- Author
-
Kokkala, M.
|
Baroudi, D.
- Title
- Transient Symmetrical Method for the Measurement of Temperature Dependent Thermal Diffusivity.
- Coporate
- VTT-Technical Research Center of Finland, Espoo
- Report
-
VTT Research Notes 1452,
1993,
26 p.
- Keywords
-
thermal diffusivity
|
temperature measurements
|
fire safety
|
thermophysical properties
|
heat transfer
|
numerical analysis
|
test methods
|
time
|
mineral wools
|
calcium silicate
|
insulating boards
|
geometry
- Identifiers
- transient analysis; curve fitting for the calculation of the derivatives; numerical validation of the method
- Abstract
- Measurement of temperature dependent thermal diffusivities using a transient symmetrical method was studied. In the method, the thermal diffusivity is determined from the temperature profile in a specimen constructed of thin slabs and heated symmetrically from both sides. The thermal diffusivity is determined as the ratio of the time derivative [see report] and the second spatial derivative [see report] at the position of the extremum of temperature. A numerical method was developed to calculate the thermal diffusivity as a function of time. The confidence interval of the diffusivity is determined by estimating the uncertainty of fitting when evaluating the required time derivative and the second derivative of temperature. The numerical methods were validated by using numerically calculated temperature profiles for a material with known thermal diffusivity. Preliminary tests were conducted to investigate the practical applicability of the method. The method proved to work for an inert material when no changes of geometry of the sample occurred. If reactions, convection, or substantial thermal expansions causing gaps inside the specimen occur, the assumptions of the method do not hold, and the results will not be well-defined.