Pressure
Module EG1083 Fluid Mechanics
PRESSURE , FLUID SYSTEMS and FLUID PRESSURES
SM(1)
Pressure
Definition of Pressure
Fluid pressure: Force per unit area exerted by a fluid in a solid wall. Force acts perpendicularly to the surface in contacts. Fluid is a co u d s common word for gas a d/o liquid. o od o and/or qu d Pressure is a scalar quantity. It has the units of: N/m2 or Pa (or kPa) in SI system of units psi in Imperial system of units Pressure can also be expressed in terms of height of a column of liquid List of units of pressure measurements & conversion of units Pascal s Pascal’s law
Scalar quantity
Units of Pressure
SM(2)
Pressure
Pressure measurements Absolute pressure Gauge Pressure
...divided into three different categories: 1. Absolute pressure – which is defined as the absolute value o pressure (force-per-unit-area) ac g o of p essu e ( o ce pe u a ea) acting on a surface by a fluid. su ace ud Abs. pressure = pressure at a local point of the surface due to fluid – absolute zero of pressure (see page 63 of lecture notes) 2. Gauge pressure – difference between abs. pressure and atmospheric pressure – is always positive 101.325 kPa or 14.7 psi
Equations
Pressure term relationships
– a –ve gauge pressure is vacuum ve vacuum. Pressure term relationships • Abs pressure = gauge pressure + atm pressure Abs. • Abs. pressure = – gauge pressure + atm pressure (vacuum) > atm < atm
SM(3)
Pressure
Pressure measurements
Relation between abs., gauge and vacuum
Absolute pressure Gauge Pressure
gauge
Equations gauge) Pressure term relationships
SM(4)
Pressure
Pressure term relationships Hydrostatic pressure
3. Differential pressure – measurement of an unknown pressure minus the reference to a o e u e e e ce o another unknown p essu e o pressure. – it is used to measure differential pressure i.e. pressure drop (ΔP) in a fluid system
SM(5)
Fluid systems and Fluid pressures
Fluid systems
Two
PRESSURE , FLUID SYSTEMS and FLUID PRESSURES
SM(1)
Pressure
Definition of Pressure
Fluid pressure: Force per unit area exerted by a fluid in a solid wall. Force acts perpendicularly to the surface in contacts. Fluid is a co u d s common word for gas a d/o liquid. o od o and/or qu d Pressure is a scalar quantity. It has the units of: N/m2 or Pa (or kPa) in SI system of units psi in Imperial system of units Pressure can also be expressed in terms of height of a column of liquid List of units of pressure measurements & conversion of units Pascal s Pascal’s law
Scalar quantity
Units of Pressure
SM(2)
Pressure
Pressure measurements Absolute pressure Gauge Pressure
...divided into three different categories: 1. Absolute pressure – which is defined as the absolute value o pressure (force-per-unit-area) ac g o of p essu e ( o ce pe u a ea) acting on a surface by a fluid. su ace ud Abs. pressure = pressure at a local point of the surface due to fluid – absolute zero of pressure (see page 63 of lecture notes) 2. Gauge pressure – difference between abs. pressure and atmospheric pressure – is always positive 101.325 kPa or 14.7 psi
Equations
Pressure term relationships
– a –ve gauge pressure is vacuum ve vacuum. Pressure term relationships • Abs pressure = gauge pressure + atm pressure Abs. • Abs. pressure = – gauge pressure + atm pressure (vacuum) > atm < atm
SM(3)
Pressure
Pressure measurements
Relation between abs., gauge and vacuum
Absolute pressure Gauge Pressure
gauge
Equations gauge) Pressure term relationships
SM(4)
Pressure
Pressure term relationships Hydrostatic pressure
3. Differential pressure – measurement of an unknown pressure minus the reference to a o e u e e e ce o another unknown p essu e o pressure. – it is used to measure differential pressure i.e. pressure drop (ΔP) in a fluid system
SM(5)
Fluid systems and Fluid pressures
Fluid systems
Two
References: •Transport Phenomena by Bird, Stewart, Lightfoot •Fluid Mechanics and Hydraulic machines by R K Rajput R.K. •http://www.freescale.com/files/sensors/doc/app_note/AN1573.pdf (18 F 10) •http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Pressure/Hydro Static.html (18 F 10) SM(15)