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The tracer tests were carried out for five combinations of three different flow rates (Q = 0.05, 0.075 and 0.10 L/s) and three water volumes in the tank (V = 290, 580 and 870 L), in two trials for each combination, as shown in Table 1 along with the results. N = 1 was obtained for all tests. Figure 3 shows the results for one of the tracer tests, corresponding to Q = 0.10 L/s and V = 870 L, fitted to the three parameter model. For this test, the model obtained 1–M = 18% stagnation space and 1–n = 2.60% bypassing. Figure 4 shows the velocity distribution obtained by the CFD model for the same test conditions and a photograph of the instantaneous colour tracer distribution at the very beginning of the test (30 s after the tracer injection). Figures 5 and 6 show the same results for another test with Q = 0.10 L/s and V = 290 L, where the model obtained 1–M = 0 and 1–n = 2.10%. These results show that the mixing model corresponds to one completely stirred flow reactor with a small portion of bypassing and a stagnation zone for larger tank volumes. The visual observation of the colour tracer and the output of the CFD model, partially shown in Figure 4, confirmed these results.
Table 1

Results from the tracer tests

Q (L/s)V (L)Mean residence time (min)
1–M (%)
1–n (%)
Trial 1Trial 2Trial 1Trial 2Trial 1Trial 2
0.05 870 162.57 155.03 25 26 
0.1 870 101.28 112.68 18 19 2.6 1.2 
0.075 580 93.4 95.4 21 21 1.4 1.8 
0.05 290 87.36 84.87 1.8 1.7 
0.1 290 51.98 60.27 2.1 1.9 
Q (L/s)V (L)Mean residence time (min)
1–M (%)
1–n (%)
Trial 1Trial 2Trial 1Trial 2Trial 1Trial 2
0.05 870 162.57 155.03 25 26 
0.1 870 101.28 112.68 18 19 2.6 1.2 
0.075 580 93.4 95.4 21 21 1.4 1.8 
0.05 290 87.36 84.87 1.8 1.7 
0.1 290 51.98 60.27 2.1 1.9 
Figure 3

The result of a tracer test for Q = 0.10 L/s and V = 870 L, and its three parameter model fitting.

Figure 3

The result of a tracer test for Q = 0.10 L/s and V = 870 L, and its three parameter model fitting.

Figure 4

The velocity distribution inside the tank obtained by CFD for Q = 0.10 L/s and V = 870 L (left) and the instantaneous colour tracer distribution at time 30 s after the tracer injection (right).

Figure 4

The velocity distribution inside the tank obtained by CFD for Q = 0.10 L/s and V = 870 L (left) and the instantaneous colour tracer distribution at time 30 s after the tracer injection (right).

Figure 5

The result of the tracer test for Q = 0.10 L/s and V = 290 L, and its three parameter model fitting.

Figure 5

The result of the tracer test for Q = 0.10 L/s and V = 290 L, and its three parameter model fitting.

Figure 6

The velocity distribution inside the tank obtained by CFD for Q = 0.10 L/s and V = 290 L.

Figure 6

The velocity distribution inside the tank obtained by CFD for Q = 0.10 L/s and V = 290 L.

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