Some cautionary notes on the measurement and use of thermophysical property data
Kenneth Mills, Brian Monaghan, Robert Brooks, Peter Quested
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 Cp peaks recorded by differential scanning calorimetry (DSC) for fusion (or solidification) are only apparent Cp values since they contain enthalpy contributions, and use of these apparent Cp 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.