Pipes

A Pipe represents a conduit through which fluid flows between components in the network. It is defined by its geometric and material properties, such as length, diameter, roughness, and pressure loss model to be used. The software calculates pressure drop, flow rate, and velocity within each pipe based on the governing hydraulic equations and fluid properties. The following piping materials are available:

Material	FlowDesigner Icon	Material	FlowDesigner Icon
Steel Pipe		Polyvinyl Chloride (PVC) Pipe
Stainless Steel Pipe		Polyethylene (PE) Pipe * (To be added)

Each piping material includes a range of nominal pipe sizes, and for each nominal size, multiple pipe classes are defined.

FlowDesigner maintains a comprehensive pipe database containing dimensional, thermal, and economic properties for each material and class. This database includes parameters such as thermal conductivity, sizing data, and cost information, which are essential for accurate system modeling. The inclusion of these parameters enables the software to automatically determine economical flow velocities, heat transfer coefficients, and other hydraulic characteristics, thereby minimizing the need for manual data input by the user.

Calculation Method

Fundamental Principle of Hydraulics

Note: This section provides an overview of the theoretical background used in FlowDesigner. It is not intended to include detailed derivations or exhaustive explanations. For more comprehensive theoretical discussions, refer to the Reference Literature chapter.

Overview

The fundamental laws of conservation of mass, energy, and momentum govern Fluid Mechanics. When a fluid flows through a pipe, a pressure loss occurs due to friction, elevation changes, and velocity variations. For all phase states, the total pressure loss can be expressed as:

ΔP_tot=(ρ₁U₁ + z₁ρ₁g + p₁ + 0.5N1ρ1v₁²)-(ρ₂U₂ + z₂ρ₂g + p₂ + 0.5N₂ρ₂v₂²)

Total Pressure Loss Expression

Implementation in FlowDesigner

FlowDesigner performs internal calculations based on total pressure losses. The computational methods implemented within the software do not assume that energy is dissipated. Instead, the program continuously tracks the total energy balance throughout the system.

In compressible, non-isothermal liquid and two-phase flow conditions, energy is dynamically transformed between the various components of the total pressure loss expression. To ensure accurate results, FlowDesigner maintains a continuous energy balance across all elements and flow paths within the network.

Incompressible Newtonian Liquid

Overview

For the flow of an incompressible Newtonian liquid in a pipe, FlowDesigner supports multiple friction models. When the friction model is set to Moody (default setting), the frictional pressure loss is calculated using the Darcy–Weisbach equation.

For liquid flow in a horizontal pipe, with no temperature change and neglecting compressibility effects, the friction loss and total pressure loss are considered equal.

ΔP_fric = 0.5f_D L ρ v²/D

Darcy–Weisbach Friction Loss

where:

• ΔP_fric = frictional pressure loss (Pa)

• f_D= Darcy friction factor (dimensionless)

• L= pipe length (m)

• D= internal pipe diameter (m)

• ρ= fluid density (kg/m³)

• v= average fluid velocity (m/s)