Component 24: Compressor

In This Topic

Component 24: Compressor / Fan

Specifications

Line connections
1	Inlet
2	Outlet
3	Shaft
4	Control inlet for efficiency (as H)

General User Input Values Characteristic Lines Physics Used Displays Example

General

The pressure at the outlet of the compressor must be specified e.g. with the component 33 (start value).

For Component 24 (Compressor/fan) there is no pressure calculation; here FCHR has been replaced by FSPECH.

Implementing a load-independent mechanical loss (QLOSSM) (see Release 12)

If both a mechanical efficiency ETAMN and a constant loss QLOSSM are specified, the two are combined as follows:

The sequence in which the proportional and the constant fraction are considered depends on the direction of the flow of energy.

Q_gross =( Q_net + QLOSSM) / ETAMN

The result value QLOSS comprises the entire (load-independent and load-dependent) loss

QLOSS = Q_gross – Q_net

The result value ETAM contains both fractions (as in the case of component 6), as ETAM is defined by

ETAM = Q_net / Q_gross

If a QLOSSM > 0 is specified, ETAM thus no longer equals ETAMN but is accordingly smaller (by QLOSSM/heat supply).

Logic inlet (Connection point 4) for controlling component properties

(see also : Editing components --> Ports)

To make component properties like efficiencies or heat transfer coefficients (variation quantity) accessible from the outside (for control or reconciliation) it is possible to place the respective value on an auxiliary line as an indexed measured value (specification value FIND). In the component, the same index must then be entered as specification value IPS.

It is also possible to place this value on a logic line that is directly connected to the component (please see FVALETAI=2, Variation variable ETAIN, Dimension: Enthalpy).
The advantage is that the allocation is now graphically visible, and errors (e.g. when copying) are thus avoided.

The activation of this logic line can also be made conditional on the mode of calculation. This way, this feature can also be used for designs without having to switch manually all the time.
For this, the flag FVALETAI features the settings

FVALETAI=4: use logic line in design mode, use specification value in off-design
FVALETAI=5: use specification value in design mode, use logic line in off-design

This option is available for Components 2, 6, 8, 13, 18, 19, 23, 24, and 94.

Polytropic Efficiency

As an alternative to the isentropic efficiency, the polytropic efficiency can now be output too in the case of the compressor. This is done in the specification value ETAPN. The flag FETA serves to select whether the isentropic or the polytropic efficiency is to be used.

When using the polytropic efficiency, the isentropic efficiency is calculated as well as the result value ETAI and transferred to the specification value ETAIN. This makes it easier to switch over to the isotropic efficiency, saving computing time as the polytropic efficiency requires a complex numerical integration. This makes itself felt in the case of complex physical properties in particular.

In the reverse case, ETAP is usually not calculated; however, there is a flag FOUTETAP by means of which this calculation can be activated. In this case, the calculated value of ETAP is also transferred to the specification value ETAPN.

Result Value MCORR

There is now a result value MCORR that specifies which mass flow would flow through the compressor under standard conditions. The calculation is carried out according to https://en.wikipedia.org/wiki/Corrected_flow:

MCORR = M1 * SQRT(T1[K]/TNORM) / (P1/PNORM)

with TNORM = 288.15 K and PNORM = 1.01325 bar.

User Input Values

FSPECH	Flag for specification of enthalpies and power: Like in Parent Profile (Sub Profile option only) Expression =0: Efficiency Characteristic used =11: Efficiency Characteristic used (validable) =-1: Power Specification =-11: Power Specification (validable) =-2: H2 Specification
FVALETAI	Validation of the isentropic efficiency Like in Parent Profile (Sub Profile option only) Expression =0: ETAIN used without validation =1: (Deprecated) IPS used instead of ETAIN (validable) =2: ETAIN given by enthalpy on control inlet 4 =4: Enthalpy on control inlet 4 used in design, specification value ETAIN in off-design =5: Specification value ETAIN used in design, enthalpy on control inlet 4 in off-design
ETAIN	Isentropic efficiency (nominal)
ETAPN	Polytropic efficiency (nominal)
IPS	Index on pseudo measurement point
ETAMN	Mechanical efficiency (nominal)
QLOSSM	Mechanical loss (constant fraction)
FCHR	Char Line type (deprecated) Like in Parent Profile (Sub Profile option only) Expression =-999: unused =0: ETAI/ETAIN=f(M1/M1N) =-1: Power specification =-2: H2 given
FMODE	Flag for calculation mode Expression =0: GLOBAL =1: Local off-design = -1: Local design
FADAPT	Flag for adaptation polynomial / adaptation function Like in Parent Profile (Sub Profile option only) Expression =0: Not used and not evaluated =1: correction [ETAI = ETAIN * Char Line * polynomial] =2: Replace [ETA I = ETAIN * polynomial] =1000: Not used but ADAPT evaluated as RADAPT (Reduction of the computing time) = -1: correction [ETAI = ETAIN * Char Line * adaptation function] = -2: Replace [ETA I = ETAIN * adaptation function] = -1000: Not used but EADAPT evaluated as RADAPT (Reduction of the computing time)
EADAPT	Adaptation function
M1N	Mass flow (nominal)

The parameters marked in blue are reference quantities for the off-design mode. The actual off-design values refer to these quantities in the equations used.

Generally, all inputs that are visible are required. But, often default values are provided.

For more information on colour of the input fields and their descriptions see Edit Component\Specification values

For more information on design vs. off-design and nominal values see General\Accept Nominal values

Results

ETAI	Isentropic efficiency
ETAP	polytropic efficiency
ETAM	Mechanical efficiency (including QLOSSM)
RHO1	Specific weight of flue gas at inlet
VM1	Volume flow at air intake
ETANIR	Used value for nominal isentropic efficiency
ETACL	Efficiency due to characteristic
RADAPT	Result of ADAPT / EDAPT
DP	Pressure difference
ETAINR	Used value for nominal isentropic efficiency
MCORR	Corrected mass flow
M1M1N	Relative cold side mass flow
ETAETAN	Relative efficiency

Characteristic Lines

Characteristic line 1: Isentropic efficiency ETAI/ETAIN = f (M1/M1N)

     X-axis          1         M1/M1N                      1^st point
                        2          M1/M1N                     2^nd point
                        .
                      N         M1/M1N                      last point

     Y-axis        1          ETAI/ETAIN                  1^st point
                        2          ETAI/ETAIN                  2^nd point
                        .
                        N         ETAI/ETAIN                   last Point

Physics Used

Equations

All cases

P2 from the line 2

M2 = M1

if the medium in the pipe is water/steam, then {

S1 = f(P1,H1)

H2S = f(P2,S1) }

else {

S1 = f(P1,T1)

T2S = f(P2,S1)

H2S = f(P2,T2S) }

DHS = H2S - H1

DH = DHS/ETAI

H2 = H1 + DH

T2 = f(P2, H2)

Q2 = M2 * H2

H3 = (M2*H2-M1*H1)/(ETAM*M3)

V1 = f(P1,T1)

VM1 = M1*V1 volume flow at inlet

Component Displays

Display Option 1

Example

Click here >> Component 24 Demo << to load an example.

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