# Pipe Bend (G)

**Libraries:**

Simscape /
Fluids /
Gas /
Pipes & Fittings

## Description

The Pipe Bend (G) block represents a curved pipe in a gas network. You can define the pipe characteristics to calculate losses due to friction and pipe curvature.

### Pipe Curvature Loss Coefficient

The coefficient for pressure losses due to geometry changes comprises an angle
correction factor, *C*_{angle}, and a bend coefficient,
*C*_{bend}:

$${K}_{loss}={C}_{angle}{C}_{bend}.$$

The block calculates *C _{angle}* as:

$${C}_{angle}=0.0148\theta -3.9716\cdot {10}^{-5}{\theta}^{2},$$

where *θ* is the value of the **Bend
angle** parameter, in degrees.

The block calculates *C _{bend}* from the tabulated
ratio of the bend radius,

*r*, to the pipe diameter,

*d*, for 90° bends from data based on Crane [1]:

r/d | 1 | 1.5 | 2 | 3 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 20 | 24 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|

K | 20 f_{T} | 14 f_{T} | 12 f_{T} | 12 f_{T} | 14 f_{T} | 17 f_{T} | 24 f_{T} | 30 f_{T} | 34 f_{T} | 38 f_{T} | 42 f_{T} | 50 f_{T} | 58 f_{T} |

The block interpolates the friction factor,
*f*_{T}, for clean commercial steel from tabular data
based on the pipe diameter [1]. This table contains the pipe friction data for clean
commercial steel pipe with flow in the zone of complete turbulence.

Nominal size (mm) | 5 | 10 | 15 | 20 | 25 | 32 | 40 | 50 | 72.5 | 100 | 125 | 150 | 225 | 350 | 609.5 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

Friction factor, f_{T} | .035 | .029 | .027 | .025 | .023 | .022 | .021 | .019 | .018 | .017 | .016 | .015 | .014 | .013 | .012 |

The correction factor is valid for a ratio of bend radius to diameter between 1 and 24. Beyond this range, the block employs nearest-neighbor extrapolation.

### Losses Due to Friction in Laminar Flows

The pressure loss formulations are the same for the flow at ports **A**
and **B**.

When the flow in the pipe is fully laminar, or below *Re* = 2000, the
pressure loss over the bend is

$$\Delta {p}_{loss}=\frac{\mu \lambda}{2{\rho}_{I}{d}^{2}A}\frac{L}{2}{\dot{m}}_{port},$$

where:

*μ*is the relative humidity.*λ*is the Darcy friction factor constant, which is 64 for laminar flow.*ρ*is the internal fluid density._{I}*d*is the pipe diameter.*L*is the bend length segment, which is the product of the**Bend radius**and the**Bend angle**parameters: $${L}_{bend}={r}_{bend}\theta .$$*A*is the pipe cross-sectional area, $$\frac{\pi}{4}{d}^{2}.$$$${\dot{m}}_{port}$$ is the mass flow rate at the respective port.

### Losses due to Friction in Turbulent Flows

When the flow is fully turbulent, or greater than *Re* = 4000, the
pressure loss in the pipe is:

$$\Delta {p}_{loss}=\left(\frac{{f}_{D}L}{2d}+\frac{{K}_{loss}}{2}\right)\frac{{\dot{m}}_{port}\left|{\dot{m}}_{port}\right|}{2{\rho}_{I}{A}^{2}},$$

where *f*_{D} is the Darcy friction
factor. The block approximates this value by using the empirical Haaland equation and the
**Internal surface absolute roughness** parameter. The block takes the
differential over each half of the pipe segment, between port **A** to an
internal node, and between the internal node and port **B**.

### Pressure Differential

The block calculates the pressure loss over the bend based on the internal fluid volume
pressure, *p _{I}* :

$${p}_{A}-{p}_{I}=\Delta {p}_{loss,A}$$

$${p}_{B}-{p}_{I}=\Delta {p}_{loss,B}$$

### Mass Balance

Mass conservation relates the mass flow rates to the dynamics of the pressure and temperature of the internal node representing the gas volume

$$\frac{\partial M}{\partial p}\frac{d{p}_{I}}{dt}+\frac{\partial M}{\partial T}\frac{d{T}_{I}}{dt}={\dot{m}}_{A}+{\dot{m}}_{B},$$

where:

$$\frac{\partial M}{\partial p}$$ is the partial derivative of the mass of the gas volume with respect to pressure at constant temperature and volume.

$$\frac{\partial M}{\partial T}$$ is the partial derivative of the mass of the gas volume with respect to temperature at constant pressure and volume.

*p*is the pressure of the gas volume._{I}*T*is the temperature of the gas volume._{I}*t*is time.$$\dot{m}$$

_{A}and $$\dot{m}$$_{B}are the mass flow rates at ports**A**and**B**, respectively. The flow rate at a port is positive when gas flows into the block through that port.

### Energy Balance

Energy conservation relates the energy and heat flow rates to the dynamics of the pressure and temperature of the internal node that represents the gas volume

$$\frac{\partial U}{\partial p}\frac{d{p}_{I}}{dt}+\frac{\partial U}{\partial T}\frac{d{T}_{I}}{dt}={\Phi}_{A}+{\Phi}_{B},$$

where:

$$\frac{\partial U}{\partial p}$$ is the partial derivative of the internal energy of the gas volume with respect to pressure at constant temperature and volume.

$$\frac{\partial U}{\partial T}$$ is the partial derivative of the internal energy of the gas volume with respect to temperature at constant pressure and volume.

*Φ*and_{A}*Φ*are the energy flow rates at ports_{B}**A**and**B**, respectively.

### Variables

To set the priority and initial target values for the block variables prior to simulation, use
the **Initial Targets** section in the block dialog box or
Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model.
Using system scaling based on nominal values increases the simulation robustness. Nominal
values can come from different sources, one of which is the **Nominal
Values** section in the block dialog box or Property Inspector. For more
information, see Modify Nominal Values for a Block Variable.

## Ports

### Conserving

## Parameters

## References

[1] Crane Co. *Flow of Fluids
Through Valves, Fittings, and Pipe TP-410*. Crane Co., 1981.

## Extended Capabilities

## Version History

**Introduced in R2023a**