The quantitative study of how fluids (gases and liquids) move.

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277 views

What is the real cause of the boiling (forming of bubbles) of water?

I've got a question about the boiling of water. I'm a first year physics student and from the Netherlands. I've searched alot about the boiling of water and this confused me. Everyone said something ...
7
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1answer
205 views

Navier-Stokes Energy Equation

I've been assigned (for homework in a mathematical modelling course) the task of deriving the Navier-Stokes energy equation in one space dimension: Consider a fluid flowing through a cylindrical ...
2
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2answers
46 views

Hourglass fluid mechanics issue with Bernoulli's equation

I know that I'm thinking about this problem wrong, but I've been pondering it for a while and can't understand something. On my fluid mech. exam I had a problem that asked to determine the radius of ...
0
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1answer
22 views

How would an increase in temperature affect ooblek's (non newtonian fluid) viscosity?

Due to the fact that Ooblek (cornstarch and water), contains so much water and from what I understand it is non newtonian due to the particles suspended in it, would it therefore be correct to say ...
0
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1answer
53 views

can water falling/running down in pipe cause suction capable of creating a continuous flow

can water falling under gravity create suction force and if so, how much force..if i put a huge strong tank on top of a hill and on top there is a tap connected to a huge body, then i put a another ...
2
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1answer
200 views

Bernoulli Equation for isentropic ideal gas flow

If one derives the Bernoulli Equation for the isentropic ideal gas flow you get: $$ \frac{1}{2}v^2 + g z + \left(\frac{\kappa}{\kappa -1} \right) \frac{p}{\rho} = const. $$ Two questions: Is ...
3
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0answers
49 views

A question about droplets formation

This picture shows a fuel ejector of a diesel engine that propels ships. When the fuel line pressure exceeds 380 bars, the tension of the spring is overcomed and fuel is ejected into the combustion ...
9
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2answers
301 views

Explanation of the waves on the water planet in the movie Interstellar?

We will ignore some of the more obvious issues with the movie and assume all other things are consistent to have fun with some of these questions. Simple [hopefully] Pre-questions: 1) If the water ...
2
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1answer
40 views

how to choose characteristic length in reynolds number [duplicate]

now reynolds number for a system is defined as follows $$Re=\frac{\rho*u*L}{\mu}$$ where $L$ is the characteristic length. I am wondering how this $L$ is decided (in case of flat plate it is $x$ ...
0
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0answers
23 views

Approximating the pressure drop for a centrifugal fan/blower

Is it possible to approximate the pressure drop for a centrifugal fan by using the fan's characteristics, the airflow, and the speed at which the fluid is being ejected? Would it be possible to adapt ...
3
votes
2answers
126 views

Can the Arcaboard fly?

Recently, BBC news had a video that claimed to show a "real" hoverboard: As far as I can tell, there are 36 small fans on this device, and it seems to be flying just a few inches off the ground. ...
0
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1answer
30 views

Convective heat transfer coefficients - how do you calculate them?

How do you calculate (or otherwise determine) h_i and h_o (convective heat transfer coefficients) for a heat exchanger? Standard thermodynamics equation below for reference. My specific situation ...
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3answers
57 views

Do you need to increase pressure to pump a fluid from a large pipe through a small pipe?

The application of this question is towards clogged arteries and blood flow. I am wondering why people with clogged arteries have high blood pressure if a smaller artery (assuming it is smooth and ...
0
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1answer
13 views

Calculating Pressure in Lattice Boltzman Equation

I'm new to the LBE, but have been finding them very helpful for doing some fluid dynamics simulations. I was wondering how pressure would be calculated. I'm guessing this is quite easy, but it's ...
2
votes
2answers
61 views

Why jets entrain mass?

This very beautiful picture shows a jet of fuel in the combustion chamber of a diesel engine. Does anydody could explain me what is the physical reason that the jet entrains air? Why jets and plumes ...
0
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2answers
65 views

velocity of water exiting a 20 m hole at the bottom of water column 5000 m in height

What would be the velocity of water exiting a tube that has a height of 5000 m from a hole with a diameter of 20 m at the bottom, if the height of the water remains constant at 5000 m? Would it be ...
0
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0answers
14 views

Inertial force of fluids [duplicate]

Reynold's number is the ratio of inertial force to viscous force.I also know the definition of inertial force.but where does a fluid get this force from?what are the factors responsible for this force?...
0
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2answers
40 views

Equations describing a counterflow heat exchanger [closed]

One of my experiments has a water-cooled apparatus. I plan on building a heat exchanger to keep the apparatus cool. However, I am not very good at thermodynamics and could use a hand. Also, from a ...
0
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1answer
49 views

What is the psi at the bottom of different tubes filled with water filled at the same height

if I have a 1 inch square tube with 144 feet of water I know I have about 63 pounds of water (63lbs ft**3) and 63 psi at the bottoms off the tube. If I have a 1/4 inch sq tube filled with water at ...
3
votes
1answer
71 views

Fluid Mechanics Paradox

This is a deceptively simple problem in fluid mechanics that I can't quite figure out because it produces a paradox. Suppose that there is a straw and a small column of water inside the straw, such ...
39
votes
12answers
3k views

Mechanics around a rail tank wagon

Some time ago I came across a problem which might be of interest to the physics.se, I think. The problem sounds like a homework problem, but I think it is not trivial (i am still thinking about it): ...
2
votes
2answers
93 views

Submerged water jet

I am trying to calculate at what pressure and speed water from a high pressure water jet will hit an object 100 millimeters away from the nozzle opening, but i can't figure it out. The nozzle will ...
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2answers
2k views

Why does the higher pressure of air underneath an aeroplane wing keep it flying?

With aeroplane flight, the wings are shaped so that the air that goes over the top of the wing has to travel faster than the air that goes below the wing. This means that the air below the wing has ...
0
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1answer
61 views

How long time before all the water in a lake has been replaced? [closed]

Studying hydrology, and in that context we've seen some information about lakes and the times it takes for the water to renew completely in them. This got me interested in finding out how this is ...
0
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1answer
29 views

Pressure required to overcome surface tension

Imagine I have a vertical straw, and that it is partially filled with water. If I were to decrease the radius of the straw at the bottom end, eventually surface tension would allow the water to remain ...
0
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1answer
29 views

Recommended books about vorticity

Could anyone suggest a good introductory book or any online resource about vorticity? I just now started to learn physics but I have a good mathematical background.
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0answers
26 views

flow rate measurement of a fluid

I had an experiment related to piping networks in my institute. In the experiment there was a device that was measuring flow rate based on rotations of a fan-like system. This created a doubt in my ...
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9answers
619 views

Are eductors working on the Bernoulli principle?

This is a picture of an eductor. The wikipedia article claims that it works on the Bernoulli principle. The Bernoulli principle is famous due to the misconception about how aeroplanes fly and because ...
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2answers
84 views

Atmospheric pressure changes on plastic bottle containing a liquid

We have a problem at work and I need some help on a theory. We ship a liquid in plastic bottles using a pump closure. Recently some of the bottles have been arriving to customers having leaked. The ...
6
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1answer
176 views

Continuity Equation in Differential Geometry

I'm looking for a derivation of the mass continuity that applies in general on symplectic manifolds. In particular the "the amount of change in the mass in a volume is just amount that flows in or out"...
0
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1answer
47 views

Wall Shear Stress

I have the solution of a Navier-Stokes simulation with an incompressible, Newtonian fluid with laminar flow. Now I compute the wall shear stress (vector) as $$\tau_n = \mu (\nabla u) n,$$ where $\mu$ ...
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1answer
55 views

How does capillary action work in tubes which are closed at the top?

In all textbooks the examples and descriptions use tubes which are open at both ends. Our teacher remarked that if it were closed at one end like a test tube (albeit a thin one) even then capillary ...
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0answers
24 views

Rankine Oval is oval shaped

I'm studying Rankine oval and I have a question. How do you prove the equation for its zero streamline curve is in fact oval shaped? Is there some family of oval shaped curves including Rankine Ovals? ...
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1answer
19 views

How much load does an aqueduct support?

Recently, I found out about /r/InfrastructurePorn, and I found a particularly interesting photo of the Gouwe Aqueduct in Gouda, NE: It seems like the bridge that is supporting the boat wouldn't be ...
5
votes
2answers
129 views

Must flow be supersonic for disturbances not to affect upstream?

I'm studying oil production and found a fact that puzzled me. It states that fluid flow downstream of the wellhead must be supercritical in order not to disturb the flow upstream of it. From PetroWiki:...
4
votes
1answer
70 views

Explaining the shape of a raindrop and a drop of mercury

I saw on wikipedia that the shape of a raindrop is explained by using Laplace pressure. But why? Since the drop is in motion, we shouldn't be able to use an hydrostatic law, am I wrong? ...
4
votes
1answer
13k views

What is Convective acceleration of flow velocity?

I know that $\frac {dv}{dt}=a$ is acceleration, but: What is convective acceleration of a flow velocity? What is difference between $(v\cdot \nabla) v$ and $v\cdot (\nabla v)$?
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1answer
27 views

How does a fluid force behave at different angles?

I have a mock exam problem that deals with fluid forces acting at different angles. Here are the scans: Based on the description of the systems, I know that in (a) and (c), F is going to equal the ...
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1answer
32 views

How does the viscosity of a non Newtonian fluid (ooblek) affect its resistance to electricity?

I know the conductivity of water is based on whatever is dissolved into the solution, hence pure water does not conduct electricity. However, these ions in solution must also be free to move around. ...
0
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2answers
29 views

Efficient way to move water pumping vs circulation [closed]

I have a basic question about efficiency of pumping. If I have a well of 100 meters depth, but water filled till top, and I want to circulate the water. What will be most energy efficient. A) ...
1
vote
1answer
55 views

I want to increase pressure of water in a closed vessel [closed]

I am trying to make a high pressure water jet using DIY hand pump which pushes water into a sealed vessel with non-return valve at the inlet. I am planning to do it by first closing the valve to the ...
0
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0answers
8 views

Why is a controlled shear test compared to the natural flow?

Looking for the areas where contolled shear stress (CSS, where force is fixed while rate of deformation is measured) and controlled stress rate (CSR, where conversely the force is measured while ...
0
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1answer
21 views

Phase diagrams and critical pressure

If a solid substance is pressurized past its critical pressure, what happens? Is the critical pressure only a factor when a substance is over the critical temperature also? On another note what makes ...
0
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0answers
23 views

Formula relating Pressure and Radius of a fluid in a pipe?

Let's say I have a section of straight pipe whose radius varies along its length with some sort of ideal fluid flowing through it. Is there an equation I can use to calculate the pressure of a fluid $...
0
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2answers
47 views

Why does an ideal gas not consist of identical molecules? [closed]

since the mass , temperature , and number of particles are the same , shouldn't the molecules be the same so that the pressure of the gad is inversely proportional to the volume.
3
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1answer
80 views

Why do water waves with longer wavelengths travel faster?

When wind blows over the sea, it excites a range of wavelengths. Why do longer wavelengths travel faster?
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0answers
18 views

Scale analysis for the vertical component of the Boussinesq equation to obtain a complete hydrostatic relation

This is actually an exam question which i have been trying to solve for my studies. Consider the Boussinesq vertical equation: \begin{align} \frac{\partial \widetilde{w}}{\partial t} = - \frac{1}{\...
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0answers
44 views

Plane landing into a tunnel

Typical action movies cliché is landing a plane in a tunnel or even a flight in a tunnel. Let's drop any doubts about supreme heroic piloting skills of the characters etc. and focus on aerodynamics. ...
3
votes
1answer
611 views

How much more effective is it to stir in both directions?

I have been told that industrial mixing machines (say, for cake batter) switch directions periodically, first stirring in one direction, then the other, because this mixes the material more thoroughly....
1
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1answer
85 views

If a hole is drilled at the bottom of a vessel, why is the pressure of the liquid leaving the vessel equal to atmospheric pressure?

My question is similar to this one : Should the liquid come out of the tank if a hole is drilled in the vertical wall? , but I still don't understand why the pressure within a free jet of liquid/...