Pipe (IL)

Pipe segment in an isothermal liquid network

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Description

The Pipe (IL) block models flow in a rigid or flexible-walled pipe with losses due to wall friction. The effects of dynamic compressibility, fluid inertia, and pipe elevation can be optionally modeled. You can define multiple pipe segments and set the liquid pressure for each segment. By segmenting the pipe and setting Fluid inertia to On, you can model events such as water hammer in your system.

Pipe Characteristics

The pipe block can be divided into segments with the Number of segments parameter. When the pipe is composed of a number of segments, the pressure in each segment is calculated based on the inlet pressure and the effect on the segment mass flow rate of the fluid compressibility and wall flexibility, if applicable. The fluid volume in each segment remains fixed. For a two-segment pipe, the pressure evolves linearly with respect to the pressure defined at ports A and B. For a pipe with three or more segments, you can specify the fluid pressure in each segment in vector or scalar form in the Initial liquid pressure parameter. The scalar form will apply a constant value over all segments.

Flexible Walls

You can model flexible walls for all cross-sectional geometries. When you set Pipe wall specification to Flexible, the block assumes uniform expansion along all directions and preserves the defined cross-sectional shape. This may not result in physical results for noncircular cross-sectional areas undergoing high pressure relative to atmospheric pressure. Two options are available for modeling the volumetric expansion of a cross-sectional area:

1. Cross-sectional area vs. pressure, where the change in volume is modeled by:

   $$\dot{V}=L\left(\frac{S_N+K_{ps}\left(p-p_{atm}\right)-S}{\tau }\right),$$

   where:

   • L is the Pipe length.

   • S_N is the nominal pipe cross-sectional area defined for each shape.

   • S is the current pipe cross-sectional area.

   • p is the internal pipe pressure.

   • p_atm is the atmospheric pressure.

   • K_ps is the Static pressure-cross sectional area gain.

     Assuming uniform elastic deformation of a thin-walled, open-ended cylindrical pipe, you can calculate K_ps as:

     $$K_{ps}=\frac{\Delta D}{\Delta p}=\frac{\pi D_N^3}{4tE},$$

     where t is the pipe wall thickness and E is Young's modulus.

   • τ is the Volumetric expansion time constant.

2. Hydraulic diameter vs. pressure, where the change in volume is modeled by:

   $$\dot{V}=\frac{\pi }{2}DL\left(\frac{D_N+K_{pd}\left(p-p_{atm}\right)-D}{\tau }\right),$$

where:

• D_N is the nominal hydraulic diameter defined for each shape.

• D is the current pipe hydraulic diameter.

• K_pd is the Static pressure-hydraulic diameter gain. Assuming uniform elastic deformation of a thin-walled, open-ended cylindrical pipe, you can calculate K_pd as:

  $$K_{pd}=\frac{\Delta D}{\Delta p}=\frac{D_N^2}{2tE}.$$

When flexible walls are not modeled, S_N = S and D_N = D.

Circular

The nominal hydraulic diameter and the Pipe diameter, d_circle, are the same. The pipe cross sectional area is: $$S_N=\frac{\pi }{4}{d}_{circle}^2.$$

Annular

The nominal hydraulic diameter, D_h,nom, is the difference between the Pipe outer diameter and Pipe inner diameter, d_o – d_i. The pipe cross sectional area is $$S_N=\frac{\pi }{4}\left(d_{{}_o}^2-d_{{}_i}^2\right).$$

Rectangular

The nominal hydraulic diameter is:

$$D_N=\frac{2hw}{h+w},$$

where:

• h is the Pipe height.

• w is the Pipe width.

The pipe cross sectional area is $$S_N=wh.$$

Elliptical

The nominal hydraulic diameter is:

$$D_N=2a_{maj}{b}_{\min }\frac{\left(64-16{\left(\frac{a_{maj}-b_{\min }}{a_{maj}+b_{\min }}\right)}^2\right)}{\left(a_{maj}+b_{\min }\right)\left(64-3{\left(\frac{a_{maj}-b_{\min }}{a_{maj}+b_{\min }}\right)}^4\right)},$$

where:

• a_maj is the Pipe major axis.

• b_min is the Pipe minor axis.

The pipe cross sectional area is $$S_N=\frac{\pi }{4}{a}_{maj}{b}_{\min }.$$

Isosceles Triangular

The nominal hydraulic diameter is:

$$D_N=l_{side}\frac{\sin \left(\theta \right)}{1+\sin \left(\frac{\theta }{2}\right)}$$

where:

• l_side is the Pipe side length.

• θ is the Pipe vertex angle.

The pipe cross sectional area is $$S_N=\frac{l_{side}^2}{2}\sin \left(\theta \right).$$

Pressure Loss Due to Friction

Haaland Correlation

The analytical Haaland correlation models losses due to wall friction either by aggregate equivalent length, which accounts for resistances due to nonuniformities as an added straight-pipe length that results in equivalent losses, or by local loss coefficient, which directly applies a loss coefficient for pipe nonuniformities.

When the Local resistances specification parameter is set to Aggregate equivalent length and the flow in the pipe is lower than the Laminar flow upper Reynolds number limit, the pressure loss over all pipe segments is:

$$\Delta p_{f,A}=\frac{\upsilon \lambda }{2D^{2}S}\frac{L+L_{add}}{2}{\dot{m}}_A,$$

$$\Delta p_{f,B}=\frac{\upsilon \lambda }{2D^{2}S}\frac{L+L_{add}}{2}{\dot{m}}_B,$$

where:

• ν is the fluid kinematic viscosity.

• λ is the Laminar friction constant for Darcy friction factor, which you can define when Cross-sectional geometry is set to Custom and is otherwise equal to 64.

• D is the pipe hydraulic diameter.

• L_add is the Aggregate equivalent length of local resistances.

• $$\dot{m}$$_A is the mass flow rate at port A.

• $$\dot{m}$$_B is the mass flow rate at port B.

When the Reynolds number is greater than the Turbulent flow lower Reynolds number limit, the pressure loss in the pipe is:

$$\Delta p_{f,A}=\frac{f}{2{\rho }_I{S}^2}\frac{L+L_{add}}{2}{\dot{m}}_A\left|{\dot{m}}_A\right|,$$

$$\Delta p_{f,B}=\frac{f}{2{\rho }_I{S}^2}\frac{L+L_{add}}{2}{\dot{m}}_B\left|{\dot{m}}_B\right|,$$

where:

• f is the Darcy friction factor. This is approximated by the empirical Haaland equation and is based on the Surface roughness specification, ε, and pipe hydraulic diameter:

  $$f={\left\{-1.8{\log }_{10}\left[\frac{6.9}{\mathrm{Re}}+{\left(\frac{\epsilon }{3.7D_h}\right)}^{1.11}\right]\right\}}^{-2},$$

  Pipe roughness for brass, lead, copper, plastic, steel, wrought iron, and galvanized steel or iron are provided as ASHRAE standard values. You can also supply your own Internal surface absolute roughness with the Custom setting.

• ρ_I is the internal fluid density.

When the Local resistances specification parameter is set to Local loss coefficient and the flow in the pipe is lower than the Laminar flow upper Reynolds number limit, the pressure loss over all pipe segments is:

$$\Delta p_{f,A}=\frac{\upsilon \lambda }{2D^{2}S}\frac{L}{2}{\dot{m}}_A.$$

$$\Delta p_{f,B}=\frac{\upsilon \lambda }{2D^{2}S}\frac{L}{2}{\dot{m}}_B.$$

When the Reynolds number is greater than the Turbulent flow lower Reynolds number limit, the pressure loss in the pipe is:

$$\Delta p_{f,A}=\left(\frac{f\frac{L}{2}}{D}+C_{loss,total}\right)\frac{1}{2{\rho }_I{S}^2}{\dot{m}}_A\left|{\dot{m}}_A\right|,$$

$$\Delta p_{f,B}=\left(\frac{f\frac{L}{2}}{D}+C_{loss,total}\right)\frac{1}{2{\rho }_I{S}^2}{\dot{m}}_B\left|{\dot{m}}_B\right|,$$

where C_loss,total is the loss coefficient, which can be defined in the Total local loss coefficient parameter as either a single coefficient or the sum of all loss coefficients along the pipe.

Nominal Pressure Drop vs. Nominal Mass Flow Rate

The Nominal Pressure Drop vs. Nominal Mass Flow Rate parameterization characterizes losses with a loss coefficient for rigid or flexible walls. When the fluid is incompressible, the pressure loss over the entire pipe due to wall friction is:

$$\Delta p_{f,A}=K_p{\dot{m}}_A\sqrt{{\dot{m}}_A^2+{\dot{m}}_{th}^2},$$

where K_p is:

$$K_p=\frac{\Delta p_N}{{\dot{m}}_N^2},$$

where:

• Δp_N is the Nominal pressure drop, which can be defined either as a scalar or a vector.

• $${\dot{m}}_N$$ is the Nominal mass flow rate, which can be defined either as a scalar or a vector.

When the Nominal pressure drop and Nominal mass flow rate parameters are supplied as vectors, the scalar value K_p is determined from a least-squares fit of the vector elements.

Tabulated Data – Darcy Friction Factor vs. Reynolds Number

Pressure losses due to viscous friction can also be determined from user-provided tabulated data of the Darcy friction factor vector and the Reynolds number vector for turbulent Darcy friction factor parameters. Linear interpolation is employed between data points.

Momentum Balance

For an incompressible fluid, the mass flow into the pipe equals the mass flow out of the pipe:

$${\dot{m}}_A+{\dot{m}}_B=0.$$

When the fluid is compressible and pipe walls are rigid, the difference between the mass flow into and out of the pipe depends on the fluid density change due to compressibility:

$${\dot{m}}_A+{\dot{m}}_B={\dot{p}}_I\frac{d{\rho }_I}{d{p}_I}V,$$

When the fluid is compressible and the pipe walls are flexible, the difference between the mass flow into and out of the pipe is based on the change in fluid density due to compressibility, and the amount of fluid accumulated in the newly deformed regions of the pipe:

$${\dot{m}}_A+{\dot{m}}_B={\dot{p}}_I\frac{d{\rho }_I}{d{p}_I}V+{\rho }_I\dot{V}.$$

The changes in momentum between the pipe inlet and outlet comprises the changes in pressure due to pipe wall friction, which is modeled according to the Viscous friction parameterization and pipe elevation. For a pipe that does not model fluid inertia, the momentum balance is:

$$p_A-p_I=\Delta p_{f,A}+{\rho }_I\frac{\Delta z}{2}g,$$

$$p_B-p_I=\Delta p_{f,B}-{\rho }_I\frac{\Delta z}{2}g,$$

where:

• p_A is the pressure at port A.

• p_I is the fluid volume internal pressure.

• p_B is the pressure at port B.

• Δp_f is the pressure loss due to wall friction, parameterized by the Viscous friction losses specification according to the respective port.

• Δz is the pipe elevation. In the case of constant-elevation pipes, this is the Elevation gain from port A to port B parameter; otherwise, it is received as a physical signal at port EL.

• g is the gravitational acceleration. In the case of a fixed gravitational constant, this is the Gravitational acceleration parameter; otherwise, it is received as a physical signal at port G.

For a pipe with modeled fluid inertia, the momentum balance is:

$$p_A-p_I=\Delta p_{f,A}+{\rho }_I\frac{\Delta z}{2}g+{\ddot{m}}_A\frac{L}{2S},$$

$$p_B-p_I=\Delta p_{f,B}-{\rho }_I\frac{\Delta z}{2}g+{\ddot{m}}_B\frac{L}{2S},$$

where:

• $$\ddot{m}$$ is the fluid acceleration at its respective port.

• S is the pipe cross-sectional area.

Ports

Conserving

A — Liquid port

isothermal liquid

Liquid entry or exit port.

B — Liquid port

isothermal liquid

Liquid entry or exit port.

Inputs

EL — Elevation

physical signal

Variable elevation from port A to port B, specified as a physical signal. The elevation magnitude must be less than or equal to the pipe length. If the signal falls below the value of –Pipe length, the value at EL is maintained at –pipe length. If the signal exceeds the value of Pipe length, the value at EL is maintained at pipe length.

Dependencies

To enable this port, set Elevation gain specification to Variable.

G — Gravitational acceleration

physical signal

Variable gravitational acceleration, specified as a physical signal.

Dependencies

To enable this port, set Gravitational acceleration specification to Variable.

Parameters

Configuration

Pipe length — Pipe length

5 m (default) | positive scalar

Total pipe length across all pipe segments.

Number of segments — Number of pipe divisions

1 (default) | positive integer

Number of pipe divisions. Each division represents an individual segment for which pressure is calculated, depending on the pipe inlet pressure, fluid compressibility, and wall flexibility, if applicable. The fluid volume in each segment remains fixed.

Cross-sectional geometry — Pipe geometry

Circular (default) | Annular | Rectangular | Elliptical | Iscosceles triangular | Custom

Cross-sectional pipe geometry. A nominal hydraulic diameter and nominal cross-sectional area is calculated based on the cross-sectional geometry.

Pipe diameter — Pipe diameter

0.1 m (default) | positive scalar

Diameter for circular cross-sectional pipes.

Dependencies

To enable this parameter, set Cross-sectional geometry to Circular.

Pipe inner diameter — Pipe inner diameter

0.05 m (default) | positive scalar

Inner diameter for annular pipe flow, or flow between two concentric pipes.

Dependencies

To enable this parameter, set Cross-sectional geometry to Annular.

Pipe outer diameter — Pipe outer diameter

0.1 m (default) | positive scalar

Outer diameter for annular pipe flow, or flow between two concentric pipes.

Dependencies

To enable this parameter, set Cross-sectional geometry to Annular.

Pipe width — Rectangular pipe width

0.1 m (default) | positive scalar

Width of rectangular pipe.

Dependencies

To enable this parameter, set Cross-sectional geometry to Rectangular.

Pipe height — Rectangular pipe height

0.1 m (default) | positive scalar

Height of rectangular pipe.

Dependencies

To enable this parameter, set Cross-sectional geometry to Rectangular.

Pipe major axis — Ellipsoidal pipe major axis

0.1 m (default) | positive scalar

Major axis for ellipsoidal pipes.

Dependencies

To enable this parameter, set Cross-sectional geometry to Elliptical.

Pipe minor axis — Ellipsoidal pipe minor axis

0.05 m (default) | positive scalar

Minor axis for ellipsoidal pipes.

Dependencies

To enable this parameter, set Cross-sectional geometry to Elliptical.

Pipe side length — Triangular pipe side length

0.1 m (default) | positive scalar

Length of the two equal sides of isosceles-triangular pipes.

Dependencies

To enable this parameter, set Cross-sectional geometry to Isosceles triangular.

Pipe vertex angle — Triangular pipe vertex angle

30 deg (default) | positive scalar

Vertex angle for triangular pipes. The value must be less than 180 degrees.

Dependencies

To enable this parameter, set Cross-sectional geometry to Isosceles triangular.

Hydraulic diameter — Hydraulic diameter

0.1128 m (default) | positive scalar

Hydraulic diameter used in calculations of the pipe Reynolds number. For noncircular pipes, the hydraulic diameter is the effective diameter of the fluid in the pipe. For circular pipes, the hydraulic diameter and pipe diameter are the same.

Dependencies

To enable this parameter, set Cross-sectional geometry to Custom.

Cross-sectional area — Pipe cross-sectional area

0.01 m^2 (default) | positive scalar

Pipe cross-sectional area for a custom pipe geometry.

Dependencies

To enable this parameter, set Cross-sectional geometry to Custom.

Fluid dynamic compressibility — Whether to model fluid compressibility

On (default) | Off

Whether to model any change in fluid density due to fluid compressibility. When Fluid compressibility is set to On, changes due to the mass flow rate into the block are calculated in addition to density changes due to changes in pressure. In the Isothermal Liquid Library, all blocks calculate density as a function of pressure.

Fluid inertia — Fluid acceleration

Off (default) | On

Whether to account for resistance to changes in the flow rate due to the fluid mass.

Dependencies

To enable this parameter, set Fluid dynamic compressibility to On.

Elevation gain specification — Pipe elevation specification

Constant (default) | Variable

Whether the pipe elevation remains constant or variable from port A to B.

Elevation gain from port A to port B — Constant pipe elevation differential

0 m (default) | scalar

Elevation differential for constant-elevation pipes. The elevation gain must be less than or equal to the Pipe length.

Dependencies

To enable this parameter, set Elevation gain specification to Constant.

Gravitational acceleration specification — Acceleration specification

Constant (default) | Variable

Whether the gravitational constant is constant or variable.

Gravitational acceleration — Gravitational acceleration

9.81 m/s^2 (default) | positive scalar

Gravitational acceleration for environments with constant gravitational acceleration.

Dependencies

To enable this parameter, set Gravitational acceleration specification to Constant.

Viscous Friction

Viscous friction parameterization — Method of calculating pressure loss due to wall friction

Haaland correlation (default) | Nominal pressure drop vs. nominal mass flow rate | Tabulated data - Darcy friction factor vs. Reynolds number

Parameterization of pressure losses due to wall friction. Both analytical and tabular formulations are available.

Local resistances specification — Method for quantifying pressure losses in the Haaland correlation

Aggregate equivalent length (default) | Local loss coefficient

Method for quantifying pressure losses due to pipe nonuniformities.

Dependencies

To enable this parameter, set Viscous friction parameterization to Haaland correlation.

Total local loss coefficient — Defines loss coefficient over the pipe

0.1 (default) | positive scalar

Loss coefficient associated with each pipe nonuniformity. You can input a single loss coefficient or the sum of all loss coefficients along the pipe.

Dependencies

To enable this parameter, set Viscous friction parameterization to Haaland correlation and Local resistance specifications to Local loss coefficient.

Aggregate equivalent length of local resistances — Contribution of pipe geometry to hydraulic losses

1 m (default) | positive scalar

Length of pipe that would produce the equivalent hydraulic losses as would a pipe with bends, area changes, or other nonuniform attributes. The effective length of the pipe is the sum of the Pipe length and the Aggregate equivalent length of local resistances.

Dependencies

To enable this parameter, set Viscous friction parameterization to Haaland correlation and Local resistance specifications to Aggregate equivalent length.

Surface roughness specification — Pipe material for roughness specification

Commercially smooth brass, lead, copper, or plastic pipe: 1.52 um (default) | Steel and wrought iron : 46 um | Galvanized iron or steel : 152 um | Cast iron : 259 um | Custom

Absolute surface roughness based on pipe material. The provided values are ASHRAE standard roughness values. You can also input your own value by setting Surface roughness specification to Custom.

Dependencies

To enable this parameter, set Viscous friction parameterization to Haaland correlation.

Internal surface absolute roughness — Pipe wall roughness

15e-6 m (default) | positive scalar

Pipe wall absolute roughness. This parameter is used to determine the Darcy friction factor, which contributes to pressure loss in the pipe.

Dependencies

To enable this parameter, set Viscous friction parameterization to Haaland correlation and Surface roughness specification to Custom.

Laminar flow upper Reynolds number limit — Laminar flow upper threshold

2000 (default) | positive scalar

Upper Reynolds number limit to laminar flow. Beyond this number, the fluid regime is transitional, approaches the turbulent regime, and becomes fully turbulent at the Turbulent flow lower Reynolds number limit.

Dependencies

To enable this parameter, set Viscous friction parameterization to either:

• Haaland correlation

• Tabulated data - Darcy friction factor vs. Reynolds number

Turbulent flow lower Reynolds number limit — Turbulent flow lower threshold

4000 (default) | positive scalar

Lower Reynolds number limit for turbulent flow. Below this number, the flow regime is transitional, approaches laminar flow, and becomes fully laminar at the Laminar flow upper Reynolds number limit.

Dependencies

To enable this parameter, set Viscous friction parameterization to either:

• Haaland correlation

• Tabulated data - Darcy friction factor vs. Reynolds number

Nominal mass flow rate — Mass flow rate for calculating loss coefficient

[.1, 1] kg/s (default) | positive scalar | 1-by-n vector

Nominal mass flow rate used for calculating the pressure loss coefficient for rigid and flexible pipes, specified as a scalar or a vector. All nominal values must be greater than 0 and have the same number of elements as the Nominal pressure drop parameter. When this parameter is supplied as a vector, the scalar value K_loss is determined as a least-squares fit of the vector elements.

Dependencies

To enable this parameter, set Viscous friction parameterization to Nominal pressure drop vs. nominal mass flow rate.

Nominal pressure drop — Pressure drop for calculating loss coefficient

[.001, .01] MPa (default) | positive scalar | 1-by-n vector

Nominal pressure drop used for calculating the pressure loss coefficient for rigid and flexible pipes, specified as a scalar or vector. All nominal values must be greater than 0 and must have the same number of elements as the Nominal mass flow rate parameter. When this parameter is supplied as a vector, the scalar value K_loss is determined as a least-squares fit of the vector elements.

Dependencies

To enable this parameter, set Viscous friction parameterization to Nominal pressure drop vs. nominal mass flow rate.

Mass flow rate threshold for flow reversal — Mass flow rate threshold

1e-6 kg/s (default) | positive scalar

Mass flow rate threshold for reversed flow. A transition region is defined around 0 kg/s between the positive and negative values of the mass flow rate threshold. Within this transition region, numerical smoothing is applied to the flow response. The threshold value must be greater than 0.

Dependencies

To enable this parameter, set Viscous friction parameterization to Nominal pressure drop vs. nominal mass flow rate.

Reynolds number vector for turbulent Darcy friction factor — Vector of Reynolds numbers for tabular parameterization

[400, 1000, 1500, 3000, 4000, 6000, 10000, 20000, 40000, 60000, 100000, 100000000] (default) | 1-by-n vector

Vector of Reynolds numbers for the tabular parameterization of the Darcy friction factor. The vector elements form an independent axis with the Darcy friction factor vector parameter. The vector elements must be listed in ascending order. A positive Reynolds number corresponds to flow from port A to port B.

Dependencies

To enable this parameter, set Viscous friction parameterization to Tabulated data - Darcy friction factor vs. Reynolds number.

Darcy friction factor vector — Vector of friction factors for tabular parameterization

[.264, .112, .071, .0417, .0387, .0268, .025, .0232, .0226, .022, .0214, .0214] (default) | 1-by-n vector

Vector of Darcy friction factors for the tabular parameterization of the Darcy friction factor. The vector elements must correspond one-to-one with the elements in the Reynolds number vector for turbulent Darcy friction factor parameter, and must be unique and greater than or equal to 0.

Dependencies

To enable this parameter, set Viscous friction parameterization to Tabulated data - Darcy friction factor vs. Reynolds number.

Laminar friction constant for Darcy friction factor — Friction constant for laminar flows

64 (default) | positive scalar

Friction constant for laminar flows. The Darcy friction factor captures the contribution of wall friction in pressure loss calculations. If Cross-sectional geometry is not set to Custom, this parameter is internally set to 64.

Dependencies

To enable this parameter, set Viscous friction parameterization to either:

• Haaland correlation

• Tabulated data - Darcy friction factor vs. Reynolds number

and Cross-sectional geometry to Custom.

Pipe Wall

Pipe wall specification — Specifies wall flexibility

Rigid (default) | Flexible

Specifies wall flexibility. This parameter is independent of pipe cross-sectional geometry. The Flexible setting preserves the initial pipe shape and applies equal expansion of the cross-sectional area. It may not be accurate for non-circular cross-sectional geometry under high deformation.

Dependencies

To enable this parameter, set Fluid dynamic compressibility to On.

Volumetric expansion specification — Linear expansion correlation

Cross-sectional area vs. pressure (default) | Hydraulic diameter vs. pressure

Linear expansion correlation. The settings correlate the new cross-sectional area or hydraulic diameter to the pipe pressure.

Dependencies

To enable this parameter, set Fluid dynamic compressibility to On and Pipe wall specification to Flexible.

Static pressure-cross sectional area gain — Coefficient for area-dependent pipe deformation

1e-6 m^2/MPa (default) | positive scalar

Coefficient for calculating pipe deformation for the Cross-sectional area vs. pressure setting. The gain is multiplied by the pressure differential between the segment pressure and atmospheric pressure.

Dependencies

To enable this parameter, set Fluid dynamic compressibility to On, Pipe wall specification to Flexible, and Volumetric expansion specification to Cross-sectional area vs. pressure.

Static pressure-hydraulic diameter gain — Coefficient for diameter-dependent pipe deformation

1e-6 m/MPa (default) | positive scalar

Coefficient for calculating pipe deformation for the Hydraulic diameter vs. pressure setting. The gain is multiplied by the pressure differential between the segment pressure and atmospheric pressure.

Dependencies

To enable this parameter, set Fluid dynamic compressibility to On, Pipe wall specification to Flexible, and Volumetric expansion specification to Hydraulic diameter vs. pressure.

Volumetric expansion time constant — Pipe deformation time constant

0.01 s (default) | positive scalar

Time required for the wall to reach steady-state after pipe deformation. This parameter impacts the dynamic change in pipe volume.

Dependencies

To enable this parameter, set Fluid dynamic compressibility to On and Pipe wall specification to Flexible.

Initial Conditions

Initial liquid pressure — Initial pressure in pipe or pipe segment

0.101325 MPa (default) | positive scalar | 1-by-n vector

Initial liquid pressure, specified as a scalar or vector. A vector n elements long defines the liquid pressure for each of n pipe segments. If the vector is two elements long, the pressure along the pipe is linearly distributed between the two element values. If the vector is three or more elements long, the initial pressure in the nth segment is set by the nth element of the vector.

Dependencies

To enable this parameter, set Fluid dynamic compressibility to On.

Initial mass flow rate from port A to port B — Initial mass flow rate for inertia calculation

0 kg/s (default) | scalar

Initial mass flow rate for pipes with simulated fluid inertia.

Dependencies

To enable this parameter, set Fluid dynamic compressibility to On and Fluid inertia to On.

Model Examples

Water Hammer Effect

This demo shows how the Isothermal Liquid library can be used to model water hammer in a long pipe. After opening a valve to slowly establish steady flow in the pipe, the valve is quickly shut. If the Valve is shut quickly enough, it triggers a water hammer effect. A water hammer arrestor suppresses the pressure spikes.

Open Model

Front-Loader Actuation System

A simplified version of an actuation system consisting of the lift and tilt cylinders. Each cylinder is controlled by an open center, 6-way, 3-position directional valve. The valves are connected in series through their unloading branch such that the system pump is unloaded when both command levers are in neutral position. If either tilt or lift command is applied, the unloading path is closed.

Open Model

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2020a