Compressed air system design and pressure-drop analysis
Compressed air is one of the most expensive utilities on a plant, and most of that cost leaks away as pressure drop in the distribution system. An undersized main forces the compressor to run at a higher discharge pressure than the tools actually need, and every extra bar of generation pressure is energy you pay for and never recover. Fluid Network Studio is browser-based compressed air network analysis software that lets you size air mains, check the pressure drop along a run, and read the velocity in every branch before any pipe is ordered.
The gas solver runs entirely in your browser. You draw the network, set the supply and delivery pressures, pick the gas, and solve. There is no desktop licence and no install, and the compressible-flow modes are part of the Advanced plan from A$50/month.
Sizing air mains and the pressure-drop trade-off
Sizing an air main is a balance. Go too small and friction eats your delivery pressure; go too large and you have spent money on pipe and fittings you did not need. The honest way to settle it is to run the candidate sizes through a solver and compare the pressure drop and the velocity each one gives at the design flow.
In Fluid Network Studio you enter each pipe's length, internal diameter and roughness, set the draw-off as a mass flow in kg/s, and read the pressure at every node. The built-in compressed-air line example shows the pattern directly: an air line at about 6 bar gauge feeding a 1.15 kg/s draw-off through 300 m of 100 mm pipe and then 200 m of 80 mm pipe. Because the duct narrows and the gas density falls as pressure drops, the velocity climbs along the run. Watching that velocity rise is the quickest way to spot a main that is too small before you commit to it.
Why compressible flow is different
For a liquid, density barely changes and the pressure drop is close to linear along a pipe. A gas does not behave that way. As pressure falls along the main the gas expands, density drops and the same mass flow has to move faster, so velocity and friction both rise toward the outlet. Treating a long air main as if it were a water pipe will under-predict the drop near the delivery end.
The solver handles this properly. It works in absolute pressure and solves the network in pressure-squared, using an exact isothermal pipe relation that includes the acceleration term, with the Churchill friction factor across laminar and turbulent flow. Mass is conserved at every node and the mass balance is reported on every solve, so you can see the residuals rather than take conservation on trust. If a line accelerates past the point where the compressible-flow assumptions hold, the solver raises a high-velocity advisory. The air blow-down example is built to trigger exactly that: a short 20 m line dumping 300 kPa air to 120 kPa, where the gas reaches roughly 210 m/s near the outlet and the advisory fires.
Velocity limits
Velocity is the number most engineers reach for when sizing air mains, because it is a good proxy for both pressure drop and noise. Common practice keeps main-line velocity modest and allows higher figures in short branch runs to tooling. Fluid Network Studio reports the velocity in every pipe and lets you colour the whole network by velocity, so a hot branch stands out at a glance. You set the limit that suits your design and the advisory threshold is configurable, rather than baked in.
Fans versus compressors
Not every air-moving problem is a high-pressure one. Ventilation, combustion air and low-pressure conveying are fan or blower duties, where the pressure rise is measured in pascals or kilopascals, not bar. Fluid Network Studio models both.
- A fan carries a pressure-rise versus flow curve, scaled to inlet density, and settles at the operating point where the fan curve meets the duct resistance. The fan and duct example shows a fan drawing air from atmosphere and pushing it through a 60 m duct back to atmosphere, with the Delta-p versus Q chart and the operating-point marker on the fan itself.
- A compressor is a set-point machine. You give it a pressure ratio or a discharge pressure and an isentropic efficiency, and it reports the discharge temperature and shaft power. The compressor and line example takes air at 200 kPa, compresses it to a 2:1 ratio, then carries it 150 m to a 300 kPa delivery point, reporting the discharge temperature as it goes.
Choosing between a fan and a compressor early, and sizing the downstream pipe to match, is exactly the kind of question this tool is built to answer quickly.
Gauge versus absolute pressure
This is where air calculations most often go wrong. Compressible-flow relations are written in absolute pressure, but gauges and datasheets nearly always read in gauge. Get the two mixed up and a 6 bar gauge main can be solved as if it were 6 bar absolute, which understates the density by about 15 per cent and throws off every downstream number.
Fluid Network Studio keeps this clean. You enter boundary pressures in whichever convention suits the data, the solver works internally in absolute pressure against a configurable atmospheric pressure, and results are reported back so you can read either. The atmospheric pressure is yours to set for site altitude. If you are new to the distinction, the glossary explains gauge and absolute pressure alongside the other terms the solver uses.
What the solver does and does not claim
Fluid Network Studio computes steady-state pressures, flows, velocities and temperatures from the data you enter. It supports your engineering work; it does not replace it. Results should be reviewed by a qualified engineer for the specific application before you rely on them, and Fluid Network Studio does not claim compliance with or certification against any particular standard.
Frequently asked questions
How do I size a compressed air main?
Run the candidate pipe sizes through the solver and compare the pressure drop and the velocity each one gives at the design flow. Enter each pipe's length, diameter and roughness, set the draw-off as a mass flow, and read the pressure and velocity at every node.
Why is compressible gas flow different from water?
As pressure falls along an air main the gas expands, its density drops, and the same mass flow has to move faster, so velocity and friction both rise toward the outlet. Treating a long air main as if it were a water pipe under-predicts the pressure drop near the delivery end.
Does it use gauge or absolute pressure?
Either. You enter boundary pressures in whichever convention suits the data; the solver works internally in absolute pressure against a configurable atmospheric pressure, which you set for site altitude, and reports results back so you can read either.
Can it model fans and compressors?
Yes. A fan carries a pressure-rise versus flow curve scaled to inlet density and settles where it meets the duct resistance; a compressor is a set-point machine, taking a pressure ratio or discharge pressure and reporting the discharge temperature and shaft power.
How much does compressed air analysis cost?
The compressible-gas modes are part of the Advanced plan, from A$50 a month or A$500 a year.
Try it on your own air system
The fastest way to see whether a main holds its pressure is to draw it and solve it. Open the Studio, drop in your pipes, fittings, fan or compressor, set the supply and draw-off, and read the pressure and velocity in every branch. Start from the compressed-air line example and change the diameters to match your own design.
Open the Studio and solve your compressed air system in your browser. Compressible gas is part of the Advanced plan, A$50/month or A$500/year.