A Numerical Study of Jet-to-Jet Impingment in a Mixing Head

Abstract

<p>A numerical method has been developed to model the jet-to-jet impingement in a mixing head. The governing equations are discretized in non-orthogonal curvilinear coordinates and higher-order upwinding methods are used for convection term discretization. Several problems with known solutions are used to test accuracy of the method. The results show that the method can predict the flow fields at moderate and high Reynolds numbers accurately.</p> <p>The opposed jet flow field is used by the reaction injection moulding mixhead to mix pre-polymers. The stready state flow field exists at Reynolds numbers below 90 and unsteady state exists at Reynolds numbers above 90. The results of numerical simulations show that at the Reynolds number 50, the flow field is symmetrical and rotating ring vortices are formed around the impingement point. Symmetry breaks down as the Reynolds number is raised. Time integration showed that the flow field oscillates at Reynolds numbers above 100 and multiple frequencies exist at the Reynolds number of 125. The results are consistent with experimental results.</p> <p>In the last chapter, the dynamical system theory is used to examine the opposed jet flow field. The stagnation point is a hyperbolic point of a dynamical system and can promote mixing. The elliptic points which exist at the core of vortices hinder mixing. The (D:D)1/2 field was evaluated and confirmed the results of the dynamical system theory. The area surrounding the hyperbolic point had highest (D:D)1/2 values indicating that the flow field can stretch more efficiently. A flow pattern which consists of multiple hyperbolic points is proposed as an alternate design for the mixhead.</p>