The pressure in one point of the network is the sum of energies of dynamic and static pressures. The transformation of energy is reversible or irreversible
the head 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 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:
Absolute pressure and gauge pressure units
The unit of pressure is N/m2 or Pascal (Pa). 1 Pascal represents a force of 1 Newton applied on an area of 1 m²: Pressure (pascal) = Force (newton) / Surface(m²)
The pressure generated by a force of 10 N applied to 0.1 m² is equal to the pressure generated by a force of 100 N on 1 m²::
This allows to increase the forces depending on pressure surfaces of. (hydraulic cylinders, pressure multipliers ...)
- the absolute pressure (P abs) pressure is measured with reference to a zero pressure (full vacuum).
- Pressure Gauge indicates the difference between the fluid pressure and the atmospheric pressure (P atm).
to convert a value from gauge pressure (PG) to absolute pressure (Pas), simply add the atmospheric pressure:
Pabs = PG + Patm
To convert from absolute pressure to pressure gauge, subtract the atmospheric pressure:
Meteorologists use the pressure in millibars.
1 mb = 0,1 kPa
1 Pa = 1 N/m2, 1 kPa = 1 x 103 Pa
Within a volume of fluid, pressures types are distinguished depending on the physical phenomena that generate them:
- The hydrostatic pressure, or hydrostatic head: This is the pressure generated by the height difference between two points. It represents the force applied by the weight of a fluid column to its base.
- The dynamic pressure represents the inertia of the fluid, the force produced to generate the acceleration of the fluid mass.
Dynamic pressure (Pascals) = 0.5 x density (kg/m3) x speed² (m / sec)
The sum of the energies of pressure in a same volume of fluid is constant: See bernoulli:
- output power Watt = flow (m3/sec) x Pressure (pascals)
- Exemple: a non reversible pressure drop (head loss) of 10 pascals in a 1 m3/sec fluid flow , is a power loss of 10 Watts
The pressure formula : Pressure = Force / Surface is associated in mecaflux to a unit converter.
inMecaflux Standard , the pressures in the ducts are parameterized using the pressure tank (absolute). .
To enter a tank pressure other than ambient atmospheric pressure, uncheck the box atm. and enter the absolute pressure.
data powers will be updated accordingly ...