A common method for diluting a concentrated solution is to use a venturi mixer. These mixers can provide precise control over the level of dilution achieved. However, to obtain maximum performance, the venturi section must be quite long. To assist in designing a suitable mixer, Stress Engineering has used CFD modeling of flow in these devices.
Two potential designs for a venturi mixer are shown below, one of standard length and the other compact. In both cases the main flow enters from the left and the flow of concentrate enters through a disk-shaped port at the throat of the venturi. CFD results are illustrated by displaying flow streamlines for each model. The presence of a large looping streamline in the diffuser section of the compact venturi indicates flow separation. This suggests that the diffuser section for this design is too short and will degrade the performance of the compact mixer.
The graphics below summarize results of mixing two fluids in each venturi. The main flow enters as 100% water (blue) and concentrate enters at full strength (red). The degree of mixing at any point is shown by color contours, with green being fully mixed. Results of the simulation show that separated flow in the diffuser section of the compact mixer causes this design to draw only 76% as much concentrate as the standard mixer. This calculation allows a quantitative comparison of the efficiency of the two designs which can be used to guide the design process as trade-offs between size and efficiency are considered.
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