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Becht Engineering Blog

In this section of the site contributing authors submit interesting articles relating to the various services, industries and research & development efforts of Becht Engineering.

CFD Modeling of a Mixing Tee – Part 1: Model Validation

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by Dave Dewees, Zumao Chen and L. Magnus Gustafsson This 2-part blog deals with CFD modeling of a mixing tee that is often found in industry. Traditional simulation is validated against experiment, as well as a new commercially available method that offers the possibility of substantial solution time reduction.  In fact, the new method is shown to give accurate results in a much shorter computer time than the traditional analysis, allowing much more rapid turnaround of difficult problems such as the turbulent mixing behavior of industrial mixing tees. When there is a large temperature difference between two fluid streams, large temperature fluctuations can occur, which can lead to thermal fatigue of the piping system, even at “steady-state” bulk flow conditions. Advanced CFD modeling is capable of predicting these fluid temperature fluctuations at the mix point, as well as characterizing the corresponding temperature variations in the pipe wall itself. Specifically, large eddy simulation...
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CFD Modeling of a Mixing Tee – Part 2: Predictions of Temperature Fluctuations

cfd-mixing-T-cover
by Dave Dewees, Zumao Chen and L. Magnus Gustafsson Miss Part 1? Click Here This is the second part of a 2-part blog.  In Part 1, the stress-blended eddy simulation (SBES) and large eddy simulation (LES) approaches for simulating turbulence have been validated against test data obtained from a mixing tee. In this part, the SBES approach is used to predict temperature fluctuations in a mixing tee where light gas oil mixes with a recycled gas.  Depending on the characteristics of the streams being mixed (momentum and temperature), protection from rapid temperature variations occurring even at steady-state bulk flow conditions is a necessity. While a CFD model can predict these temperature variations with good fidelity as shown in Part 1 of this blog, once a problem is found, the same CFD model can also be used to design solutions that protect the piping at the mix point.  Here thermal sleeve length...
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Cooling Towers: Benefits of a Cold Eyes Review

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One key decision that often needs to be made is repair vs. replace. When has a cooling tower arrived at the point where a new tower should be considered? Maintenance costs, overall tower condition, environmental constraints, and performance optimization are all factors that need to be evaluated. If a new cooling tower is justified, how are the specifications for performance selected? What range, fan horsepower, approach to wet bulb, and water flow rate should be specified to best match plant requirements? The range is the difference between the hot water (return) temperature and the cold water (supply) temperature. The approach to wet bulb is due to the fact that, if the cooling tower were infinite in size, the cold water temperature would be at the wet bulb temperature. However, just like a shell and tube heat exchanger with a temperature difference between two streams, a finite cooling tower results in some...
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Acceptable Practices for High Voltage Motor Lead Routing

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Are Your Wires Crossed?   By Rick Hoffman and Joe Rammage We recently evaluated a 15kV, 5000 hp, induction motor in a WPII enclosure manufactured by a foreign company.  During an on-site inspection of the main terminal box it was discovered that the high voltage leads were touching.  This raised significant concerns about the long-term reliability of the motor. Becht Engineering investigated the issue to determine the industry standards and best practices concerning routing of the motor high voltage leads.    Shielded vs Non-Shielded Cables The National Electric Code requires all cables rated above 2.4kV to be shielded to prevent concentrated electromagnetic stresses from forming between the cable conductor and ground when the cable is in close proximity to a grounded surface.  The addition of the metallic shield smooths out the electromagnetic field eliminating high stress points.  Without it, the increased density of electromagnetic stresses where the cable is in close...
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