Pressure Head Water

Overview

Engineering reference data for Pressure Head Water 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

Symbol	Description	Unit
$Re$	Reynolds number	—
$\rho$	Fluid density	kg/m³
$v$	Flow velocity	m/s
$D$	Characteristic dimension	m
$\mu$	Dynamic viscosity	Pa·s
$P$	Pressure	Pa
$f$	Darcy friction factor	—

Pressure and Head Conversion Factors

Key Conversions

• $1 \, \text{ftH}_2\text{O} = 0.4335 \, \text{psi}$
• $1 \, \text{ftH}_2\text{O} = 62.43 \, \text{lbs/ft}^2$
• $1 \, \text{psi} = 2.307 \, \text{ftH}_2\text{O}$

Other Pressure Units for 1 psi

$1 \, \text{psi} = 144 \, \text{psf}$ $1 \, \text{psi} = 6894.8 \, \text{Pa}$ $1 \, \text{psi} = 6.895 \times 10^{-3} \, \text{N/mm}^2$ $1 \, \text{psi} = 6.895 \times 10^{-2} \, \text{bar}$ $1 \, \text{psi} = 27.71 \, \text{in H}_2\text{O at } 61^\circ\text{F} \, (16.7^\circ\text{C})$ $1 \, \text{psi} = 703.1 \, \text{mm H}_2\text{O at } 61^\circ\text{F} \, (16.7^\circ\text{C})$ $1 \, \text{psi} = 2.0416 \, \text{in mercury at } 61^\circ\text{F} \, (16.7^\circ\text{C})$ $1 \, \text{psi} = 51.8 \, \text{mm mercury at } 61^\circ\text{F} \, (16.7^\circ\text{C})$ $1 \, \text{psi} = 703.6 \, \text{kg/m}^2$ $1 \, \text{psi} = 0.06895 \, \text{atm}$ $1 \, \text{psi} = 16 \, \text{ozf/in}^2 \quad \text{(ounce-force per square inch)}$

Example Conversion

A head of 64 ftH₂O can be converted to pressure using the factor $0.4335 \, \text{psi/ftH}_2\text{O}$:

## References - [Original Source](https://www.engineeringtoolbox.com/pressure-head-water-d_1354.html)