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

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What concepts/rules apply for multi-stage pumping of water

For single stage (ie one pump) water transfers calculations for pressure loss are commonly done by adding the elevation difference of the start and end of the pipe line to the friction losses that ...
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26 views

Viscosity and surface tension

Both viscosity and surface tension are dependent on the intermolecular forces between the molecules of the liquid. Supposing from this, shouldn't there be a directly proportional relationship between ...
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11 views

Equal volumetric rate versus area open to flow [on hold]

A vertical water disposal well has been drilled and cased. There are two horizontal rock formations that the wellbore intersects and these formations will be targeted for water disposal. To allow ...
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In hydroelectric power stations, can i use valves in place of turbines? [on hold]

In hydroelectric power stations, can i use valves in place of turbines? by replacing turbines with valves, we can control flow of water, so we can totally handle hydro electric power stations ...
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12 views

Is work done on a fluid in a communicating vessel necessarily equal to work done by the fluid inside it?

During the explanation of Pascal's law the argument that work done by a force to move the fluid inside communicating vessel is equal to the work done by the fluid at the other end of the vessel was ...
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Why should fluids be confined for Pascal's Law to be applicable

When is Pascal's law about fluid pressure propagation applicable? Is it applicable to a closed circular pipe with a pump rotating the fluid, but not to a tub of water. Most statements require only ...
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28 views

Fluid dynamics - immiscible liquids

Question: A U-tube of uniform cross-section is partially filled with a liquid I. Another liquid-II, which does not mix with liquid I is poured into one side. It is found that the liquid levels of the ...
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Complete the formula that relates standard volumetric flow (Qstd) with Actual volumetric flow(Qact), knowing ρact and ρstd [on hold]

Complete the formula that relates standard volumetric flow (Qstd) with Actual volumetric flow(Qact), knowing ρact and ρstd. this is a question i must complete in my online instrumentation course ...
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13 views

Air unit selection and duct sizing [on hold]

I am not sure if this is the right place to post this. But would you please provide me with a concrete example showing the selection of an air heating/cooling unit along with the required duct sizing ...
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Why does hot food give off vapor?

Does your food melt and then boil to give off this gas? What is the vapor here?
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69 views

Why to write the Navier-Stokes equation with dimensionless quantities?

The Navier-Stokes equation is $$\rho \dfrac{D\mathbf{u}}{Dt} = -\nabla p+(\lambda+\mu)\nabla(\nabla\cdot\mathbf{u})+\mu\nabla^2\mathbf{u}$$ Then if the flow is incomprresible, and the fluid is ...
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Torricelli with constant vertical drain speed

Now I've been playing with this for some time but I can't seem to put things into perspective. I wan't to find out the curvature of the bowl so that the vertical drain speed of the liquid is ...
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2answers
34 views

Is the amount of hydro-electricity harvested, proportional to the number of turbines? [on hold]

I've looked on this site and people have said that it wouldn't make more energy that it would cost to have water turbines on a water tower. But if it only takes say three pumps (I don't know what it ...
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Diffusion Equation [on hold]

Please give me some guidance on my following assignment of Simulations in fluid flow: Thank you. Solve the following differential equation for transport of f(x,y,z,t) by MS Excel ∂f/∂t+Ux ∂f/∂x+Uy ...
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3answers
2k views

How can rising bubbles shrink and disappear?

I was recently looking at a Wurlitzer juke box, and noticed something strange. It's decorated with liquid-filled tubes. Gas bubbles are injected at the bottoms of the tubes, and the bubbles naturally ...
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26 views

Why are lubicants like grease or oil slippery?

I know that grease or oil are slippery in nature but never thought of why? I want to know what causes this tendency.
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1answer
546 views

Pressure loss in a syringe

I'm currently working on a problem which is really giving me some issues. The problem concerns the force required to expel water from a syringe. We have a 20 ml syringe (which is $2\times10^{-5}$ ...
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Hit a bottle of beer on the top with another causes the first to spit all the gas, why?

So, on the other day me and my colleges were discussing the following phenomena: Pick two open bottles of beer. With the bottom of the first, hit the second on the bottleneck, in the following way: ...
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22 views

How water and honey behave with increasing pressure?

Is there any relation between pressure and viscosity of water and honey? I hardly found the topic. Is it related to the Laplace law?
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1answer
22 views

Interaction between body and fluid

I'm trying to understand locomotion of bodies in fluids with low Reynolds number and I'm having a hard time to understand the interactions between the body and the fluid. Suppose $D\subset ...
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2answers
61 views

Friction Between Liquid and Solid Surface

How does friction between liquid surface and solid surface differ from viscosity, the friction between liquid and liquid surfaces? Also has a word describing the process been invented or is ...
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1answer
1k views

Paper plane between two fans - is this possible?

The setup: two fans facing each other, distance around 1m. Both are turned on. In between them, place a simple paper plane and according to this video, it will fly. ...
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1answer
305 views

Fuel tank draining [closed]

A cylindrical fuel tank is being drained from the bottom as in this picture : Conservation of flow rate : $v_A = \frac{S_B}{S_A}v_B = \alpha v_B$ Assuming that $z_B = 0$, Bernoulli's theorem ...
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How can q=mcp(deltaT) be made dimensionless?

Specifically, how can I make $m C_p$ dimensionless? I've tried using the Reynolds number and Peclet number definitions to plug into there but the closest I've gotten to was: $q=\pi D Re Pe ...
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4answers
178 views

Particles scattering on fluids: breakdown of the effective continuum description

When does the macroscopic continuum description of a medium like a fluid break down? Say I'm interested in a scattering process of some particles with momentum $p$ and energy $E$ off a fluid of ...
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5answers
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How far can water rise above the edge of a glass?

When you fill a glass with water, water forms a concave meniscus with constant contact angle $\theta$ (typically $\theta=20^\circ$ for tap water): Once you reach the top of the glass, the water-air ...
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Flash evaporation

What is the greatest cooling that can be effected by flash evaporation of water? Will any other liquid cool better? What conditions allow for that maximal temperature drop? And, finally, will the ...
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11answers
8k views

Why does dust stick to rotating fan propeller?

Why does dust stick to rotating fan propeller? Intuitively, most people (including I) think of the dust will not stick to rotating fan propellers. EDIT 1: Thank you for the great explanations. I am ...
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31 views

Why the viscosity $\mu$ is called “dynamic” viscosity? [closed]

In fluid mechanics we have the co-efficient of viscosity $\mu$. Why is the adjective "dynamic" added to it?
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1answer
181 views

Calculating water flow as function of the height of water above the inlet pipe

The Source of Water is Pond where the water level do change randomly. A pipeline of 200mm pipe diameter run for around 2500 m. The Height difference between the level of the inlet pipe and the level ...
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1answer
40 views

Estimate the maximum distance of water spatter

There is a faucet dripping water from height $H$ onto a smooth, horizontal ceramic surface, and I need to give a upper bound of the maximum distance between the water spatter and the point directly ...
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Why does water pouring from a glass sometimes travel down the side of the glass?

If you have a glass of water, say, three quarters full and you pour it at an angle of say, $45^{\circ}$ with respect to the the table, the water comes out of the glass and goes directly down towards ...
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1answer
387 views

Force required to move a fluid out of piston at depth

I have a cylinder filled with water in it at the bottom of the ocean. Say 100 meters down. In this cylinder is a piston that moves up and down. Its job is to squish the water out the bottom of the ...
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28 views

Liquid placed in a rotating cylinder

The Question A closed vertical cylinder is filled with an incompressible liquid of mass m completely. The cylinder is now sealed from all sides and rotated about ...
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1answer
31 views

Streamlines for the velocity field $(x, y, 0)$?

Using the equation $$\frac{dx}{x} = \frac{dy}{y}$$ the streamlines for the velocity field $u = (x, y, 0)$ are given by $x = By$ where $B$ is some arbitrary constant. This will give us infinitely ...
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102 views

Movement of a cylinder filled with water

Not long ago I was pretty bored at a dinner and I started playing with a water bottle that was not empty: I've been quite interested in its behavior when putted on its side and pushed: the bottle of ...
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2answers
5k views

Determine viscosity using falling sphere (Stokes Law, Ladenburg correction)

Introduction I am trying to determine the viscosity of a fluid. Therefore, I let a sphere of known mass m and radius r fall ...
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22 views

Non-steady state gas expansion

Please look at the following link for the sketch of the problem: Adiabatic Expansion with expanding control volume I have a certain amount of gas at a certain pressure and temperature at the start. ...
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1answer
634 views

Calculate flow rate of air through a pressurized hole

I was wondering about this: If there is a pressurized container, like a tank of compressed air at some pressure that is greater than the ambient air pressure, and this tank of air has a hole in it, ...
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1answer
228 views

Pipe in a flowing river problem

I'm working on a certain problem in fluid mechanics, which isn't really my strongest area. The problem is as follows: Curved pipe is partially submerged in a flowing river so that one end is pointing ...
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14 views

Wind water interface [closed]

can anyone tell me how to model the effects caused by a gusty wind blowing over the surface of a rain water puddle please? Thanks Donovan
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2answers
181 views

At what speed would you die upon impact with water?

If we hit the water at great speeds, we die. This is because the water has no time to "move out of the way" and acts as a "solid" surface. At what falling speed can we consider the water as a ...
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2answers
106 views

Will the box move if I blow air inside it?

Suppose that I have a box in space and it is filled with air in it. I keep a fan at one end and blew the air to other end. The air will hit the box with some velocity, so it should move. I know that ...
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1answer
113 views

Integrating pressure over a surface

Consider the 2D airfoil below. In engineering (and maybe physics) you will often see something like the following as an expression for the pressure force acting on a surface (in this case a curve ...
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1answer
75 views

Computing the force generated by a sail on a boat

This is a follow up question to the question I asked yesterday: Problem understanding basic sail mechanics I am focusing purely on the Newtonian aspect of motion and I am computing this as ...
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1answer
89 views

Rayleigh-Taylor Instability dependence on acceleration direction

I'm trying to bolster my understanding of the Rayleigh-Taylor instability, and I've gotten stuck on the point of which fluid (more or less dense) is being accelerated into the other. Cases of uniform ...
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1answer
48 views

Isothermal compressibility

How does one get from the thermodynamics definition : $$ \chi_T = -\frac{1}{V} \left(\frac{\partial V}{\partial p}\right)_T$$ to the fluid dynamics definition : $$ \chi_T = \frac{1}{\rho} ...
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What is the minimum bend radius of a square optical fiber on a microfluidic chip interface?

I want to make a microfluidic chip with colorimetry cuvettes with 100um square optical fibers coupled to the side of them. They should bend at a 90 degree angle to exit the side of the chip in a ...
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1answer
206 views

Torque on a rotational cylinder in viscous fluid

I've been stuck on what I'm pretty sure is a simple part of a larger question. It's a cylinder (radius a) spinning in a viscous fluid. It's rotating at rate $\Omega$ .During this question we get that ...
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1answer
272 views

Considerations and questions for a DIY heat pipe; how to choose a working fluid?

I plan to build a DIY heat pipe! For more info on what a heat pipe is, see Wikipedia. I would like to use it to cool a desktop graphics card I have. I am having trouble deciding how to choose the ...