All Questions
Tagged with fluid-dynamics thermodynamics
609 questions
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Intertial finite-size effects in fluid simulations
A gradient $\nabla \rho$ in the density field $\rho$ of fluids at thermodynamic equilibrium is suppressed at a rate given by $D \nabla^{2} \rho$, allowing to measure the diffusivity $D$ of the fluid ...
- 905
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Would a candle in very high gravity blow itself out?
A candle creates an upward draft of hot air, without which the flame would be spherical. The buoyancy generated is proportional to the density difference as well as the strength of gravity.
Suppose a ...
- 6,665
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2
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84
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Do negative pressures in Thermodynamics lead to a negative stress energy tensor?
If we have a gas or liquid described by the van der Waals gas law with negative pressure, does that lead to a negative stress energy tensor?
Does a stretched liquid for example have a negative stress ...
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Mach number: understanding incompressibility through acoustic time scale
In the past I have always recognized the mach number as being the ratio between the bulk velocity of a fluid $v$ in relation to the speed of sound in that medium. I have also seen how one can derive ...
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Can ideal gas equation be used in presence of gravity? [closed]
While assuming the ideal gas we need to neglect gravity and other forces acting on the molecules but I have seen in many questions that ideal gas equation is used even in presence of gravity
Please ...
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Does air gap between enclosed chamber and manometer influence the manometer reading?
We have an enclosed chamber filled with water. From the top of the chamber there is a metallic tube connecting the chamber to a monometer. We increase the pressure of the water inside the chamber buy ...
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3
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312
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What is the liquifaction pressure for hydrogen?
According to the most reliable source on the internet. Hydrogen has a density of 0.07099 Kg/L. Thus divided by it's molecular mass, in one liter of liquid hydrogen we should have 35.21888395 mol.
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243
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How to cool a cup of coffee faster?
Here is a question I have always wondered about.
I have a family member that dislikes drinking hot beverages (e.g. coffee, tea). https://www.flickr.com/photos/adamcohn/16290609394
This family member ...
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How can hydrodynamic fluctuations induce repulsive force?
The paper https://doi.org/10.1039/C5SM02346G considers a compressible fluid subject to thermal fluctuations and confined between two planar rigid walls. The fluid is modeled with stochastic ...
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The viscosity of Natural gas
At low pressures, gas viscosity increases as temperature
increases, which is mainly due to increase in the intermolecular collision that is
caused by an increase in molecular friction. However, at ...
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Is sound really adiabatic because it is a fast process?
In many books I have consumed so far there is the statement that sound is adiabatic because heat transfer does not have nearly enough time to reach isothermal equilibrium. Doesn't this contradict ...
- 1,391
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How do I interpret the energy per particle in the Smoothed Particle Hydrodynamics (SPH) formulation?
I'm working on a basic Smoothed Particle Hydrodynamics simulation. I figured I would start with an ideal gas with equation of state $p=K\rho$. However, in calculating the SPH equations of motion, we ...
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How come the pressure gradient is equal to the divergence of pressure in incompressible fluids?
The net force due to pressure on a surface can be calculated by integrating the pressure over the surface. The equation for the surface integral of pressure is:
$$\vec{F} = \iint_S p\hat{n} dS$$
where ...
- 11
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102
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Does mercury spin when heated by a flame?
I heard that if a dish of mercury is heated by a moving flame placed under it, the mercury will spin around -
Sanderson [Ivan T. Sanderson, biologist and paranormal researcher] then goes on to make ...
- 81
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Coupled degenerate wave equation and heat equation via transmission with Gurtin-Pipkin or Coleman-Gurtin thermal law
I am a mathematician and I am working on studying the stability of coupled degenerate wave equation and heat equation under with Gurtin-Pipkin or Coleman-Gurtin thermal law.
The classic wave equation ...
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1
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86
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Help with understanding Kinetic Energy change of compressible and incompressible flow through a nozzle
When a compressible (say, ideal gas) fluid and an incompressible fluid (when flowing, the divergence of velocity is zero) flow through a adiabatic converging nozzle, will the exit velocity of the ...
- 649
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Why do we move the spoon in a plate to cool it down?
Say we have a plate full of soup, why to cool it down we move the spoon around in the plate? Is it to facilitate the thermal interchange between the air and the soup? Also why is the edge of the plate ...
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166
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How does the pressure inside a pipe drop for a compressible gas (hydrogen)?
It is about turbulent compressible fluid, in this case, hydrogen gas.
I have hydrogen gas at Ti = 25 K, pi = 3 bars, and ṁi = 0.001 kg/s (so 2.214 m/s) at the inlet of the tube. The pipe is 12.7 mm in ...
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Why does a dump yard stink more in the night?
There was an open dump yard a few miles away from where I used to live for an internship. It was not noticeable during the daytime, but once the sun sets, the dump yard reminded us of its presence ...
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How could we caluculate the amount of heat transferred through convection when a fluid flows over a curved surface?
In the case of convection heat transfer during fluid flow over a flat plate , we deduce the governing equations based on conservation of mass , momentum and energy, using this equations we find the ...
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Fluid dynamics and venturi
A coworker and I were discussing this issue related to fluids dynamics, Venturi and Bernoulli. We are both a bit rusty with our knowledge, so we know something is wrong in our reasoning, but I need ...
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104
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Internal pressure in rigid gasoline tank from increase in temperature [closed]
I was hoping to find a chart (or detailed table) that depicts the increase in internal pressure for a rigid tank full of gasoline from increases in temperature.
If this is not available then I wanted ...
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77
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Relation of first adiabatic exponent to adiabatic index
I'm going through a fluid dynamics text and I'm a little confused by a listed relation. The first adiabatic index is defined as
$$ \Gamma_1 = \left(\frac{\partial \ln P}{\partial \ln \rho}\right)_s, $$...
- 472
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59
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How to modify kinetic gas theory to work for macroscopic particles? (2D)
For the first time I framed a question on my own when I was recently playing carrom pool with my cousin and a striking thought ran across my mind!
I was thinking if a square frame is fixed rigidly on ...
2
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1
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76
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How can I derive this thermodynamically equivalent expression for the speed of sound?
Background
In Viscous Fluid Flow by White, the speed of sound for a gas is given as
$$\tag{1-71}
a^2 = \frac{\partial p}{\partial \rho}\big|_s
$$
where the partial derivative is computed at constant ...
- 292
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82
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Airflow between two rooms (one hot, one cold) [closed]
Scenario —
It is night time and somewhat cold outside.
Room 1 (Bedroom): The window is slightly creaked open. I have a space heater going on continually heating room 1. One door is closed to the ...
4
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3
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623
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Why friction increase subsonic speed through pipe?
I know equations of Fanno flow but can anyone explain physically how friction increases subsonic velocity and decreases supersonic velocity through pipe ? is that for sake of boundary layer ...
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370
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Is natural gas transported as a liquid or supercritical fluid? [closed]
is natural gas transported as a liquid or supercritical fluid?
I am curious as to what phase natural gas is in when being transported in pipelines over long distances. Both liquid and supercritical ...
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4
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466
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Why wouldn't this perpetual motion machine work? [closed]
The water is supposed to run infinitely in this container, since when water drops the pressure inside the container decreases, which makes the water in the pipe ascend. I know that perpetual motion ...
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How does Temperature of a system change if doing work on the environment? Can the temperature of the system increase?
I am just a bit confused about how to relate Temperature and work. If my system is doing work on the environment, could the temperature increase? I know that you can lower energy while raising entropy ...
- 51
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575
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Work done by free expansion of gas and the energy of the piston
So this has been bothering me for a while. I know that for a free expansion of a gas, work done by it is zero. However, I have a doubt regarding the kinetic energy gained by a piston during this free ...
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313
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What is the underlying concept in case of finding pressure inside a balloon kept at some height in atmosphere? [closed]
If we have a balloon containing air at sea level. Is the value of absolute pressure inside the balloon decided by the temperature of the enclosed air or by the height of atmospheric column above it ...
- 1,395
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Howe energy is exchanged in vortex tubes?
In vortex tubes, energy is transferred from some particles (which will be pushed to the centre (how?) and form the cold stream) to some other particles (peripheral particles, which will form the hot ...
- 1,148
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182
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What's the $T$ around a candle?
I think most of you have already heard of the candle lift/elevator. It's a funny experiment that is easy to perform too. If you don't know what I'm talking about I would recommend you to watch the ...
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In a non-rotating sphere of fluid heated from the centre, what does the flow look like?
Consider a perfect sphere of fluid which is not rotating, is under the influence of its own gravity only, and is heated from the centre. What does the flow of fluid in the body look like?
In the ...
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Are the force frequencies the same in the discrete and continuous case?
Let's say I have an ideal gas of particles and the strike zone of area $\sigma=\pi d^2$ of a molecule of the molecule is what is the sub system considered. The end of the face of the cylinder is the ...
- 1,349
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Would turbulence from flowing streams into a system be a form of work or heat loss?
Imagine a situation like this. If we consider the T-elbow to be our system, both the hot and cold streams are bringing energy into it (KE, flow energy, $u$).
However, in the middle where the streams ...
- 1,106
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Relaxation of the Boltzmann transport equation
My professor in kinetic gas theory said that when considering the Boltzmann Transport Equation (BCE)
$$
\partial_tf + \frac{\vec{p}}{m}\cdot\nabla_{\vec{q}}f + \vec{F}\cdot\nabla_{\vec{p}}f = (\...
- 324
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Derivation of vorticity equation (incompressible flow)
In the following derivation of the vorticity equation, I do not understand how $\nabla \cdot v=0$ implies $\frac{1}{\rho^2}\nabla \rho \times \nabla p=0$.
We start with the Euler equation
$$\frac{\...
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72
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How can the Boussinesq Approximation simplify the general form of the temperature equation for fluids? [closed]
In Transport Phenomena by Bird, Stewart, Lightfoot (2nd edition), on page 337 (11.2–5), the equation for the change in temperature is derived:
$$
\rho\hat{C}_{p}\frac{DT}{Dt}=-\left(\nabla\cdot\mathbf{...
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82
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How can you add pressure and internal energy in relativistic enthalpy?
In relativistic fluid dynamics the relativistic enthalpy in natural units is defined as:
\begin{equation}
h = \frac{e+p}{\rho},
\end{equation}
Where $e$ is the total energy density and $p$ is the ...
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Would pumping warm humid air through a pipeline up to the top of a mountain produce a lot of fresh water?
I have been doing a lot of research on the Internet lately about desalination processes and desalination plants and this led me to studying mountain weather and the orographic effect or orographic ...
user300400
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86
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What algebraic manipulations make this two equations equivalent?
I have a very basic mathematical backround. I kind of understand the concept of a partial derivative but i dont know what algebraic manipulations make this two equations equivalent (the ones on 2A.4) ...
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Can a cold gas be considered as ideal at a very high speed?
Considering a plane flying in the atmosphere, my book uses the perfect gas law $pV=n\bar RT$. Yet, as the plane itself is taken as the reference, the air ($T=-50°C$) has a speed of $800 \ \mathrm{km/h}...
user343933
3
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Burning a match in a one-exit tunnel (or Heavy Rain trial of the butterfly scene)
If you light a match in a narrow labyrinth tunnel where there is only one way the air is coming from, will the flame of a match bend in that direction?
In other words, I want to know if the trick one ...
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3
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882
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Why does a chimney sometimes create a "draft"?
Sometimes, while lighting a fire in a wood stove in a basement, the smoke does not exit through the chimney like it normally does. Rather, a large amount of the smoke seems to get "pushed back&...
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Derivation of thermal boundary conditions at fluid-fluid interface?
I am solving a problem in thermoelectric magnetohydrodynamics (TEMHD). I am currently going through the process of understanding the boundary conditions at a fluid-fluid interface. I understand that ...
- 21
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Enthalpy in Euler's Equations: Does Isentropic Flow Imply Homentropic Flow?
In the derivation of the Euler's equation of motion for ideal fluids by Landau and Lifshitz, I am able to follow the derivation of the following equation
$$ \frac{Dv}{Dt} = \frac{\partial v}{\partial ...
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1
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133
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Disappearing cola in a hot car
I unadvisably left an unopened can of cola in my car on a very hot, sunny day. The top blew off and when i recovered the can it was clean and dry inside. Except for a few sticky droplets on the ...
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Compressed air efficiency if expansion cooling is used [closed]
Compressed air energy storage is looked down upon because of the inefficiencies it brings along. Every article I've found till today, makes use of the stored energy by converting it into mechanical ...
- 350