Abstract: Drop size distribution (DSD) or mean droplet size (d₃₂) and liquid holdup are two key parameters in a liquid-liquid extraction process. Understanding and accurately predicting those parameters are of great importance in the optimal design of extraction columns as well as mixer-settlers. In this paper, the method of built-in endoscopic probe combined with pulse laser was adopted to measure the droplet size in liquid-liquid dispersions with a pump-impeller in a rectangular mixer. The dispersion law of droplets with holdup range 1% to 24% in batch process and larger flow ratio range 1/5 to 5/1 in continuous process was studied. Under the batch operation condition, the DSD abided by log-normal distribution. With the increase of impeller speed or decrease of dispersed phase holdup, the d₃₂ decreased. In addition, a prediction model of d₃₂ of kerosene/deionized system was established as d₃₂/D=0.13(1+5.9φ)We^-0.6. Under the continuous operation condition, the general model for droplet size prediction of kerosene/water system was presented as d₃₂/D=C₃(1+C₄φ)We^-0.6. For the surfactant system and extraction system, the prediction models met a general model as d₃₂/D=bφⁿWe^-0.6.

Key words: Dispersion, Droplet size distribution, Liquid-liquid, Mean drop size, Mixer-settler

摘要： Drop size distribution (DSD) or mean droplet size (d₃₂) and liquid holdup are two key parameters in a liquid-liquid extraction process. Understanding and accurately predicting those parameters are of great importance in the optimal design of extraction columns as well as mixer-settlers. In this paper, the method of built-in endoscopic probe combined with pulse laser was adopted to measure the droplet size in liquid-liquid dispersions with a pump-impeller in a rectangular mixer. The dispersion law of droplets with holdup range 1% to 24% in batch process and larger flow ratio range 1/5 to 5/1 in continuous process was studied. Under the batch operation condition, the DSD abided by log-normal distribution. With the increase of impeller speed or decrease of dispersed phase holdup, the d₃₂ decreased. In addition, a prediction model of d₃₂ of kerosene/deionized system was established as d₃₂/D=0.13(1+5.9φ)We^-0.6. Under the continuous operation condition, the general model for droplet size prediction of kerosene/water system was presented as d₃₂/D=C₃(1+C₄φ)We^-0.6. For the surfactant system and extraction system, the prediction models met a general model as d₃₂/D=bφⁿWe^-0.6.

关键词: Dispersion, Droplet size distribution, Liquid-liquid, Mean drop size, Mixer-settler