The Effect of Reynolds Number on Jet in Asymmetric Co-Flows: A CFD Study

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The Effect of Reynolds Number on Jet in Asymmetric Co-Flows: A CFD Study by Mind Map: The Effect of Reynolds Number on Jet in  Asymmetric Co-Flows: A CFD Study

1. In rotary kilns in grate-kiln systems for iron ore pelletizing, a long and stable jet flame is needed to ensure a high quality of the pellets.

1.1. The primary jet issuing from the nozzle interacts with two asymmetric co-flows creating a very complex flow. In order to better understand and eventually model this flow with quality and trust, simplified cases need to be studied.

2. A grate kiln can be a part of an iron ore pellet sintering process, and it consists of a travelling grate, a rotary kiln, and a cooler. The rotary kiln can be about 35 m long and 6 m in diameter, and it carries iron ore pellets from the travelling grate to the cooler as the pellets are sintered at temperatures over 1000°C

2.1. At the inlet of the rotary kiln, a burner is placed providing heat to the pellets.

2.2. The flow from this burner can be modeled as a primary jet flow.

2.3. Along with the primary jet, there are also two asymmetric co-flows from secondary air channels emanating from the cooler

2.3.1. The two air channels provide excessive air for both the combustion and other important and earlier stages of the pelletizing process.

3. The pelletizing process is complex since it is large scale and involves high temperatures and large amounts of air lowing in intricate geometries

4. The standard k-ε model gave the closest prediction to the measurements in previous work.

4.1. The prediction of the spreading rate S of the streamwise velocity is quite accurate with an error of about 3%.

4.2. There is an overprediction of the centerline decay term B of the velocity by about 45% and of the spreading rate SΦ of the passive scalar by about 20% compared to the results in previous measurements

5. The model is capable of predicting a Re dependency of the jet development as the jet with higher initial Re is longer, which is beneficial to the sintering of pellets, but the centerline velocity decays faster downstream

6. One of the reasons behind this Re dependency could be the enhanced shear layer between the jet and co-flows resulting from higher velocity difference when Re increases.

7. The k-ε model can be improved for better accuracy

7.1. but no matter how accurate it can predict the mean properties of the jet development, two equation models are still not capable of capturing the underlying flow structures such as vortex shedding and its effect on small-scale mixing.

7.2. For better validation and understanding of the flow field in this virtual kiln model, more measurements and advanced turbulence models or methods will be considered in future work.