A helical mixer with contraction-expansion connections combines helical pipes and sudden expansion and contraction array

which was optimally designed in this paper for enhancing the mixing in the regular helical mixer. The effect of the number of mixed elements

the pitch and curvature

the ratio of the lengths of contraction part to expansion part and Reynolds number on the mixing efficiency of the contraction-expansion helical mixer

was experimentally investigated by use of a fast competitive-consecutive diazo coupling reaction. It is found that: the radius of curvature of the helical mixer

ratio of the lengths of the contraction part to expansion part and the Reynolds number affect significantly the mixing efficiency

while the pitch of helical mixer had little influence. The best mixing performance is achieved by the contraction-expansion helical mixer with the radius of the curvature R 10.5 mm

the ratio of the lengths of contraction part to expansion part 4:1

the numbers of mixed elements 40 in the ranges of Reynolds number from 1000 to 1575. The mixing efficiency of the optimized contraction-expansion helical mixer is superior in comparison to both of the regular helical mixer and contraction-expansion straight mixer.