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engineering › fluids ›


Evaluates the Reynolds number of given parameters.
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doubleviscosity )[inline]
Reynolds number, named after Osborne Reynolds who proposed it in 1883, is the ratio of inertial forces to viscous forces in a fluid. Besides other applications, it can be used to determine whether a flow inside a pipe is laminar, turbulent or in the so-called critical zone. The formula for this dimensionless measure is: where D is the characteristic length, v is the average velocity of the flow, \rho is the weight density and \mu is the absolute viscosity of the fluid.

It has been established that in the case of a fluid going through pipes, for Reynolds values less than 2000 the flow is laminar, for values greater than 4000 the flow is turbulent, while for numbers between 2000 and 4000 the flow becomes unpredictable. For this reason the domain from 2000 to 4000 is also called the "critical zone".

Example 1

#include <stdio.h>
#include <codecogs/engineering/fluids/reynolds.h>
int main()
  double Re = Engineering::Fluids::Reynolds(5, 10, 23, 0.45345);
  printf("Re = %.13lf\n", Re);
  if (Re < 2000) printf("Laminar flow.\n");
  else if (Re > 4000) printf("Turbulent flow.\n");
  else printf("Unpredictable flow (critical zone).\n");
  return 0;


Re = 2536.1120299922814
Unpredictable flow (critical zone).


The Engineering Division, Crane Co., "Flow of fluids through valves, fittings, and pipe", Chicago, 1957


diametercharacteristic length (ft)
velocitymean velocity of flow (ft/s)
densityweight density of fluid (lb/ft)
viscosityabsolute viscosity of fluid (lb/ft s)


The Reynolds number corresponding to the given parameters.


Lucian Bentea (July 2006)
Source Code

This module is private, for owner's use only.

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