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How to Calculate Flow Rate across an Air Hose

Flow rate through an air hose is determined by several forces of physics. Flow through any tube is called laminar flow. Laminar flow is parallel flow through the tube; in this case, an air hose. Laminar flow travels smoothly, in contrast to turbulent flow. The calculation of laminar flow through a straight tube or air hose is executed with the use of the equation FR = ( pi * r )(P - Po) / 8 NL.


Laminar Flow Equation

Calculate the flow rate of fluids through a tube.
  1. Calculate the radius of the tube. This is represented by the letter R in the equation in the introduction. The radius is half the diameter of the tube.
  2. Calculate the pressure at the end of the length of the tube by using a pressure gauge to measure it. Manometers are used to measure gases close to atmospheric pressure. This measurement will be represented by Po in the equation above. The P in the equation is the pressure at the other end of tube or air hose. The "pi" is a given; the mathematical constant 3.14.
  3. Calculate the fluid or gaseous viscosity. The viscosity of fluids js determined by a kinematic viscosity chart that can be found online on The Engineering ToolBox website. Different viscosity measurements are used for gases compared to fluids, and viscosity will change if the temperature of the fluid changes. The viscosity measurement is represented by N in the equation.
  4. Calculate the length of the air hose. The length of the air hose is represented by L in the equation.
  5. Plug the measurements you've taken into the equation above and it will yield the FR or flow rate through an air hose.

About the Author

Sonya Kanti has more than five years of experience writing professionally. Currently in medical school, she focuses her writing on health-related issues. She's written for the "PITT MED" medical magazine published by the University of Pittsburgh Medical School. She has a Bachelor of Arts degree in political science with a minor in biochemistry from Loyola University Chicago.

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