The dehydration experiments of the NaOH·3.5H2O crystals obtained from the continuously-well-stirred crystallizer by employing the secondary refrigerant freezing process were carried out. And for these experiments a conturbex type centrifuge was used, and the permeability of the crystal bed was also measured. From these experiments, the apparent residual equilibrium saturation of the solid product was found to be zero. The experimental equation of saturation S was given from the surface mean size of crystal l, the centrifugal effect Z and the production rate P as follows: S=0.05 (lav2Z/P) -0.563. The operating diagram of crystallization-dehydration was obtained from the experimental equation about saturation and from the crystallization diagram reported in the previous in consideration of the size distribution function of crystals produced from the well-stirred crystallizer.
Four low boiling organic compounds of Fron-11, Fron-12, Fron-114 and n-butane were selected and used in this experiment, as usable secondary refrigerants for the crystallization of NaOH·2H2O in NaOH solution by secondary refrigerant freezing method. The hold up and drop size distribution of the dispersed refrigerant liguid (dispersion phase) in 49.1% NaOH solution were directly measured by taking photographs and using a glass vessel equipped with an agitator. The limited agitator speed for dispersion was determined with the correlation between the hold up and agitator speed. The total surface area of dispersion phase was calculated by using the hold up and the average drop diameter. The limited agitator speed was correlated to the density difference between the dispersion phase and the solution, and then, was increased according to the order of Fron-11, Fron-114, Fron-12 and n-butane. But, the total surface area of the dispersion phase, which was related to the evaporation rate of the secondary refrigeran tin the NaOH·2H2O crystallizer, was mainly characterized by the viscosity of the dispersion phase, and the total surface area of dispersed Fron-12 liquid was larger than that of Fron-11. From these experimental results, it was found that Fron-12 was the most suitable secondary refrigerant for the crystallization of NaOH·2H2O.
The limitign current density in the electrodialytic equipment with spacers has been studied quite extensively. However, the estimating equation which represents exactly the effect of the spacer on the limiting current density has not been presented yet. In order to make clear the relation between the limiting current density and the characteristics of spacers, this study was conducted to measure limiting current densities in the electrodialytic equipment by varying the kind of spacer, the clectrolyte, the operating temperature, the concentration of the inlet solution, and the flow velocity. From the above results, the values of the constants m and β in the estimating equation on the limiting current density which were derived by assuming the eddy diffusivity with spacer were 0.5 and 0.007, respectively, in all cases. Therefore, it became evident that the limiting current density i the electrodialytic equipment with spacer could be estimated from the above equation. Further, the spacer of the honey-comb textile was found to be the best among all the spacers tested for the equipment.