# Questions tagged [flow]

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

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### Why does hot water shoot out of my reusable coffee cup when I invert it during cleaning?

In an effort to keep my reusable coffee cup clean, before washing it I rinse it out and half fill it with near-boiling hot water (from an instant hot water tap at work), and invert it aimed at the ...
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### Fluid-mechanics: Scalar field associated with velocity field

I have just started studying fluid mechanics (without a proper physics education :) and came across the following equation for incompressible steady-state fluids. $$\nabla\cdot \mathbf{u} = 0$$ ...
1 vote
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### Time Derivative of Fluid Map Jacobian (Page 10 of 'A Mathematical Introduction to Fluid Mechanics' by Chorin and Marsden)

Context and Notation I'm self-studying from the book mentioned in the post title and I'm struggling to follow a calculation performed by the authors on pages 8 and 9. Please see the pictures attached ...
1 vote
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### Liquid or powder that passes through an orifice at a consistent rate

This I a really odd and specific question, and I'm not sure this is even where to ask. A few weeks ago I thought about making a clock based on water flowing from an orifice. The obvious issue is that ...
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### Electricity is a wave of electron. But my question is from where the electrons come and where do they go?

We know that electricity is a wave of electrons bit from where do they come and where do they go? Does electricity have mass?
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### Volume of a horisontal cylindrical kerosene tank (2 methods) [closed]

Imagine a horisontal cylindrical container with a unknown amount of kerosene. Volume = Area × Length The Area of a circular segment is calculated Area of Segment = Area of Sector − Area of Triangle ...
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### Graph of velocity versus time [duplicate]

The figure shows the dependence of blood flow rate as a function of time through the aorta during a single heartbeat. Assuming that the distance of the heart to the brain is 30 cm, approximately ...
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### No slip boundary condition in Hele-Shaw Cell

A Hele-Shaw cell can be used to visualise potential flow around a cylinder. See this image from Van Dyke Album of fluid motion with the z axis of the cylinder pointing out of the page: Potential ...
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### Analytical calculation for pressure loss for an external flow across a row of cylinders

I would like to know a way to find pressure loss of air flowing across a single row of cylindrical tubes of a Heat exchanger. The heat exchanger consists of a row of cylindrical pipes with rectangular ...
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### Calculating water pressure

We've built a waterwheel to use in a small stream and are trying to calculate it's efficiency. The Hydropower equation goes as: KiloWatts = P * Q / 600, P being pressure in bars and Q being flow in ...
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### Mass flow rate of fluid flowing over flat plate

When fluid flows over a flat plate, it forms boundary layer. Then velocity drops inside boundary layer. But how does mass conserved in this case? Initially total mass is having constant velocity ...
1 vote
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### Building up pressure in the helix coil pump

My question is about building up pressure in a coil pump. Beginning at the scoop where the water pours into the hose and looking towards the center of the mill wheel, does the coil pump need to have ...
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### Pulsed Fluid jets

While feeling my shower head, switched to "pulsed jet" mode, exert a higher force on my body as compared to a regular flow jet, I have wondered why a pulsed jet is stronger than a non-pulsed ...
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### Do fluids flow from high pressure areas to low pressure areas? What theory explains that?

Do fluids flow from high pressure areas to low ones? Why ?
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### What is the mathematical derivation for no diffusion term in the mass continuity equation of the Navier-Stokes/Euler equations?

In this post the fact that the mass continuity equation in a mixture of gases has no diffusion term, i.e., $$\frac{\partial\rho}{\partial t}+\nabla\cdot(\rho\vec{v})=0$$ has been discussed. ...
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### Navier-Stokes equation viscosity term

I cannot understand how the term μ$\nabla^2(\vec u)$ is derived. Can anyone help?
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### How does gravity affect the formation of vortices?

Context: I understand the axis of vortices can form in any direction (like underwater used by fishes). However, in large vortices in water bodies, for example, in a closed water bottle, the centre of ...
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### Inaccurate flow rate measurements of an engine diesel fuel due to change of its viscosity

I am measuring the volumetric flow rate of a diesel fuel using "Turbines" flow meter, both in the supply and return fuel lines of an industrial diesel engine (Caterpillar 3512B – coupled ...
38 views

### Why does air not flow backwards in Jet Engines in the combustion chamber? [duplicate]

In jet engines air is taken in, compressed and then fuel is injected and then ignited forcing the turbine to spin powering the compressor. What I am curious about is why the combusted air isn't forced ...
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### When the mass flux is constant, why does $v d\rho = - \rho dv$?

I'm reading about mass fluxes and I came across when the mass flux is constant $$j = \rho v$$ then the following equation is true $$v d\rho = - \rho dv$$ What does that last equation even represent? ...
34 views

### How do the macroscopic observables $T$, $ρ$, and $P$ change in an ideal gas after flowing through a turbine?

I’m trying to better understand how turbines effect the flow of gas and gain or expend energy in the process. It’s easy to understand with incompressible fluids as all you need to know is the pressure ...
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### Depressurization formula for multiple holes with varying outside pressures

I'm working on a simulation that should with relative accuracy simulate the flow of air/pressure in a system of rooms (on a space ship). I found http://www.spaceacademy.net.au/flight/emg/spcdp.htm ...
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### Why is the unsteady Bernoulli equation inconsistent when applying at different points? I've probably misconceptualised the theory

Unsteady Bernoulli equation: $$\frac{P_1}{\rho}+\frac{{v_1}^2}{2}+gz_1 = \frac{P_2}{\rho}+\frac{{v_2}^2}{2}+gz_2 + \frac{f_hg}{\rho} +\int_{1}^{2}{{\frac{dv}{dt}}ds}$$ I've attempted to apply the ...