Questions tagged [convection]
transport mechanism involving bulk motion of a medium
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questions
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Effect of volumetric flow rate on convection and radiation heat fluxes
Say we have two hot objects of the same material but of different width and same thickness.
The objects are moving horizontally, have initially the same temperature and are cooled by a gas blown from ...
3
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1answer
38 views
The convective analog to Fourier's equation of conduction?
The differential form of the thermal conduction law is given by
$J=-\kappa\nabla T$
where $\kappa$ is the thermal conduction coefficient, or in the one-dimensional case,
$J=-\kappa \frac{\partial ...
2
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3answers
74 views
Conduction, convection, radiation: Does evaporation count as one of those?
The forms of heat transfer are traditionally described as conduction, convection, and radiation. Is evaporation (or any other change of state) counted as one of those forms? Or is it considered its ...
2
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1answer
48 views
The solution to the non-linear convection equation
The non-linear convection equation
$$u_{t} +uu_{x}=0$$ admits implicit solutions of the form $$u=f(x-ut).$$
How does one interpret this solution intuitively? Is there an example of a solution of this ...
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1answer
48 views
Are there no convection currents in ice-boxes and aerogel?
Technologies dealt with
Ice-boxes have been used for a long time to prevent ice from melting for a longer time than keeping it in open. Aerogel is still an emerging technology (I came across it on ...
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3answers
69 views
From kinetic theory - why does heat rise?
I know the explanation from fluid elements and densities however I don't find it satisfying. Is there an explanation from kinetic theory?
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2answers
88 views
Density of ice < water?
In the situation of an ice cube placed in water and eventually melting, it is supposed that natural convection is the process in which heat transfer from water to ice occurs.
However, natural ...
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1answer
31 views
What is oscillatory convection?
I come across this term in a lot of papers which talk about convection and instabilities but could not find a proper explanation of what oscillatory convection is. Is it the fluid which is oscillating ...
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2answers
56 views
Does the Boussinesq approximation imply 'incompressible' flow?
Does the Boussinesq approximation imply that compressible inertial effects in the flow can be neglected (i.e. density can otherwise be treated as constant)?
It seems that it must be the case and ...
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0answers
26 views
Rayleigh-Benard convection criterion
So, every text starts with a uniform heating of the bottom plate of a horizontal fluid for Rayleigh-Benard (RB) convection. Is "uniform heating" and "horizontal plate" an essential starting point?
If ...
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0answers
54 views
How much conduction, radiation and convection influence in a thermos flask?
It has been thoroughly repeated that thermos flasks prevent heat loss by minimizing heat conduction, radiation and convection from the bottle to its ambient. This has been answered in this SE. However,...
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0answers
60 views
Heat transfer on Mars
SCENARIO:
I have been tasked with finding the heat transfer across a composite wall on Mars.
On the left of the wall there is air maintained at Earth atmospheric conditions and room temperature (101 ...
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0answers
61 views
Material Derivative in Fluid Dynamics and Bernoulli Flow
If a fluid flow, such as water, is incompressible then the convective derivative term in the material derivative is equal to zero. How then, in a Bernoulli flow where there is an increase in velocity ...
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1answer
107 views
How to develop a model for cooling rate of steel tube in air?
I am trying to develop an equation to determine the cooling rate of a steel tube in air. I'm using Fourier's Law, Stefan-Boltzman Law, Newton's Law as well as the specific heat capacity equation. The ...
2
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0answers
18 views
Stopping overflow of boiling milk [duplicate]
We all know that milk overflows from the container when boiled.
The reason is air trapped under the skin of the milk, can't escape and hence, pushes the skin upwards until it overflows.
My mother ...
0
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1answer
47 views
Heat Transfer Coefficient
What is the relationship between time and heat transfer coefficient? Actually are there any at all? What happens to time taken in heat transfer if the coefficient is value is raised or lowered?
All ...
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0answers
122 views
Shear stress and surface heat transfer rate with various Pr values
I'm revising for my Fluid Mechanics exam, and came across a question that ask us to explain the behaviour of the shear stress and surface heat transfer rate with various Pr values.
The question is ...
2
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1answer
82 views
The derivation of the advection-diffusion equation uses $\nabla\cdot(c\vec{v})=(\vec{v}\cdot\nabla)c$. Why doesn't the order of the derivative matter?
In a derivation of the advection-diffusion equation, it is exploited that $\vec{\nabla} \cdot (c \vec{v}) = ( \vec{v}\cdot \vec{\nabla})c$, where $\vec{v}$ and c respectively are the velocity and ...
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2answers
75 views
which give higher cooling rate , strong circulated water or thick copper plate? [duplicate]
imagine if I have hot metal piece I want to cool it as fast as possiple, should I put it in strong circulated water bath or just stick it between 2 thick copper plates ?
the calculated heat ...
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32 views
What is the rotation profile for radiative zone of Sun - Instability and convection?
I am exercising on Stellar Physics topics and in particular the questions below:
1) First of all on the rotation profile for the radiative zone: I know that unlike the convective zone, where the ...
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0answers
52 views
Boundary layer thickness on a cylinder
Consider axial flow over a cylindrical body inside a tube:
Before fully developed flow occurs, I am interested in how the boundary layer thickness grows on the center cylindrical body.
We know for a ...
0
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1answer
227 views
Evaporation rate of water with forced convection
A steel pot (diameter 200 mm) is fully filled with water (2 kg of water) and the water is maintained at a constant temperature of 40°C by supplying heat from an electrical tabletop burner.
Assume ...
0
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2answers
45 views
Air temperature equilibrium
Suppose an ideal airtight room, filled with air, no changes in volume, amount of air or energy.
On the one hand, "hot air rises" (less dense, flotation, convection...) ((there's gravity, we are on ...
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1answer
45 views
Effect of pressure when drying wet clothes in a windy environment
When we hang wet clothes outside, they dry faster if it is windy.
The wind causes forced convection and removes the air saturated with vapor, and the rate of evaporation does not decrease much in ...
2
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2answers
95 views
Question on convective heat transfer
Why is the following formula used when we define heat transfer due to convection on a flat plate?:
$$ q=h(T_s-T_\infty)$$
Where $T_s$ is the temperature of surface at a particular location and $T_\...
1
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1answer
108 views
What is meant by “stable/unstable to convection” in the context of the solar atmosphere?
In studying the Schwarzschild stability criterion (for the solar atmosphere); $$\left\lvert\frac{dP}{dr} \right\rvert\lt\frac{\gamma P}{\rho}\left\lvert\frac{d\rho}{dr}\right\rvert$$ From my notes are ...
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0answers
114 views
Finding the temperature of the glass envelope in an incandescent light bulb
I've been trying to evaluate the temperature of an incandescent light bulb, using radiation for the filament and convection for the bulb, the radiation's equation works fine, but the problem is the ...
3
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1answer
77 views
Coupling Navier-Stokes and stochastic models for particle tracking in micro-scale free convection?
I have been using a commercially available software to simulate laminar free convection in a specific small domain (let's use channel w/ heated lower wall as an example). The scale is approx 50-100 ...
0
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1answer
99 views
How buoyancy and convection are related?
If I'm not wrong buoyancy formula is $$F_{B}=\rho gv_{sub}$$
In convection it is said that fluids with less density come up and parts with lower density ,which are cooler , go down and this cycle ...
10
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3answers
232 views
Why do distinct temperature layers form in bodies of water?
This may not be the correct place to ask a question about limnology (which I just found out is the science of lakes) but it seems like the place most likely to produce a good answer.
In my diving ...
0
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1answer
76 views
Is there heat transfer through radiation in a drinking flask with styrofoam insulation?
Suppose we have a drinking flask with styrofoam between outer and inner walls. The heat can be transferred through styrofoam by conduction. Is the heat transferred by radiation as well?
My lecturer ...
3
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4answers
218 views
Atmospheric pressure And heat convection
If hot air rises due to convection, why does it get colder when we climb mountains?
After some research, I found out that atmospheric pressure affects the temperature of the surroundings.
Another ...
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1answer
140 views
Combined radiation with conductive and convective heat transfer
I have a tube(only the cross-section displayed in the figure!), where gas flow is used to heat up the water. The water flows inside the steel tube, where the walls have been marked red. The heat ...
2
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4answers
186 views
Energy Transport in stars
I'm trying to understand why convection is an efficient mode of energy transport in the outer layers of the solar interior.
Could anyone give me a little bit of knowledge?
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1answer
36 views
Inertial reference frames in an atmospheric science context
A Hadley cell cycles air meridionally between the equator and 20 ◦ latitude. Assuming no
zonal wind at the equator, what is the mean speed and direction of the trade winds at 20 ◦ ?
My instructor ...
2
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1answer
82 views
Understanding the meaning of a certain boundary condition
Given,
$$
-k\frac{\partial T }{ \partial y}=h(T_f-T),
$$
what does this term $$\left.{\partial T \over \partial y}\right|_{y =0}$$ physically describe in the convective boundary condition?
1
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1answer
38 views
Convection through a bigger window
So I am currently doing an investigation and the location that I chose for the project is a rainforest. So I was wondering if the window is bigger in my tree house will it affect the way convection ...
3
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1answer
355 views
How do convective clouds form?
What are necessary conditions to form convective clouds with their flat cloud base, like this one:
I know that convective instalibity at the ground is at start of the process, but I have realized ...
0
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1answer
78 views
Convection current
I am a master student (geology), I seek to ask how one can simulate convection current movement. What the difference between Boussinesq approximation and non Boussinesq approximation, and what are the ...
0
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1answer
538 views
Prevost Theory of Exchange
I am having a trouble in understanding this concept.
If bodies are at thermal equilibrium, there is no heat transfer.
Heat is transferred through three different ways: Conduction, convection and ...
3
votes
1answer
335 views
mysterious waves while boiling water
When you take a container with water and begin to heat it, after a while, you will notice that bubbles begin to form. If you wait a bit longer, you will easily (it's so clear) start noticing smudgy ...
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2answers
75 views
Air temperature that would cause same rate of heating to human body as a 40°C hot tub
My son was wondering why a 104°F (40°C) hot tub feels so much hotter than a 104° day. I explained the difference between conduction and convection but we started wondering how hot the air would have ...
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3answers
240 views
Air pressure and convection currents
Air pressure decreases with increasing altitude. So why is
air near the surface not continuously drawn upward toward the
lower-pressure regions above?
Does this have anything to do with ...
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0answers
49 views
Nusselt number in Rayleigh-Bénard convection derivation
I read, that for a box with length L, with heated bottom and cooled top and boundary layers of thickness $\delta$, the Nusselt number Nu can be approximated as
$$
\text{Nu}=
\begin{cases}
1,& ...
0
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1answer
210 views
Nusselt Number Correlation of long cylinder in axial flow
What is the Nusselt number correlation of long cylinder in axial (forced) laminar flow?
Assume gravity does matter.
I have seen numerous sources and lists for cylinders in crossflow which is not ...
0
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1answer
188 views
Heat transfer inside a rectangular cross-section box
I am required to design a water cooling system to a motor controller (unfortunately our application doesn’t support the use of ambient air as a coolant), the controller usually as an aluminum plate ...
1
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1answer
740 views
How large does an air gap have to be to allow for heat transfer by convection? [duplicate]
Heat transfer by convection is often prevented by using fibers that have small air voids between the fibers crisscrossing so that air has a lot of trouble flowing. After doing some research I was not ...
0
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1answer
26 views
How to have high agitation caused by high air flow while heating the same air?
It may not be possible but I am trying to create an environment that has decent air flow for agitation. I want that environment to receive heat though through convection so increasing temperature over ...
0
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1answer
818 views
Vertical surface would lose heat faster by convection than a horizontal surface?
Is the heat coeff affected by gravity?
Vertical surface would lose heat faster by convection than a horizontal surface?
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2answers
585 views
What is the proper way to model diffusion in inhomogeneous media (Fokker-Planck or Fick's law) and why?
I'm quite confused with the following problem. Normally a one-dimensional Fokker-Planck equation is written in the following form:
$$\frac{\partial \psi}{\partial t}=-\frac{\partial}{\partial x}(F\...
