What is a Piping Network?
In general, networks consist of a number of components (Pipes, Ducts, Pumps, Valves, Filters, Orifice Plates, Fixed Pressure Drops and Nozzles) all connected together. The points at which the components may be joined to other components are referred to as nodes. Consider, for example, the simple system shown below, which consists of a single pipe with a nozzle on one end. A fluid enters at the open end of the pipe and is discharged through the nozzle.
This network can be represented schematically by the diagram shown below (Fig. 1)
Notice how the pipe, nozzle and nodes have each been given a label. When preparing a network for simulation every component and every node must be given a label which identifies it uniquely. The production of a fully labelled schematic diagram is an essential part of any simulation. Labels may either be tagged or untagged. Tags can be used to make labels more meaningful, and to allow sections of large networks to be more easily identified. In our schematic diagram we have labelled the pipe as P/1(tagged label), the nozzle as 100 (untagged label), and the nodes as 1 and 2(untagged label).
Inlets and Outlets:
In the drawing of a network, each pipe, pump, valve and filter component should have two nodes (one at each end). One of these nodes is designated the component’s input node and the other is designated its output node. Note that fluid does not necessarily flow from the input node to the output node.
- -Sizing calculation.
- -Pressure Drop calculation.
- -Adjust/Regulate/Control of the piping systems.
- Pressure drops.
- System requirements and contract (client) recommendations.
High velocity in piping systems increases the following effects:
- -Pressure Drop.
- -Pipe corrosion.
- -Water hammer.
- -Noise (sound) emission.
In the other hand low velocities increases pipe diameter (Increase the total cost) and also increase the possibility of illuviation (Sedimentation) in a piping system.
For fluid velocities of different systems, it is better to refer to the piping hand books.
Generally, if is preferable to reduce pressure drop in piping system as far as possible because :
- -To decreases the size of pump or compressor (Cost reduction).
- -To reduces the initial pressure (i.e. in case of gravity flows).
- -To decreases the energy losses.
- -To reduce downstream velocity of gases and the related corrosion and noise emission.
For admissible pressure drop for different media system it is better to refer to piping hand books (For example for Water it is 2.5 m/100m and for natural gas the total pressure drop shall be less than 10% of initial pressure).
System requirements & contract (client) recommendations:
Sometimes we must meet some conditions in Terminal points / input/output points (according to technical matters, contract specifications or client requirements). For example:
- For a long water piping system with gravity flow maybe it is needed to use velocities less than what was mentioned before.
- For a system with predefined flow characteristics in inlet and out let points (flow characteristics have been defined in terminal points).
- Climatic conditions.
Pipe sizing calculation:
After calculation of the pipe inside diameter, according to the pipe schedule and pipe dimension standard the suitable nominal diameter is selected.
Now the actual velocity of the medium in the pipe shall be calculated according to the selected nominal diameter.
Note: The metal pipe dimensions are basically according to ANSI B36.10 or API 5L. Also, for PE pipe please refer to DIN 8074.
STEADY SINGLE-PHASE COMPRESSIBLE FLOW IN PIPING:
According to Darcy formula, the friction head loss in an incompressible fluid is calculated from the following formula:
Pressure losses which occur in piping systems due to bends, elbows, joints, valves, and so forth are called form losses. For the recommended values of local flow resistance coefficients (K-factors) please refer to Crane Flow of Fluids.
Sequence of simulation:
- -Prepare a pipe route (single line) according to the technical specification and system requirements.
- -Specify the process characteristics of flow in I/O points (Regarding to the Terminal point data, consumers and system component specifications)
- -Specify each pipe section and its node numbers and extract its relevant information from the pipe route and technical specifications (length of the pipe section, its start & end nodes identification, it’s fitting, fixed pressure drops,…).
- -Calculate the pipe size of each pipe section.
- -Calculate the total pressure drop in each pipe section. It is noted that out put pressure of each pipe section shall be used as input pressure of the next pipe section. The total pressure drop is the difference between inlet pressure pipe section and outlet pressure of the farthest pipe section.