The Evolution Of The Mushy Zone During The Phase Change Process Of Binary Nitrate Salts

In this study,an experimental setup was built to investigate the evolution of the mushy zone during the melting process of a binary nitrate salt(40%mol.LiNO3-60%mol.KNO3)and Solar salt(64%mol.NaNO3-36%mol.KNO3).The phase change process of the salt was conducted in a thin container with one-sided heating.Firstly,the thermophysical properties of the salts,including the solidus and liquidus temperatures and latent heat,were firstly determined.Then,the temperature variations of the salts were measured and the change of the melting front were recorded by a digital camera for the phase change processes.In each experiment,the existing problems were analyzed and the experimental device was improved.For the LiK-NO3 salt melting experiment,based on the recorded transient locations,the moving rate of the melting front was calculated.The resulting moving rate,together with the measured temperatures,was further used to calculate the mushy zone width.Moreover,the effect of the heating temperature on the mushy zone was studied.The results show that the moving rate of the melting front decreases during the melting process while the mushy zone width increases.It is also found that the moving rate of the melting front increases while the mushy zone width decreases with the increasing heating temperature.Finally,both the dimensionless location of the melting front and the dimensionless mushy zone width during the melting process were developed as functions of Stefan and Fourier numbers.As for the Solar salt melting experiment,due to the relatively high heating temperature,the experimental container was thermally deformed,resulting in natural convection inside the Solar salt,so the subsequently analysis could not be carried out.For the solidification experiments,owing to the large temperature difference between the PCM and the external environment,the PCM will rapidly solidify during the photographing process,so the pictures of the evolution of the interface cannot be obtained,which leads to the inability to perform detailed analysis.