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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

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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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CFD Analysis with Scale Model Verification - A Proven Cost-Effective Approach

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Contributing Authors - Dave Dewees (Becht) and Dr. Keith Kirkpatrick (McHale Performance)  Reducing HRSG & Stack Pressure Drop to Improve Profitability Many operating Simple and Combined Cycle HRSG (Heat Recovery Steam Generator) ducts and stack exhaust system designs can be optimized to reduce pressure drop, improve combustion turbine backpressure, improve performance and increase revenue.  CFD analysis with Scale Model Verification is a proven and cost-effective tool for quantifying recoverable performance loss and improving generation plant profitability. Combustion Turbine exhaust/HRSG/SCR ductwork, breeching and stack systems require careful attention during detailed engineering and design. While EPC Contracts typically include both performance guarantees and liquidated damage provisions which are highly dependent on Combustion Turbine backpressure, the design of this critical stack system is many times “farmed out” to 3 rd party stack, HRSG or other less qualified suppliers. This practice can result in an un-optimized design with higher than necessary pressure drop resulting in reduced...
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Computational Fluid Dynamics (CFD) Confirms Cause of Deaerator Cracking

Computational Fluid Dynamics (CFD) Confirms Cause of Deaerator Cracking
CFD was used to confirm that poor design of the steam inlet nozzle was the main contributor to deaerator head to shell weld cracking, and confirmed proposed design improvements.  This recent Becht project illustrates one of the causes of deaerator cracking. A through-wall crack had been found at the head-to-shell junction at the steam inlet end of the drum. This crack was attributed to corrosion fatigue, a common occurrence in deaerators. The crack was most likely initiated at a weld surface defect on the I.D. of the drum and grew with time. The daily operating cycles of the drum during periods of reduced steam demand and thermal stresses which we attributed to a poorly designed steam inlet nozzle were the main contributors to the crack growth.   A large diameter superheated steam inlet nozzle extended through the head of the drum terminating 18” into the vessel. The steam exited through a...
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