Ludwig Prandtl brought together in 1905
 the hydraulics and the hydrodynamics, two disciplines of the fluid mechanics which had been developped independantly from each other,
The hydraulics is the experimental and user-oriented fluid mechanics, which is needed by engineers in order to solve practical problems. The assembly of a hydraulics
or flow network is based on the empirical pressure loss coefficients from Bernoulli; this method is also called 1D-CFD (Computational Fluid Dynamics).

The hydrodynamics is a field, in which physicians, mathematicians and developers of flow software are mostly theoretically engaged. They analyze and develop solving schemes for the complex non-linear flow equations from Navier-Stockes.

The hydraulics can be used as a design tool for a wide range of industries and applications. From the concept phase, users can quickly conceptualize fluid system designs with minimal geometric data and evaluate design alternatives against performance targets. The cooling system of a large installation is too big and too complex, in order to be completely analyzed with 3D simulations. It is best practice to calculate it with the hydraulics formulas; this method is used for the engineering of combine cycle and coal thermal power plants: for the water-steam cycle, the closed-cooling water system, lube oil distribution systems as well as other balance of plant systems.
As the flow calculation is an approximation, a multitude of conditions can be simulated: gas and fluids, stationary or time-dependant, closed or open system, compressible or incompressible flow, heating and cooling as well combustion and multi-phase flows.
These networks can be programmed in Excel, Fortran or in any programming languages. New networks tend to be developed with thermo-fluid sub-system software like Flowmaster ®. These tools differentiate each others in the components library, where elements like pumps, fans, valves, bends and junctions are predefined. Passive components like heat exchangers are defined be a constant or flow dependant pressure drop.


Axial fan                                                     Radial fan ER..C © Ziehl -Abbeg


Pipes are defined by their geometry and mean wall friction.The flow can be calculated and the pipes sized with a flow network.  As the complete system of pipes must be erected in a specific room, the arrangement of the system must be later checked with the generation of a complete 3D CAD model.

Pumps and fans

A fan is defined by its fan curve and its rotational speed; only the fan load (pressure generation and volume flow) has to be evaluated, in order to choose the corresponding fan in a fan catalog.

A pump conveys fluids; it is defined by its pump curve and head. If the system contains heat exchangers, their cooling might necessitate the design of the corresponding fans as well.


Small flow network generated with Flowmaster


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