Reynolds number is main factor or different kind of tubulisation.

Hi,

Flow in laminar or turbulent regime depends on the feed nature. If feed is simple mixture of two components (L-L) or (G-G) then separation will take place in both regime without any fouling or concentration polarization.  

However, if feed is mixture of solid and liquid (in case of NF, UF, RO, MF) then laminar regime can cause fouling or concentration polarization of the membrane.

It is required to calculate the Reynolds number the check the flow regime.

It also depends on Separation module Cross flow or Dead -end.

Hope this helps you.

Regards,

Parimal

In addition, here is some literature:

http://www.nature.com/nature/journal/v443/n7107/full/nature05089.html

http://www.nature.com/nature/journal/v526/n7574/abs/nature15701.html

https://www.researchgate.net/publication/294724353_Directed_percolation_phase_transition_to_sustained_turbulence_in_Couette_flow

https://phys.org/news/2013-04-turbulence-inertia.html

https://www.newscientist.com/article/dn7187-first-membrane-free-alkaline-fuel-cell-built/

Regards,

Joachim

Article Directed percolation phase transition to sustained turbulenc...

Its simple !!

Adverse pressure gradient creates the transition from laminar to turbulent mode.

Factors affecting the separation :

Reynolds number - think of the ratio of two quatities

Surface smoothness

etc

Kannan is right in his submission.

The pressure gradient may be as a result of sudden/abrupt change in bathymetry in case of channel flows or existence of constrictions, entrapped air or flow impediments in the case of pipeline and others. These occurrences sometimes coexist and compete with laminar motion, resulting in irregular continually changing flow patterns.

The main reason is the cooling of the liquid, which leads to phase separation. In the following, the interaction between the atoms of A and B types 'with feedback' take place and between mixture and walls with nonlinear interaction energy with feadback. This interaction leads to period-doubling bifurcations and then to distributions of turbulent type But there are many types of chaos  

With best regards

Separation and laminar/turbulent transition are often linked, but are different concepts.

Separation may be "true" 2D-like, involving a recirculating separation bubble, or 3D-like, involving a vortex sheet detaching from a solid surface. The two may coexist, i.e. on a wing profile at large incidence where (2D-like) trailing-edge separation is followed by the wake. Alternatively, the vortex sheet may separate laterally from a smooth surface, i.e. in the case of an oblate obstacle at incidence, without a recirculating flow.

2D-like separation may be induced by an adverse pressure gradient, which is especially strong at the foot of a shock, and is delayed by transition to turbulence, which may be triggered by a roughness strip. Otherwise, transition is mainly influenced by the Reynolds number, which defines the basic (in)stability of the flow (Tollmien-Schlichting waves). In the special case of a swept leading edge, the relevant Reynolds number Rθ is computed with the momentum thickness.

Excluding the cases of separation induced by the geometry, I can just think about the most famous example of the flow over a flat plate. The transition from laminar to turbulence has the onset in the amplification of oscillations at certain wavelenghts. Experimentally, that depends on some factors as roughness, sound disturbances, etc.

The mechanism in the flow ecolution is non linear and due to the quadratic product of the convective terms, a small oscillation at high wavelengh tends to generate smaller wavelenghts, so that at a certain local Reynolds number the oscillation is no longer dissipated and generates the separation in the flow.