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Global setup |
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Ü Project | Project | 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).
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In Panel Design point you have to enter the design point data:
(1) Flow rate:
| ▪ | for pumps, ventilators: volume flow Q |
| ▪ | 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 pressure difference Δp |
| ▪ | for ventilators: pressure difference Δp |
| ▪ | for compressors: total pressure ratio πt or total pressure difference Δpt or specific work Y |
| ▪ | for turbines: total pressure ratio πtt or specific work Y or Machine-Mach-number M1 or Inlet peripheral speed u1 or Inlet diameter d1 or total-to-static pressure ratio πts |
(3) Number of revolutions n
In panel General you can define the rotational direction of the impeller seen from the drive side (axial view to backside of hub).
Furthermore the Casing efficiency can be defined optionally, which contains all flow losses in none rotating components and can be used for overall efficiency calculation in connection with the impeller efficiency.
In panel Fluid the fluid properties has to be defined.
For incompressible fluids (pumps, ventilators) this is the density ρ only.
For compressible fluids (compressors, turbines) some additional gas properties are required. In case of the consideration of real gas behavior a compressibility factor needs to be known. Otherwise (perfect gas behavior) the specification of the isentropic coefficient κ, gas constant R and specific heat (at constant pressure) cp is sufficient.
Optionally you can select one of the predefined fluids to avoid manual input of the fluid parameters. The list of existing fluids can be modified in the fluid manager.
[ for pumps, ventilators, compressors only ]
On panel Inflow you may define the inflow swirl at hub and shroud. You have the following possibilities:
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Flow angle |
Swirl number |
Swirl energy number |
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Positive swirl Negative swirl No swirl |
αS < 90° αS > 90° αS = 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 - αS is only valid for certain diameters dN and dS.
[ for compressors only ]
On panel Inlet conditions you have to define the total state on suction side by total pressure pt and total temperature Tt.
[ for turbines only ]
In the panel In- and outlet conditions the static pressure at the suction flange (pressure in the connection flange of the work piece attached to the turbine at the outlet) as well as the total temperature at the inlet has to be specified. This design concept is based on a mean flow area, therefore a mean blade angle βB1 as well as a mean incidence angle i has to be given. In order to yield best efficiency the angle of incidence should be 20..30°.
Some calculated variables are displayed in the right Information sector:
Specific speed nq |
points to machine type and general shape of impeller:
10... 50: Radial impeller 50...170: Mixed-flow impeller 150...400: Axial impeller |
Specific speed nq (Asia) |
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Specific speed NS |
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„Type number“ ωs |
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Speed coefficient σ |
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Specific energy Y |
Pumps, Ventilators: Y = gH = Δpt/ρ Compressors: |
Power output PQ |
Pumps, Ventilators: PQ = ρgHQ |
Mass flow m |
Pumps, Ventilators: Compressors: |
Total pressure difference Δpt |
Pumps, Ventilators: Δpt = ρgH Compressors: |
Compressor:
Total pressure ratio |
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Inlet speed of sound (total) |
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Volume flow (total) |
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Inlet density (total) |
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Outlet density (total) |
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Outlet temperature (total) |
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Turbine:
Total pressure drop Δp |
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Specific work Y |
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Rotor power PQ, Power transported in a isentropic process |
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Total speed of sound at inlet at1 |
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Total temperature at outlet Tt2 |
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Relative flow angle at inlet β1 |
β1 = i + βB1 |
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 < 150 – radial and mixed-flow impellers.
Page url: http://www.cfturbo.com/fileadmin/content/manual/en/index.html?global_setup.html
