Dynamic pressure and velocity head. The dynamic pressure in a fluid flow can be expressed as Water Flow - Head to Velocity Calculator flow velocity by measuring static and dynamic pressure difference; Static Pressure Head in Fluids . Static pressure is the pressure you have if the fluid isn't moving or if Dynamic pressure is the pressure of a fluid that results from its motion. This lesson looks at the definition of static pressure as well as how to Coming up next: What is Dynamic Pressure? Gauge Pressure & Absolute Pressure: Relation & Conversion . Hydrostatic Pressure Diagram.
Dynamic losses are proportional to dynamic pressure and can be calculated using the equation: A local loss coefficient can be related to different velocities; it is important to know which part of the velocity profile is relevant.
Frictional Pressure Frictional losses in duct sections are result from air viscosity and momentum exchange among particles moving with different velocities. These losses also contribute negligible losses or gains in air systems unless there are extremely long duct runs or there are significant sections using flex duct.
Total Pressure, Velocity Pressure, and Static Pressure It is convenient to calculate pressures in ducts using as a base an atmospheric pressure of zero. Airflow through a duct system creates three types of pressures: Each of these pressures can be measured. Air conveyed by a duct system imposes both static and dynamic velocity pressures on the duct's structure. The static pressure is responsible for much of the force on the duct walls. However, dynamic velocity pressure introduces a rapidly pulsating load.
Static pressure Static pressure is the measure of the potential energy of a unit of air in the particular cross section of a duct.
Air pressure on the duct wall is considered static. Imagine a fan blowing into a completely closed duct; it will create only static pressure because there is no air flow through the duct.
A balloon blown up with air is a similar case in which there is only static pressure.
Air Flow, Air Systems, Pressure, and Fan Performance
Dynamic velocity pressure Dynamic pressure is the kinetic energy of a unit of air flow in an air stream. Dynamic pressure is a function of both air velocity and density: Total Pressure Consists of the pressure the air exerts in the direction of flow Velocity Pressure plus the pressure air exerts perpendicular to the plenum or container through which the air moves.
Air Systems For kitchen ventilation applications an air system consists of hood sduct work, and fan s. The relationship between the air flow rate CFM and the pressure of an air system is expressed as an increasing exponential function.
Definition and Units The classical definition of pressure is the amount of force acting on a surface per unit area, as shown in Figure 1.
Other units commonly used for pressure include the atmosphere, bar, kilopascal, torr, inches or mm of mercury and inches or mm of water.
Pressure is force per unit area. The total pressure is the sum of the static pressure and the dynamic pressure. Static Pressure Static pressure is felt when the fluid is at rest or when the measurement is taken when traveling along with the fluid flow. Since static pressure is what most pressure gauges measure, static pressure is usually what is implied when the term "pressure" is used in discussions.
Dynamic pressure is a function of the fluid velocity and its density and can be calculated from: Measuring Total, Static, and Dynamic Pressure.
When to Make the Distinction Depending on the application, the difference between total and static pressure may be negligible, but for others, neglecting the difference may result in costly mistakes. For many liquid applications, the pipelines are sized to ensure low fluid velocities to reduce the head loss and pressure drop for a given flow rate, resulting in a small value of dynamic pressure. In Figure 3, the pipe size is changed to result in different fluid velocities for gpm of water flow, resulting in different amounts of dynamic and static pressure for an inlet total pressure of psig.