# Gate Valve (TL)

Flow control valve actuated by transverse motion of circular gate

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• Simscape / Fluids / Thermal Liquid / Valves & Orifices / Flow Control Valves

## Description

The Gate Valve (TL) block represents a flow control valve with a circular opening and a circular gate. The gate moves in a direction orthogonal to the fluid flow. The opening and gate are equal in diameter. The figure shows a schematic of the gate valve in three different positions—closed, partially open, and fully open.

Gate Valve in Different Positions

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.

### Valve Opening Area

The block computes the valve opening area directly from valve geometry parameters using the expression

`$A=\frac{\pi {d}_{0}^{2}}{4}-{A}_{Covered},$`

where:

• A is the valve opening area.

• d0 is the valve orifice diameter.

• ACovered is the portion of the valve orifice area covered by the gate:

`${A}_{Covered}=\frac{{d}_{0}^{2}}{2}\text{acos}\left(\frac{\Delta l}{{d}_{0}}\right)-\frac{\Delta l}{2}\sqrt{{d}_{0}^{2}-{\left(\Delta l\right)}^{2}}$`

• Δl is the net displacement of the gate center relative to the orifice center.

`$\Delta l=\left\{\begin{array}{ll}0,\hfill & \left({S}_{d}-{S}_{\mathrm{min}}\right)\le 0\hfill \\ {d}_{0},\hfill & \left({S}_{d}-{S}_{\mathrm{min}}\right)\ge {d}_{0}\hfill \\ \left({S}_{d}-{S}_{\mathrm{min}}\right),\hfill & \text{Else}\hfill \end{array},$`

• Smin is the Gate position when fully covering orifice parameter specified in the block dialog box.

• Sd is the gate displacement specified through physical signal input port S.

### Numerically-Smoothed Displacement

At the extremes of the gate displacement range, you can maintain numerical robustness in your simulation by adjusting the block . When the smoothing factor is nonzero, a smoothing function is applied to every calculated displacement, but primarily influences the simulation at the extremes of this range.

The normalized gate displacement is:

`$\Delta \stackrel{^}{l}=\frac{\Delta l}{\Delta {l}_{\mathrm{max}}},$`

where Δlmax is the Valve orifice diameter.

The Smoothing factor, s, is applied to the normalized displacement:

`$\Delta {\stackrel{^}{l}}_{smoothed}=\frac{1}{2}+\frac{1}{2}\sqrt{\Delta {\stackrel{^}{l}}_{}^{2}+{\left(\frac{s}{4}\right)}^{2}}-\frac{1}{2}\sqrt{{\left(\Delta \stackrel{^}{l}-1\right)}^{2}+{\left(\frac{s}{4}\right)}^{2}}.$`

The smoothed displacement is:

`$\Delta {l}_{smoothed}=\Delta {\stackrel{^}{l}}_{smoothed}\Delta {l}_{\mathrm{max}}.$`

### Mass Balance

The mass conservation equation in the valve is

`${\stackrel{˙}{m}}_{A}+{\stackrel{˙}{m}}_{B}=0,$`

where:

• ${\stackrel{˙}{m}}_{A}$ is the mass flow rate into the valve through port A.

• ${\stackrel{˙}{m}}_{B}$ is the mass flow rate into the valve through port B.

### Energy Balance

The energy conservation equation in the valve is

`${\varphi }_{A}+{\varphi }_{B}=0,$`

where:

• ϕA is the energy flow rate into the valve through port A.

• ϕB is the energy flow rate into the valve through port B.

### Momentum Balance

The momentum conservation equation in the valve is

`${p}_{A}-{p}_{B}=\frac{\stackrel{˙}{m}\sqrt{{\stackrel{˙}{m}}^{2}+{\stackrel{˙}{m}}_{cr}^{2}}}{2{\rho }_{Avg}{C}_{d}^{2}{S}^{2}}\left[1-{\left(\frac{{S}_{R}}{S}\right)}^{2}\right]P{R}_{Loss},$`

where:

• pA and pB are the pressures at port A and port B.

• $\stackrel{˙}{m}$ is the mass flow rate.

• ${\stackrel{˙}{m}}_{cr}$ is the critical mass flow rate:

`${\stackrel{˙}{m}}_{cr}={\mathrm{Re}}_{cr}{\mu }_{Avg}\sqrt{\frac{\pi }{4}{S}_{R}}.$`

• ρAvg is the average liquid density.

• Cd is the discharge coefficient.

• S is the valve inlet area.

• PRLoss is the pressure ratio:

`$P{R}_{Loss}=\frac{\sqrt{1-{\left({S}_{R}/S\right)}^{2}\left(1-{C}_{d}^{2}\right)}-{C}_{d}\left({S}_{R}/S\right)}{\sqrt{1-{\left({S}_{R}/S\right)}^{2}\left(1-{C}_{d}^{2}\right)}+{C}_{d}\left({S}_{R}/S\right)}.$`

## Ports

• A — Thermal liquid conserving port representing valve inlet A

• B — Thermal liquid conserving port representing valve inlet B

• S — Physical signal input port for the control member displacement

## Parameters

### Parameters Tab

Orifice diameter

Diameter of the valve flow area in the fully open position. The default value is `7e-3` m.

Gate position when fully covering orifice

Gate offset from the zero position. The instantaneous gate displacement is the sum of the gate offset and input signal S. The default value is `0` m.

Leakage area

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 `1e-12`.

Smoothing factor

Portion of the opening-area curve to smooth expressed as a fraction. Smoothing eliminates discontinuities at the minimum and maximum flow valve positions. The smoothing factor must be between `0` and `1`. Enter a value of `0` for zero smoothing. Enter a value of `1` for full-curve smoothing. The default value is `0.01`.

Cross-sectional area at ports A and B

Flow area at the valve inlets. The inlets are assumed equal in size. The default value is `0.01` m^2.

Discharge coefficient

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 value is `0.7`.

Critical Reynolds number

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 `12`.

### Variables Tab

Mass flow rate into port A

Mass flow rate into the component through port A at the start of simulation. The default value is ```1 kg/s```.

## Version History

Introduced in R2016a