Multiple-gas cooling method for constant-pressure heat capacity measurement of liquid metals using aerodynamic levitator.

Yifan Sun,Hiroaki Muta,Yuji Ohishi

doi:10.1063/5.0055555

Abstract

Until now, heat capacity measurements performed with levitation techniques have required accurate knowledge of the sample's emissivity beforehand. For a sample levitated using an aerodynamic levitator, it experiences both radiative and forced convective heat loss. The sample's emissivity only allows for the calculation of the radiative heat loss term, and a model has yet to be developed to accurately describe the total combined heat loss for aerodynamic levitation (ADL). In this study, we will introduce a novel multiple-gas cooling method for heat capacity measurement for ADL where two types of inert levitation gases (Ar and Kr) with different thermal conductivities were used to generate two cooling curves for the same sample. For samples being cooled at different cooling rates, the total heat loss is the same. The radiative heat loss was expressed using Stefan-Boltzmann's law, and the convective heat loss using Ranz-Marshall's equation. The two independent parameters (i.e., emissivity and heat capacity) of one given sample could then be solved using the two independent cooling curves. The heat capacities of gold, copper, nickel, iron, and palladium around the melting pointwere measured using this method. The multiple-gas cooling method for heat capacity measurement introduced in this study is the first heat capacity measurement method available for ADL and can be performed for materials with unknown emissivity. This newly developed method is important for the study of the thermophysical properties of high-temperature liquids, especially molten oxides with low electrical conductivity.

Highlights

Heat capacity is a key thermophysical property that determines the amount of energy transfer with changes in temperature
The high-temperature heat capacity is measured using drop calorimetry,3,4 in which a sample is heated to the target temperature and dropped quickly into a calorimeter at a known initial temperature
We focused on the heat capacity at temperatures near the melting point (Tm ± 50)

Summary

Introduction

Heat capacity is a key thermophysical property that determines the amount of energy transfer with changes in temperature. It is closely related to calculations of thermal conductivity, enthalpy, and Gibbs free energy.. The high-temperature heat capacity is measured using drop calorimetry, in which a sample is heated to the target temperature and dropped quickly into a calorimeter at a known initial temperature. The sample is generally heated in a furnace, and it sometimes needs to be kept in a container. These factors limit the temperatures at which drop calorimetry can be used. The sample can be contaminated when kept in the container because it requires a long time to reach thermal equilibrium

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Conclusion