Non-Uniform Temperature Distribution in Multilayer Thermal Protective Coating with Curved Interfaces

2016 ◽  
Vol 685 ◽  
pp. 251-256 ◽  
Author(s):  
Yurii A. Chumakov ◽  
Anna G. Knyazeva
Keyword(s):  
Thermal Conductivity ◽  
Heating Temperature ◽  
Temperature Gradients ◽  
Curved Surfaces ◽  
Uniform Temperature ◽  
Fourth Layer ◽  
Initial Stage ◽  
Thermal Conductivity Problem ◽  
Porosity Changes ◽  
Thermal Protective Coating

In this work, the thermal conductivity problem is solved for fourth layer plate at the heat flux action on one of surfaces. The interfaces between layers are assumed non ideal that leads to appearance of thermal resistances between layers. Additionally thermal resistances are inhomogeneous due to curved surfaces of materials. The existence of curved surfaces and porosity of layers are connected with the way of specimen manufacturing. Thermal conductivity coefficients of layers can by changed when their porosity changes. The problem is solved numerically. It was found that curved interfaces and thermal resistance affect process only at initial stage of the heating. Temperature gradients depend essentially on porosity and thickness of layers.

A Transient Formulation of Newton's Cooling Law for Spherical Bodies

2000 ◽  
Vol 123 (1) ◽  
pp. 63-64 ◽  
Author(s):  
S. S. Sazhin ◽  
V. A. Gol'dshtein ◽  
M. R. Heikal
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Diesel Engine ◽  
Effective Thermal Conductivity ◽  
Spherical Body ◽  
Fuel Droplet ◽  
Transient Effects ◽  
Newton's Law ◽  
Initial Stage ◽  
Newton’S Law

Newton's law of cooling is shown to underestimate the heat flux between a spherical body (droplet) and a homogeneous gas after this body is suddenly immersed into the gas. This problem is rectified by replacing the gas thermal conductivity by the effective thermal conductivity. The latter reduces to the gas thermal conductivity in the limit of t→∞, but can be substantially higher in the limit of t→0. In the case of fuel droplet heating in a medium duty truck Diesel engine the gas thermal conductivity may need to be increased by more than 100 percent at the initial stage of calculations to account for transient effects during the process of droplet heating.

scholarly journals Variation of thermal conductivity of DPPC lipid bilayer membranes around the phase transition temperature

2017 ◽  
Vol 14 (130) ◽  
pp. 20170127 ◽  
Author(s):  
Sina Youssefian ◽  
Nima Rahbar ◽  
Christopher R. Lambert ◽  
Steven Van Dessel
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Thermal Properties ◽  
Transition Temperature ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Phase Transition Temperature ◽  
Temperature Gradients ◽  
Phase Behaviour ◽  
Gel Phase

Given their amphiphilic nature and chemical structure, phospholipids exhibit a strong thermotropic and lyotropic phase behaviour in an aqueous environment. Around the phase transition temperature, phospholipids transform from a gel-like state to a fluid crystalline structure. In this transition, many key characteristics of the lipid bilayers such as structure and thermal properties alter. In this study, we employed atomistic simulation techniques to study the structure and underlying mechanisms of heat transfer in dipalmitoylphosphatidylcholine (DPPC) lipid bilayers around the fluid–gel phase transformation. To investigate this phenomenon, we performed non-equilibrium molecular dynamics simulations for a range of different temperature gradients. The results show that the thermal properties of the DPPC bilayer are highly dependent on the temperature gradient. Higher temperature gradients cause an increase in the thermal conductivity of the DPPC lipid bilayer. We also found that the thermal conductivity of DPPC is lowest at the transition temperature whereby one lipid leaflet is in the gel phase and the other is in the liquid crystalline phase. This is essentially related to a growth in thermal resistance between the two leaflets of lipid at the transition temperature. These results provide significant new insights into developing new thermal insulation for engineering applications.

Steady-State Investigation of Vapor Deposited Micro Heat Pipe Arrays

1995 ◽  
Vol 117 (1) ◽  
pp. 75-81 ◽  
Author(s):  
A. K. Mallik ◽  
G. P. Peterson
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Surface Temperature ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Heat Pipes ◽  
Temperature Gradients ◽  
Bottom Surface ◽  
Micro Heat Pipe ◽  
Micro Heat Pipes

An experimental investigation of vapor deposited micro heat pipe arrays was conducted using arrays of 34 and 66 micro heat pipes occupying 0.75 and 1.45 percent of the cross-sectional area, respectively. The performance of wafers containing the arrays was compared with that of a plain silicon wafer. All of the wafers had 8 × 8 mm thermofoil heaters located on the bottom surface to simulate the active devices in an actual application. The temperature distributions across the wafers were obtained using a Hughes Probeye TVS Infrared Thermal Imaging System and a standard VHS video recorder. For wafers containing arrays of 34 vapor deposited micro heat pipes, the steady-state experimental data indicated a reduction in the maximum surface temperature and temperature gradients of 24.4 and 27.4 percent, respectively, coupled with an improvement in the effective thermal conductivity of 41.7 percent. For wafers containing arrays of 66 vapor deposited micro heat pipes, the corresponding reductions in the surface temperature and temperature gradients were 29.0 and 41.7 percent, respectively, and the effective thermal conductivity increased 47.1 percent, for input heat fluxes of 4.70 W/cm2. The experimental results were compared with the results of a previously developed numerical model, which was shown to predict the temperature distribution with a high degree of accuracy, for wafers both with and without the heat pipe arrays.

scholarly journals A NOTE ON THE CONSTANT THERMAL CONDUCTIVITY HYPOTHESIS AND ITS CONSEQUENCE FOR CONDUCTION HEAT TRANSFER PROBLEMS

2014 ◽  
Vol 13 (2) ◽  
pp. 48
Author(s):  
R. M. S. Gama
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
High Temperature ◽  
Heat Generation ◽  
Strong Dependence ◽  
Temperature Gradients ◽  
Conduction Heat Transfer ◽  
Kirchhoff Transformation ◽  
Constant Thermal Conductivity ◽  
Transfer Problems

This work discuss the usual constant conductivity assumption and its consequences when a given material presents a strong dependence between the temperature and the thermal conductivity. The discussion is carried out considering a sphere of silicon with a given heat generation concentrated in a vicinity of its centre, giving rise to high temperature gradients. This particular case is enough to show that the constant thermal conductivity hypothesis may give rise to very large errors and must be avoided. In order to surpass the mathematical complexity, the Kirchhoff transformation is used for constructing the solution of the problem. In addition, an equation correlating thermal conductivity and the temperature is proposed.

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