# Flow patterns in gas-assisted injection molding process in a channel

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## Abstract

The flow field of a long bubble steadily expelling a viscous fluid confined by two closely located parallel plates is examined. In order to investigate the influence of bubble size on the flow field, a theoretical bubble profile is used to replace the complicated procedure for computing simultaneously the interface between the gas surface and fluid flows. The present study showed the two typical flow patterns and also a third flow pattern of the stagnation point moving in the region of the bubble tip front during transformation of the two typical flow patterns. The vorticity patterns are also drawn for various bubble profiles and are examined for their effect on the flow. The velocity field is also presented from two different viewpoints and the phenomena is examined. The stagnation point located on the center line between the bubble tip to the upstream is only found in the small range of \(2/3 <\lambda < 0.685\) in a channel, where *λ* is ratio of the bubble width to the distance between two parallel plates.

## Keywords

Gas-assisted Expelled fluid flow Stagnation point Two-phase flow## Abbreviations

*H*Half distance between the two parallel plates

*U*Constant velocity of the bubble

- \({\overrightarrow{V}}\)
Velocity

*m*Fractional converge

*n*The normal unit vector on the bubble interface

*p*Pressure in the fluid expelled by bubble

*t*The tangential unit vector on the bubble interface

*u*The velocity of the fluid expelled by the bubble

*x*The axial direction in coordinate system

*y*The radial direction in coordinate system

*α*The over-relaxation factor

*θ*The angle between the normal of the interface and the axial direction

*λ*The ratio of asymptotic bubble width to half distance of the two parallel plates

*υ*Kinematic viscosity

*ρ*Density

*ψ*Stream function

*ω*Vorticity

*K*Iterative time

- *
Dimensionless form

*Ca*Capillary number (dimensionless parameter)

*i*The number of grid in the axial direction

*j*The number of grid in the radial direction

*s*The grid index in the

*y*-direction on the wall

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