The quantitative study of how fluids (gases and liquids) move.
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8 views
Bernoulli principle and viscous loss
Imagine I have a fluid flowing at a rate Q in a closed circuit with no viscous losses (Bernoulli's principle applies + total energy is equal to the kinetic energy). Now, I add a resistor with ...
5
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2answers
119 views
Does continuity equation hold if the flow is accerelated?
I'm Studying the streamline flow, specifically the continuity equation Bernoulli's Principle.
Consider the following system where a liquid flows through the pipe of a uniform area of cross section ...
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0answers
14 views
In enthalpy, is PV the pressure energy?
In the case of a fluid, does the $PV$ contribution to the enthalpy correspond to the pressure energy in fluid mechanics? (Related: What is Pressure Energy?)
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2answers
38 views
Which vessel is emptied first and why among water, mercury and kerosene?
Three identical vessels A,B and C are filled with water,mercury and kerosene respectively up to an equal height. The three vessels are provided with identical taps at the bottom of the vessels. If the ...
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1answer
35 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.Could someone explain how water accelerates at the nozzle when the diameter of the pipe ...
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0answers
16 views
Terminal Velocity and Drag Force: Doubt [duplicate]
I'm afraid that my previous thread was not clear. Let me begin again:
Let's assume that I'm dropping steel balls into oil or another viscous fluid, and I want to calculate the terminal velocity.
...
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0answers
31 views
Urgent Question on Terminal Velocity and Drag Equation
I'm currently performing a physics experiment, in which I'm determining the relationship between radius of steel balls and their terminal velocities in a highly viscous liquid. However, I'm unsure of ...
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1answer
23 views
Why do we need the kinematic viscosity?
Kinematic viscosity is the well known dynamic viscosity divided by density. What difference does it make to divide by density? What is so useful about this?
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16 views
Heat system: Dynamic - quasi-stationary - static
I am an engineer in the field of district heating and in the future I will work together with people from computer science and physics. I have a question regarding dynamic/quasi-stationary and ...
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0answers
31 views
Toricelli's law of efflux in moving container
Suppose there is a big tank of water with a small hole near the bottom. Now if this tank starts moving with say a velocity 'v', then will Toricelli's law hold? I tried directly applying Bernoulli's ...
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0answers
22 views
What is the impeller flow rate of a watercraft with the given information? [on hold]
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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0answers
52 views
Why propellers are curved?
A naval architect told me that the water leaves a ship propeller at unchanged axial speed, but with a substantial rotation whereas it came in axially. If this rotation is not produced there, will be ...
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2answers
71 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
36 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
30 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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4answers
48 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
35 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
38 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
961 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
13 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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0answers
40 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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0answers
24 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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0answers
22 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
43 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
37 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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0answers
24 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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0answers
36 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
39 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
17 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
35 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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0answers
20 views
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 ...
3
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0answers
22 views
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
51 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
64 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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0answers
11 views
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
31 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
27 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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0answers
34 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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41 views
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
64 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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0answers
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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49 views
How to find all the axiomatic formula needed for the PHD level fluid mechanics and heat & mass transfer [closed]
How to find the list of all the axiomatic formula needed for the PHD level fluid mechanics and heat & mass transfer before the year of 2017?
Axiomatic formula refer to the formula that are unable ...
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0answers
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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0answers
21 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
25 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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0answers
15 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
105 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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0answers
20 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
39 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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28 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 ...
