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Questions tagged [convection]

transport mechanism involving bulk motion of a medium

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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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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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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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51 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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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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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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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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63 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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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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43 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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86 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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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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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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44 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
163 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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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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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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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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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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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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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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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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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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Dimensionless numbers and fluxes

What is the meaning of dimensionless fluxes? Which are Nusselt number in case of heat transfer and Sherwood number in case of mass transfer. What is the use of these numbers? What is the difference ...
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73 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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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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122 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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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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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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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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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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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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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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469 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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272 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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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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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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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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203 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
178 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 ...
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1answer
656 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 ...
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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 ...
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754 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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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\...
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1answer
117 views

Explain Egawa Electric field with reference to PIN diode?

By Egawa electric field I meant the flattening of electric field in the intrinsic field. And after that, when avalanche multiplication occurs, the dipping of electric field in the intrinsic region and ...
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2answers
201 views

Natural convection and buoyancy: What is a better description of $g$?

In their derivation of the Grashof number (Gr), Çengel and Ghajar make the following comment: Note that there is no noticeable gravity in space, and thus there can be no natural convection heat ...
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What does it mean that a substance can be smelled from far away?

I thought about this question in the middle of this video. Ok, Thioacetone takes the price for the World's smelliest chemical, I can accept it (why not?), but what about You can smell one drop of ...
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How does the Newton Law of Cooling should be modified in case of free convection?

According to "Mathematical Modeling: a Differential Equations approach" by Barnes and Fulford 2nd edition, it should be $ T' = k (T-T_0)^{5/4} $ where $T_0$ is the temperature of external gas or ...