# Questions tagged [flow]

The motion of fluids (gases, liquids and granular material).

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### Reconciling various expressions of flux and flow in kinetic theory

There are a few expressions I have been shown to describe the flux $\vec{\Phi}_A$ of some quantity $A$ described in kinetic theory. I am having trouble understanding how they are related or if they ...
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### Pressure distribution around an aerofoil

Some notes that I'm reading right now show a picture of the distribution of pressure around an aerofoil with zero angle of attack. The notes say that the pressure is identical at the top/bottom ...
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### How does a viscous fluid flow?

In all problem involving viscosity, while applying $f=nA \frac{du}{dz}$ why do we consider velocity of the bottom layer to be zero?
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### Fluid mechanics

I have seen the following equation of continuity for fluid dynamics for compressible as well as incompressible fluids $$\rho_1V_1A_1 = \rho_2V_2A_2,$$ and it is derived from conservation of mass ...
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### Airflow velocity and volume loss due to friction

I have a vacuum that the manufacturer claims capable of moving 20,000 cfm of air. In my application we often connect 150 feet of 6 inch diameter, smooth bore, flexible tubing to the vacuum. I know ...
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### What is the physical meaning of irrotational flow?

I am studying fluid dynamics and while searching on the internet, found many videos explaining the mathematical aspect of rotational and irrotational flow, but i need more clarity on what actually it ...
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### What happens to the fluid flow velocity and concentration in a tube that branches out

Suppose that liquid is flowing through a tube with a constant velocity of, say 10 m/s. Within the liquid, there is a constant concentration of some substance, [S], lets say of 20 uM. Then, at some ...
239 views

### Why textbooks use geometric center/centerline of the pipe when calculating/measuring pressure?

Studying Fluid Mechanics, I started to notice that almost every textbook/website uses a specific point to make calculations about the pressure in a liquid at a given depth (hydrostatic pressure): the ...
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### Transitioning between Lagrangian and Eulerian fluid variables

I'm having trouble understanding the motivation between wanting to transition between the two descriptions. I figure that switching from Eulerian to Lagrangian fluid variables is useful if we want to ...
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### Why using average pressure in calculations gives the most accurate results?

In the saga of trying to answer the question that came into my mind while studying the basic concepts of Fluid Mechanics, "Why textbooks use geometric center to calculate hydrostatic pressure when ...
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### Does the drag equation only apply to turbulent flow

I am doing an analysis of the motion of an object in air and so I'm first finding whether the flow is laminar or turbulent. From my research, I'm still a bit confused as to whether the drag equation ...
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### How to calculate the power required by a fountain pump?

How can I calculate the power required by a fountain pump, if just the efficiency of the pump, the height of the fountain and the diameter of the water jet is given?
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### How do “pouring spouts” prevent liquid from escaping through the air intake?

You may be familiar with the types of pouring spout found in many professional cocktail bars, similar to the following: The hole on the top of the spout is an air intake, which connects to the narrow ...
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### Can all 2D solenoidal fluid flows be given in terms of a stream function?

Is it true that for any 2D solenoidal fluid flow $\mathbf{u}$ ( i.e one with zero divergence, $\mathbf{\nabla\cdot u = 0}$ ), that $\mathbf{u}$ may be obtained from a stream function? I had always ...
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### Minimal drop size

I am trying to do something that requires very high precision, so I got stuck in a question: What is the lower bound of a size of a water droplet (and what is the equation, I want to use different ...
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### Density of particles in the Lagrangian description of fluid flow

I am trying to learn about the material (or particle) derivative in fluid dynamics. I was looking through this explanation, and they mention things at the beginning and the end that confuse me. ...
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### How to get constant water pressure in a circular distribution pipe?

I have a circular 3/4" pipe( 62" in diameter). It has 11 tee outlets, 3/4"x3/4" to 1/2", which each have a 1/2" hose that funnels the water downward. The pump(400gph) is pumping the water vertically ...
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### Does molten solder flow towards a heat source?

When soldering both plumbing and wiring I have heard the advice that you shoulf apply solid solder opposite to your heat source, since the solder "will flow towards the heat" once it melts. Is this a ...
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### Bernoulli's Effect on Blood Pressure [closed]

What is the impact of height, let's say being on top of a 4,000 m high mountain, on blood pressure / flow velocity given Bernoulli's Equation?
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### Bernoulli principle

I've been trying to deduce the Bernoulli's theorem but i have a few problems Why is it restricted to a streamline? Thank you very much
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### Fluid Pressures at the End of the Pipe

Consider the very standard pipe problem used to calculate the force required to hold a pipe with a bend that has some fluid flowing through it, as shown in the image. We use Newton's second law of ...
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### Mass flow rate of evaporating water in a vacuum

I'm melting ice in a vacuum using a heating plate, and attempting to condense any water vapor evaporated from the melted water onto a cold plate. Is there a way to describe the mass flow rate of the ...
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### Hydroponics Recirculating water flow [closed]

I hope this is the right place to post this, and help would be appreciated. I've have been working on a multi tower hydroponics system for the past couple of weeks. I'm currently trying to figure ...
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### What is the force being applied? (Water Pump Problem)

Lets talk about the water pump problem where you must pump water up and out of a tank and figure out how much work was needed to accomplish this. So assume we have a cubic container with length 1 on ...
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### Is it possible to calculate natural gas (i.e. methane) flow in pipe based on temperature and pressure?

Given a known pipe diameter, pressure, and temperature, is it possible to calculate the flow rate of natural gas (i.e. methane et al) in the pipe? To me, this doesn't seem possible without some sort ...
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### Why is the contour of a stream function the same as the streamline?

I am studying acoustic streamlines. As this paper Singular points of intensity streamlines in two-dimensional sound fields says the level curves or contours of stream function represents the ...