It is a combination of the two flow conditions. Here the flow is neither wholly laminar nor wholly turbulent. When flow occurs between the Laminar and Turbulent flow conditions (Re 2300 to Re 4000) the flowĬondition is known as critical and is difficult to predict. The relative roughness of the pipe and the Reynolds number can be used to plot the You can use this link to view information on the internal roughness for various pipe materials. For pipes with a large diameter the overall effect of the eddy currents are less significant. When Eddy currents occur within the flow, the ratio of the pipe's internal roughness to the internal diameter of the pipe needs to be considered to calculate the friction factor, which in turn is used to calculate the friction loss that occurs.įor pipes with a small diameter, the internal roughness can have a major influence on the friction factor. Turbulent flow occurs when the Reynolds number calculation exceeds 4000. The resistance to flow is independent of the pipe wall roughness. Laminar flow occurs when the calculated Reynolds number is less than 2300 and in this case Reynolds number = (Fluid velocity x Internal pipe diameter) / Kinematic viscosity Kinematic viscosity = dynamic viscosity/fluid density Viscosity (viscous force per unit length).
The Reynolds number (Re) of a flowing fluid is calculated by multiplying the fluid velocity by the internal pipe diameter (to obtain the inertia force of the fluid) and then dividing the result by the kinematic Therefore friction occursįluids with a high viscosity flow more slowly and generally not produce eddy currents, thus the internal roughness of the pipe has little or no effect on the frictional resistance to flow in the pipe. More quickly than the fluid flow towards the edge of the stream.
The velocity profile of fluid flow in a pipe shows that the fluid at the centre of the stream moves Pipes that have a smooth wall such as glass, copper, brass and polyethylene cause less fritional resistance and hence they produce a smaller frictional loss than those pipes with a greater internal roughness, such as concrete, cast iron and steel. Calculation of the Reynolds Number helps to determine if the flow in the pipe is Laminar Flow or Turbulent Flow. Fluid flow in a pipe encounters frictional resistance due to the internal roughness (e) of the pipe wall, which can create local eddy currents within the fluid.
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