Simulation helical flow

Figure 1.143 Model geometry of the curved square channel used for simulating helical flows. Only half the geometry is shown due to reflection symmetry a and R denote the channel dimension and the radius of curvature, respectively [152].

ScHONEELD, F., Haedt, S., Simulation of helical flows in microchannels, AlChE J. (2003) accepted for publication. 

M 70a] [P 62] Computational flow simulation of the secondary flow, depicted by velocity vectors, was performed for Dean numbers of 10 and 100 [47]. The helical flow is weak for the smaller Dean number. The center of rotation is located close to the midpoint of the patch. For a Dean number of 100, a notable increase in the relative strength of the helical flow is observed the center of the vortex is shifted towards the outer channel wall. 

The results obtained on mixing time also give experimental evidence for the existence of a threshold value around K = 140, which is associated with a change in vorticity [47]. At this point, the helical flow pattern switches from a two- to the four-vortex fluid system. Besides qualitatively confirming such a threshold value, the experiments are also in very good quantitative accord with the value predicted by the simulations. 

Simulation of helical flows for channel with oblique ridges - relative transverse velocity... 

Fig. 8. (a) Helical coordinate system and (b) effect of the pressure gradient in the circumferential direction (30/39) on the secondary flow structure. [From Wang, J.W., and Andrews, J.R.G., Numerical simulation of flow in helical ducts. AIChE J. 41(5), 1071 (1995). Reproduced with... 

ABSTRACT The characteristic of turbulent flow in jackets with triangular helical ducts was simulated and the velocity fields of fully developed turbulent fluid flow in the jackets were obtained. The features of the local coefficient of resistance C/Reiocai) on outer walls and inner wall were summed up and the effects of dimensionless curvature ratio and Reynolds number on the flow field and the flow resistance were analyzed. The results indicate that the structure of secondary flow is with two steady vortices at turbulent flow conditions. The distribution of/ eiocai on the outer walls differs from that of/ eiocai on the inner wall. The mean coefficient of resistance (/Rem) on the outer walls is about 1.41 1.5 7 times as much as that on the iimer wall. With the increase of dimensionless curvature ratio or Reynolds number,/Rem on the boundary walls increases. 

Turbulent flow in the jackets with triangular helical ducts is simulated applied CFD software. The fully developed flow field and the distribution of the turbulence kinetic energy are obtained. When turbulent fluid flows in the jackets, the structure of secondary flow in the cross section is steady two vortices. The turbulent kinetic energy near the outer walls is larger than that near the inner wall. The fRe oc on the inner wall is almost symmetric about / = 0 and the variation of/ iocai on the outer walls with y is vastly different from that on the inner wall. In the study range, the mean coefficient of resistance on the outer walls is about 1.41 1.57 times of that on the inner wall. The effects of Re and k on the flow field, the local coefficient of resistance at the boundary walls and the mean coefficient of resistance are analyzed. With the increase o Re, the intensity of secondary flow and the turbulent kinetic energy are all enhanced and the /K iocai on the boundary walls is increased as well. However, the locai near the center of the inner wall decreases with increasing k. The mean coefficient of resistance can increase as Re or k increases. 

The mixing and flow patterns of gravitational dry particulate flows in continuous mixer tubes with helical, Kenics-type [1] static mixer elements have been simulated by the distinct element method (DEM) under steady state conditions. In the particular system the subsequent mixer elements were twisted in opposite direction a mixing element twisted clockwise is followed by an element twisted counter-clockwise and so on. A state diagram that gives a general relationship between the mass flow rate and the solids volume fraction in the mixer tube was determined for various construction parameters. 

The flow and mixing characteristics of dry particulate flows were studied in continuous mixer tubes with helical static mixer elements. In accordance with the visual observations and the actual experimental results, DEM simulation confirmed the presence of three different flow regimes. 

---