On page Parameters you have to put in or to modify parameters resulting from approximation functions in dependence on specific speed nq or flow rate Q (see Approximation functions).

For this purpose some specific edit fields are used.

 

 

 

The panel Parameters allows defining alternative values in each case for the calculation of the following impeller main dimensions:

 

For d2-calculation

 

For b2-calculation

 

For d1-calculation (optional)

 

For b1-calculation (optional)

 

for dS-calculation

 

The relative inlet Mach number can be implemented in a certain range only. The lower limit is a certain suction diameter. If this limiting suction diameter is increased the peripheral speed uS is also increased as well as the suction temperature TS. This yield a raised relative inlet Mach number, because the relative velocity wS will rise faster than TS. If the limiting suction diameter is decreased the meridional velocity cm will raise whereas TS will fall. This also yields a raised relative inlet Mach number. Above this limit two suction diameters are possible. Both correspondent to the same relative inlet Mach number.

In this context it's important to know that the fluid density is dependent on the velocity and therefore on the geometrical dimensions.

 

 

In panel Efficiency you have to specify several efficiencies. You have to distinguish between design relevant efficiencies and efficiencies used for information only:

Design relevant

Information only

 

The casing efficiency ηc (see Global setup) is used additionally for impeller dimensioning in order to compensate the flow losses in the casing.

 

The losses resulting in energy dissipation from the fluid form the impeller efficiency.

 

Impeller, casing and mechanical efficiency form the overall efficiency (coupling efficiency) of the stage ηSt.

When considering motor losses additionally the overall efficiency of the stage incl. motor ηSt* is defined.

 

The following summary illustrates the single efficiencies and their classification:

 

 

The obtainable overall efficiency correlates to specific speed and to the size and the type of the impeller as well as to special design features like bypass installations and auxiliary aggregates. Efficiencies calculated by approximation functions are representing the theoretical reachable values and they should be corrected by the user if more information about the impeller or the whole machine are available.

 

The impeller efficiency ηtt describes the energy losses caused by friction and vorticity. Friction losses mainly originate from shear stresses in boundary layers. Vorticity losses are caused by turbulence and on the other hand by changes of flow cross section and flow direction which may lead to secondary flow, flow separation, wake behind blades etc.. The impeller efficiency is the ratio between the actual specific energy Y and the energy transmitted by the impeller blades without any losses:

 

The volumetric efficiency is a quantity for the deviation of effective flow rate Q from total flow rate inside the impeller which also includes the circulating flow within the casing:

(rising with impeller size)

 

The mechanical efficiency mainly includes the friction losses in bearings and seals:

(rising with impeller size)

 

Impeller efficiency and volumetric efficiency are most important for the impeller dimensioning because of their influence to and/or . The mechanical efficiency is affecting only the required driving power of the machine.

 

 

In the right panel of the tab sheet Parameter you can find again some calculated values for information:

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