The Pressure in Bubbles

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities and you. In this blog we’ll be discussing the pressure in bubbles.

The Pressure in Bubbles

The surface tension of the interface between liquid and gas creates a pressure difference. For a soap bubble, the pressurized bubble of air is contained within a thin, elastic surface of liquid. When the bubble bursts, the difference in pressure causes an audible pop.

The pressure difference can be calculated by using a simplified version of the Laplace pressure equation since the inner radius is essential the same as the outer radius. In this case,

Pi-Po = ΔP = 2*(2γ/R)

Where:

ΔP is the pressure difference in N/m2 or Pascals (Pa)

γ is the surface tension in N/m

R is the radius of the bubble in meters, and

2γ/R is the Laplace pressure.

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The ΔP is 2 times the Laplace pressure since there is a complete sphere instead of a semi sphere on a layer of water.

Based on the diameter, the pressure inside an air bubble in pure water, where γ = 72 mN/m at 25°C (298 K), can vary greatly.

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What do you think/Comments?
Do you have a pressure sensing question? Let me know and I’ll address it in an upcoming blog.
-Han Mai, Senior Marketing Specialist, All Sensors Corporation (hmai@allsensors.com)