Study On The Heat And Mass Transfer Performance Of Droplets Freezing And Desalination Process Under The Effect Of Ultrasonic Field

Recently,ultrasonic assisted freezing technology has been widely applied to strengthen the heat and mass transfer in the related fields like food freezing storage and solution crystallization.This technology has shown enormous potential in decreasing the freezing time of liquid solutions.The analysis of ultrasonic assisted freezing process concerning the mechanism of ultrasound in accelerating freezing rate and the phase transition in the droplet freezing process.It is acknowledged that the study of this freezing model contributed to the improvement of liquid freezing researches.However,the physical process is complicated,the equations are difficult to mathematically solved,and the influencing factors are numerous.Therefore,the solution of ultrasonic assisted freezing model is a hot and challengeable research subject which gets more attentions in recent years.In this paper,a droplet freezing model,considering the influence of ultrasonic cavitation and thermal effect,was established based on the energy conservation and ultrasound theory.The variation of droplet's diameter,temperature,liquid proportion and the position of phase interface under different ultrasonic frequencies and intensities were studied through the mathematical and experimental methods.Because the absorbed energy of droplets from ultrasound has the potential to hinder the freezing process,the heat dissipation induced by cavitation and heat production caused by ultrasonic thermal effect were quantitively compared and the optimum loading conditions of ultrasound was provided in this study.The study shows that the loading of ultrasound can significantly improve the droplet's freezing process and there are critical points,after which the loading of ultrasound cannot accelerate the freezing rate,exist in the freezing process.Through the comparison of freezing process with different ultrasonic parameters,the low-frequency and high-intensity ultrasound has notable effects on increasing the freezing rate.Meanwhile,the ultrasonic thermal effect should be carefully considered in the freezing analysis of droplets with a larger initial diameter and higher ultrasonic intensity.Simultaneous,an innovative seawater freezing desalination method was proposed on the basis of above studies.After the 1 min desalination treatment under the same setting parameters,the salinity of the brine droplet(initial concentration before desalination was 15.1 wt%)was 2.4 wt%,2.1 wt%,1.8 wt%,1.5 wt%,and 1.4 wt%,when the separating factors(the relative value of centrifugal force compared with the gravity)were 600,800,1000,1200,and 1400 respectively.With the same setting parameters,the residual rate of brine dropped to 12.6 %,11 %,9.5 %,7.9 % and 7.3 %when the separating factors were 600,800,1000,1200,and 1400 respectively.Meanwhile the salinity of the whole droplet decreased to 0.66 wt%,0.57 wt%,0.48wt% and 0.44 wt%.Based on the obtained results,the increase of the separating factor can significantly improve the freezing performance?In this paper,total of 48 figures,3 tables,and 100 references.