Some cautionary notes on the measurement and use of thermophysical property data

摘要

Thermophysical property data are needed for the mathematical modelling of high-temperature processes, and techniques have been developed to provide reliable results. However, it is necessary to exercise care when analysing the experimental results. The following cases are discussed: (i) the C_p peaks recorded by differential scanning calorimetry (DSC) for fusion (or solidification) are only apparent C_p values since they contain enthalpy contributions, and use of these apparent C_p values for the conversion of thermal diffusivities to conductivities can lead to massive overestimation of conductivities for temperatures in the transition range; (ii) there is a temperature lag between the sample and reference pans in DTA-type DSC (DTSC) instruments which causes some uncertainty in the temperature scale for fraction solid-temperature relations; (iii) thermal diffusivity measurements for the mushy region are prone to error because some of the energy supplied may be used for further melting of the alloy; (iv) oxide films on the surface of the molten alloy can affect measurements of physical properties; (v) wettability of the metal on the crucible and/or rotor can affect viscosity measurements, non-wetting leading to low values for the viscosity.