Fluid power principles: properties and behaviour of air and hydraulic fluids

1. Gas laws: Boyles Charles, Gay-Lussacs general gas dew point

2. Fluid flow Bernoullis principle volumetric rate receiver volume actuator flow requirements

Fluid power principles: properties and behaviour of air and hydraulic fluids

3. Fluid pressure units of measurement Pascals law inlet and outlet pressure pressure drop actuator efficiency clamping force

4. Formulae: P1 V1 / T1 = P2 V2 / T2 displaced volume = piston area x stroke volumetric flow rate = displaced volume/time absolute pressure = gauge + atmospheric pressure force = pressure x area actuator force = pressure x area x efficiency

Fluid mechanicsFluid mechanics is the branch of physics that studies fluids (liquids, gases, and plasmas) and the forces on them.Fluid mechanics can be divided into fluid statics, the study of fluids at rest; fluid kinematics, the study of fluids in motion; and fluid dynamics, the study of the effect of forces on fluid motion.

Assumptions:Conservation of massConservation of energyConservation of momentumThe continuum hypothesis

1. Conservation of massThe law of conservation of mass, or principle of mass conservation, states that for any system closed to all transfers of matter and energy (both of which have mass), the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed. Hence, the quantity of mass is "conserved" over time. The law implies that mass can neither be created nor destroyed, although it may be rearranged in space, or the entities associated with it may be changed in form, as for example when light or physical work is transformed into particles that contribute the same mass to the system as the light or work had contributed.2. Conservation of energyIn physics, the law of conservation of energy states that the total energy of an isolated system cannot changeit is said to be conserved over time. Energy can be neither created nor destroyed, but can change form, for instance chemical energy can be converted to kinetic energy in the explosion of a stick of dynamite.

3. Conservation of momentumIn classical mechanics, linear momentum or translational momentum (pl. momenta; SI unit kg m/s, or equivalently, N s) is the product of the mass and velocity of an object.For example, a heavy truck moving quickly has a large momentumit takes a large or prolonged force to get the truck up to this speed, and it takes a large or prolonged force to bring it to a stop afterwards. If the truck were lighter, or moving more slowly, then it would have less momentum.Like velocity, linear momentum is a vector quantity, possessing a direction as well as a magnitudeP = m v

Linear momentum is also a conserved quantity, meaning that if a closed system is not affected by external forces, its total linear momentum cannot change.

4. The continuum hypothesisFluids are composed of molecules that collide with one another and solid objects. The continuum assumption, however, considers fluids to be continuous. That is, properties such as density, pressure, temperature, and velocity are taken to be well-defined at "infinitely" small points at the geometric order of the distance between two adjacent molecules of fluid. Properties are assumed to vary continuously from one point to another.The fact that the fluid is made up of discrete molecules is ignored.The continuum hypothesis is basically an approximation, in the same way planets are approximated by point particles when dealing with celestial mechanics, and therefore results in approximate solutions. Consequently, assumption of the continuum hypothesis can lead to results which are not of desired accuracy. That said, under the right circumstances, the continuum hypothesis produces extremely accurate results.

Ideal gas

An ideal gas is a theoretical gas composed of many randomly moving point particles that do not interact except when they collide elastically. The ideal gas concept is useful because it obeys the ideal gas law, a simplified equation of state:

P V = n R T

At normal conditions such as standard temperature and pressure, most real gases behave qualitatively like an ideal gas.

Many gases such as nitrogen, oxygen, hydrogen, noble gases, and some heavier gases like carbon dioxide can be treated like ideal gases within reasonable tolerances.

Generally, a gas behaves more like an ideal gas at higher temperature and lower pressure, as the work which is against intermolecular forces becomes less significant compared with the particles' kinetic energy.

Dew point

The dew point is the temperature at which the water vapour in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates.

At temperatures below the dew point, water will leave the air. The condensed water is called dew when it forms on a solid surface. The condensed water is called either fog or a cloud, depending on its altitude, when it forms in the air.

The dew point is the saturation temperature for water in air.

The dew point is associated with relative humidity. A high relative humidity implies that the dew point is closer to the current air temperature.

Relative humidity of 100% indicates the dew point is equal to the current temperature and that the air is maximally saturated with water. When the moisture content remains constant and temperature increases, relative humidity decreases.

Dew point

This graph shows the maximumpercentage, by mass, of water vapourthat air at sea-level pressure across arange of temperatures can contain.

For a lower ambient pressure, acurve has to be drawn above thecurrent curve.

A higher ambient pressure yieldsa curve under the current curve

Boyles law

At constant temperature, the product of an ideal gas's pressure and volume is always constant:

p1 V1 = p2 V2

OR: if the temperature remains constant, the volume of a given mass of gas is inversely proportional to its pressure:

V = k ( 1 / p )

where k is a constant of proportionality.

Boyles law

Charles law

Also known as the law of volumes, states that: for an ideal gas at constant pressure, the volume is directly proportional to its absolute temperature:

V1 / T1 = V2 / T2

Charles law

Gay-Lussacss law

Also known as the pressure law, states that: the pressure exerted on the sides of a container by an ideal gas of fixed volume is proportional to its temperature:

p1 / T1 = p2 / T2

General gas law

The combined gas law or general gas equation is formed by the combination of the three laws. It shows the relationship between the pressure, volume, and temperature for a fixed mass of gas:

p1 V1 / T1 = p2 V2 / T2 = k

Bernoulli's principle

Bernoulli's principle states that: for an inviscid flow of a nonconducting fluid, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.

Notes: An inviscid flow is the flow of an ideal fluid that is assumed to have no viscosity Nonconducting thermal conduction

Bernoulli's principle

Bernoulli's principle states that: for an inviscid flow of a nonconducting fluid, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.