.AixLib.Fluid.Movers.Compressors.BaseClasses.PartialCompression .AixLib.Fluid.Movers.Compressors.BaseClasses.PartialCompressionThis is a base model for compression processes that are used, for example, in rotary or scroll compressors.
Seven equations need to be added by an extending class using this component:
ṁ.
Pel.
pInl and
pOut.
hInl and
hOut.
port_b.h_outflow for flow in design direction.
port_a.h_outflow for flow in reverse direction.
Moreover, appropriate values shall be assigned to the following parameters:
dp_start for a guess of the pressure drop
m_flow_small for regularization of zero flow.
dp_nominal for nominal pressure drop.
m_flow_nominal for nominal mass flow rate.
Actually, three different efficiency models are suggested and the
modelling approaches of these efficiencies are shortly characterised
below:
| Efficiency | Formula | Comment |
|---|---|---|
| Engine |
ηeng = Q̇ref /
Pel
|
Used for calculation of compressor's power consumption |
| Isentropic |
ηise = (houtIse -
hinl) / (hout - hinl)
|
Used for calculation of thermodynamic change of state |
| Volumetric |
ηvol = V̇ide /
V̇rea
|
Used for calculation of mass flow rate |
These efficiency models are stored in AixLib.Fluid.Movers.Compressors.Utilities.EngineEfficiency, AixLib.Fluid.Movers.Compressors.Utilities.IsentropicEfficiency and AixLib.Fluid.Movers.Compressors.Utilities.VolumetricEfficiency. Therefore, the calculation procedure of the efficiencies are introduced as replaceable models and must be defined by the User.
The base model has a parameter useInpFil that is
used to model the compressors's transient behaviour while
changing rotational speed. Generally, this approach uses the same
modeling attempt as the stat-up and shut-down transients
introtuced for flow machines (see AixLib.Fluid.Movers.UsersGuide).
Therefore, just the parameter's affections are presented here:
useInpFil=false, then the input signal
opeSet.y is equal to the compressor's rotational speed.
Thus, a step change in the input signal causes a step change in
the rotational speed.
useInpFil=true, which is the default, then
the rotational speed is equal to the output of a filter. This
filter is implemented as a 2nd order differential equation. Thus,
a step change in the compressor's input signal will cause a
gradual change in the rotational speed. The filter has a
parameter risTim, which by default is set to
1 second. The rise time is the time required to reach
99.6% of the full rotational speed, or, if the compressor
is shut-down, to reach a rotational speed of 0.4%.
In the following, some general references are given for information about modelling compressors. The modelling approach presented here is alligned to the modelling approaches presented in the literature:
W. Eifler, E. Schlücker, U. Spicher and G. Will (2009): Küttner Kolbenmaschinen: Kolbenpumpen, Kolbenverdichter, Brennkraftmaschinen (in German). Publisher: Vieweg + Teubner
H. Qiao, R. Radermacher and V. Aute (2010): A review for numerical simulation of vapor compression systems. In: International Refrigeration and Air Conditioning Conference
P.C. Hanlon (2011): Compressor Handbook. Publisher: McGraw-Hill
V. A. Cara Martin and R. Radermacher (2015): AHRI Project 8013: A Study of Methods to Represent Compressor Performance Data over an Operating Envelope Based on a Finite Set of Test Data. Publisher: Air-Conditioning, Heating, and Refrigeration Institute (AHRI)
| Name | Description |
|---|---|
 EngineEfficiency | Model that describes the calculation of the overall mechanic efficiency |
 VolumetricEfficiency | Model that describes the calculation of the overall volumetric efficiency |
 IsentropicEfficiency | Model that describes the calculation of the overall isentropic efficiency |
 CompressorStates | Record that contains compressor's thermodynamic states at inlet and outlet |
 CompressorQualities | Record that contains compressor's qualities at inlet and outlet |