Drop size distribution (DSD) or mean droplet size (

d

32

) 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

d

32

decreased. In addition

a prediction model of

d

32

of kerosene/deionized system was established as

d

32

/

D

=0.13(1+5.9

φ

)

We

-0.6

. Under the continuous operation condition

the general model for droplet size prediction of kerosene/water system was presented as

d

32

/

D

=

C

3

(1+

C

4

φ

)

We

-0.6

. For the surfactant system and extraction system

the prediction models met a general model as

d

32

/

D

=

bφ

n

We

-0.6

.