# Reynolds Number

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. Calculation of the Reynolds Number helps to determine if the flow in the pipe is Laminar Flow or Turbulent Flow.

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.

The velocity profile of fluid flow in a pipe shows that the fluid at the centre of the stream moves more quickly than the fluid flow towards the edge of the stream. Therefore friction occurs between layers within the fluid.

Fluids 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. This condition is known as laminar flow.

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 viscosity (viscous force per unit length).

The Reynolds Number Calculation library must be imported.If the fluid type is water so we should be written same as like below. If the fluid type choosen air,it should be written instead of **Water**.
Also you can write “import *” so, you can call all fluid type. For instance;

```
1from TwinAPI.EngineeringParameters import ReynoldsNumber as Re
2from TwinAPI.MaterialLibrary.Fluids import Water
```

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) by the density and then dividing the result by the dynamic viscosity (viscous force per unit length).

Reynolds Number calculation by using kinematic viscosity.

```
1Velocity=1
2Characteristic_Length=1
3nu=1.311e-06
4ReKin = Re.Kinematic(Velocity, Characteristic_Length, nu)
```

Reynolds Number calculation by using dynamic viscosity.

```
1rho=999.73
2Velocity=1
3Characteristic_Length=1
4mu=0.001311
5ReDyn = Re.Dynamic(rho, Velocity, Characteristic_Length, mu)
```

Reference:www.pipeflow.com