CFD Investigation of Gear Pump Mixing Using Deforming/Agglomerating Mesh

Abstract

A moving-deforming grid study was carried out using a commercial computational fluid dynamics (CFD) solver, FLUENT® 6.2.16. The goal was to quantify the level of mixing of a lower-viscosity additive (at a mass concentration below 10%) into a higher-viscosity process fluid for a large-scale metering gear pump configuration typical in plastics manufacturing. Second-order upwinding and bounded central differencing schemes were used to reduce numerical diffusion. A maximum solver progression rate of 0.0003 revolutions per time step was required for an accurate solution. Fluid properties, additive feed arrangement, pump scale, and pump speed were systematically studied for their effects on mixing. For each additive feed arrangement studied, the additive was fed in individual stream(s) into the pump-intake. Pump intake additive variability, in terms of coefficient of spatial variation (COV), was >300% for all cases. The model indicated that the pump discharge additive COV ranged from 45% for a single centerline additive feed stream to 5.5% for multiple additive feed streams. It was found that viscous heating and thermal/shear-thinning characteristics in the process fluid slightly improved mixing, reducing the outlet COV to 3.2% for the multiple feed-stream case. The outlet COV fell to 2.0% for a half-scale arrangement with similar physics. Lastly, it was found that if the smaller unit’s speed were halved, the outlet COV was reduced to 1.5%.

Study of a High-Pressure External Gear Pump with a Computational Fluid Dynamic Modeling Approach

“…However, for the study of pumps like external gear ones, even if the 2D modeling approaches give interesting results, they cannot predict the internal flow behavior like 3D models [9,10]. This depends on the fact that during the operation of an external gear pump, the flow is really complex because of the rotation speeds (typically in the range 500-3000 rpm) and high pressure.…”

Towards the optimization of a pulsatile three-stream coaxial airblast injector

“…There are multiple effects which dictate whether or not a relatively finer mesh would produce inherently smaller droplets. These effects are popularly considered in the context of a false surface tension, such as a lower order numerical scheme creates a false numerical diffusion (Fuster et al, 2009 andStrasser, 2007). The first grid effect is the basic VOF foundational assumption that there are multiple cells per droplet; droplet length scales far below the cell length scale simply cannot be resolved.…”

“…The minimum liquid sheet thickness that can be resolved in the model is an important issue. For the typical mesh, this minimum ranged from about 10 À4 m at the upstream boundary of the pre-filming zone to 5Â10 À4 m at the model outlet, with the vast majority of cells in the pre-filming zone being limited to about 2Â10 À4 m. Effects of mesh resolution will be discussed later and have been further explored in Strasser (2007). Two 3-D models were tested.…”

“…QUICK would have been preferred, but was found to be unstable for this field. Details for the discretisation schemes can be found in Strasser (2007) and in ANSYS (2009). The transient term is also discretized using first-order upwinding, but this is an 12.1 ANSYS limitation.…”

Commercial scale slurry bubble column reactor optimization

“…More on these concepts can be found in the transonic gas turbine blade passage research of Strasser et al [19]. Also, the effects of gridding methods on the computational results are explored in Strasser [20]. Typical total cell counts ranged from 100,000 to 1,000,000 cells, depending on the complexity of the feeds.…”