Effect of droplet deformation on determination of thermal conductivity in modulated laser calorimetry

•The key factors affects the phase lag of an EML droplet using modulated calorimetry were investigated.•The thermal conductivity of molten melts were determined accordingly.•The discrepancy of determined thermal conductivity increases linearly with deformation rate. The modulated laser calorimetry method using electromagnetic levitation is a superior way for measuring the thermal conductivity of molten materials. In this method, the top of droplet is periodically heated by modulated laser and the temperature response of bottom droplet is monitored by promoter simultaneously. By fitting the numerically obtained phase lag between laser and temperature response to that measured in experiments, the thermal conductivity is determined. However, in numerical analysis, the shape of droplet is usually fixed to be sphere while visible deformation of molten droplet is observed during experiments. The omitting of droplet deformation would surely affect the accuracy of measured thermal conductivity. In this work, a series of axisymmetric simulations are performed to investigate the influence of deformation of an electromagnetically levitated droplet on the determination of thermal conductivity. The results show that although the temperature distribution is inhomogeneous due to the physical nature of skin effect, the phase lag between modulated laser and temperature response is completely unaffected. Besides, the phase lag decreases with more intense convection and increases with droplet deformation. The effective thermal conductivity measured is about 16.8% smaller than inherent value under deformation rate of 12.2%. Moreover, a wider gap between the effective thermal conductivity and inherent value can be predicted under severer deformation. The relationship between thermal conductivity and deformation rate is linear and it applies to droplets with different radii and materials. Therefore, effective thermal conductivity can be corrected to determine the inherent value according to deformation rate. With this work, it is expected that the measurement accuracy of thermal conductivity can be further enhanced by taking the deformation of droplet into account.