.AixLib.Fluid.Actuators.Valves.ExpansionValves.UsersGuide.Approaches

Information

Expansion valve models implemented in this library use a flow coefficient model by default to calculate the relationship between mass flow rate and pressure drop. In the following, all flow coefficient models implemented in this library are shortly summarised. Furthermore, all expansion valve models have a parameter to calculate transient behaviour of opening and closing the valves. This approach is also summarised in this information section.

Modeling approaches

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:

"Modelling approaches" border="1" cellspacing="0" cellpadding="2" style="border-collapse:collapse;">
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. Further information is given in the following sections:

  1. Polynomial approaches
  2. Power approaches

Naming and abbreviations

In the following, a guideline of naming flow coefficient models is summarised:

Approach of calculating flow coefficient _ Valid refrigerants _ Type of expansion valve _ Diameter of cross-sectional area of expansion valve

  1. Approach: Approach of calculating flow coefficient, e.g. polynomial or power.
  2. Refrigerant: Refrigerants the flow coefficent model is valid for, e.g. R134a or R410a.
  3. Type: Type of expansion valve, e.g. electric expansion valve (EEV).
  4. Diameter: Diameter of the cross-sectional area of expansion valves if it is fully opened, e.g. 1.6 mm.

Transient behaviour

All expansion valve models have 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:

  1. If 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.
  2. If 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%.

Contents

NameDescription
 PolynomialApproachPolynomial Aprroaches
 PowerApproachPower Aprroaches

Revisions

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