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A computer program for the analysis of timber structures exposed to fire

Fredlund, Bertil LU (1985) In LUTVDG/TVBB--3020--SE 3020.
Abstract
The fundamental equations for the theoretical treatment of wood during the process of pyrolysis are presented in Chapter 1. Expressions which must be specially introduced for combustible materials are those which describe the pyrolyctic reaction and reactions at the surface of the material. The reactions are assumed t o conform to first order Arrhenius functions. The treatment also includes the variation in heat capacity and thermal conductivity as a function of the decrease in density due to pyrolysis. When pyrolysis comnences, an internal convective flow is set up which affects heat transfer both inside the material and at the surface of the material. The numerical solution is carried out by the finite element method using the computer... (More)
The fundamental equations for the theoretical treatment of wood during the process of pyrolysis are presented in Chapter 1. Expressions which must be specially introduced for combustible materials are those which describe the pyrolyctic reaction and reactions at the surface of the material. The reactions are assumed t o conform to first order Arrhenius functions. The treatment also includes the variation in heat capacity and thermal conductivity as a function of the decrease in density due to pyrolysis. When pyrolysis comnences, an internal convective flow is set up which affects heat transfer both inside the material and at the surface of the material. The numerical solution is carried out by the finite element method using the computer program W0001 written in FORTRAN 77. The heat balance equation is solved incrementally by the forward difference method, and the critical time increment is calculated successiveiy for each computation stage. In view of the nature of the problem, with rapid reductions in density in the pyrolysis zone, internal convective heat flow and boundary elements which diminish in size, it is necessary to employ both small elements and short time increments in the comutations. The calculations are compared with experiments, but the paucity of well defined pyrolysis tests is evident, There is also a shortage of relevant material data, particularly at elevated temperatures, and the scatter in the reported kinetic constants is extremely large (10), (11). The comparison between calculated and measured temperature distributions shows that it is essential to take misturn content into consideration, and also that further development of the model for wet wood is important. It is evident from the parmetric study which has been carried out that the conductivity of carbon and the rate of reaction at the surface of the material have great significance for the depth of charring. It follows from this that it is important for these material properties to be better elucidated and for knowledge concerning surface reactions to be improved. Since the computation times in these simulations were very long, it is desirable that the solution procedure should be made more efficient, especially if a two dimensional program is to be developed. This computer program has been developed primarily as an aid in research, but , if computation times can be appreciably reduced, it can also be used for design calculations. (Less)
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publication status
published
subject
in
LUTVDG/TVBB--3020--SE
volume
3020
pages
47 pages
publisher
Division of Building Fire Safety and Technology, Lund Institute of Technology
ISSN
0282-3756
language
English
LU publication?
yes
id
496d7d50-522b-4584-b6f3-7505de1f28aa (old id 1270238)
date added to LUP
2008-11-24 12:15:00
date last changed
2016-04-16 04:41:08
@techreport{496d7d50-522b-4584-b6f3-7505de1f28aa,
  abstract     = {The fundamental equations for the theoretical treatment of wood during the process of pyrolysis are presented in Chapter 1. Expressions which must be specially introduced for combustible materials are those which describe the pyrolyctic reaction and reactions at the surface of the material. The reactions are assumed t o conform to first order Arrhenius functions. The treatment also includes the variation in heat capacity and thermal conductivity as a function of the decrease in density due to pyrolysis. When pyrolysis comnences, an internal convective flow is set up which affects heat transfer both inside the material and at the surface of the material. The numerical solution is carried out by the finite element method using the computer program W0001 written in FORTRAN 77. The heat balance equation is solved incrementally by the forward difference method, and the critical time increment is calculated successiveiy for each computation stage. In view of the nature of the problem, with rapid reductions in density in the pyrolysis zone, internal convective heat flow and boundary elements which diminish in size, it is necessary to employ both small elements and short time increments in the comutations. The calculations are compared with experiments, but the paucity of well defined pyrolysis tests is evident, There is also a shortage of relevant material data, particularly at elevated temperatures, and the scatter in the reported kinetic constants is extremely large (10), (11). The comparison between calculated and measured temperature distributions shows that it is essential to take misturn content into consideration, and also that further development of the model for wet wood is important. It is evident from the parmetric study which has been carried out that the conductivity of carbon and the rate of reaction at the surface of the material have great significance for the depth of charring. It follows from this that it is important for these material properties to be better elucidated and for knowledge concerning surface reactions to be improved. Since the computation times in these simulations were very long, it is desirable that the solution procedure should be made more efficient, especially if a two dimensional program is to be developed. This computer program has been developed primarily as an aid in research, but , if computation times can be appreciably reduced, it can also be used for design calculations.},
  author       = {Fredlund, Bertil},
  institution  = {Division of Building Fire Safety and Technology, Lund Institute of Technology},
  issn         = {0282-3756},
  language     = {eng},
  pages        = {47},
  series       = {LUTVDG/TVBB--3020--SE},
  title        = {A computer program for the analysis of timber structures exposed to fire},
  volume       = {3020},
  year         = {1985},
}