Pressure control valve for maintaining reduced pressure in fluid network portion
Thermal Liquid/Valves/Pressure Control Valves
The Pressure Reducing Valve (TL) block represents a valve for maintaining a reduced pressure in portion of a fluid network. The valve stays fully open when the pressure at port B is lower than the valve set pressure. At the set pressure, the valve control member moves to reduce the flow rate through the valve. The valve opening area continues to decrease with increasing pressure until only leakage flow remains.
A smoothing function allows the valve opening area to change smoothly between the fully closed and fully open positions. The smoothing function does this by removing the abrupt opening area changes at the zero and maximum ball positions. The figure shows the effect of smoothing on the valve opening area curve.
Opening-Area Curve Smoothing
The mass conservation equation in the valve is
is the mass flow rate into the valve through port A.
is the mass flow rate into the valve through port B.
The momentum conservation equation in the valve is
pA and pB are the pressures at port A and port B.
is the mass flow rate.
is the critical mass flow rate.
ρAvg is the average liquid density.
Cd is the discharge coefficient.
SR is the valve opening area.
S is the valve inlet area.
PRLoss is the pressure ratio:
The valve opening area is computed as
SLeak is the valve leakage area.
SLinear is the linear valve opening area:
SMax is the maximum valve opening area.
pcontrol is the valve control pressure:
pset is the valve set pressure:
pMin is the minimum pressure.
pMax is the maximum pressure:
Δp is the portion of the pressure range to smooth.
λL and λR are the cubic polynomial smoothing functions
The critical mass flow rate is
The energy conservation equation in the valve is
ϕA is the energy flow rate into the valve through port A.
ϕB is the energy flow rate into the valve through port B.
Minimum gauge pressure at port B required to actuate the valve. A
pressure rise above the set pressure causes the valve to gradually close
until only leakage flow remains. The default value is
Difference between the maximum and set pressures at port B. The valve
begins to close at the set pressure. It is fully closed at the maximum
pressure. The default value is
Flow cross-sectional area in the fully open state. This state
corresponds to pressures lower than the set pressure. The default value
Aggregate area of all fluid leaks in the valve. The leakage
area helps to prevent numerical issues due to isolated fluid network
sections. For numerical robustness, set this parameter to a nonzero
value. The default value is
Fraction of the opening-area curve, expressed as a fraction from 0 to
1, to smooth. The block replaces the discontinuities in the opening area
curve with smooth transitions that span the specified fraction of the
curve. The default value is
A smoothing factor of 0 corresponds to a linear function that is discontinuous at the set and maximum-area pressures. A smoothing factor of 1 corresponds to a nonlinear function that changes continuously throughout the entire function domain.
A smoothing factor between 0 and 1 corresponds to a continuous piece-wise function with smooth nonlinear transitions at the set and maximum-area pressures and linear segments elsewhere.
Opening-Area Curve Smoothing
Flow area at the valve inlets. The inlets are assumed equal in size.
The default value is
Approximate length of the valve. This parameter provides a measure
of the longitudinal scale of the valve. The default value is
Semi-empirical parameter commonly used as a measure of valve performance. The discharge coefficient is defined as the ratio of the actual mass flow rate through the valve to its theoretical value.
The block uses this parameter to account for the effects of
valve geometry on mass flow rates. Textbooks and valve data sheets
are common sources of discharge coefficient values. By definition,
all values must be greater than 0 and smaller than 1. The default
Reynolds number corresponding to the transition between laminar
and turbulent flow regimes. The flow through the valve is assumed
laminar below this value and turbulent above it. The appropriate values
to use depend on the specific valve geometry. The default value is
Mass flow rate into the component through port A
at the start of simulation. The default value is
A — Thermal liquid conserving port representing valve inlet A
B — Thermal liquid conserving port representing valve inlet B