Pressure

Overview

Engineering reference data for Pressure in fluid mechanics.

Key Formulas

Reynolds Number

$Re = \frac{\rho v D}{\mu}$

Ratio of inertial to viscous forces — determines flow regime.

Bernoulli's Equation

$P + \frac{1}{2}\rho v^2 + \rho g h = \text{const}$

Conservation of energy for steady, inviscid, incompressible flow.

Continuity Equation

$A_1 v_1 = A_2 v_2$

Conservation of mass for incompressible flow.

Darcy-Weisbach

$\Delta P = f \frac{L}{D} \frac{\rho v^2}{2}$

Pressure drop due to friction in a pipe.

Variables

Absolute vs. Gauge Pressure

Standard Atmospheric Pressure

The Standard Atmospheric Pressure ($p_{atm}$) serves as a reference pressure for many engineering calculations:

$1 \, \text{atm} = 101325 \, \text{Pa} = 101.325 \, \text{kPa} = 1.01325 \, \text{bar}$

In imperial units:

$1 \, \text{atm} = 14.696 \, \text{psi} = 29.92 \, \text{inHg} = 33.90 \, \text{ftH}_2\text{O}$

Important note: All gas law calculations (Ideal Gas Law, etc.) require absolute pressure and absolute temperature values.

Pressure Unit Conversions

Practical Pressure Examples

Pressure Measurement Devices

Common instruments for measuring pressure:

• Manometers: Use fluid columns to measure pressure differential
• Bourdon tubes: Mechanical gauges for gauge pressure
• Piezoelectric sensors: Convert pressure to electrical signals
• Membrane/Bellows sensors: For differential pressure measurement
• Digital pressure gauges: Electronic measurement with digital display

Key Applications by Pressure Range

Interactive Charts

References

• Original Source