The pressure in one point of the network is the sum of energies of dynamic and static pressures. These transformations of energy are reversible or irreversible
the pressure loss is irreversible loss of pressure because the head loss is converted into heat or noise that we do not know re-transformed into pressure.
The pressure generated by changing altitude or height of load (hydrostatic pressure) is reversible: If the duct up of 1 meter, and down of 1 meter, the balance is zero:l:
the pressure generated by the change in velocity (dynamic pressure) is reversible:If for a given flow a converging cone accelerates the fluid the pressure decreases (see Bernoulli), but if another diverging cone, positioned downstream, slows down the fluid to its original speed, the balance of dynamic pressure is zero:
head loss software pressure drop calculation Reynolds number minor head loss head loss Formula head loss major head loss pressure drop hydrailics head loss Flow Regime aeraulic pressure drop major pressure drop Colebrook-White Formulas pressure drop Viscosity roughness pipes
head loss and pressure drop air water gas hydraulic aeraulic
- The calculation of major losses air water hydraulic aeraulic.
- The calculation of minor losses air water hydraulic aeraulic.
- Minor loss coefficient (air hydraulic aeraulic water) with mecaflux pro 3D
- Minor loss coefficient (air water hydraulic aeraulic) with standard mecaflux
Definition head loss air water hydraulic aeraulic:
The losses in the pipes and networks aeraulic or hydraulic (air water gas) designates the irreversible loss of pressure energy, that undergoes a liquid or a gas as it passes through a conduit, or another fitting of fluid network .
these energy losses related to the fluid velocity (low speed = low pressure drop), is caused by the conversion into heat of the internal friction caused by:
- the viscosity of the fluid (a perfect fluid, without viscosity, does not generate a pressure drop),
- the roughness of the walls,
- the speed variations
- and changes in direction of the fluid.
L'unité de la perte de charge est une pression (pascals,bars...)The unit pressure drop is a pressure (Pascal, bars ...) or a height of water column that produces a hydrostatic head (head loss) (hydrostatic pressure) equivalent.The term "head loss" therefore means "loss of hydrostatic head." From this definition we can already say that the losses in the networks are important if:
- The fluid velocity is high and the roughness is important.
- Speed variation due to the change of section is important and sudden.
- the change of direction is important and sudden.These energy losses are therefore minimum if:
- the speed is low and surfaces are smooth.
- the speed variation due to a change in section is gradual and low.
- the change of direction is low and progressive.
- There are 2 types of pressure losses:
- The major head loss , representing frictional head loss in the pipes. They are caused by the fluid viscosity.They depend on the degree of turbulence (described by the Reynolds number)..
- The minor head loss, are the result of changes in speed and direction changes of the fluid caused by the shapes and obstacles encountered by the fluid passing through an object: Cones, elbows, grids, racordements, junctions ...
In reality, these two types of pressure losses may not be separate, and in a rounded elbow, it is some minor head loss due to change of direction and a part of major load loss due to friction along the length of conduit formed by the elbow. An addition of the two pressure losses may be necessary if the friction surfaces are important (a coil constituted of elbows) But usually, the major head loss are Neglected for fittings or other networks elements.
The coefficient of head loss:
The pressure drop coefficient is a unitless value which calculates the pressure drop as a function of the dynamic pressure of the fluid.
- Dynamic pressure= 0.5 x Density(kg/m3) x Velocity²(m/sec)
Since there are two types of losses, there are two types of coefficients head loss:
- Major head loss coefficient.
- Minor head loss coefficient.
There are various formulas to determine themajor loss coefficient ,The choice of formula depends on the flow regimewhich is estimated with the Reynolds number.
A description of the method of calculation of the coefficient of head loss based on a measure of loss (Image taken from pro3D mecaflux software)
For more information on head loss and pressure loss factors:
Determine the minor head loss coefficient with mecaflux 3D