Pressure drop

The pressure drop, and pressure drop is the etc. produced by wall friction and internal fluid friction in pipes, fittings, valves pressure difference. In the technique, a resistance factor is recognized locally for ζ in a pipeline built elements (valves, orifices, flow union, division, etc. ), the table works can be removed. The resistance factor itself may be the volume flow, geometry, Reynolds number, etc. dependent. The pressure drop due to wall friction is determined by the pipe friction coefficient λ. The friction factor is a function of the Reynolds number in case of a laminar flow. If the flow is turbulent, the roughness of the surface is a particular with.

The empirical equation for pressure losses in flow through pipes including fittings (eg bends, reducers and fittings) under the assumption of a constant density is according to Darcy - Weisbach:

This is a pressure drop approach of the extended Bernoulli's energy equation. This first frictionless ( ideal ) Bernoulli energy equation ( in differential pressure form) is added to the pressure loss term:

So

Where:

When closed current thread systems (eg, hot water heaters ) The altitude is basically removed from consideration because the fluid around the same height difference moves upward as it is moved down ( this is true only under the assumption of constant density along the current thread, otherwise would be a gravity heating is not possible).

Even with open current thread systems ( eg drinking water systems ) the geodetic pressure difference from the consideration is pragmatically removed, as these can also be subsequently accounted for along the current thread on the condition of constant density and pure altitude dependence. This simplifies the calculation process significantly.

Pressure losses shall be borne by the static pressure differential share because the geodetic pressure change only a function of the location and the kinetic pressure change is a function of varying cross -section or velocity change. These two pressure difference Shares are not influenced by pressure losses.

Pressure losses always correspond to energy losses. After the extended energy equation, the pressure losses from the potential pressure energy in the fluid and the pipe wall in frictional heat and sound energy is converted ( dissipated ). The sound energy fraction is, however, very small and thus technically negligible. The extended energy equation, it is assumed that the energy of the system limit the tube wall, and thus is transmitted to the fluid is not available.

In fact, the pressure energy is dissipated as frictional heat in the fluid and leading to an increase in the fluid temperature. The increase of the fluid temperature is because of the low dissipation energy per unit time for incompressible fluids (eg water ) is hardly measurable, so that the model assumption of constant density is always guaranteed technically.

Pressure loss calculation in pipe flow (liquid, vapor, gas)

The calculation of pressure losses in pipes due to pipe friction, and by individual resistors must be made depending on the medium as incompressible or compressible flow as. Very detailed algorithms exist for example for parts and for small networks for self- programming and a computer program applicable for liquid, gas and steam flow.