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Computational Modelling Of Heat Transfer In Reheat Furnaces

Electronic Theses of Indian Institute of Science

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Field Value
 
Title Computational Modelling Of Heat Transfer In Reheat Furnaces
 
Creator Harish, J
 
Subject Mechanical Engineering
Furnaces - Heat Transmission
Reheat Furnaces
Computational Modelling
Radiation Heat Transfer Modelling
Heat Flux
Pusher-type Furnace
Walking Beam Furnace
 
Description Furnaces that heat metal parts (blooms) prior to hot-working processes such as rolling or forging are called pre-forming reheat furnaces. In these furnaces, the fundamental idea is to heat the blooms to a prescribed temperature without very large temperature gradients in them. This is to ensure correct performance of the metal parts subsequent to reheating. Due to the elevated temperature in the furnace chamber, radiation is the dominant mode of heat transfer from the furnace to the bloom. In addition, there is convection heat transfer from the hot gases to the bloom. The heat transfer within the bloom is by conduction. In order to design a new furnace or to improve the performance of existing ones, the heat transfer analysis has to be done accurately. Given the complex geometry and large number of parameters encountered in the furnace, an analytical solution is difficult, and hence numerical modeling has to be resorted to.

In the present work, a numerical technique for modelling the steady-state and transient heat transfer in a reheat furnace is developed. The work mainly involves the development of a radiation heat transfer analysis code for a reheat furnace, since a major part of the heat transfer in the furnace chamber is due to radiation from the roof and combustion gases. The code is modified from an existing finite volume method (FVM) based radiation heat transfer solver, The existing solver is a general purpose radiation heat transfer solver for enclosures and incorporates the following features: surface-to-surface radiation, gray absorbing-emitting medium in the enclosure, multiple reflections off the bounding walls, shadowing effects due to obstructions in the enclosure, diffuse reflection and enclosures with irregular geometry.

As a part of the present work, it has now been extended to include the following features that characterise radiation heat transfer in the furnace chamber
· Combination of specular and diffuse reflection as is the case with most real surfaces
· Participating non-gray media, as the combustion gases in the furnace chamber exhibit highly spectral radiative characteristics

Transient 2D conduction heat transfer within the metal part is then modelled using a FVM-based code. Radiation heat flux from the radiation model and convection heat flux calculated using existing correlations act as boundary conditions for the conduction model. A global iteration involving the radiation model and the conduction model is carried out for the overall solution.

For the study, two types of reheat furnaces were chosen; the pusher-type furnace and the walking beam furnace. The difference in the heating process of the two furnaces implies that they have to be modelled differently. In the pusher-type furnace, the heating of the blooms is only from the hot roof and the gas. In the walking beam furnace, the heating is also from the hearth and the blooms adjacent to any given bloom.

The model can predict the bloom residence time for any particular combination of furnace conditions and load dimensions. The effects of variations of emissivities of the load, thickness of the load and the residence time of billet in the furnaces were studied.
 
Publisher Indian Institute of Science
 
Contributor Dutta, Pradip
 
Date 2006-08-24T08:17:34Z
2006-08-24T08:17:34Z
2006-08-24T08:17:34Z
2000-12
 
Type Electronic Thesis and Dissertation
 
Format 2956025 bytes
application/pdf
 
Identifier http://etd.iisc.ernet.in/handle/2005/234
null
 
Language en
 
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