Local slip velocity is an important factor in mass

momentum and heat transfer of riser reactors.Based on the EMMS model

the qualitative and quantitative analysis is made for local slip velocity and its components (the slip velocity in the dense phase (cluster)

the slip velocity in the dilute phase and the slip velocity between dense phase and dilute phase).It is found that the slip velocity between dense phase and dilute phase makes the most contribution to the local slip velocity and clusters lead to the high local slip velocity

from which the correlation of local slip velocity with local voidage is derived.Using this correlation

the local gas-solids slip velocities in gas-solids up-risers are predicted.Calculation results are well consistent with experimental data. Furthermore

the effects of operating conditions on local slip velocities are discussed. It is concluded that local slip velocity increases with the increase of solids circulating rate and decreases with the increase of superficial gas velocity.