.AixLib.Fluid.Actuators.Valves.ExpansionValves.BaseClasses.PartialExpansionValve .AixLib.Fluid.Actuators.Valves.ExpansionValves.BaseClasses.PartialExpansionValveThis is a base model for simple expansion valves that are used, for example, in close-loop systems like heat pumps or chillers.
Three equations need to be added by an extending class using this component:
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 modelling approaches are suggested and
saved as enumeration in
AixLib.Fluid.Actuators.Valves.ExpansionValves.Utilities.Choices.CalcProc.
In the following, these modeling approaches are characterised
shortly:
| Approach | Formula | Comment |
|---|---|---|
| Linear |
ṁ = C Avalve dp
|
Used for testing or initialisation |
| Nominal |
ṁ = ṁnominal / dpnominal
Avalve dp
|
Used mainly for initialisation |
| Flow coefficient |
ṁ = C Avalve sqrt(2 ρinlet
dp)
|
Chosen by default and follows from Bernoulli's law |
For the third approach (i.e. flow coefficient), different calculation models are stored in AixLib.Fluid.Actuators.Valves.ExpansionValves.Utilities.Choices.FlowCoefficient. Therefore, the calculation procedure of the flow coefficient C is introduced as replaceable model and must by defined by the User.
The base model has a parameter useInpFil that is
used to model the valve's transient behaviour while opening or
closing. 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 valve's opening degree. Thus, a
step change in the input signal causes a step change in the
opening degree.
useInpFil=true, which is the default, then
the opening degree is equal to the output of a filter. This
filter is implemented as a 2nd order differential equation. Thus,
a step change in the fan input signal will cause a gradual change
in the opening degree. 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 opening degree, or,if the ventil is closed, to reach a
opening degree of 0.4%.
In the following, some general references are given for information about modelling expansion valves. The modelling approach presented here is alligned to the modelling approaches presented in the literature:
Li, W. (2013): Simplified modeling analysis ofmass flow characteristics in electronic expansion valve. In: Applied Thermal Engineering 53(1), S. 8–12
X. Cao, Z.-Y. Li, L.-L. Shao and C.-L. Zhang (2016): Refrigerant flow through electronic expansion valve: Experiment and neural network modeling. In: Applied Thermal Engineering 92, S. 210–218
| Name | Description |
|---|---|
 FlowCoefficient | Model that describes the calculation of the flow coefficient |