It has been widely recognized that the mixing process has significant impacts on the performance of low-density polyethylene (LDPE) reactors due to the rapid radical polymerization occurred in the reactors

but how the macro- and micro-mixing affect the reactor performance was still controversial in publications. In this work

a cold-flow LDPE autoclave with multi-feedings was scaled down (1/2) from an industrial reactor and built to systematically investigate the macro- and micro-mixing characteristics of fluid by experiments. Furthermore

the effects of macro- and micro-mixing on the polymerization were comprehensively analyzed. The results showed that according to the delay time

t

d

and macro-mixing times

t

M

calculated from residence time distribution (RTD) curves

the macro-mixing states are significantly different at various axial positions (

h

/

H

)

especially at lower agitation Reynolds number

Re

. But with the increase of

Re

since the circulation flow in the reactor is strengthened

the

t

d

for each feed gradually decreases to 0

and the

t

M

at different axial positions tend to be identical. For micro-mixing

the qualities of micro-mixing at different axial positions are similar

and the average micro-mixing time

t

m

in the reactor decreases exponentially with the increase of

Re

. Moreover

a fitting model was established. Through the comparison of the chara

cteristic times of macro-mixing (

t

d

t

M

)

micro-mixing (

t

m

) and elementary reactions within the industrial range of

Re

it can be concluded that the properties of LDPE products are dominated by the macro-mixing behavior

and the consumption of initiators is affected by both the macro- and micro-mixing behaviors. This conclusion is of great significance for the design

optimization and operation of LDPE reactors.