Study of an optical non-contact measurement technique of the solidification rate for latent heat-storage materials

Abstract

A new technique is developed for the measurement of the solidification rate for a latent-heat storage material that consisted of spherical n-paraffin particles and water (emulsion slurry). This method utilizes the correlation between the optical characteristics of the slurry and the solidification rate of the paraffin particles. From experiment, it was shown that the increase in the solidification rate of the particles causes the rise in the transimissivity and the drop in the reflectivity of the slurry. Each paraffin particles has a conical crater on the surface when it solidifies. Based on these observations, a new radiative transfer model has been developed for a transparent particle with a conical crater and a three-dimensional radiative transfer model for a particulate medium by the Monte Carlo method. The analytical results for the slurry using the model well agreed with the experimental ones. From the analysis, it was shown that the crater on the particle surface makes the forward scattering weak and scattering in the backward and the lateral direction strong. Therefore, it was concluded that the rise in the transmissivity and decrease in the reflectivity of the slurry by the increase in its solidification rate is caused by the craters on the particle surfaces due to their phase-change.