Study on the mixing behaviors between the intrusive side fluid and the main fluid in a LDPE tubular reactor

Abstract

The intrusive tee-junction mixing process in LDPE tubular reactors is investigated through computational fluid dynamics (CFD) simulation, and a special climbing mixing pattern under a large main-to-side flow rate ratio is observed. The formation mechanism of climbing mixing is the result of the interaction between the main fluid, side fluid, and side feed pipe, especially due to the formation of local low-pressure areas and vortex structures that push the flow along the wall of the side feed pipe in the direction opposite to the side feed. Influences of the side feed pipe’s insertion length on the critical conditions for the transition from jet mixing to climbing mixing are discussed. A dimensionless parameter ΔP/(v_m,L²·ρ_m) is proposed to explain the mixing pattern transition quantitatively. It is concluded that as the insertion length increases, the main fluid velocity should increase to provide enough radial static pressure difference and form the climbing mixing pattern.