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

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What is the impeller flow rate of a watercraft with the given information? [closed]

Given Information: Total craft mass: 100kg. Dimensions: 200cm x 60cm x 10cm thick. Water density 1,000kg/m3. Acceleration: 0 – 12m/s in 5s. Top speed: 12m/s Impeller diameter: 10cm. What is the ...
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80 views

Pressure in a fluid

If a fluid is flowing along a vertical line with a constant velocity, will the pressure at every point be the same and irrespective of height?
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1answer
43 views

Question about propellers

A ship moves forwards because a rotating propeller sends water backwards. The diameter of the propeller is as large as possible because in order to be efficient it must push the the greatest feasible ...
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1answer
34 views

Symmetry Arguments: Flow Through Cylinder

Why can for symmetry reasons a steady, viscous, incompressible flow, obaying the N.S equation: $$\rho(v \nabla)v = -\nabla p + \eta \Delta v $$ That flows through a cylindrical(very long) pipe not ...
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55 views

What makes the magnitude of the force of friction velocity dependent in one scenario, but not the other?

When a solid objects makes contact with another solid object, I believe the magnitude of the force of friction between them does not depend on the relative speed of the two objects. When a solid and a ...
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1answer
42 views

Conterflow heat exchanger with different flow rates

If we have tube in tube heat exchanger, in classic situation surface area in contact with both fluids is the same (if we ignore wall thickness of the tube). If fluids have significantly different ...
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1answer
41 views

How should I think of a liquid in terms of interatomic potential and molecular speed?

A rather simple question for liquids specialists I guess but I have hard time finding information about this. Here is my problem. I understand the ideal gas theory and the Maxwell's speed ...
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4answers
1k views

Is the velocity with which molecules of the medium oscillate same as velocity of the sound in that medium?

I wanted to know that under sound field applied molecules of the medium oscillate with some velocity in the direction of sound propagation. Is this velocity same as velocity of the sound in that ...
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1answer
23 views

How are probe liquids selected for Surface Energy measurements?

Why are water, ethylene glycol and diiodomethane generally used for surface energy measurement?
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104 views

What is the exact value of the constant in the similarity solution for blast waves?

Recently I used the Rankine-Hugoniot equation to reason that the limit of the speed of shock waves for extremely strong shocks is $\bigl(\frac{6P}{5r_0}\bigr)^{1/2}$ where $P$ is the pressure of the ...
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26 views

How can frequency of waving in water change the direction object on the surface goes?

In an Australian experiment the physicists studied effects of a simple object that causes waves in fluid. They found that if it vibrates slow, the objects on the surface moves away from the vibration ...
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24 views

Equation of state for a radiation fluid

Can anyone give me (point me to a reference of) a derivation of the equation of state for a radiation fluid: pressure = energy/3 Much thanks.
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1answer
49 views

Terminal Velocity in Water

Another question concerning classical physics. On Earth, the combination of air resistance and gravity interact in a way that creates the phenomenon of terminal velocity. Do other fluids (for example, ...
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1answer
48 views

Physics behind blowing soap bubbles

Is it possible, using the surface tension of a soap bubble, to calculate the maximum pressure (created by the air flow) it can withstand while still attached to the orifice to prevent it from ...
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28 views

What makes some air bubbles in water more persistent?

In a plastic bottle of water, near the walls, it is common to observe the presence of little bubbles (I would estimate them to be $\approx0.5$mm in diameter. In my experience, most of these bubble ...
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1answer
57 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? ...
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2answers
45 views

Why do bubbles group when one pops? [duplicate]

I was recently observing the way bubbles move as they pop and disappear. I noticed that when bubbles destabilize and pop, the remaining bubbles immediately surrounding it will move to fill its place. ...
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0answers
27 views

Gas diffusion through a flat plate boundary layer

Set-up Suppose we have a flat plate with a flow of gas parallel to the plate. The flow creates a boundary layer on the surface of the plate. Now, the gas is carrying a reactive species, which is ...
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1answer
37 views

Integral of a velocity profile?

Part of my fluid mechanics homework asks me to solve: $${\partial u\over \partial x} = 0$$ Which represents how the velocity profile, u, changes in the x. I'm not sure whether you can integrate ...
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About the fluid friction along the wall in pipes

I wonder how can the friction between the fluid and the wall in a cylinderical pipe can be calculated. Is there any theory that i can refer to? i also want to check if there's any relation between the ...
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How does air going through silica gel change its humidity

Assume that the properties(temperature,humidity,velocity and so on) of the incoming air flow stay constant. The air flow goes through a silica gel plate. Humidity of the air will decrease, but how to ...
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1answer
53 views

Energy taken to move volume of blood through a blood vessel

I am trying to find simple ways to get rough answers to how much energy it would take for a unit volume of blood to move along a blood vessels. My main aim is to compare energies it would take for a ...
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1answer
68 views

Fluid filled open container in space/vacuum

I have water in a bottle, as I open it in space(or vacuum for that case ). From what I have read in books the water will instantly vapourize,as the vapour pressure of the water inside, far exceeds the ...
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Diesel injector sac pressure calculation [closed]

I am trying to calculate the nozzle sac pressure required to deliver 60mm3/ms of diesel fuel into a pressurised cylinder (19MPa). The nozzle has 5 delivery holes of diameter 0.157mm and the discharge ...
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2answers
37 views

Does eq. of continuity hold in vacuum too?

When a streamlined flow of water flows down through an ordinary tap, it's cross-sectional area decreases according to eq. of continuity due to atmospheric pressure. If the same apparatus were to be ...
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1answer
32 views

Does water have shear thinning property? [closed]

I'm working on a project and I need to know if the water is viscoelastic? does water have shear thinning property?
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41 views

What is the filling time of this liquid storage tank?

A spherical storage tank ($R=3\:\mathrm{m}$, heated just enough to keep the sodium liquid) has to be filled from the lowest point with liquid sodium (at just above its melting point). A pump, very ...
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What is the difference between the pressure and “pressure force”?

I am in the process of going through a question pertaining to inviscid flow over a cylinder. The velocity field is, in polar co-ordinates: $$\vec{u} = U_{\infty}(1 - (\frac{a}{r})^2\cos2\theta,- ...
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1answer
81 views

Why does pressure decrease as velocity increases?

Bernoulli's principle states that as velocity increase pressure decreases. But higher the velocity, greater is the temperature and pressure must be high. Can you explain the situation in both the ...
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16 views

What is the significance of the characteristic length in the Reynolds number formula? [duplicate]

It is said to be the diameter of the duct in closed flow cases, but what is its actual physical meaning in other types of flows, such as the flow over a flat plate?
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14 views

Should tunnel calibration factor be less than 1?

Regarding an experiment in which air is blown past a small-scale object (i.e. a cylinder) in a wind tunnel, should the tunnel calibration factor be less than 1? I couldn't find anything about this ...
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32 views

How do impurities affect the surface tension of fluids? [closed]

I want to know what happens to the surface tension of fluids if we add impurities and the reason behind it.
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2answers
35 views

Why boundry molecules have more energy?

In a system of a solid or a liquid, why the molecules in interface have more energy compared to the bulk of solid or liquid?
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19 views

Can the flow of hydrogen in a fuel cell be modelled as adiabatic?

Okay, so right off the bat I'll admit I need this for a problem I'm working on. Not homework though, a project, as a matter of fact. I'm considering taking compressibility effects into account, but ...
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2answers
108 views

How fast does the water have to go? [closed]

I have a pot of water. There is a one-way filter at the bottom right: How fast would the water have to be travelling to go into the tank via the one-way filter? Also, I would like to have some ...
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21 views

Hydraulic conductivity and flow rate

I have several sources that have the following equation relating the change of volume in a cell to the hydraulic conductivity (permeability coefficient) $L$ and pressure differential $\Delta P$: $$ ...
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1answer
43 views

Why we have a leak in the pipe if the fluid pressure is lower than the atmosphere

I've read in many books that if our flow pressure is lower than the atmospheric pressure then we'll have a leak in our pipe, but I already know that the flow is always from the high pressure point to ...
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33 views

Identity in continuum mechanics [closed]

For a problem in the textbook I am reading, I need to prove that $$\int_Vw_{i,j}v_jdV = \int_Sw_iv_jn_jdS,$$ where $S$ is the boundary of the volume $V$, $v_i$ is the velocity vector field of a ...
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1answer
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vorticity not zero - why

I am quite new to fluid dynamics and I cannot seem to understand the concept of vorticity. It is defined as $\nabla\times\vec{v}$ where $\vec{v}$ is the velocity vector. Now (working in cartesian ...
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Standing waves and acoustic levitation

i am doing a new personnal project about acoustic levitation with standing waves into ambiant air using a piezo ultrasonic tranceiver and a reflective pannel. I modelised both of the emission and the ...
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1answer
107 views

Mach no. should be constant for existence of similarity solution

I am reading some research papers on Taylor-Sedov type self-similar solution to the blast wave problems... It is written that for the existence of similarity solutions Mach number should be ...
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3answers
58 views

Calculate acceleration based on differential pressures

In my example, water is in a tube and is being accelerated by a compressed air. I already know that $P = \frac{F}{A}$ so if you know the pressure and you know the surface area its acting on, you can ...
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1answer
36 views

Water coming out of a vertical tube lifts a weight to a certain height [closed]

Before I even start the question I would like to apologize in advance for some grammar mistakes since I translated this question from another language. Water is coming out of a vertical tube at a ...
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1answer
43 views

How the flow is distributed when the water flow from one river/drain to multiple rivers/drains?

Assuming that water ( total amount $Q$) flows down from one river/drain, into multiple rivers/drains, under the action of gravity, as shown below: How the flow ($Q$) will be divided among different ...
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23 views

Why the meandering ratio of river different from different study?

Referring to this question Is the meander ratio of a river $=π$? According to the accepted answer, based on a paper by Leopold and Langbein The resulting curve is not quite a semi-circular ...
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2answers
21 views

Would a hybrid mixed medium balloon allow you to use less helium to lift equivalent weight?

Suppose you had two balloons, one inside the other (a inside b). Would filling balloon "a" with the 80% nitrogen/20% oxygen mix you find in the surrounding air at ground level, and then filling ...
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2answers
41 views

Example of basic(?) fluid dynamics [closed]

I am completely new to the world of fluid dynamics, I have tried to come up with what I hope will be a simple case. How does one go about calculating the following? I am far more interested in the ...
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0answers
26 views

Resonant frequency(s) of system of resonant objects?

I am trying to gain a better understanding of resonance when we are dealing with a coupled system of resonating objects. For example, say we have a single gas bubble in liquid and suppose it ...
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1answer
34 views

What causes fizz?

When you go to a soda fountain and pour some soda into your cup, frothy fizz is generated at the top of the cup. What causes this? Obviously has something to do with carbonation, but when my cup is ...
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1answer
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How do I find a stream function given a volumetric flow rate?

How do I find a stream function given a volumetric flow rate? The flow only occurs in one direction, between 2 plates, and I have no knowledge of velocity. I know that volumetric flow rate = ...