# Questions tagged [fluid-mechanics]

Questions relating to fluids at rest (fluid statics) or the forces and effects of fluids in motion (fluid dynamics).

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### Why do all quantities used in the formulation of a physical law must be coordinate-invariant?

So I have just started reading the book "Introduction to Continuum Mechanics_third edition" written by W. Michael Lai, David Rubin, and Erhard Krempl. At the end of the book's introduction, ...
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### Why don't engineers put tesla valves in the airboxes of carbureted internal combustion engines?

Before I ask the full question, I want to quickly cover two common issues that come up in high performance engine design. When intake valves close in an engine a small shockwave moves backwards ...
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### Why funnelling air in order to increase the velocity is a bad idea when generating power

Disclaimer: I’m not trying to violate the conservation of energy here; I know that’s impossible for us mortals. I think I’m either wrong or not considering something, I just want someone to point it ...
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### Why aircraft refrigeration uses a centrifugal compressor in place of reciprocating compressor?

Why aircraft refrigeration uses a centrifugal compressor in place of reciprocating compressor and a gas turbine in place of reciprocating expander?
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### Sutherland's law for other gasses

Sutherland's Law seems to be a fairly well-accepted relationship between dynamic viscosity and temperature and was originally created to work for ideal gases, though it is often extended to be used ...
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### Advice wanted on time to digital converters for speed of sound in fluids

I'm using the speed of sound to analyze the composition of aqueous solutions with sound velocities between around 1000 and 1400 meters per second. It's a process control application with continuous ...
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### Determining the final surface temperature and final gas temperature flow through a tube in a room

I am trying to calculate the final temperatures as stated above. There is hot gas flowing through a tube that is insulated and inside of a room (no wind). I will try to walk you through my thought ...
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### Determine in and out momentum in shell momentum balance [closed]

How to decide what is in momentum and what is out momentum in using shell momentum balance? My main motive is to understand why at 25:26 in the balance equation at https://www.youtube.com/watch?v=...
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### Hydraulic lift connected to two pistons

I just finished a problem, and got the correct answer, however I am confused on one of the mathematical operations that must be performed in order to get the correct answer. The problem is as reads: ...
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### Stop Spa-to-Pool Siphoning Thru Spa Pump

I have a partially above ground Spa and an in-ground pool. When the spa is filled to spillover with pumps off, water siphons through the spa pump and into the pool until the spa water level drops ...
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### Slow Driving an Air Compressor

Do off-the-shelf air compressors have minimum driving speeds, below which they cannot build the necessary pressure? Reciprocating compressors and scroll compressors are available—is there a difference ...
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### Will coefficient of discharge remain same when it is used for measuring either liquid or gas flow rate?

I would like to measure air flow rate. I have a orificemeter but do not know its coeficient of discharge. Will the Cd remain same for both the liquid and gases or it will be different.?
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### Archimedes screw pump

i want to know if an Archimedes screw pump is more eficent that a modern screw pump to elevete clean waters 4 meters i saw many modern screw pumps smaller and want to now about the efcency of ths two ...
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### Separate air from water for water pump in aquarium

I'm using the following setup to pump water out of a space below the gravel (yellow) in my aquarium: The tubes displayed as lines are 12/16mm silicone tubes. The pump is a 300l/h electrical water ...
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### Fluid Mechanics Question

I am preparing for GATE(Chemical). I need the answer of this question part 2 (question 54) as I am not able to find the mistake in my logic. I have applied the logic here as: Initial energy stored in ...
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### Throttle vs Choke vs Damper vs Valve?

Throttles, chokes, dampers, and valves all restrict fluid flow. Aside from specific terminology/usage in internal combustion engines, are these really interchangeable terms, or do they have some ...
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### Would this air amplifier attachment increase a leaf blower's effectiveness?

With the start of the leaf raking/blowing season just a month away, I have been thinking of a way in which I could make my old leaf blower more effective so I can spend less time doing leaf blowing. I ...
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### How do you maintain a constant pressure in a pipe with multiple outlets?

I've seen in piping and ventilation systems, when they branch off, the continuation of the main trunk gets smaller. Presumably this keeps the pressure (sorta) constant along the whole length of the ...
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### determine if the flow is laminar or turbulent [closed]

what would be the the type of flow if the water flows through stainless steel channel? would it be a laminar flow or turbulent flow. I assume the adhesive force of water to stainless steel is minimum.
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### Does filter surface area affect resistance?

I am in the process of designing the enclosure for a small kiosk like project, and intend on having two fans (Noctua NF-A12x25, chosen for their high runtime rating, quietness, as well as other ...
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### Why is the friction factor in laminar flow independent of pipe roughness?

The Darcy friction factor is defined as: $$f_D =\frac{64}{Re}$$ with $Re$ I mean Reynolds number (global). I was wondering why Darcy in laminaire flow is independent of pipe roughness (wall roughness)?...
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### incompressible fluid approximation and fluid vs sound velocity

consider the following case: A straight tube, with a constant mass flow rate of water $\dot m_{in}=\dot m_{out}$ , and with a linear power entering in it $\dot Q [\frac W m]$. And the water is the ...
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### Coefficient of viscosity equation/answer issue

So I feel like my current answers are wrong but I am unsure, i feel like some could be a little high at -223 but I dont have the best experience in the field as this is my first time working with ...
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### Not too sure how to approach this equation - fluids mechanics

Apologies if anything has been left out. Ok, so there is just 1 equation which I am struggling to understand, I have made an attempt and also written out the full equation in 2 parts, but I dont know ...
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### Axial fan for HVAC with HEPA filters

I have a background in mechanical engineering but HVAC is not my specialization. I am trying to properly size an axial fan to get a determined airflow from a duct. Both inlet and outlet are at ...
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### Unequal water level in connected containers - Aquarium Sump

I have recently designed and had fabricated the following two sumps for my Aquarium (See image). I have a pump in the right hand container (section 4), and the return is coming back into the left ...
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### Can a riverboat tack upriver?

Note: This question originally appeared on the Physics site (see here) and was closed for being off-topic. Whoops! If ships at sea can tack in a zigzaggy pattern by converting backwards force from the ...
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### How are the conditions after the shock calculated for a shockwave formed on a cone?

How do oblique shockwaves differ from 2D to 3D problems? More specifically, how are the conditions after the shock calculated for a shockwave formed on a cone (e.g. the inlet cone on a ramjet)? I am ...
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### Fan blower with less airflow in the center

I'm building a ducted fan and I would like it to: have a uniform airflow at the output have good static pressure have a square section output (see figure: air enters the circular edge and exits from ...
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### How can I keep my soda bottle at atmospheric pressure while dispensing the liquid via a sealed system pump?

I am making a "bar bot" and I am trying to figure out a way to dispense soda without it going flat. I am using a bunch of peristaltic pumps: Which luckily remain sealed at rest. I was ...
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### UV radiation simulation in ANSYS

I am setting up a simulation in fluent to estimate the UV radiation dosage of an air stream passing through a cylindrical duct with the UV source in line with its main axis. It is a very simple system,...
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### Accounting for pressure energy in Euler turbine/pump equation

For all the analysis to find work done by a compressor or work done on a turbine, the book I'm reading (Fundamentals of Turbomachinery by Venkanna B.K) uses the Euler turbine and pump equation, W=\...
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### Why is conservation of mass holds on filling balloon with gas?

Given a ballon and only one inlet, where some gas enters at a constant rate and the control volume of the balloon changes with time, why does conservation of mass hold? To give some background, this ...
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### Will an electric water pump has slower flow if it must pump through a longer tube?

I am planning a series of ponds, where the first pond (near the source of electricity) has the highest water level, the water flows to the second, lower pond, via a small water fall, and to a third, ...
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### hydraulic Motor/pump minimum speed

I have seen in many data sheets of Hydraulic Gear motor a spec called : "Minimum Speed = 450 RPM" ( 450 is an example) here is a capture from the linked datasheet below : In your experience ...
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### Ducted fan thrust in confined space

I would greatly appreciate any insight into this. I'd like to place a ducted fan inside of a box with the bottom cut out. The fan is attached to the sides of the box by support rods. The ducted fan ...
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### Can I calculate the amount (mol or mass) of water in a gas, in a heat exchanger, if I know the partial pressure of the water?

Is it possible to calculate the amount of water (mol, mass...) in a gas, in a heat exchanger, if I know the partial pressure of the water? The stream through the tubes is mainly benzene and ...
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### Determine the length of the tube

I need to determine the size of the tube having the flow rate of the liquid (water) which is 5 ml/min and assuming the diameter of the tube is 4mm. How can i determine the size of the tube that takes ...
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### How do stators in axial compressors work?

How do the stators in axial compressors convert kinetic energy to pressure? Is this equivalent to a water hammer?
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### Help with Mass Flow Rate

I'm a beginner in chemical engineering so apologies in advance if this question is very basic! The Problem You are required to measure the mass and volumetric flow rate of a slurry stream. The slurry ...
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### Stagnation,static and dynamic pressures

Please can someone help out with the actual concept of stagnation,static and dynamic pressures . I have learnt all that stagnation pressure is when velocity of flow is 0 when isentropically stopped ...
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### Can you channel more air into a nozzle by creating a vortex inside of it?

There are designs for ducting in wind turbines to channel a wider cross section of wind into the rotor area. This is unpractical for structural and economical reasons but does actually increase power ...
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### Pressure difference/drop(or loss?) in a Laminar pipe flow

Consider a "pressure-driven" flow ( inlet $P_1$ and outlet $P_2$ pressures "imposed" by an engineer) in a pipe of some length. Under a steady-flow, fully developed region : My understanding: For "...
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### Boundary layer momentum equation

How does the author get that formula(d alpha formula) using the momentum equation . The book here is Mechanics and thermodynamics of propulsion by Philip Hill and Carl Peterson.
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### How to calculate flowrate of water through a crosssection of pipe?

Assume we have a pipe with a diameter of 10mm. Water is flowing through that pipe and we know that the water pressure at the 'open' end of the pipe is 2 atm. How would one go about calculating the ...
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### Air flow at the outlet of a reactor

I wish to calculate the air flow in cubic meters per second of a system that is not exactly a jet engine, but seems close to it, mathematically speaking. The data available to me is the following : ...
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### Can you help me to source a screw thread G1 3/4 inch to anything to fit in my stainless steel heat exchanger?

Last year I bought s heat exchanger for my above ground 12 foot paddling pool. I also bought a pair of 'gee' one and three quarter thread pva plastic adaptors to push in 50mm plain blank tapered holes....
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### Superimposing a Vector Field onto a Toroid in Matlab

I am a systems and control PhD student in Aerospace Engineering. Currently, I am trying to create a wind shear model of a toroidal thermal "bubble" in Matlab similar to the one in this paper (shown ...