Term

Description

Absolute Pressure

Pressure measured with respect to zero pressure.

Atmosphere

A standard atmospheric pressure of 1.01325 bar a or 14.696 psi a.

Centipoise

Absolute viscosity of a fluid expressed in Pa • s x 10-3

Centistokes

Kinematic viscosity of a fluid expressed in m2/s x 10-6

Colebrook-White equation

An equation used to calculate accurate friction factors from the internal diameter and internal roughness of a pipe and the Reynolds number for the flow conditions.

Darcy-Weisbach equation

An equation used to calculate the frictional head loss due to fluid flow from the friction factor, the length and diameter of the pipe, the velocity of the fluid and the gravitational constant.

Friction Factor

A factor to be used in the Darcy-Weisbach equation.  Either calculated from the Colebrook-White equation or ready from the Moody diagram.

Entry Pressure

The pressure at the start of the pipe.

Exit Pressure

The pressure at the end of the pipe.

Fixed Pressure Loss

A static pressure loss which is independent of the flow rate.

K Value

Coefficient of frictional loss through a valve or pipe fitting.

Moody Diagram

A graphical representation of the relationship between Reynolds number, relative roughness and Friction factor.

Pressure Loss

The friction loss due to fluid flow expressed in a relative fluid head or a non-relative unit of pressure.

Reynolds Number

A dimensionless number derived from the fluid velocity, the internal diameter of the pipe and the Kinematic viscosity of the fluid.

Vapor Pressure

The absolute pressure at which a liquid will start to evaporate.

Viscosity

A measure of a fluid’s resistance to flow.