Experimental and Numerical Investigation of Mixing Phenomena in Double-Tee Junctions

Abstract

This work investigates mixing phenomena in a pressurized pipe system with two sequential Tee junctions and experiments are conducted for a range of different inlet flow ratios, varying distances between Tee junctions and two pipe branching configurations. Additionally, obtained experimental results are compared with results from previous studies by different authors and are used to validate the numerical model using the open source computational fluid dynamics toolbox OpenFOAM. Two different numerical approaches are used—Passive scalar model and Multiphase model. It is found that both numerical models produce similar results and that they are both greatly dependent on the turbulent Schmidt number. After the calibration procedure, both models provided good results for all investigated flow ratios, double-Tee junction distances, and pipe branching configurations, therefore both numerical models can be applied for a wide range of pipe networks configurations, but passive scalar model is the viable choice due to its much higher computational efficiency. Obtained results also describe the relationship between the double-Tee distances and complete mixing occurrence.

Efficient Double-Tee Junction Mixing Assessment by Machine Learning

“…The complete mixing model can be assumed correct only if there is a single outlet at a junction and if the distance between two junctions is great enough. For certain distances [11,12], it does not describe the physical process of mixing correctly.…”

“…The mixing that occurs at two sequential Tee junctions is especially complex due to increased chaotic eddying of flow, which in turn increases the diffusion between the streams. It is proved in several studies [12,16,17] that the length between double-Tee junctions is important since it determines the behavior of mixing of fluids or rather the transport of contaminant into each diverging pipe. In addition, variation of flows at both inlet and outlet pipes causes the mixing behavior to vary [11,12].…”

“…It is proved in several studies [12,16,17] that the length between double-Tee junctions is important since it determines the behavior of mixing of fluids or rather the transport of contaminant into each diverging pipe. In addition, variation of flows at both inlet and outlet pipes causes the mixing behavior to vary [11,12]. Another property of a pipe system that can cause an incomplete mixing behavior are uneven pipe diameters, where a large difference between pipe diameters can produce a more complete mixing [18].…”

“…Another property of a pipe system that can cause an incomplete mixing behavior are uneven pipe diameters, where a large difference between pipe diameters can produce a more complete mixing [18]. The orientation of pipes for a double-Tee junction also affects the mixing behavior, and it is shown that mixing for a case when the pipes are at a opposite side compared to the case where they are at the same side, behaves differently [11,12] (assuming planar configuration). It is also shown that transitional and laminar flows in pipes exhibit a specific mixing behavior [19].…”

“…Instead of an experimental approach to studying mixing behavior in double-Tee junctions, computational fluid dynamics (CFD) can also be used. A species transport model coupled with RANS turbulence models yields good results [12,16] that can be used to further enhance simpler 1D mixing models (such as EPANET-BAM). Additionally, a high fidelity LES turbulence model can also be used to study mixing with more detail [20].…”