Junctions

A Junction represents a connection point where two or more pipes meet. It allows flow to split or combine and serves as a node for balancing mass flow and energy. Junctions can also include minor losses due to fittings or geometry changes.

Junctions are automatically assigned by FlowDesigner on the flowsheet by making a pipe connection to an existing junction (or deleting a pipe from an existing junction), the junctions available in FlowDesigner are shown below:

Component Name	FlowDesigner Component Icon	Description
Connector		Connectors can accommodate multiple pipe connections. Connectors have no associated charts or calculation methods.
Bend		Automatically added when two pipes are connected. A Bend represents a curved section of pipe that changes the direction of flow. The component introduces a local pressure loss dependent on the bend angle, radius, and number of bends. FlowDesigner applies standard loss coefficients to account for frictional and secondary flow effects through the curvature.
Tee		Automatically added when three pipes are connected. Tee and wye junctions are used to split or merge two flow streams. The nomenclature used by FlowDesigner to describe the various connections follows the naming conventions used by Idelchik.
Cross Junction		Automatically added when four pipes are connected. Cross junctions are used to split or merge flow streams with 4 connections. The nomenclature used by fluid flow to describe the various connections follows the naming conventions used by Idelchik.

Calculation Method

Connector Calculation Method

Connectors have no associated charts or calculation methods. The only calculation made at a Connector is the average pressure.

Bend Calculation Method

For all phase states, the pressure loss across a bend is calculated using the expression:

ΔP = 0.5 K ρ v²

where the pressure loss coefficient, K, is independent of fluid properties, making this approach applicable to all fluids and phase states. For a more detailed discussion on the universality of loss coefficients, refer to Miller.

FlowDesigner allows the calculation of the pressure loss coefficient K according to five different correlations:

• Rennels & Hudson

• Crane TP 410

• 3-K Darby

• Miller

• Idelchik

Note: The Crane method assumes that each pipe connection has the same diameter and a 90° bend angle. Idelchik, 3-K Darby, Rennels & Hudson, and Miller correlations allow for unequal pipe diameters and user-defined angles. Detailed explanations of the estimation of K can be found in the referenced sources.

When the tee definition is set to Crane, the K values for a 90° bend or elbow are as follows:

r/d	K
1	20 ft
1.5	14 ft
2	12 ft
3	12 ft
4	14 ft
6	17 ft
8	24 ft
10	30 ft
12	34 ft
14	38 ft
16	42 ft
20	50 ft

The Kvalue for standard threaded elbows is calculated as K = 30 ft.

Where:

• ft = turbulent friction factor

Elbow/Bend illustration showing the measurements for r and d.

Tee Calculation Method

For all phase states, the pressure loss across a branch or straight pipe is calculated using the expression:

ΔP = 0.5 K ρ v²

where the pressure loss coefficient, K, is independent of fluid properties, making this approach applicable to all fluids and phase states. For a more detailed discussion on the universality of loss coefficients, see Miller.

FlowDesigner allows the calculation of the pressure loss coefficient K according to four different correlations:

• Rennels & Hudson

• Crane TP 410

• Miller

• Idelchik

Detailed explanations of the estimation of K can be found in the references.

There are two types of tee directions, diverging and converging. The illustration below provides an overview of converging and diverging tee junctions:

Cross Junction Calculation Method

The current version of Cross junction in FlowDesigner does not calculate any pressure losses associated with this component. This is because the literature relationships are totally inconsistent between the various sources. In addition, many of the relationships, expressed as formulas, are discontinuous and/or do not appear to tie up with published loss charts, which means that they present special challenges during convergence.