LFA
Difusividade e Condutividade Térmica
for measuring the Thermal Diffusivity and Thermal Conductivity
A condutividade e difusividade térmicas são os parâmetros termofísicos mais importantes dos materiais para a descrição das propriedades de transporte de calor de um material ou componente. Para a medição precisa das propriedades termofísicas como a difusividade térmica, a técnica do laser flash (LFA), provou-se como um método absoluto e rápido, versátil e preciso. A NETZSCH oferece três modelos de LFA, cobrindo todo o espectro de materiais e de temperaturas.
A condutividade térmica, tal como uma outra propriedade termofísica de grande significado, é determinada por meio de medidores de fluxo de calor (HFM) com o método de placa para materiais isolantes.
Os instrumentos da NETZSCH estão de acordo com as respectivas normas para instrumento e para aplicação de LFA (por exemplo, ASTM E1461, DIN EN 821), para o HFM (por exemplo, ASTM C518, ISO 8301, DIN EN 12667 EN 12, JIS A 1412) e GHP (ISO 8302, ASTM C177, DIN EN 12939, DIN EN 12667, DIN EN 13163).
Principle of the LFA Method
The laser or light flash method is used for measurement of the Difusividade TérmicaThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity of a variety of different materials.
The front surface of a plane-parallel sample is heated by a light pulse and the resulting temperature rise at the sample’s rear face is recorded as a function of time. The higher the thermal diffusivity, the faster the temperature rise reaches the rear face.
In a one-dimensional, the thermal diffusivity rise is calculated from this temperature rise as follows:
a = 0.1388 ⋅ d² / t0.5 with
a – Difusividade TérmicaThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.Thermal diffusivity in cm²/s
d – Thickness of the sample in cm
t0.5 – Time to half minimum in s
With all NETZSCH laser flash apparatuses (LFAs), the thermal diffusivity and Specific Heat Capacity (cp)Heat capacity is a material-specific physical quantity, determined by the amount of heat supplied to specimen, divided by the resulting temperature increase. The specific heat capacity is related to a unit mass of the specimen.specific heat capacity can be determined. This data is then used for calculation of the Condutividade TérmicaThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity.
MEASUREMENT WANTED?
Our NETZSCH applications laboratory is providing contract testing services for a wide range of industries and research centers. It is equipped with state-of-the-art testing instruments allowing for a variety of thermal analysis measurements to be carried out.
Consult with the experts in our applications labs to choose the best-suited measuring method for your specific needs.