Description

q - volumetric flow rate

Fluid flow rate in terms of units of volume per unit of time

ṁ - mass flow rate

Fluid flow rate in terms of units of mass per unit of time

V - velocity

Flow velocity in terms of units of distance per unit of time

D - pipe diameter

Internal circular pipe diameter

H - channel height

The height of channel for rectangle shaped pipe

W - channel width

The width of channel for rectangle shape pipe

A - area

Internal pipe cross section area

ρ - fluid density

Mass per unit of volume

T - temperature

Fluid temperature for gas density calculation based on the ideal gas state equation

p - pressure

Fluid pressure at the start of the pipe for gas density calculation based on the ideal gas state equation

R - gas constant

Gas constant in terms of energy per unit of mass and temperature, for gas density calculation using ideal gas state equation

ν - kinematic viscosity

Result of fluid particles colliding to each other and moving at different velocities in terms of area per square unit of time

μ - dynamic viscosity

Result of fluid particles colliding to each other and moving at different velocities in terms of mass per square unit of distance and time

Re - Reynolds number

Dimensionless number representing viscous versus inertial forces ratio

Calculation setup

Select value to input. You should enter selected one. The other two will be calculated

q

volumetric flow rate

ṁ

mass flow rate

V

flow velocity

Select value to input. You should enter selected one. The other one will be calculated. Available only if the gas is selected fluid

ρ

fluid density

T

temperature

Select value to input. You should enter selected one. The other one will be calculated

ν

kinematic viscosity

μ

dynamic viscosity

Select fluid type

liquid

for incompressible fluids

gas

for fluids where ideal gas state equation is used. Enables selection between density and temperature to input.

Select pipe shape

round pipe

full cross section fluid flow

rectangular duct

for rectangle channels and full cross section flow

When is this calculator suitable?

You can use the calculator for all fluids and flow rates without any restriction. The calculator applies to fluid mixtures also, but you have to enter the viscosity of a mixture.

Calculator description

Reynolds number named after Osborne Reynolds (1842 – 1912), gives the relation between inertial and viscous forces of fluid flow. If inertial forces (flow rate) are much bigger, and Reynolds number is higher than critical, Re > 2320, fluid flow is turbulent, and if viscous forces are big enough in comparison to inertial (flow rate), Reynolds number is lower than critical, Re < 2320, fluid flow is laminar.

For calculation of Reynolds number in closed pipe fluid flow average velocity, fluid viscosity, and internal pipe diameter should be known. Reynolds number is proportional to fluid flow average velocity and pipe diameter and inversely proportional to fluid viscosity.

With Reynolds number calculator you can analyze what makes fluid flow regime laminar and what is needed to force the fluid to flow in the turbulent regime. For example - in pipes with minimal internal diameter it is more likely to have laminar flow regime with small Reynolds number even for a fluid with low viscosity. In fluid flow with temperature change flow regime can change from turbulent to laminar flow regime, as viscosity is changing depending on the fluid temperature.