Depends on the type of fluid, does it show Newtonian flow behaviour? If so, you'll probably get laminar flow, with a parabolic velocity profile. The velocity profile will be different if your fluid has a shear-dependent viscosity, or if you manage to reach turbulent flow in this tube.

Also, how do you intend to drive your flow? Using a pump? Or a plunger? Or some other method? Generally, with single-phase flow, the way to maximise flow rate/velocity would be to maximise driving pressure, so to maximise pump speed, plunger speed, etc. In case of shear-dependent viscosity, pumps can be tricky though.

If it's an option for you, you could take a look at core-annular flow (see e.g. image on this website: https://www.iitbmonash.org/research-stories-archives/story-76/), where a thin layer of low-viscosity liquid is used as a sort of lubricant for the high-viscosity "core" flow.

Hope this helps,

Sita

Thanks for the response. Working fluid is Saliva.

I think maximizing flow velocity is aimed in order to increase the mass flow rate. The problem is momentum transport to walls by the friction between fluid layers due to viscosity. Heating fluid may lead to change in viscosity, therefore can be tried. Also inducing vibration to pipe may alter boundary layer in favor of you. So it can be tried too. However the most prominent solution would be increasing pipe diameter :) I wish you luck. Please inform us when you have a solution.

Thanks for the response.I will share the paper with you.Once again Thanks