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Questions tagged [convection]

transport mechanism involving bulk motion of a medium

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Calculating temperature change out of a room [closed]

Currently I'm trying to find how the outside temperature affects the internal temperature of a room through its walls. I'm trying to use the convection heat transfer equation to find the exterior wall ...
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If I'm inside water, is the amount of heat energy I can receive capped because water can't go above 100°C?

I just learned about double-boiling, where instead of putting a pot directly on the flame stove (where it can get too hot), you put a big tub of water on the flame, and put the pot in the tub of water....
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The roles of convection and advection in the absolute flux for species $i$ in mass transfer

I am confused as I have been reading on mass transport on multiple sources and they seem to use "advection" and "convection" interchangeably in the equation for the absolute flux ...
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Lumped body analysis

$k$ - thermal conductivity, $h$ - heat transfer coefficient, $\rho C_p$ - Volumetric heat capacity, $T$ - temperature $T_\infty$ - Temperature of exposed cooling surrounding environment Consider two ...
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At what circumstances is Nusselt's theory of evaporating falling films valid?

Nusselt's theory of evaporating falling films assumes no convection and neglects the effect of inertia. At what circumstances is that valid? Any books or articles that discuss this in depth would be ...
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Explain how convection is a type of heat transfer

So, from my understanding convection is when a gas or liquid is unevenly heated and the warmer portion rises, as it is less dense, and the cooler portion sinks creating a cycle(something along those ...
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How does the height of the hole on the bottle affect the burning time of the candles?

We took 3 identical bottles and drilled some holes on the side, each bottle had a hole but at different heights. Then we covered the burning candles with the 3 bottles and measured the burning time. ...
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Conduction in liquid and gas

Is this condition correct, "if liquid and gas heated from top, then it will be possible for 'conduction' to occur" ? One reason i can think is : when liquid or gas is heated from sideways or ...
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What creates the Global Dipole Magnetic Field in the Sun?

I understand that the Sun undergoes convection and with rotation, the convective cells have a helical motion because of the Coriolis Force. My confusion comes from the fact that via the right-hand ...
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How to measure actual conductive & convective losses inside an enclosed container?

I've been studying convection and come across empirically-derived formulas for calculating the Nusselt number for various geometries. For my particular use case, I'd like to measure the actual ...
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How do I calculate the rate of heat loss from an enclosure when I have a plot of temperature vs time and the enclosure's material details? [closed]

I have an enclosure running an ON/ OFF temperature control system. The below graph shows internal air temperature over time. I have the raw data providing actual values. I have the dimensions of the ...
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How to determine air flow required? [closed]

I am making a sound dampening box for a vacuum pump. It’s loud almost 96dB. I have an ultra quiet fan to vent heat out of the box. I want to calculate how to make a couple small inlet holes while ...
Evan Guengerich's user avatar
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Can land breezes be an example of perpetual motion?

Since perpetual motion refers to a never-ending motion with no external energy provided whatsoever, can land breezes or sea breezes be an example? Or perhaps even trade winds, since this, I believe, ...
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Rigorous definition of convective heat transfer

Through all textbooks I've come across, convective heat transfer is traditionally defined along the line of "[...] a process by which heat is transferred by movement of a heated fluid such as air ...
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Local and convective acceleration in 'water tank-pipe' systems

I found this elegant solution to the Euler equation when the classic 'water tank-pipe' system opens the valve - the initial unsteady flow "stabilizes" and the equation turns into the ...
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Why does a stream of smoke interact with a light source?

The photo in the top row shows the stages of interaction of a stream of smoke that is formed from a smoking stick with a light source. The light source turns on at the moment when the smoke rises ...
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Convection and the Strouhal number

Whenever I look into information about the Strouhal number, I always see it reference vortex shredding. But the Strouhal number can also be used in the context of turbulent convection where $$ St=\...
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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 ...
Srinish Reddy's user avatar
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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 ...
Amila Edirisinghe Edirisinghe 's user avatar
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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 ...
Johann Wagner's user avatar
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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 ...
Cloudyman's user avatar
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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-...
SurfaceIntegral's user avatar
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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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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 ...
Roger V.'s user avatar
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3 answers
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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 ...
Ambrose Swasey's user avatar
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3 answers
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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 $...
TriJB's user avatar
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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 ...
Howard Stark's user avatar
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1 answer
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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 |\...
imbAF's user avatar
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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 ...
nullspace's user avatar
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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 ...
Bakizza's user avatar
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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 ...
Harshit Rajput's user avatar
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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 ...
E Jones's user avatar
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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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