The unit of measurement for absolute viscosity is: A thick oil has a high viscosity water has a low viscosity. Viscosity can also be considered to be a measure of the resistance of a fluid to flowing. Viscosity is the internal friction of a fluid which makes it resist flowing past a solid surface or other layers of the fluid. Viscosity is a fluid property that measures the resistance of the fluid to deforming due to a shear force. Practically, the student should use an average value that is half of the center line value. Technically, this is done by means of integral calculus. If the flow regime is laminar (the velocity profile is parabolic), the problem still exists of trying to represent the 'average' velocity at any given cross-section since an average value is used in the fluid flow equations. It is reasonable to assume that the average velocity is the same as the velocity at the center of the pipe. This is fairly simple for turbulent flow since the velocity profile is flat over the majority of the pipe cross-section.

In many fluid flow problems, instead of determining exact velocities at different locations in the same flow cross-section, it is sufficient to allow a single average velocity to represent the velocity of all fluid at that point in the pipe. A smoother wall results in a more uniform velocity profile than a rough pipe wall. Note from Figure 5 that the velocity profile depends upon the surface condition of the pipe wall.

The velocity of the fluid in contact with the pipe wall is essentially zero and increases the further away from the wall.įigure 5: Laminar and Turbulent Flow Velocity Profiles Figure 5 helps illustrate the above ideas. In turbulent flow, a fairly flat velocity distribution exists across the section of pipe, with the result that the entire fluid flows at a given single value. If the flow in a pipe is laminar, the velocity distribution at a cross section will be parabolic in shape with the maximum velocity at the center being about twice the average velocity in the pipe. The shape of the velocity curve (the velocity profile across any given section of the pipe) depends upon whether the flow is laminar or turbulent. Not all fluid particles travel at the same velocity within a pipe. The particles travel in irregular paths with no observable pattern and no definite layers. There is no definite frequency as there is in wave motion. Turbulent flow is characterized by the irregular movement of particles of the fluid.

These terms are descriptive of the flow because, in laminar flow, (1) layers of water flowing over one another at different speeds with virtually no mixing between layers, (2) fluid particles move in definite and observable paths or streamlines, and (3) the flow is characteristic of viscous (thick) fluid or is one in which viscosity of the fluid plays a significant part. Laminar flow is also referred to as streamline or viscous flow. This is also an important consideration in certain applications that involve heat transfer to the fluid. The amount of fluid friction, which determines the amount of energy required to maintain the desired flow, depends upon the mode of flow. The flow regime, whether laminar or turbulent, is important in the design and operation of any fluid system. These two flow regimes are laminar flow and turbulent flow. To understand why turbulent or laminar flow is desirable in the operation of a particular system, it is necessary to understand the characteristics of laminar and turbulent flow.Īll fluid flow is classified into one of two broad categories or regimes. The characteristics of laminar and turbulent flow are very different.

Laminar flow pipe