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A Computational Fluid Dynamics Model of a Perforated Polyethylene Tube Ventilation System for Dairy Operations

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASABE. 59(6): 1585-1594. (doi: 10.13031/trans.59.11909) @2016
Authors:   Mario R. Mondaca, Christopher Y. Choi
Keywords:   CFD, Dairy, Polytube, Ventilation.

Abstract. The primary objective of this study was to create and validate a computational fluid dynamics (CFD) model capable of replicating the flow distribution created by a positive-pressure polyethylene tube (polytube) ventilation system. A polytube system was designed and installed at the University of Wisconsin-Madison. To properly compare the model and experimental data, precise magnitude and direction measurements, as well as their spatial locations, were recorded. In addition, a simple cost-effective rubber deflector, mounted on one of the discharge holes, was tested to ascertain the effects it would have on the jet‘s discharge angle and how this would affect the jets downstream from the deflected jet. Results showed that the CFD model created a flow field similar to that found in the field experiments. Testing also revealed that the first few jets in both the model and the actual setup tended to discharge air at an angle that aligned with the axis of the tube and in consequence failed to strike their intended targets. Additionally, the swirl effect created by the inlet fan proved to be a major influence affecting the distribution patterns of the air jets. To improve the model in this regard, a special boundary condition was added, after which the CFD model was able to replicate the damping effect created by backpressure generated at the end of the tube and a nearly identical air velocity at cow level. In addition, when the rubber deflector redirected the first jet to a more perpendicular angle, the jet no longer affected the downstream jets. The study thus was able to confirm that a polytube ventilation system could effectively cool dairy cows and that CFD can help optimize the design and predict the system‘s operational efficiency.

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