The Reynolds number contains the density in the numerator and the dynamic viscosity in the denominator. The kinematic viscosity is equal to the dynamic viscosity divided by the density. So, if you know the dynamic viscosity and the density, you can calculate the kinematic viscosity. So, in practice, you use whichever is more convenient / available.PhyIsOhSoHard said:When calculating Reynolds number, when do I use dynamic viscosity and when do I use kinematic viscosity?
In a pipe with air flowing inside it, what would you use when calculating Reynolds number and why?
The type of viscosity used in the Reynolds number calculation depends on the flow regime. For laminar flow, use dynamic viscosity. For turbulent flow, use kinetic viscosity.
The flow regime can be determined by looking at the Reynolds number value. If it is less than 2300, the flow is laminar. If it is greater than 4000, the flow is turbulent. Values in between may indicate transitional flow.
No, it is important to use the correct type of viscosity for the corresponding flow regime. Using the wrong viscosity can result in inaccurate calculations and predictions.
The units for dynamic viscosity are Pascal-seconds (Pa·s) or centipoise (cP). The units for kinetic viscosity are square meters per second (m^2/s) or centistokes (cSt).
No, the Reynolds number is not the only factor. Other factors such as surface roughness and fluid properties can also affect the flow regime. However, the Reynolds number is an important parameter in determining the type of flow.