All Questions
Tagged with thermodynamics fluid-dynamics
609 questions
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How Dump Tubes (arrangement with lot of perforation) reduces the pressure of Steam flow. How to derive a scientific basis of designing a dump tube
Recently I have come across simple yet intriguing device - The steam dump pipe with multiple perforations (orifices).
The dump pipe is typically used to reduce the steam flow pressure. The inlet steam ...
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34
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Can a window fan keep heat indoors? [closed]
Can a window fan keep heat indoors when it is colder outside than inside? Suppose a window with 1 unit of area must be open. If the goal is to decrease the rate at which the inside / outside ...
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Does viscosity increase temperature of a fluid at the cost of macroscopic kinetic energy?
Viscosity on molecular level can be stated as a transfer of momentum from fast moving layers to slow moving layers through random molecular collisions. So can we state that (in case of no external ...
user366132
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Throwing near-boling water into minus 20C air
I have observed my daughter throw a flask of near-boiling water into the air outside at -20C. The water appears to turn into "steam" which actually appears to be ice crystals. She also tried ...
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Why can I hear when my shower gets hot?
I noticed recently that when I turn on my shower, I can hear the moment that the water heats up. The hissing sound gets slightly louder and its pitch changes. The pressure doesn't noticeably change ...
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Nusselt number for developing turbulent flow
I need to develop a uniform method to cool a plate 1 degree, our idea was to let helium flow under it to transfer heat via convection. I concluded by some calculations that the Nusselt number for ...
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2
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Doubt with Heat and Potential Energy. (Warning: Many Assumptions) [closed]
I had a question in my Textbook which reads as follows,
Before that, we have to assume that the flowing water is ideal.
So, here we have to equate Change in Potential Energy to Heat Energy/Internal ...
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37
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Explosions in high viscosity liquids
I was watching The Score (2001) in which De Niro manages to make a hole in a cobalt and titanium infused steel safe. he fills it with water. inserts an explosive and boom! the safe is open.
It made me ...
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Evaporation of water due to vacuum aspiration?
In my research, I have encountered the following problem:
I have a vacuum pump that I would like to use aspirate water from below an elastic surface. The water resides under the elastomere and a tube, ...
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Why is the air speed of a general fan less than 500 meters per second?
I am confused. Since the thermal motion speed of air molecules is about 500 meters per second, why is the air speed of a general fan less than 500 meters per second?
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How to bends in a pipe influence the heat transfer rate?
We can calculate the energy required to heat water flowing through a pipe using the formula
𝑄˙=𝑚˙𝐶Δ𝑇
Where
𝑄 is the heat transfer rate (in watts, W), 𝑚 is the mass flow rate (in kilograms per ...
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Smoke simulations and how to render them
I recently began a real time smoke simulation system, and I need some help with the rendering. I didnt know if to ask here or on the game development stack exchange, but I decided here as it is ...
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Why isn't there a term of temperature in Navier-Stokes equations, despite that gradients of temperature cause transfer of energy?
There is something that I don't understand it at all, which is the non existence of temperature in the Navier-Stokes equation! Isn't these equations are found in the first place to describe the motion ...
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134
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Why is pouring hot water visibly different from pouring cold water?
Every morning, I fill my electric kettle from the fridge at room temperature or below ($\approx 70 \ ^\circ \text{F}$, $\approx 20 \ ^\circ \text{C}$), set the water to boil, then leave the room to ...
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Why the exhaust pressure should be equal to ambient pressure? (Part 2) [closed]
I'm asking a follow-up question to J. Pipiskin's post: Why the exhaust pressure should be equal to ambient pressure?.
TRF's answer shows a plot of normalized thrust vs exhaust-to-ambient pressure ...
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Deriving the general energy balance equation of an open system from Reynold's Transport Theorem applied for energy
The general energy balance equation for open systems is as follows:
$$\frac{\mathrm{d}(mu)_{cv}}{\mathrm{d}t} + \Delta \left(u + \frac{1}{2} v^2 + gz\right)\dot{m}_{fs} = \dot Q + \dot W,$$
and the ...
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Advection equation of heat transfer during fluid flow in pipe with heat loss
I am trying to model transient temperature profile during fluid flow in pipe considering heat exchange with the surrounding. I am trying to use overall heat transfer coefficient to model heat exchange ...
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Universal equation of state for fluids and gases
I would like to ask, is there any universal equation of state that holds for any and all classical fluids and gases, derived purely from first principles (though constants in it should be measurable, ...
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Why is the thermal expansion coefficient of an incompressible substance constant with pressure?
Upon learning that $C_P=C_V$ for incompressible substances, the takeaway for why this is true is due to volume being constant, which comes from the thermal compressibility, $\beta_T=0$ for an ...
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How the heck do liquids work?
Liquids are denser than gases with similar molecular weight, which seems to indicate a strongly attractive intermolecular force; on the other hand they have a negative Joule-Thomson coefficient which ...
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How to calculate the thickness of ice formed on a lake with a known temperature gradient?
I've been working on a problem involving the formation of ice on a small lake. The surface of the lake is in thermal equilibrium with the air at $-4^{\circ} \mathrm{C}$, while the bottom remains at $4^...
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How to Measure Temperature Difference in Fluids? [closed]
I have an assignment, in which I have to measure the difference of temperature between the base and the surface of a fluid (e.g. oil) that is being gently heated from its bottom, in order to explain ...
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How to calculate the surface tension limit theoretically?
When an object is submerging in a fluid with strong surface tension (e.g. a plastic cup sinking in a lake), it's very easy to see the surface tension in action. However, at some point, the surface ...
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Is a humans gravitational pull strong enough to attract germs and make us sick all the time?
Since humans are so much bigger than bacteria, and large objects attract small objects, are we attracting bacteria and virus?
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Stretching vs bending of thin membrane
Stretching refers to the deformation of a material when a tensile (pulling) force is applied. The material elongates along the direction of the applied force.
Bending involves the deformation of a ...
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Effect of condensation pressure drop in open flow
If saturated gas flows through a tube that is being cooled, the gas will start to condense, forming droplets at some point in the tube. Looking at the individual condensation "cells", I ...
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Why there is a delay before canned fruits float to the top?
This question may appear silly compared to others asked on this site, yet, I can't get my head around it.
After pouring boiling water into a canning jar with berries, berries stay at the bottom of the ...
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Does the isotropy definition of a perfect fluid imply no heat conduction?
Weinberg defines a perfect fluid (Chapter 2, Section 10) as one where each fluid element appears isotropic in a reference frame moving with that element.
From the definition of the stress-energy ...
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Bubble behaviour during water / vapour coexistence in the most idealised scenario without boundaries
Consider the following statement: during a 1st order phase transition, the temperature of the system stays constant and any extra heat goes into turning a larger portion of the system into the new ...
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157
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Energy of a flowing fluid
A pump transfers mechanical energy to a fluid by raising its pressure. The pressure of a flowing fluid is associated with its mechanical energy.
$\mathrm{Pa}=\mathrm{N}/\mathrm{m}^2=\mathrm{N}.\mathrm{...
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Why is the First Law of Thermodynamic related to Fluid Equation?
In Cosmology, there is a equation called Fluid Equation:
$$\dot{{\varepsilon}}+3\frac{\dot{a}}{a}(\varepsilon+P)=0.$$
It is derived by taking time derivative of the First Law of Thermodynamic:
$\dot{E}...
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49
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Friedmann fluid equation in the non-relativistic case
The Friedmann fluid equation I am referring to is:
$$ a\frac{d\rho}{da} = -3(\rho+P) .$$
In the non-relativistic (low temperature) case for an ideal gas universe (representing matter), I know that the ...
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Origin of ideal gas fluid dynamics equations including the adiabatic index
I was given a system of equations that supposedly describes the fluid dynamics of an ideal gas.
The equations are:
$$
\begin{align}
&\frac{\rho}{m} = \frac{p}{T} &\text{(ideal gas law)} \\\\
&...
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Relationship between density and temperature - How to know the precise temperature at which a bell inside a Galileo Thermometer will sink?
A Galileo Thermometer consists of bells placed inside a tube that's filled with liquid. As the temperature increases, the fluid density decreases. This leads to a decrease in the buoyant force, and ...
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How fast does a gas expand in vacuum?
A gas is initially confined to a small portion of an empty container.
At time $t=0$ gas is allowed to expand to homogeneously occupy the container after some time $t$.
What is the time $t$?
This ...
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A problem to understand the stability analysis in the Cahn-Hillard equation
Let us suppose the general diffusion equation (Cahn-Hillard equation):
$$\frac{\partial c}{\partial t} = M \nabla^2 \mu, \tag{1}$$
where $c (\underline{r},t)$ is the concentration of a given species ...
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What is the entity that resides at a point with a radial coordinate $r$?
In his groundbreaking paper The formation of a blast wave by a very intense explosion I. Theoretical discussion, G.I.Taylor presented a number of equations, including the ones depicted below:
In ...
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Finding formulas for molar internal energy and molar enthalpy of mixing fluids
There is a Y-shaped pipe connection. One fluid flows through one pipe with molar flow $\nu_1$, molar internal energy $U_1$, molar enthalpy $H_1$; through the second pipe - another fluid with molar ...
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Finding stress associated to a free energy
I am trying to find the stress tensor associated to the following free energy
$F = \int dV [ a |\nabla L|^2 + b |\nabla^2 L|^2]$
Where L is the heigh of the fluid interface, and is only a function of $...
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General differential equation for Energy transfer
In my textbook of Fundamentals of Momentum, Heat, and Mass Transfer by Welty, it is said that $$\nabla \cdot k\nabla T + \dot q + \Lambda = \rho \frac{Du}{Dt}+\rho\frac{D(gy)}{Dt}+\mathrm v \cdot \rho ...
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A problem to find the the chemical potential from the free energy (Ginzburg-Landau/Cahn-Hillard)
I have a problem to derive exactly the spatial term of the chemical potential from the free energy of the Cahn-Hillard equation
So, let us start with the free energy of a binary mixture (A and B). The ...
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4
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What is the difference between heating and cooling, fundamentally?
Context: My physics friend told me that heating and cooling effects are identical if you flip the vertical coordinates accordingly. If you heat a room from below, the warm air rises. Identically, air ...
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Boiling water using kinetic energy
Assuming the following: An isolated space, 1 atm pressure throughout, standard surface tension, vapour pressure and no external force like gravity, Can we provide enough impulse to a drop of water (or ...
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Boundary conditions for the stagnation point axisymmetric boundary layer equations
Good morning,
I am trying to solve the Boundary Layer equations in the stagnation point in order to compute the stagnation point heat flux. In particular, the fluid is:
-A continuum
-In thermal and ...
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2
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102
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The sign of Work in Turbomachines point of view
As I know from Thermodynamics work done by the system is negative and equals to $U=Q-W$. In this picture it clearly describes the process in which when we take some pebbles from the piston the system ...
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Newton's law of cooling and mixing warm+ cold water (each of equal volume)
I am trying to understand some of the dynamics in Stommel's two-box model of ocean circulation in a way that I can explain to someone without too intense of a calculus or physics background. I want to ...
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How to explain the phenomenon of air bag, when have one object hit air bag and one object catapult from air bag
Problem of this phenomenon is in title.To describe this, I separate it into 3 phases;
M1 hit airbag, 2) Air moving inside air bag caused by pressure gradient ,
3)M2 flew away caused by air moving to ...
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Long-range fluctuations induced forced (or the classical Casimir effect)
According to literature, the Casimir effect refers to attraction of two parallel neutral metal plates due to the wavelength cutoff of quantum fluctuations between the two plates.
I come from condensed ...
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Okay, I know the risks. ( Amateur Rocket.) [closed]
I am currently attending a school for electrical science. A small group of students and our instructor are attempting group project to build a liquid fuel rocket. (I know it is a bit out of the scope ...
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Why can't Rayleigh Flow admit total temperature ratios higher than 1?
In a constant area duct inviscid flow where heat is added, there are some well established results in the literature known as Rayleigh flow (https://en.wikipedia.org/wiki/Rayleigh_flow). In this ...
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