﻿ Technical Information

Fundamentals

When calculating temperature in fire exposed structures non-linearity must be considered. Boundary conditions and thermal properties vary significantly with temperature, which gives rise to non-linearity. Analytical solutions with non-linearity included, are difficult, if not impossible to obtain. Therefore, numerical methods must be employed.  TASEF is based on the finite element method (FEM).

Heat Conduction

TASEF solves the heat conduction equation in two dimensions.  Plane and axi-symmetric problems can be solved.

Radiation and convection boundary conditions

Heat is transferred by radiation and convection to fire exposed surfaces.  These two processes are independent. Boundary conditions are specified in TASEF as radiation and gas temperatures which are input as functions of time. Parameters required are emissivity of the exposed surface, the Stefan-Boltzmann constant and the convection heat transfer coefficient. When simulating furnace tests, radiation and gas temperatures are in general assumed equal.  That is, however, not the case when analysing exposures from façade fires, local fires, or any pre-flashover conditions. Then radiation and gas temperatures must be specified individually, which is possible in TASEF.

Voids and shadow effects

Many structural assemblies contain voids and enclosures.  In these, heat is transferred by radiation and convection which must be considered particularly at elevated temperatures. TASEF has a very accurate method of computing heat transfer between the surfaces surrounding enclosures which may be of different materials.  A special case of using this ability is when considering reduced thermal exposure, so called shadow effects, as introduced in Eurocodes.

Thermal properties of materials

Material parameters required are specific conductivity, specific heat and density. Thermal conductivity of materials is input dependent on temperature.  TASEF requires calculation of volumetric enthalpy in the process which combines specific heat and density. Enthalpy is input as function of temperature. This is computationally advantageous when analysing materials with moisture, which has a significant effect on temperatures above the boiling point of water.

Further information  