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The laser flash analysis or laser flash method is used to measure
The laser flash method was developed by Parker et al. in 1961.
In a vertical setup, a light source (e.g.
thermal diffusivity
In thermodynamics, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It is a measure of the rate of heat transfer inside a material and has SI, SI units of m2/s. It is an intensive ...
of a variety of different materials. An energy pulse heats one side of a plane-parallel sample and the resulting time dependent temperature rise on the backside due to the energy input is detected. The higher the thermal diffusivity of the sample, the faster the energy reaches the backside. A laser flash apparatus (LFA) to measure thermal diffusivity over a broad temperature range, is shown on the right hand side.
In a one-dimensional, adiabatic case the thermal diffusivity
In thermodynamics, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It is a measure of the rate of heat transfer inside a material and has SI, SI units of m2/s. It is an intensive ...
is calculated from this temperature rise as follows:
:
Where
* is the thermal diffusivity in cm2/s
* is the thickness of the sample in cm
* is the time to the half maximum in s
As the coefficient 0.1388 is dimensionless, the formula works also for and in their corresponding SI units.Measurement principle
The laser flash method was developed by Parker et al. in 1961.
In a vertical setup, a light source (e.g. laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
, flashlamp) heats the sample from the bottom side and a detector on top detects the time-dependent temperature rise. For measuring the thermal diffusivity, which is strongly temperature-dependent, at different temperatures the sample can be placed in a furnace at constant temperature.
Perfect conditions are
* homogeneous material,
* a homogeneous energy input on the front side
* a time-dependent short pulse – in form of a Dirac delta function
In mathematical analysis, the Dirac delta function (or distribution), also known as the unit impulse, is a generalized function on the real numbers, whose value is zero everywhere except at zero, and whose integral over the entire real line ...
Several improvements on the models have been made. In 1963 Cowan takes radiation and convection on the surface into account.
Cape and Lehman consider transient heat transfer, finite pulse effects and also heat losses in the same year.
Blumm and Opfermann improved the Cape-Lehman-Model with high order solutions of radial transient heat transfer and facial heat loss, non-linear regression routine in case of high heat losses and an advanced, patented pulse length correction.
See also
*Thermal conductivity
The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1.
Heat transfer occurs at a lower rate in materials of low ...
* Thermal conductivity measurement
*Thermal diffusivity
In thermodynamics, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It is a measure of the rate of heat transfer inside a material and has SI, SI units of m2/s. It is an intensive ...
*Thermal physics
Thermal physics is the combined study of thermodynamics, statistical mechanics, and kinetic theory of gases. This umbrella-subject is typically designed for physics students and functions to provide a general introduction to each of three core he ...
References
{{DEFAULTSORT:Laser Flash Analysis Materials testing Heat transfer Heat conduction