6.3 Results and discussion
6.3.3 Flow of bidisperse suspension in a converging channel
6. Shear-induced particle migration and size segregation in bidisperse suspension
the other hand, a quite different behavior is observed in the case of smaller particles. For aL/aS = 1.5, the concentration peak of the smaller particles shifts towards the center of the daughter branches after bifurcation. Whereas, foraL/aS = 3, it is shifted towards the inner walls of the daughter branches. As the suspension moves towards the downstream locations of the daughter branches, the gradients in the shear-rate and concentration again cause the particles to move towards the channel center. It is clearly seen from Figs. 6.12 and 6.13, the asymmetric profiles observed in the upstream locations of the daughter branches eventually become symmetric in the downstream locations of the daughter branches. The qualitative nature of the overall particle concentration profiles is observed to be similar to that of larger particles.
6.3. Results and discussion
Figure 6.15: Comparison of the concentration profiles (a) at location C0 with the fully- developed concentration profile in the straight channel and (b) at various locations in the outlet branch for monodisperse suspension in the converging bifurcating channel. The av- erage inlet concentration was (φ) 0.25 and the particle size (a) was 10 µm.
arm with an average velocity of U = 0.0063 m/s. In both inlet arms, the shear-induced migration causes the particles to move towards the center of the channel. Two separated concentration peaks can be visible as the suspension converges into the outlet branch from the two inlet branches. However, as the suspension flows through the downstream locations of the outlet branch, the two concentration peaks gradually merge at the center of the channel. The quantitative nature of the particle distribution at different locations in the bifurcating channel is shown in Fig. 6.15. The Fig. 6.15(a) shows the comparison of concentration profile at locationC0 with and without bifurcation. As the suspension reaches the converging section (location C0), the flow bends towards the outlet section and the concentration profile becomes asymmetric. Whereas, the symmetric profile was observed in the case of the straight channel. It was observed that at location C1, ini- tially two separated concentration cores appear as a result of the flow of suspension from the two inlet branches. However, the gradients in the shear-rate and the particle concentration which were present cause the redistribution of the particles. As we move downstream in the outlet section the two streams gradually come closer. At location
6. Shear-induced particle migration and size segregation in bidisperse suspension
C3 these two streams of concentration mix completely. As we move down further in the outlet section we observe that the concentration peak at the channel center increases gradually and the profile becomes fully-developed beyond location C5 (Fig. 6.15(b)).
The qualitatively similar behavior can be observed for other particle sizes.
Fig. 6.16 depicts the concentration contour planes of the smaller (φS) and larger particles (φL) along with the overall concentration (φoverall) in converging bifurcating channel foraL/aS = 1.5. The corresponding contour planes foraL/aS = 3 are shown in Fig. 6.17. For particle size ratioaL/aS= 1.5, there exist two concentration peaks of the smaller particles in the inlet arms. As soon as the suspension reaches the converging sec- tion, four separated concentration streams of smaller particles were observed. Whereas, for particle size ratioaL/aS = 3, three separated concentration streams of smaller par- ticles were observed. On the other hand, only two were observed for the larger particles irrespective of the particle size ratio. As the suspension flows through the downstream locations of the daughter branches, the separated streams gradually merge each other.
The quantitative nature of the concentration profiles of bidisperse suspension at different locations in the converging channel for aL/aS= 1.5 is shown in Fig. 6.18. The corresponding profiles for aL/aS = 3 are shown in Fig. 6.19. As the suspension reaches the converging point (location C0), the particles bend with the flow towards the outlet section. As a result, the profiles at location C0 become asymmetric in nature when compared with the corresponding concentration profiles in the straight channel. As the suspension converges from the both inlet arms, two concentration peaks were observed at the locationC1 for the larger particles. This is true for both the particle size ratios. On the other hand, the smaller particles in the bidisperse case behave differently depending on the particle size ratio. For particle size ratio aL/aS = 1.5, the two concentration peaks of the smaller particles which were present in each inlet arm converge to form two symmetric peak-valley-peak patterns at the entrance of the outlet section. Whereas, for aL/aS = 3, the concentration peaks which were present on the inner walls of the inlet
6.3. Results and discussion
Figure 6.16: The particle concentration contour planes of (a) smaller particles, (b) larger particles and (c) overall concentration of bidisperse suspension in the converging bifurcating channel. The particle sizes wereaS = 20µm andaL = 30µm.
6. Shear-induced particle migration and size segregation in bidisperse suspension
Figure 6.17: Particle concentration contour planes of (a) smaller particles, (b) larger particles and (c) overall concentration of bidisperse suspension in the converging bifurcating channel. The particle sizes wereaS = 10µm andaL = 30µm.
6.3. Results and discussion
Figure 6.18: Comparison of the concentration profiles of (a) smaller particles, (b) larger particles and (c) overall concentration of bidisperse suspension at different locations in the converging bifurcating channel. The particle sizes wereaS = 20µm andaL = 30µm.
arms follow with the walls of the outlet branch. The concentration peaks which were present on the outer walls of the inlet arms merge together and enter into the outlet
6. Shear-induced particle migration and size segregation in bidisperse suspension
Figure 6.19: Comparison of the concentration profiles of (a) smaller particles, (b) larger particles and (c) overall concentration of bidisperse suspension at different locations in the converging bifurcating channel. The particle sizes wereaS = 10µm andaL = 30µm.
section. As a result, peak-valley-peak pattern was observed. One interesting observation was that the smaller particles enriched the channel center at locationC2. From the6.19