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Fundamental Journal of Thermal Science and Engineering

ISSN: 2249-975X
 
Volume 2, Issue 2, 2012, Pages 53-87
 
On heat-flow direction inertia effect
Author(s): Jumber Khantadze, Domenti Gabunia and Levan Chkhartishvili
Pages: 53-61
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Abstract
There is proposed a theoretical description of inertia effect of the heat-flow direction, which for a finite period of time τ maintains the same after the mean temperature-gradient in the heating system has been instantly reversed. Analyzing solutions of the heat equation with appropriate initial and boundary conditions, the inertia time is shown to be proportional of the squared heat-conductor length ⁄ that is its size in the temperature-gradient direction, and inversely proportional of the material thermal diffusivity α:τ~L2/α Numerical estimate made for the heat-conductor in form of a steel bar is in satisfactory agreement with the experimental results.



Keywords and phrases

non-stationary thermal process, reversible temperature-gradient, heat-flow inertia.
 
Effect of axial wall conduction on heat transfer parameters for parallel-plate channel having radiation participating medium and step change in boundary conditions
Author(s): M. A. Hassab, M. Khamis Mansour and M. Shawky Ismail
Pages: 63-87
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Abstract
This paper presents a theoretical model to investigate the effect of axial wall conduction on the heat transfer characteristics for laminar flow through a thick-walled channel, taking into account the radiation effect in gases as a participating medium in the radiation exchange. A partition separates the channel of interest into two regions (upstream and downstream region) in which two different coolant fluids bound the channel in those regions. A numerical model has been developed in this study using a finite-difference technique to solve the conjugate heat transfer problem by creating a self-made computer code. The modified P-1 approximation is employed to solve the radiation part of the problem. The calculated results from the computer program have been compared with a commercial code "ANSYS FLUENT 12" and a good agreement has been obtained. The effects of the optical thickness τ0 the conduction-to radiation parameter N, single scattering Albedo coefficient ω and the wall emissivity ζ on the heat transfer characteristics are presented in this study. The heat transfer characteristics are represented by local Nusslet number Nu, fluid temperature distribution, and solid temperature distribution.

The study shows that the significant change in those parameters could lead to an enhancement of 24% for the average Nusselt number (nu) at certain conditions.



Keywords and phrases

axial wall conduction, conjugate heat transfer, laminar flow, step change, numerical study, P-1 approximation, participating medium.
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