# What is Gas flow: Definition and 48 Discussions

In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and modelling fission weapon detonation.
Fluid dynamics offers a systematic structure—which underlies these practical disciplines—that embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves the calculation of various properties of the fluid, such as flow velocity, pressure, density, and temperature, as functions of space and time.
Before the twentieth century, hydrodynamics was synonymous with fluid dynamics. This is still reflected in names of some fluid dynamics topics, like magnetohydrodynamics and hydrodynamic stability, both of which can also be applied to gases.

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1. ### I Flow rate calculation for laser cutting nozzles

I am in need to calculate the required gas flow for a given nozzle orifice. In laser cutting we use various "nozzle orifice sizes" to cut different materials. For example, when cutting 1/4" mild steel we would use a 5mm orifice nozzle using 20 bar. I would like to make a calculator in excel...
2. ### I Does gas flow from low to high pressure?

Here's a grab at 1:50 from the Bernoulli's Principle Demo: Venturi Tube video It appears to show the air flowing from the viewer's right to left where the pressure in the third manometer appears to be higher than in the middle one. Is there some complexity from the manometers being...
3. ### I What is the equation for calculating average gas flow in a compressed syringe?

Hi, I tried looking for similar topics but nothing really solved my problem. How can I calculate the average gas flow on a syringe that was compressed over time, if the starting and ending pressure and volume are known? I am guessing there must be an equation which can relate these variables...
4. ### What Is the Best Method to Calculate Gas Flow Through an Orifice?

Summary:: How to find gas flow through an orifice that links two vessels at different pressures. Two vessels containing the same gas are linked through an orifice with diameter ##d##. The pressure inside vessel 1 is ##P_1## and the pressure inside vessel 2 is ##P_2##, and let's have...
5. ### I Compressible choked gas flow through an orifice -- Excel formula

Hello, I normally get these things working but I am a bit stuck as i don't feel I am getting sensible answers... The problem is simple (!): Q: Model the flow through an orifice with an upstream/supply pressure of 301BarA where the downstream pressure is in the range 1BarA to 301BarA. The...
6. ### What % reduction in gas flow results from changing to LPG?

There are 70 jets of 1/16" diameter along the tube and I neeed to create flames 1" high. I know the calorific value of natural gas is much less than LPG (39 MJ/m3 Vs 93 MJ/m3) . I am not sure what assumptions to make from there in order to compare the predicted natural gas to the LPG volume...
7. ### I Does combusted gas travel faster in a vacuum tube?

Hey all, So if a gas is combusted, would it travel faster through a vacuum tube or a regular ole' tube? I would assume the vacuum tube, as there are less particulates collisions in the way of the fast-moving gas molecules. Yet this also implies pressure on the outside of the thin barrier _ 2...
8. ### I What happens when gas is combusted while moving?

If a combustible gas mixture (say O2 and H2 are combusted to form H2O) are already moving before combustion, what would happen? Intuition tells me the previous velocity (say the gas was moving 150 feet per second) would just add to the velocity achieved when standing still and then combusted...
9. ### Pressure profile of a gas flow through an orifice

Hello, The question will probably be related to mechanical engineering / chemical engineering / aeronautics. I come from the field of optics and have no background at all on fluid dynamics. I'm trying to calculate the dependence of pressure on distance, i.e. P(x) in a gas flow problem: I...
10. ### Pressure drop necessary to have desired gas flow rate

Hello, I'm a chemist and I'm currently working on my PhD on materials science. I'm trying to determine the pressure difference necessary to achieve the desired gas flow inside a chamber. The scheme of the chamber is the following: I have a big chamber which is evacuated to 0.2 bar, and another...
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### Hardy Cross method with open loops

Hi. I am using the Hardy Cross method to simulate the gas flow inside a multiple hearth furnace (as shown in figure A). Figure B is a representation of the furnace's body as a pipe network. The segment A-AH represents the actual hEarth's, while segments B-AI and C-AJ represent the exhaust ducts...
12. ### Gas Flow split into four hoses

If I have a 1/2" source hose with 60PSI and a Flow sensor then split to four 3/8" hoses with a flow rate limited to 30SCFH. Should I expect to have a 120SCFH flow rate across my flow sensor? The gas will be 90% Argon/10%CO2, but we could assume an Ideal Gas for this... Right? I understand...
13. ### Selecting a Valve for Natural Gas Flow

Homework Statement A valve is required to regulate the flow of natural gas. Details of the gas are given in table below. It can be assumed that the pipe size and the valve size are the same [i.e. piping geometry does not have to be allowed for]. The chosen valve type is the V250 rotary ball...
14. ### Calculate Flue Gas Flow Rate for 5 Bar Steam Generation

Homework Statement A fuel gas consists of 75% butane (C4H10), 10% propane (C3H8) and 15% butene (C4H8) by volume. It is to be fed to the combustion chamber in 10% excess air at 25°C, where it is completely burnt to carbon dioxide and water. The flue gases produced are to be used to generate 5...
15. ### Gas flow from high to low pressure

Edit: Eh, sort of changed the question part way though, so if a mod could change the title to "Question regarding gas flow from high to low pressure". Moderator edit: Done I'm about 99% sure I already answered this question for myself but just wanted to make sure my logic was correct, so if...
16. ### Modeling ideal gas flow using Bernoulli's equation

Hello, PF! I'm currently brushing up my fluid mechanics and came across some questions while studying the compressible flow of an ideal gas using Bernoulli's equation. First, consider incompressible flow in the following system Neglecting any changes in elevation, the Bernoulli equation for...
17. ### I Calculating gas flow trough a pipe and a nozzle

Hello there. I am struggling with some gas flow calculations that, I think, should be quite basic. However, I think that I miss the knowledge background for it. I have a setup that I am showing in the attached file but here are more details: -I have a vacuum chamber pumped with a turbo pump to...
18. ### Optimizing Gas Flow in Capillaries: Calculating Flow Rates in Gas Chromatography

Can anyone help on this problem encountered in gas chromatography: Two helium incoming gas lines A and B are connected together via a cross-shaped connector to two outlets C and D. All in and out lines are capillaries with diametre in the 0.1-1 mm range and lengths in the 10s of cm to 10s of...
19. ### Nominal Linear Velocity Gas flow

Hello, thanks in advance for your help, I am not a physicist, however have a fairly good grasp on mathematics, also this isn't homework or an assignment but a real world problem. Currently trying to create a system with a nebulising gas at a linear velocity of 350 m/s. The calculations...
20. ### Automotive Car exhaust, gas flow system in the car,air pollution filter

In this time I try to search after information about 2 things: 1. the gas flow system in the car and the car exhaust 2. the materials that use in air pollution filters If you know good website / professor / paper / book / video lecture / other in one of this area so I will glad if you can let me...
21. ### Is there a way to calculate gas flow rate from output PSI?

I've noticed that certain propane torches will have a seemingly linear relationship between their PSI and BTU/hr. IE, 18 PSI -> 220,000 BTU/hr. From this a person could calculate how much gas is being burned per sec/minute/hr. So, is there a general relationship/formula that I can use to...
22. ### Coana-Effect over a convex surface-causes(liquid and gas flow)

hello first of all i'd like to appologise for eventual speeling mistakes i am going to make in this thread :D ive chosen as subject for my maturity paper the coanda-effect applied in the common experiment with water flowing along the curved-convex surface of a spoon. i want to make a model of...
23. ### Compressed gas flow rate calculation

Folks, I'm new to this thread. I'm a mechanical engineer, but I haven't done much fluids work since I graduated, 20 years ago. I have a question about calculating gas flow rate, so any help would be greatly appreciated. I have a design that I'm working on that will use a compressed gas...
24. ### How to Size Vent and Orifice for Effective Nitrogen Purging?

I have a steel box that I am trying to purge with gaseous nitrogen (GN2). Just say the dimensions are A x B x C (ft^3). I would like to maintain a continuous purge at a very minimal pressure (~0.5 inH20). To conserve money (i.e. so that I don't need to purchase an expensive flow regulation...
25. ### Gas Flow Equation: Calculating Force & Velocity

First off hello and I hope I have this right Homework Statement My problem- I have a cylinder of a specific value. One end of the cylinder has a piston and the other end is restricted by a nozzle that is attached to a tube. The information I need is how the flow out the smaller nozzle is...
26. ### Gas Flow Rate Calculation using Pressure Drop

Homework Statement Hi everyone, I'm trying to calculate the flow rate of air in straight tubing that is 30cm long and has a diameter of .1875 in and has an outlet into a 100 mL vial which is vented to the atmosphere. The starting of the system pressure is 20 psi and the ending psi is 14.6...
27. ### Gas flow from one chamber to another

Hi, I don't know a ton of fluid mechanics, and haven't been able to mathematically define this problem, so I was hoping someone might have an idea. The problem I want to solve is the time it takes for gas to flow from one chamber (with finite pressure) to another (vacuum). The problem is...
28. ### How altitude effects gas flow rate or not?

I am considering the effects on volumetric and mass flow rate for two conditions: Condition 1) 1013mBar, 21C (Air density as per) Condition 2) 700mBar (10,000ft) 21C (Air density as per) Setup: A variable flow restrictor is connected to a constant source of oxygen at 50 psig. The variable...
29. ### Is directional gas flow possible in a circular closed pipe system?

If I have a series of pipes and containers (containing liquid) soldered together to create a circular path, and then heated at a particular point or multiple points, is it possible to somehow have the gas move in a particular direction without the gas every leaving the system? I'd prefer not to...
30. ### Conductance, gas flow and pressure question

Hi there, I have been doing some research about vacuum system setup and I've seen the setup shown in the attachment. Pressure: P1a, P1b, P2a, P2b Throughput/gas flow: Q1, Qs Pump speed: Sp (pumping speed of the pump) Conductance:Ca, Cb, C Some papers have assumed that P2a = P2b, but...
31. ### Gas flow units MSCMD, KM^3 and SM^3x10

Is kM3/d 1000 m^3 a day or a kilometre^3 a day? I know it should be little m but this is what is written on our gas measuring instrument Are the units kM3/day 1000 cubic metres per day, or a kilometre cubed per day eg 1000x1000x1000 m^3 = 1e9 Thanks
32. ### Gas flow, time required to fill a tank

Hi all, I've been searching through the forum, and found some related posts, but still can't wrap my head around this. I would greatly appreciate any help. I'm trying to fill a box with carbon dioxide from a tank, that has attached to it a regulator and tube. I used PV = nRT to find the...
33. ### Differential equation for gas flow motion?

I am having some confusion in computation fluid dynamics. navier-stokes equation is the differential equation for fluid motion, but does this equation apply to gas as well? to my understanding gas qualifies as a fluid but I am having trouble seeing how the same equation applies to both liquid...
34. ### How to calculate gas flow rate through a system?

The pressure at the start of a 180km stainless steel natural gas pipeline is 4MPa and at the end is 2MPa. if the diameter is 0.4m, what will be the gas flow rate through the system? (ignore losses other than friction, ρ= 40 kg/m^3, μ= 11x10^-6 Pa) Could anybody please point me in the right...
35. ### How Do You Calculate Gas Flow Rate in a Pipeline?

1. Homework Statement The pressure at the start of a 180Km stainless steel natural gas pipeline is 4MPa and at the end is 2MPa. If the diameter of the pipe is 0.4m, what will be the gas flow rate through the system? (ignore losses other than friction) (For natural gas, ρ = 40 kg/m^3, μ =...
36. ### Can internal pressure be equated to gas flow rate?

Hello, first post here. I had a bit of an odd question that I can't get my head around, but I think is possible. Given the environment described in the picture, can you measure the amount of gas that is flowing from the hole in the box given that the pressure in the box has stabilized at a...
37. ### Calculating gas flow trough a pipe

Homework Statement I have nitrogen gas in a bottle compressed to about 150 bars. I want to know how many nitrogen will flow trough a pipe with diameter=6mm for the time of 1 sec if I open the bottle and allow to the nitrogen to exit with pressure 4 bars. pressure for the exiting nitrogen...
38. ### Estimating Gas Flow Rate Through a Line Puncture or Blowdown Orifice

The Pipeline Rules of Thumb Handbook uses the equation Q = D^2*P to estimate the flow rate of escaping gas from a pressured line (see link below for excerpt) under standard conditions. Where Q is flow rate in Mcf/hr, D is diameter of the nipple or orifice in inches, and P is the absolute...
39. ### Learning to Simulate Rocket Nozzle Gas Flow

Can someone provide me to a guide, book or some kind of tutorial that would help me in learning how to simulate the flow of gases in a rocket nozzle? I am trying to investigate the effect of my expansion ratios, nozzle geometry and other design parameters and simulate it. I would be very...
40. ### Fluid mechanics: Pressure and Velocity of gas flow in a heated pipe

Homework Statement Please note this is for my own understanding -- I am no longer in school! I simply cannot find this addressed in introductory texts. Suppose you have a long pipe of constant cross-sectional area with a heated section in the middle. The system has flowing gas such that...
41. ### Does Capillary Diameter Affect Flow Rate Stability in a Decreasing Vacuum?

we vacate a cannister using a vacuum pump using a range from 200-900 mbar of vaccum. Will the flow rate remain constant as the vacuum decreases over 24 hrs or does it tail off at a given pressure, a capillary of diameter 0.102mm is used ?
42. ### Gas Flow into Vacuum Paradox ?

Gas Flow into Vacuum Paradox ?? Hi, I've just been reading up on 1-D isentropic, compressible flow through a nozzle (constant cross-sectional area) and have hit a bit of a conceptual road block which I was hoping someone would help resolve. I'm interested in the mass flow rate of the gas...
43. ### Gravity's Impact on Perfect Gas Flow in Constant-Area Duct

Homework Statement Consider a perfect gas flowing in a constant-area. Duct adiabatically and without friction. Changes in state come about as the result of changes in elevation in the Earth's gravity field. The z-direction is away from the center of the earth, and hence gravity acts in the...
44. ### Attempting to relate pressure and velocity for gas flow in a tube

-snip- problem solved, nevermind
45. ### Understanding Gas Flow through Tubes: Choking at the Speed of Sound

Hiya ! Got a problem about gas flow ... I understand that gas flow speed through an orifice is choked to the local speed of sound once the upstream to downstream pressure ratio crosses a certain number. Any increase of pressure beyond that point does not speed up the flow anymore (though the...
46. ### Looking for a gas flow switch/sensor any leads?

I'm sorry if this is in the wrong forum or posted wrong. I'm new here my name is Troy and I'm a student at Akron University in Ohio. I am a junior studying to be a mechanical polymer engineer. I'm wondering does anyone know of a flow switch/sensor that only senses that there is flow above 0...
47. ### Calculating Reynolds Number for Turbulent Gas Flow

Hello Im currently looking at turbulent gas flow in circular pipe sections by calculating the Reynolds the number. Does the Reynolds equation hold for say flow of an ideal gas - air as it does for a real fluid say water. This may sound like a stupid question and I supose I've got my head...
48. ### How can Bernoulli's equation be applied to calculate gas flow rate in a tube?

My statistical dynamics and other useful areas of physics was sorely lacking in my undergrad education. Take this for instance, at work I need to calculate the gas flow rate from a tube into a very large chamber. I know the diameter of the tube and pressures of the gas. Bernoulli's equation...