what and where viscocity plays a role in transport phenomena?

Hello,

Momentum transport deals with the transport of momentum which is responsible for flow in fluids. Momentum transport describes the science of fluid flow also called fluid dynamics. A few basic assumptions are involved in fluid flow:

No slip boundary condition

This is the first basic assumption used in momentum transport. It deals with the fluid flowing over a solid surface, and states that whenever a fluid comes in contact with any solid boundary, the adjacent layer of the fluid in contact with the solid surface has the same velocity as the solid surface. Hence, we assumed that there is no slip between the solid surface and the fluid or the relative velocity is zero at the fluid–solid interface. For example, consider a fluid flowing inside a stationary tube of radius R as shown in Fig 7.1. Since the wall of the tube at r=R is stationary, according to the no-slip condition implies that the fluid velocity at r=R is also zero.Newton’s law of viscosity may be used for solving problem for Newtonian fluids. For many fluids in chemical engineering the assumption of Newtonian fluid is reasonably acceptable. Hence thus viscosity plays an important role in having no boundary slip conditions as well as using the newton's law.

To get in detail into the transport phenomena, please go through the following link

https://nptel.ac.in/courses/103102024/7