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Questions tagged [convection]

transport mechanism involving bulk motion of a medium

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2answers
22 views

How is fin efficiency a useful quantity for a fin's heat dissipation performance? [closed]

I mean, it's the ratio of actual heat transfer to heat transfer if the material had infinite conductivity. How is it of any practical, or even theoretical use? How does it help, in saying one fin ...
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1answer
54 views

Is a Microwave oven without a faraday cage a health hazard?

Microwave ovens have something of a Faraday-cage/shield to keep from leaking (emitting) EM radiation. What would happen if the shield or the door was removed? No doubt it would be less efficient as ...
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31 views

Limits to natural convection in a non-infinite medium

I'm trying to understand the temperature profile of a fluid in an underground vertical pipe without flow. The fluid is subject to a boundary condition of the form: $$Q = h[T_e(z) - T],$$ where $Q$ ...
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Conservative or non conservative convection

I want to describe the convection of a species $B$ by another species $A$. Meaning that $A$ is bringing $B$ with it, and there is no other velocity associated to $B$. So I have 2 conservation ...
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1answer
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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 ...
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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 ...
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3answers
84 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 ...
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1answer
51 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
51 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
74 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
91 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
39 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
65 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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29 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
69 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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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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74 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
145 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 ...
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0answers
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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 ...
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1answer
49 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
165 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 ...
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1answer
107 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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80 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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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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62 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 ...
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1answer
257 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 ...
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2answers
47 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
50 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 ...
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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_\...
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1answer
134 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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127 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 ...
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1answer
79 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 ...
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1answer
109 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 ...
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3answers
235 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 ...
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1answer
79 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 ...
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4answers
224 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
151 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 ...
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4answers
208 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
37 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 ...
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1answer
85 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?
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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 ...
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1answer
394 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 ...
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1answer
79 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 ...
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1answer
584 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 ...
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1answer
382 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
248 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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52 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,& ...
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1answer
224 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 ...
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1answer
211 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 ...