermal properties on the different layers composing a commercial ceramic tile

2019 ◽  
Vol 65 (2) ◽  
pp. 124
Author(s):  
J. J. A. Flores Cuautle ◽  
G. Lara Hernandez ◽  
A. Cruz Orea ◽  
E. Suaste Gomez ◽  
C. Hernandez Aguilar ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Energy Transfer ◽  
Thermal Properties ◽  
Ceramic Tile ◽  
Building Materials ◽  
Photothermal Techniques ◽  
Essential Factor ◽  
Wide Range ◽  
Thermal Insulations ◽  
Enamel Layer

In this study is determined the thermal conductivity of a commercial ceramic considering that this property on the building materials is an essential factor, and it is the primary indicator of the suitableness of the material in the energy transfer considering that this kind of materials has many applications as thermal insulations. In this sense and considering that a commercial tile is usually composed of three layers, a substrate, a so-called engobe layer, and an enamel layer. Likewise, the thermal properties of the different layers were obtained individually by using two photothermal techniques on the ceramic material; the ceramic tile density was obtained using the Archimedes method. The calculated values show a wide range of thermal conductivity values for the different layers, ranging from1.3 to 4 W m-1K-1. 

scholarly journals Natural Convection Flow from an Isothermal Sphere with Temperature Dependent Thermal Conductivity

1970 ◽  
Vol 2 (2) ◽  
pp. 53-64 ◽  
Author(s):  
Md Mamun Molla ◽  
Azad Rahman ◽  
Lineeya Tanzin Rahman
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Convection Flow ◽  
Temperature Dependent ◽  
Boundary Layer Equations ◽  
Wide Range ◽  
Conductivity Parameter ◽  
Marine Engineering ◽  
Temperature Dependent Thermal Conductivity

Laminar free convection flow from an isothermal sphere immersed in a fluid with thermal conductivity proportional to linear function of temperature has been studied. The governing boundary layer equations are transformed into a non-dimensional form and the resulting nonlinear system of partial differential equations is reduced to local non-similarity equations, which are solved numerically by very efficient implicit finite difference method together with Keller box scheme. Numerical results are presented by velocity and temperature distribution of the fluid as well as heat transfer characteristics, namely the heat transfer rate and the skin-friction coefficients for a wide range of thermal conductivity parameter γ (= 0.0, 0.5, 1.0, 2.0, 3.0, 5.0) and the Prandtl number Pr (= 0.7, 1.0, 3.0, 5.0, 7.0).   Keywords: Natural convection, temperature dependent thermal conductivity, isothermal sphere.    doi:10.3329/jname.v2i2.1872  Journal of Naval Architecture and Marine Engineering 2(2005) 53-64

scholarly journals Preparation and Thermal Properties of Polypropylene Foils Filled with Talc or Boron Nitride Microparticles

2019 ◽  
Author(s):  
Stoyan Gutzov ◽  
Nina Danchova ◽  
Strashimir Djoumaliisky
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Boron Nitride ◽  
Linear Increase ◽  
Foil Thickness ◽  
Volume Percent ◽  
Temperature Dependent

The preparation and thermal properties of polypropylene foils, filled with ceramic microparticles, talc or boron nitride, are described. A slow, linear increase of thermal conductivity with volume percent of filler up to 30 vol % is detected. Reduction of the foil thickness bellow 200 micrometers leads to a significant increase of thermal conductivity. Specific thermal capacities of foils are temperature dependent, they decrease with filler incorporation.

scholarly journals Comparison of experimental and modelling results of thermal properties in Cu-AlN composite materials

2013 ◽  
Vol 61 (2) ◽  
pp. 507-514 ◽  
Author(s):  
M. Chmielewski ◽  
W. Weglewski
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Metal Matrix ◽  
Coefficient Of Thermal Expansion ◽  
Analytical Models ◽  
Matrix Composites ◽  
Pressing Method ◽  
3D Space ◽  
Automotive Electronic

Abstract Copper-based composites could be widely used in automotive, electronic or electrical industry due to their very promising thermal properties. In the present paper, Cu-AlN metal matrix composites with ceramic volume fractions between 0.1 and 0.4 were fabricated by hot pressing method in vacuum. Dependence of the coefficient of thermal expansion (CTE) and the thermal conductivity (TC) on the chemical composition of composites has been investigated. The measured values of the thermal expansion coefficient have been compared with the analytical models’ predictions. A numerical model based on FEAP 7.5 in 3D space has been used to evaluate the influence of the porosity on the thermal properties (thermal conductivity) of the composite. A fairly good correlation between the FEM results and the experimental measurements has been obtained.

Compact Analytical Models of Effective Thermal Conductivity of Rough Spheroid Packed Beds

2004 ◽  
Author(s):  
M. Bahrami ◽  
M. M. Yovanovich ◽  
J. R. Culham
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Present Model ◽  
Thermal Analyses ◽  
Contact Load ◽  
Analytical Models ◽  
Packed Beds ◽  
Wide Range ◽  
Temperature And Pressure

New compact analytical models for predicting the effective thermal conductivity of regularly packed beds of rough spheres immersed in a stagnant gas are developed. Existing models do not consider either the influence of the spheres roughness or the rarefaction of the interstitial gas on the conductivity of the beds. Contact mechanics and thermal analyses are performed for uniform size spheres packed in SC and FCC arrangements and the results are presented in the form of compact relationships. The present model accounts for the thermophysical properties of spheres and the gas, contact load, spheres diameter, spheres roughness and asperities slope, and temperature and pressure of the gas. The present model is compared with experimental data for SC and FCC packed beds and good agreement is observed. The experimental data cover a wide range of the contact load, surface roughness, interstitial gas type, and gas temperature and pressure.

Thermal Characterization of IM7/8552-1 Carbon-Epoxy Composites

2014 ◽  
Author(s):  
Messiha T. Saad ◽  
Sandi G. Miller ◽  
Torrence Marunda
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Carbon Fiber ◽  
Specific Heat ◽  
High Performance ◽  
Critical Role ◽  
Flash Method ◽  
Handling Characteristics ◽  
Wide Range

Thermal properties of composite materials such as, thermal conductivity, diffusivity, and specific heat are very important in engineering design process and analysis of aerospace vehicles as well as space systems. These properties are also important in power generation, transportation, and energy storage devices including fuel cells. Thermal conductivity is the property that determines the working temperature levels of the material; it plays a critical role in the performance of materials in high temperature applications, and it is an important parameter in problems involving heat transfer and thermal structures. The objective of this paper is to develop a thermal properties data base for the carbon fiber-epoxy (IM7/8552-1) composite. The IM7 carbon fiber is a continuous, high performance, intermediate modulus, PAN based fiber. This fiber has been surface treated and can be sized to improve its interlaminar shear properties, handling characteristics, and structural properties. The 8552 is a high performance tough epoxy matrix for use in primary aerospace structures. It exhibits good impact resistance and damage tolerance for a wide range of applications. The IM7/8552-1 is an amine cured unidirectional prepreg. The manufacturer recommended cure cycle for this material was followed, which includes consolidation under vacuum and autoclave pressure. The composite has a service temperature up to 121°C (250°F). The thermal properties of IM7/8552-1 carbon-epoxy have been investigated using experimental methods. The flash method was used to measure the thermal diffusivity of the composite. This method is based on the American Society for Testing and Materials standard, ASTM E1461. In addition, the Differential Scanning Calorimeter was used in accordance with the ASTM E1269 standard to measure the specific heat. The measured thermal diffusivity, specific heat, and density data were used to compute the thermal conductivity of the IM7/8552-1 carbon-epoxy composite.

Obtaining Temperature-Dependent Thermal Properties of Investment Casting Mold

2002 ◽  
Author(s):  
Michal Pohanka ◽  
Keith A. Woodbury ◽  
Jonathan Woolley
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Steady State ◽  
Investment Casting ◽  
Search Algorithm ◽  
Silica Shell ◽  
Fused Silica ◽  
Mold Material ◽  
Temperature Dependent ◽  
Thin Region

An experiment is conducted to determine the temperature dependent thermal properties (k, ρcp) of a fused silica shell commonly used as a mold material for investment castings. The mold is constructed by building up alternating layers of binder and silica. Different binder and silica are used for the inner layer, resulting in a thin region with different thermal properties than the rest of the shell. A search algorithm based on the simplex method is used to determine the thermal properties of both kinds of layers by finding the minimum of the error between measured and computed temperatures. Two approaches are used to find the thermal conductivity: steady state and dynamic.

Numerical Evaluation of the Thermal Properties of UD-Fibers Reinforced Composites for Different Morphologies

2020 ◽  
Vol 12 (03) ◽  
pp. 2050032 ◽  
Author(s):  
Toufik Saoudi ◽  
Ahmed El-Moumen ◽  
Toufik Kanit ◽  
Mohamed El Amine Belouchrani ◽  
Noureddine Benseddiq ◽  
...  
Keyword(s):  
Thermal Properties ◽  
Analytical Models ◽  
Reinforced Composites ◽  
Test Results ◽  
Fiber Volume ◽  
Element Analysis ◽  
Unidirectional Fibers ◽  
Random Arrangement ◽  
Wide Range ◽  
Unit Cells

In this paper, the numerical homogenization technique is used to evaluate the representative volume element and to compute the effective transverse thermal properties of unidirectional fibers reinforced composites. Three unit cells are constructed including square, hexagonal and random arrangement. The results obtained by finite element analysis showed the effect of unit cells configurations on the prediction of effective transverse thermal properties of unidirectional fibers composites for a wide range of fiber volume fractions and contrasts of properties. The numerical results are compared to available analytical models in the thermal conductivity of composites and experimental test results from the literature.

The Effects of Material Properties on Heat Dissipation in High Power Electronics

1998 ◽  
Vol 120 (3) ◽  
pp. 280-289 ◽  
Author(s):  
T. J. Lu ◽  
A. G. Evans ◽  
J. W. Hutchinson
Keyword(s):  
Thermal Conductivity ◽  
Power Electronics ◽  
High Power ◽  
Heat Dissipation ◽  
Substrate Material ◽  
High Thermal Conductivity ◽  
Analytical Models ◽  
Wide Range ◽  
Power Densities

The role of the substrate in determining heat dissipation in high power electronics is calculated, subject to convective cooling in the small Biot number regime. Analytical models that exploit the large aspect ratio of the substrate to justify approximations are shown to predict the behavior with good accuracy over a wide range of configurations. The solutions distinguish heat spreading effects’ that enable high chip-level power densities from insulation effects that arise at large chip densities. In the former, the attributes of high thermal conductivity are apparent, especially when the substrate dimensions are optimized. Additional benefits that derive from a thin layer of a high thermal conductivity material (such as diamond) are demonstrated. In the insulating region, which arises at high overall power densities, the substrate thermal conductivity has essentially no effect on the heat dissipation. Similarly, for compact multichip module designs, with chips placed on both sides of the substrate, heat dissipation is insensitive to the choice of the substrate material, unless advanced cooling mechanisms are used to remove heat around the module perimeter.

scholarly journals Survey of Some Exact and Approximate Analytical Solutions for Heat Transfer in Extended Surfaces

2021 ◽  
Author(s):  
Raseelo Joel Moitsheki ◽  
Partner Luyanda Ndlovu ◽  
Basetsana Pauline Ntsime
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Properties ◽  
Analytical Solutions ◽  
Nonlinear Problems ◽  
Transient Heat Transfer ◽  
Temperature Dependent ◽  
Approximate Analytical Solutions ◽  
Extended Surfaces ◽  
Insight Into

In this chapter we provide the review and a narrative of some obtained results for steady and transient heat transfer though extended surfaces (fins). A particular attention is given to exact and approximate analytical solutions of models describing heat transfer under various conditions, for example, when thermal conductivity and heat transfer are temperature dependent. We also consider fins of different profiles and shapes. The dependence of thermal properties render the considered models nonlinear, and this adds a complication and difficulty to solve these model exactly. However, the nonlinear problems are more realistic and physically sound. The approximate analytical solutions give insight into heat transfer in fins and as such assist in the designs for better efficiencies and effectiveness.

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