How to calculate the fluid flow through a hole in a pipe

Written by j.r. kambak
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A common problem with pipes is corrosion. Over time, the corrosion in the pipe can make a hole that causes a leak. Calculating the fluid flow through a hole can be difficult, due to many variables like fluid flow velocity, pressure in the pipe and density of the fluid, just to name a few, but don’t get discouraged. You can find the answer you need by following a simple series of steps.

Skill level:

Things you need

  • Scientific calculator
  • Tape measure
  • Pen/pencil
  • Paper

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  1. 1

    Obtain measurements: diameter (d) of the hole in the pipe and height (h) of the surface of the fluid above the hole. Make sure all measurements are in the same standard unit. Know that 1 inch = 0.0254 meters, so if you use inches, convert your measurements.

  2. 2

    Calculate the cross-sectional area of the hole (A). Divide the diameter of the hole in half to get the radius. Use the formula A = 3.14 (number Pi) * r^2 (radius to the second power). The result will be in square units.

  3. 3

    Use the Bernoulli equation to find the fluid velocity (V) if it is not already provided. If the fluid pressure in a pipe is constant (the flow is steady), the fluid leaves through the hole in the pipe at a velocity of V = square root (2gh), where g is acceleration due to gravity (g = 9.8m/s^2).

  4. 4

    Multiply the cross-sectional area of the hole by the fluid velocity to find the volume of fluid (Q): Q = A * V. This will be the volume of the fluid that leaves the hole in cubic meters per second.

  5. 5

    Let's look at an example with numbers. Calculate fluid flow through the hole in the pipe with constant pressure if the water leaves the hole with a velocity of 1.7m/s and the diameter of the hole is d = 1 inch = 1 * 0.0254 = 0.0254 meters.

    First, find the cross-sectional area of the hole: A = 3.14 * (0.0254/2)^2 = 0.00051m^2. Since the pressure is constant and the velocity of the water going through the hole is 1.7m/s, use the formula from Step 4 to find the volume of water that leaves the hole: Q = 0.00051m^2 * 1.7m/s = 0.000867m^3/s.

    Since 1 cubic meter = 61,024 cubic inches, Q = 0.000867m^3/s * 61,024 = 52.9 inch^3/s. Thus, 52.9 cubic inches of water leaves the hole in the pipe per second.

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