Study of the effect of flow intensity and flow geometry on the breakage of whey protein aggregates using CFD

Experimental investigation coupled with CFD simulations allow us to conclude that aggregate breakage occurs all along the pipeline if the flow intensity is high enough and not only at the pipe diameter reduction as has been previously claimed by other researchers. A precipitate dispersion was propelled trough a pipe ID 0.736 mm at different flow velocities (5-17 ms^-1) in order to study how flow intensity affects particle breakage. The dispersion was recycled several times to investigate the effect of the exposure time on particle size reduction. Particle size reduction through different flow geometries was investigated: 60 mm straight pipe, 60 mm+45° bend, 100 mm straight pipe, 100 mm+elbow and 1000 mm straight pipe. The flow field for each experimental flow geometry was modelled using the standard κ-ε turbulent model. Particle breakage was found to be different for each flow geometry and each flow intensity. Particle diameter reduction (Δd) was coupled with both the exposure time (Δt) and the dissipation rate (ε), and hence a breakage model of the form; Δd=k*Δt*(ε_iε_th)/(ε_th)ⁿ was proposed. Here the term ε_i-ε_th is the driving force that leads to the breakage and it is the difference between the local dissipation ε_j and the maximum energy dissipation ε_th that a particle with a given size can withstand before any breakage occurs. The model was validated using both the CFD results and the experimental results for different flow geometries.