Global setup

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Global setup

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► PROJECT | General | Global setup

Here the global project settings are defined valid for all components.

Depending on the project type different input parameters are required (see below). As examples you see the Global setup dialog for pumps on the left side, for compressors on the right side.

Design point

Here you have to enter the design point data:

(1) Flow rate:

for pumps, fans: volume flow Q or mass flow m

for compressors: mass flow m or volume flow Q (referring to total state on suction side)

for turbines: mass flow m

(2) Energy transmission:

for pumps: head H or total pressure difference Δpt

for fans: total pressure difference Δpt

for compressors: total pressure ratio πt or total pressure difference Δpt or specific work Y

for turbines: total pressure ratio πtt or total-to-static pressure ratio πts

(3) Number of revolutions n

Energy transmission and number of revolutions can be specified separately for each impeller in the project, see Main dimensions.
The sum of energy transmissions of all impellers in multi-stage machines should be equal to the Global Setup value.

Fluid

Here the fluid has to be defined.

One has to select one of the predefined fluids. The list of existing fluids can be modified in the Fluid manager.

For compressors and turbines the gas model has to be specified additionally: Perfect, Redlich-Kwong, Aungier/ Redlich-Kwong, Soave/ Redlich-Kwong, Peng-Robinson or CoolProp.

Inlet conditions

Here the total state at the inlet - total pressure pt and total temperature Tt - has to be defined. The latter applies only for compressors and axial turbines. For pumps and fans the inlet total pressure is not design relevant but will be used within the interfaces for the CFD export as well as for the calculation of informative values at the interfaces of any component.

For radial-inflow turbines the static pressure at the suction flange (pressure in the connection flange of the work piece attached to the turbine at the outlet) has to be specified instead of the total pressure at inlet.

Optional

Here some optional parameters can be defined. Their default values remain unchanged normally.

Direction of impeller rotation, seen in negative axis direction.

Additional efficiency, which contains all additional (non-typical) flow losses in impeller and casing parts of the machine. This efficiency value is used for impeller dimensioning as well as overall efficiency calculation in addition to the efficiency values specified in the impeller design. [ not for axial turbines ]

Pre-Swirl [ for pumps, fans, compressors only ]
Here you may define the inflow swirl at hub and shroud. The following definitions are available:

 

Flow angle

Swirl number

Swirl energy number

Positive swirl

Negative swirl

No swirl

α < 90°

α > 90°

α = 90°

δr < 1

δr > 1

δr = 1

δY > 0

δY < 0

δY = 0

Negative swirl is increasing the head and may often have no good affect to the suction behavior. Inflow through a straight pipe usually leads to swirl-free flow.

The different parameters can be converted:

   

The conversion δr - α is only valid for certain diameters dH and dS.

Values

Except for radial-inflow turbines the general meridional shape of the machine, depending on the specific speed, is displayed in the right Values area:

centrifugal
(radial)

mixed-flow
(diagonal)

axial

 

Furthermore some calculated variables are displayed:

Specific speed

points to machine type and general shape of impeller
(see Specific speed definitions)

Specific energy  Y

Pumps, Fans:
  Y = gH = Δpt

Compressors (perfect gas model):
 

Power output PQ

Pumps, Fans:
  PQ = ρgHQ

Mass flow m

Pumps, Fans:
 

Compressors:
  (density according to gas model)

Total pressure difference Δpt

Pumps, Fans:
  Δpt = ρgH

Compressors:
 

Compressor:

Total pressure ratio

Inlet speed of sound (total)

(perfect gas model)

Volume flow (total)

(density according to gas model)

Inlet density (total)

 (density according to gas model)

Turbine:

Inlet speed of sound (total)

(perfect gas model)

Total temperature (isentropic)

(perfect gas model)

Cordier

The Cordier diagram contains relationship between specific speed and specific diameter.

See Cordier.

General remarks

In general for cost reasons single-stage & single-intake machines are preferred covering a range of about 10 < nq < 400.

In exceptional cases it may become necessary to design an impeller for extremely low specific speed values (nq < 10). These impellers are characterized by large impeller diameters and low impeller widths. The ratio of free flow cross section area to wetted surfaces becomes unfavorable and is causing high frictional losses. To prevent this one may increase either rotational speed n or flow rate Q if possible. An alternative solution could be the design of a multi-stage machine reducing the energy transmission of the single-stage.

If especially high specific speed values (nq > 400) do occur one can reduce rotational speed n or flow rate Q if feasible. Another option would be to operate several single-stage machines - having a lower nq - in parallel.

Please note: CFturbo® is preferably used between 10 < nq < 400 – radial, mixed-flow and axial impellers.

 

Possible warnings

Problem

Possible solutions

Energy transmission of all impellers is different to globally defined value.

The sum of energy transmission defined for each impeller deviates from the globally defined value in Global setup.

Check and adapt the energy transmission of the impellers (see Main dimensions) to get altogether 100% of the initially defined value of the Global setup.