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Optimizing measurements of heat capacity and thermal conductivity by non-contact modulation calorimetry in electromagnetic levitation
Regan Krizan, Lydia E. Tonani-Penha, Gwendolyn P. Bracker and Robert W. Hyers
Modulation calorimetry is the process of oscillating the heat input to a sample and measuring the oscillating temperature response. The process enables the determination of heat capacity and thermal conductivity. The heat capacity can be isolated using low frequency modulations since the primary mode of heat transfer is between the sample and its environment. The thermal conductivity can be calculated using higher frequencies when the transient internal conduction is prominent. When applied to electromagnetic levitation (EML), a containerless processing technique using an electromagnetic field to position and heat the sample, the thermophysical properties can be determined at higher temperatures. To optimize the procedure, a key free variable, oscillation frequency, is investigated. A correction function found in literature dictates the important heat transfer mode in the system as a function of modulation frequency. The ideal frequency for modulation to determine heat capacity can be calculated from a sample’s material properties and temperature. This is shown in terms of the Biot number, a measure for whether the sample can be assumed isothermal. For determination of thermal conductivity, the current standard is not a high enough frequency to reveal thermal gradients. Further research is needed to determine the frequency requirements necessary for measuring thermal conductivity.
Keywords: Modulation calorimetry, electromagnetic levitation, specific heat capacity, thermal conductivity, Biot number
DOI: 10.32908/hthp.v54.2047