Questions tagged [convection]
transport mechanism involving bulk motion of a medium
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Is stoßlüften - quick exchange of air through windows actually more efficient than slow exchange through a wall ventilation fan?
In German areas with near air-tight homes, it is recommended that full house ventilation is performed by stoßlüften - opening windows fully to exchange as much air as possible in shortest amount of ...
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Does opening both windows in a room cool the room twice as fast?
It's getting colder where I live (~40 degrees Fahrenheit). The place where I live (college dormitories) pumps the heat up into the 80's, so I keep the windows open most of the time. I noticed that, ...
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Relation between Sherwood and Peclet numbers
What's the relation between Sherwood number and Peclet number for mass transfer in a rectangular channel with fully developed laminar flow?
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Two Particles with identical temperatures at different points in the atmosphere
Quick question with probably a simple answer. For context, I am currently in undergraduate classical mechanics studying potential energy. My question is, if a conservative force is one in which is ...
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Forced convection and active temperature?
I performed anisothermal CFD computations with large eddy simulation.
Is the use of the temperature as an active scalar relevant when performing a forced convection RANS or LES computation (Ri<0....
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Is Newtons Law of cooling applicable for all forms of heat loss? [duplicate]
Can heat loss through Conduction, Convection and Radiation be explained by Newton's law of cooling?
Or it is just applicable for heat loss through Convection and Radiation?
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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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What part of my oven should be hottest, top or bottom? [closed]
My oven has the heating element in the bottom. So the bottom shelf is more directly exposed to it, and should be the hottest shelf.
But hot air rises, so the top shelf should have the hottest air, and ...
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Designing and optimizing a heatsink given tight constraints [closed]
I am trying to design a heatsink as part of a broader system and deturmine two things:
Given the size constraints of the system, commercially available fans, and heat dissipation requirements, is it ...
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Fluid viscosity, mass diffusion and Navier-Stokes equation
With the increase of fluid viscosity, mass diffusion of a fluid decreases. Then how the diffusion term in Navier-Stokes equation has a dominant effect at high viscosity? Also how the mass convection ...
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Convective term in Navier-Stokes
In the Navier-Stokes equations, there's a well-known convective term of the form:
\begin{equation}(\mathbf{v}\cdot\nabla)\mathbf{v}\end{equation}
I'm not able to understand it. As far as I know, the ...
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Is there a difference in the 'quality' of a gas if it's heated by electromagnetic radiation as opposed to conduction/convection?
According to this link, "The wavelength at which the $O_2$ molecule most strongly absorbs light is approximately $145$ nm."
According to this link, that's in the ultraviolet range of the ...
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Does warmer air rise significantly to the top of a small container?
Suppose you have a small container, say 2 cubic centimeters (1cm x 1cm x 2cm), positioned so the 2cm side is vertical, and there is a tiny light bulb or heating element at the very top.
Is it the case ...
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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:
$$
\rho\hat{C}_{p}\frac{DT}{Dt}=-\left(\nabla\cdot\mathbf{...
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Convection in stratified atmosphere
In the stability analysis of stratified atmosphere in the presence of gravity, we consider a blob of atmosphere and perturb it (move it up by a small height $\Delta z$). Initially, the blob had the ...
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Star convection gradient dependencies
In star convection you can work with radiative and adiabatic temperature gradients, that for example the radiative one can be defined as,
$$\nabla_{rad}=\frac{3\kappa L P}{16 \pi a c G m T^4}$$
This ...
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Velocity field of a fluid in a porous pipe
Consider the situation of the image:
A fluid is passing through an infinitely long two dimensional pipe, with a hole in it (form L to L+a). Clearly some fluid will be ejected out from that hole.
Now,
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Adiabatic equation of state for a star
I am a little confused. To describe stars the adiabatic equation is often used: P = k$\rho^{\gamma}$. For a monatomic gas, the following holds: $\gamma = \frac{5}{3}$.
However, since the sun is not ...
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Interpretation of fictitious forces arising from convection in fluid flow in a curvilinear coordinate system
the time rate of change of linear momentum of a fluid with density $\rho$ and velocity vector $\mathbf{u}$ is given by the material derivative:
$$\frac{\mathrm{D} \rho \mathbf{u}}{\mathrm{D}t} = \frac{...
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Plot Nusselt number between two plates [closed]
I have a free convection system between two walls (hot, and cold). And I have the temperature distribution between them, solved numerically. Now I need to plot the Nusselt number between walls.
This ...
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Equation for Convective Heat Transfer
In this Wikipedia link: https://en.wikipedia.org/wiki/Convection_(heat_transfer)#Convective_heat_transfer on convective heat transfer, the following equation for convection is provided:
$$\dot{Q}=hA(T-...
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If you moved your hand continuously through fire, would it feel hot?
If you quickly pass your finger or hand through a candle or fire, it doesn't feel very hot (great party trick). Is this because your hand spends such little time in the fire that there isn't enough ...
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Can mass transfer occur without a concentration difference? (analogous to the question, can energy transfer occur without a temperature difference?)
The driving force for diffusion of mass is a concentration gradient. However, mass can be transported both in a diffusive and a convective (due to the flow of a fluid) way. By definition, the combined ...
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Building a house that is warm in winter and cool in summer [closed]
The Northern house architecture is strikingly different from that used in the South (I am not taking extreme cases, thinking more of Northern or Germany versus Mediterranean:
Thick layers of thermal ...
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Physics of the convection oven
I don't understand how convection ovens can cook food faster than radiant heat ovens. Guides to convection ovens claim that they cook food 25-30% faster than radiant heat ovens, but do not really ...
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Why don't the "trapped warm air" just fly out of the holes in blankets?
I've read a lot of explanations that the holes of a blanket somehow trap air which keeps the air in place.(including this: https://www.reddit.com/r/explainlikeimfive/comments/10lj0h/...
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Convective derivative N-S
This is probably an easy answer, but I've not been able to find it yet -
Why in some formulations of the N-S equations (for example here https://www.grc.nasa.gov/www/k-12/airplane/nseqs.html), is the $...
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How does air cool as it nears the poles?
I understand air is heated by the equator causing it to rise towards the poles. But why does air cool and sink after nearing the poles. Shouldn't the air still possess heat, after being heated by the ...
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Geometrical Rotation and Rotation operator relation and ambiguity
In Cohen-Tannoudji's it is said (vol.1 page 694):
$|\psi \rangle$ is the state of the system before the rotation.
$|\psi ' \rangle$ is the state of the system after the rotation.
$|\psi ' \rangle= R |\...
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What causes the lamp above my gas stove to swing like a pendulum when the stove is on?
There is lamp hanging above my gas stove, which when the stove is turned on performs pendulum-like oscillations in an oval trajectory, not unlike the dynamics of Lissajous patterns. The lamp is ...
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The local and average Nusselt number in a square cavity
I am in the process of programming the local & average Nusselt number in a left vertical wall but my Matlab script gives me inappropriate values and it doesn't change with changing of Rayleigh ...
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Average Nusselt number and heat transfer coefficient
For the flow over a flat plate of length L, how the average Nusselt Number over a length L is equal to
$$Nu_{avg} = \frac{h_{avg}L}{k_f}$$
where $h_{avg}$ is the average heat transfer coefficient over ...
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Gas to solid heating?
I am doing a study on the phenomenon of pyrolysis. This is purely a study of the underlying physics. Generally, in practice, pyrolysis feedstock is heated conductively but we are examining the energy ...
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Convection from rapidly evaporating liquid inside vacuum chamber?
If we have a liquid that is is being actively heated and is rapidly evaporating (let's say around 1g/s for Ag at 1500K) inside a vacuum chamber, can convection around the liquid/vapor interface occur ...
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Small parameter expansion to obtain convective heat transfer solution of the heat equation
I'm trying to follow along with this paper on perturbative transport analysis. The section I'm stuck on analyzes the heat equation in 1D slab geometry. To get a diffusion-only solution is relatively ...
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Is destratification ventilation more efficient at ceiling level?
This question is more of a practical physics question. In buildings with heating systems, heated air tends to rise and create air temperature stratification - hottest air near the ceiling, coldest air ...
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Can conduction alone cause thermal equilibrium?
From the little I know about physics and conduction specifically, it seems to be that a system in which the heat transfer is done solely by conduction, cannot reach thermal equilibrium.
I'll preface ...
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How to treat Nusselt numbers that are smaller than one?
The Nusselt number is defined as
$$\text{Nu}=\frac{h\delta}{k},$$ with
$h$ as convection heat transfer coefficient,$\text{W}/(\text{m}^2\text{K})$,
$\delta$ as characteristic length, $\text{m}$, and
$...
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How can the rate of convection up a chimney be computed? [closed]
I have various physics textbooks, but none of them explain exactly how to compute the rate of convection.
I assume that Newton's Law of Cooling should be used by I can't figure out how to apply it to ...
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Heat Transfer Conservation in a natural convective flow
In a initially stationary area, suppose I have a heat source of say 10 W.
Now if I consider a fictional cube (box)/ boundary of say volume 1 m3 around it. And I sum up the heat across the surfaces of ...
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Spectrum of the background radiation on earth
Suppose we consider an object of temperature $T_o$, whereas the air temperature is $T_a$. The object will exchange heat with its environment via a range of processes:
Radiating and absorbing heat
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Heat Transfer Rate to Surroundings of Heating Battery
I think this is probably a trivial question, but I am trying to understand how to do a thermodynamic calculation for heat transfer. I want to make a basic resistive heater by shorting a battery, but I ...
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How does hot air rise?
If a balloon is filled with hot air, it is rising due to buoyancy: the mass of the hot air inside the balloon is lower than the mass of the same volume of the cold air outside the balloon cavity.
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Rayleigh Benard Convection analyzed as heat engine?
The treatment I've seen for Benard convection in a textbook is to derive approximate equations of motion and then show that there is a periodic solution matching the boundary conditions. This is ...
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How much energy is required to keep water hot?
I have a hot-water jug that keeps water hot (say, at about $70\, ^{\circ} C$). To compute its operation cost, I would like to compute its daily energy consumption. The label on the jug says "800 ...
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How to modify single phase fluid/solid coupled PDEs to account for a phase change?
I have two PDEs that model both fluid and solid temperature change due to fluid flow through a packed bed. Schematic and equations here (where the f and s subscripts are for the fluid and solid ...
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How to calculate convection between a hot and a cold area through a circular hole?
Consider the below problem:
where we have two half infinite worlds with $T_2 < T_1$ and a circular hole with the diameter of $D$ in an infinite isolating wall. There is no ...
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Calculate how hot air will get passing source of heat
Is there a way to calculate how warm air will get when it passes a source of heat knowing how fast the air is moving?
For example, let's say there is an object being heated by 40W of electricity and ...
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Understanding Convectional Rainfall
Consider the following explanation of convectional rainfall given in a VII grade textbook.
When air comes in contact with the hot surface of the earth, it gets heated, becomes light and rises in the ...
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In this scenario, if I continue to increase the length of heat exchanger how will the temperatures change?
Consider a counter flow double pipe heat exchanger inside which the cold fluid enters at 20 degrees Celsius and hot fluid enters at 100 degrees Celsius. Initially the length of the heat exchanger is ...
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