# What is Flow rate: Definition and 495 Discussions

In physics and engineering, in particular fluid dynamics, the volumetric flow rate (also known as volume flow rate, rate of fluid flow, or volume velocity) is the volume of fluid which passes per unit time; usually it is represented by the symbol Q (sometimes V̇). The SI unit is cubic metres per second (m3/s). Another unit used is standard cubic centimetres per minute (SCCM).
In hydrometry, it is known as discharge.
In US customary units and imperial units, volumetric flow rate is often expressed as cubic feet per second (ft3/s) or gallons per minute (either US or imperial definitions).
Volumetric flow rate should not be confused with volumetric flux, as defined by Darcy's law and represented by the symbol q, with units of m3/(m2·s), that is, m·s−1. The integration of a flux over an area gives the volumetric flow rate.

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1. ### Fluid Mechanics - Need Help on a Water Pipeline Project

My current pipeline is open ended on each side meaning I raise water level in a creek to create natural flow to the inlet and the outlet discharges from my pipe directly into a surface ditch. The surface ditch is well cleaned so that the top of the pipe is above water level at discharge meaning...
2. ### Effect of pressure due to change in diameter of pipe

The pump has an outlet size of 4 inch 1) In case 1, 4 inch pipe is connected at length of 20 m 2) In case 2, 2 inch pipe is connected using reducer In both cases the pump outlet conditions are same( having same flow rate at a given pressure) What happens to pressure at the end of the pipe in...
3. ### Flow rate of air through constriction

I've been trying to find the formula(s) to determine the flow rate of air (and properties) in a pipe of varying diameters connecting two theoretical reservoirs of infinite size. The pipe is short in length so friction can be neglected. Reservoir 1 is always a higher pressure. There is no heat...
4. ### Flow rate experiment not producing same results as the Hagen-Poiseuille law?

I have repeated the experiment several times and it always shows my longer length has the fastest flow rate. the same results occur when I apply 300mmH pressure to the fluid bag on top, the flow rate is still faster in the longer pipe
5. ### Flow rate needed to lift object inside a vertical pipe

I have an object being forced up a vertical pipe with a slightly larger ID than the object by water. Then, the object reaches an area with a much larger ID than an object. How much flow fluid do I need to keep the object moving through the larger ID section and reach back into a small ID...

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7. ### Fluid flow rates in straight vs coiled tubes

If you have 2 pipes of the same cross sectional area, same volume of fluid, and same length, the only difference is one pipe is coiled several times over a cylindrical object theoretically shortening the length of the pipe, while the other is a straight pipe. Will the flow rate be same in both...
8. ### Calculating flow rate when emptying liquid from a closed-top tank

I can imagine the experiment: the pressure at the surface will drop while the tank is emptying (if no air bubbles enter through the evacuation of course, otherwise it restores the pressure atm at the surface). The flow speed decreases as a function of time until the external pressure maintains a...
9. M

### Poiseuille equation for water flow rate

For this problem, The mains water pressure at the council tubby (just before it enters a house) is of the order of 1.5 bar. Using Poiseuille equation, estimate the flow rate in a typical home at the kitchen tap. You will need to make reasonable estimates on several parameters, clearly state...
10. ### Calculating Output Pressure for 15L N2/min

Hello, i’m not good in physics so I came here for help. I have a high pressured gas tank (200 bars) and a flow rate regulator. I need to release 15L of nitrogen per minute, but my regulator only measures output pressure between 0 and 400 bars (0 - 6000 psi). How do I measure the output pressure...
11. ### Question about source flow rate across line AB.

Q：Please hlep me to understand which ans is correct.To determine the flow rate in Line AB. $$\mathrm{Known}：V_A,q,r_A = constant.$$ so/ select：## A,{B}^{\text{'}},B,A,## is control volume {Q}_{AB}={Q}_{A{B}^{\text{'}}}=\iint _{A}^{}({V}_{A})dA={\int }_{{\theta }_{A}}^{{\theta...
12. ### Question about flow rate in the source flow

Please help me to understand what wrong with method 2. ref.Flowrate Between Streamlines (Thank you for your time and consideration.)
13. ### I Flow rate calculation of coating application

Dear all, I'm currently working on a basic coating application and I'm struggling to get the flow rate stable. I'm trying to figure out how to calculate the theoretical flow rate in the application. The coating is stored in a pressure tank, which we put on an overpressure of 15psi. From the...
14. ### How to calculate the leak rate based on pressure drop

I am currently working on a project trying to calculate leak rate and fluid loss from pressurised vessels filled with water over a time period of 30 minutes. So far I have used the Boyles Law which assumes that PV/T = constant which gets us P1 * V1 = P2 * V2 and PdV+VdP = 0 I formed this over to...
15. ### Determining Reverse Mass Flow Rate Formula for Multiple Diameter Tubes

Alright, this is more of a conceptual question than a HW question that will nonetheless help me design something. In the attached image, air is flowing through a large area tube and then a small area tube from right to left. A collaborator previously figured out the equation for measuring the...
16. ### Inconsistent flow rate measurements of an engine diesel fuel

I am measuring the volumetric flow rate of a diesel fuel using "Turbines" flow meter, both in the supply and return fuel lines of an industrial diesel engine (https://www.cat.com/en_US/products/new/power-systems/industrial/industrial-diesel-engines/18398034.html – coupled with a generator for...
17. ### I Calculate the internal pressure of a tube based on flow rate

I have pump of unknown flowrate pumping water through a tube of length L and diameter D. I know that the flowrate of water exiting the tube is X mL/min. I would like to know the internal pressure of the tubing, how can I calculate it? This all occurs at sea level elevation.
18. ### Engineering Mass flow rate as a function of time

At first, I inputted h(t), of which I solved for, into the mass flow rate formula. So it looked something like this, m-dot(t) = -(density)*[sqrt(g*(H-(g*d^4*t^2/D^4)]*(pi/4)*d^2 But I don't think that's right? Any thoughts?
19. ### Coolant Mass Flow Rate Through Subchannel in Nuclear Fuel Assembly

I am trying to find the mass flow rate of coolant through a channel within a hexagonal nuclear fuel assembly. I am given the specific heat of the fluid, the coolant inlet and outlet temperatures, the total power produced by a single fuel pin, the diameter of the fuel pin, the length of the fuel...
20. ### How to determine mdot for choked airflow through a valve, given T,P

Hello, I am working on a project that involves air at high pressure and temperature flowing through an orifice (valve) from one container to another. For each container, the volume, temperatures and pressures are known. The valve diameter is also known, and the fluid is air (which can be...
21. ### Speed/Velocity and Volume Flow Rate of Viscous Fluids

In my first attempt, I started off converting the radii of all three sections from centimeters (10, 8, 6) to meters (0.10 , 0.08 , 0.06), then used the VFR=Av formula to find the speed/velocity of section one. VFR== 0.063 m^3/s A== pi*r^2=pi*(10cm)^2=pi*(0.10)^2=pi*0.01 == 0.031415927 VFR/A=v...
22. ### I Steam flow rate in 2-chamber steam engine system

Our system of interest has a duct on the left and a piston chamber on the right that make the shape of the letter T rotated 90º clockwise. The smaller tube on the left is abbreviated as P1 has an unspecified length while the piston chamber is P2. The air in P2 heats up and expands while the...
23. ### How does a pump trade head for flow rate?

A pump’s power is a product of its pressure rise times volume flow rate. Commonly, a pump is specified by giving the pressure rise, or head, it can provide and the flow rate, such as in gallons per minute(GPM). But some pumps provide the user with a chart that shows how the pressure rise can...
24. ### How Do You Calculate the Flow Rate of Oxygen in a Pressurized System?

I am trying to calculate the flow rate of O2 from a known volume 25 in^3. The cylinder will fill up to a maximum pressure of 140 psi in 11.26 seconds. Any help to determine the flow rate will be appreciated. Do I use Bernoulli equation to find the flow rate?
25. ### Heat Exchanger: +40C rise at 16 liters/minute flow rate

Summary:: How to calculate the rate of heat transfer between hot external water and cold internal water in a pipe. The image attached is my attempt at the question however, I find myself stuck trying to work out internal and external heat transfer coefficient.
26. ### Oxygen Tank -- What if the person's flow rate is too high? (2l/min. vs 4l/min.)

Covid is surging again due to the Delta Variant. I saw in the news of many oxygen tanks with people connected to them even outside in hospital tents. I'd like to know something. If a person accidentally given more oxygen than required, for example. 4 Liter/Minute instead of 2 Liter/Minute...
27. ### What is the relationship between pressure and flow rate?

I performed an experiment where I let water flow out of a measuring cylinder through a hole at the base of the measuring cylinder. I let the water run out for 30s, recording the volume after. I did this for different heights of water in the measuring cylinder, and kept the pressure of water at...
28. ### Optimizing Flow Rate for Above Ground Pool Heater Installation

I am having a heater installed for my 12ft round above ground puddle pool. The heater is a K-Star K-5 (5kW) heater. The manual says the heater's max flow rate is 8GPM and I'll need to install a diverter with a valve to bypass it until the flow is <8GPM. How do I determine what my current flow...
29. ### Calculate flow rate in a tap and the height of a reservoir

The possible answers are: (I do not know what is the right one) A. ##H=120m## , ##S=0.0131\frac{m^3}{s}## B. ##H=60m## , ##S=0.0231\frac{m^3}{s}## C. ##H=120m## , ##S=0.0231\frac{m^3}{s}## D. ##H=240m## , ##S=0.0231\frac{m^3}{s}## E. ##H=60m## , ##S=0.0131\frac{m^3}{s}## F. ##H=240m## ...
30. ### Calculating Flow rate for an oxygen system

I'm struggling with calculating the flow rate for an oxygen system. There is a pressurised cylinder. This then joins onto a pressure reducer. Then travels down a length of pipe which branches off to 4 exits there is no restrictions on the exits it just goes to atmospheric pressure. I am yet to...
31. ### Volumetric flow rate of nitrogen through relieving pressure regulator

Hello all, I'm having trouble figuring out the volumetric flow rate upstream of a relieving pressure regulator used on a 1/4" OD nitrogen line. Upstream of the regulator P=100 PSIG and T=70F, while downstream P=80 PSIG and T=70F with downstream consumption at q=4 L/min or 0.91 SCFM (at std...
32. ### Water flow rate and drip surface tension

hello i have a drip tube with water dripping and when i increase the flow rate or frequency of drips they get bigger/more massive. i see the equation mass x gravity = 3.14(tube diameter)(surface tension) my mass is changing but not gravity, 3.14 or tube diameter so surface tension must be...
33. ### Volumetric Flow Rate through a Venturi Meter

Hi, I have designed a simple Venturi meter to measure pressure differential across to section of the pipe as pictured. However in calculations I am not sure if I am doing something wrong. I am trying to calculate Volumetric flow rate in L/s. I am using Bernoulli Equation of the Venturi meter as...
34. ### Volume Flow Rate: Open vs Closed Valves

Made an attempt at this Q but I'm unsure on how to do part c) or if I had even done part a) and b) right What difference does it make to the volume flow rate equation when the valve goes from open to closed? Any help would be appreciated! Thanks
35. ### Flow rate of a pipe - calculation

So, I actually do not know, if the formula given applies to this problem or not, so I wanted to check
36. ### Mass and Volumetric Flow rate of Natural Gas

Hi. I am currently doing my internship in the oil and gas industry (contractor) as process engineer. My supervisor give me a task to do some reverse engineering where i need to study how a spreadsheet (calculation) construct by other process engineer was been constructed. Ok the situation is the...
37. ### (Fluid mechanics) How to find the flow rate of a gas from a vessel

I am working on a project where I have to calculate various results relating to the motion of a water bottle rocket being launched. I am currently stuck on trying to find how long the thrust period of the rocket is. The model for the rocket is as follows: It is a 2L (0.002m3 bottle filled with...
38. ### Volumetric flow rate of a pipe

Hello kind people of PF I am looking to mount a fan on one end of a pipe but I'm not sure how much air can the pipe transfer. (Volumetric flow rate) The pipe is vertical and 15 meters long.It has a diameter of 10 cm. I'm looking to push air from top to bottom using a fan. Need to know the...
39. ### Flow Rate (Q) of Viscous Flow between Two Plates

I know how to derive the formula, but I have no idea how to actually use this. Where it says ##50~cm## wide, I'm not sure if that's in the x-direction or the z-direction. ##W##, the width in the equation, is in the z-direction. ##\mu## can be calculated, but I'm not sure what the pressure...
40. ### Calculating the Mass Flow Rate of a boiler

Im trying to do some past exam papers. If i can get help with the method on how to solve and have correct formulas, it will help me. I) There is one formula in the notes to get mass flow rate: Heat lost by steam = Heat taken up by water GsHfg = (GwCpw)(change in temp) Gs x 2748 x 10x103 =...
41. ### How can the molar flow rate of a two-gas mixture be calculated?

I have two Gases where i know the molar flow rate of each gas. Is there any way to calculate the molar flow rate of the two gases together or is it just the average of the two molar flow rates?
42. ### Convert Mass Flow Rate to Molar Flow Rate

how can i convert mass flow rate into molar flow rate using density of the gas.
43. ### Measure flow rate with a manometer (pressure gauge)

Hello! I have a volume of 50 liters which I pressurize with air so that I read 1 bar on the manometer. But there is a leakage in the volume so after 30 sec the manometer shows 0,5 bar. What is then the air flow ( liter / min) of the leakage?
44. ### Flow rate of fluid at a burst leakage in a pipeline due to over pressurization

we have a project to how knowing the flow rate of fluid at the burst leakage due over pressured, probably to make it easier to understand i will attach some pictures of this mechanism. Picture at above is simply mechanism of pipeline system that installed vertically, with fluid is mud and...
45. ### How do peak flow meters measure flow rate?

I am in pharmacy school and my professor recently went over lung diseases with us. An important (and cheap) tool that many patients can use to detect whether their lung function is declining is a peak flow meter, which tells the patient how much air they are moving when they exhale with as much...
46. ### Compressed air problem (pressure and flow rate calculations)

When dealing with a compressed air system I would like to know how to make some calculations to predict pressure and flow rate throughout a system. e.g. If I have a compressor that can supply 50 cfm @ 100 psi at the source, and the air flows through a system of pipes, filters, turns, etc. which...
47. ### Exit flow rate in a Plate Heat Exchanger

Hello All, I am working on a project with plate heat exchangers connected in a cascade system to heat up water connections in a huge system The Problem Statement : A boiler produces and circulates hot water at 65 degC to a Heat Exchanger and come out at 50 degC, where as the other fluid is...
48. ### Outlet Volume flow rate from a steam turbine

I am working Organic Rankine Cycle. I studied a number of research papers and in most of them, they have calculated outlet volume flow rate from the turbine or expander, but have not mentioned the calculations. So here are the available data; Pin = Turbine Inlet Pressure, 2.5 MPa Pout = Turbine...
49. ### Flow rate of steam in power plants

I want to know what's the flow rate (in kg/s) of saturated steam at 5 barA pressure to the turbines of a 250 kW power plant.
50. ### Can I calculate the flow rate of a compressed gas from pressure?

I am using a compressed gas tank to fill an otherwise empty container, The gas tank is around 50bar and the container will be filled to 6bar. If I am using a pressure transducer to determine when the container has been filled to 6bar, can I use the information I gain from it to derive the flow...