Talk:Convection

From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Meteorology (Rated Start-class, High-importance)
WikiProject icon This article is within the scope of WikiProject Meteorology, a collaborative effort to improve the coverage of Meteorology on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.
 
WikiProject Physics / Fluid Dynamics  (Rated C-class, High-importance)
WikiProject icon This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
C-Class article C  This article has been rated as C-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.
This article is supported by Fluid Dynamics Taskforce.
 

Miscellaneous[edit]

Someone has vandalised this page by replacing 'fluid' with 'poo'. Is there someone who knows how to restore it to its previous version? 7/11/2006 - Lti

You go to history and pick a version just before the change, and do "edit" then "save". Or if other changes have been made since then, you manually bring up the latest version and manually change the word then save. SBHarris 01:26, 8 May 2007 (UTC)

I thought it would be good to add that much study of convection also relates to motion of fluids such as water, in solar energy and HVAC. --User:Jdpipe

This definition of convection as a heat transfer mechanism is archaic. It might be a natural physical phenomenon relying on gravitation but it is no more a heat transfer mechanism than picking up a red hot poker and plunging into a bath of cold water.

Don't understand what you're trying to say. There's nothing archaic about it. It is a mechanism of heat transfer. Without gravity, a forest fire as you know it would be impossible. The best that would happen is everything would sit and smolder slowly. A poker into water is a specific example of a physical system. We're talking about mechanisms which transcend the specific materials. SBHarris 01:26, 8 May 2007 (UTC)

It might be more useful today to relate this process to efficiency. For example forced convection is quicker than natural convection, a heatpipe can tanfer more heat for a given volume etc. Transfer through use of Latent Heat exchange is also an extremely important mechanism. What would we call heat movement in a non-gravity situation caused by diffusion of a gas? User:rjstott

Just simple heat transfer by diffusion. There may be more efficient processes than convection, but there aren't many of them. SBHarris 01:26, 8 May 2007 (UTC)

Equation with integral[edit]

In the equation that has the integral with apparently As as the lower limit, the subscript s for As does not show well. The s looks likes it's part of the integrand instead of the lower limit. I'm not sure at this time how to fix this problem. H Padleckas 11:06, 9 Jul 2004 (UTC)


Thermal convection, Rayleigh-Benard convection, Maringoni convection, Solutal convection[edit]

Thermal convection redirects here, but isn't mentioned in the article. Is it superfluous (is all convection thermal)? Also, Weisstein's physics encyclopedia says that thermal convection is also called Rayleigh-Benard convection. This web page says that, "the stripe or roll state formed in bouyancy driven convection is today referred to as Rayleigh-Benard convection. Surface tension induced convection is known as Maringoni convection." -- Kjkolb 00:50, 28 November 2005 (UTC)

I also found something called solutal convection, but I've been unable to find out its definition. -- Kjkolb 02:59, 28 November 2005 (UTC)

There is also granular convection, where vibration in a bed of granular material causes vertical circulation. Will.Brunner 05:08, 28 January 2007 (UTC)

fluid[edit]

Adding after the use of 'fluid' in the first paragraph "which can be a liquid, gas, or plasma" would help readers who see fluid and think that it means liquid, which I am guessing is not an uncommon mistake.

--Akako| 00:15, 28 May 2006 (UTC)

convection and HVAC[edit]

For my part, I was hoping to find here a discussion relating to HVAC and ovens and how convection heaters and convection ovens differ from the conventional kinds--or whether the term in those cases is misapplied in some sense.

Thanks.

Pattern Forming[edit]

The pattern forming section is very confusing (even to someone who understands convection already). It should probably be removed or at least moved to its own article. Anonymous6494 06:13, 4 December 2006 (UTC) It also means that it is international current of the movement of the fulid.

Heat transferred from Earth's surface by convection?[edit]

The beginning of the Atmospheric Convection section begins: In the case of Earth's atmosphere, solar radiation heats the Earth's surface, and this heat is then transferred to the air by convection. Since the earth's surface is not a fluid (cf definition up top), use of "convection" here strikes me just plain wrong. Shouldn't the transfer from Earth's surface to the air be by either radiation or conduction? The convection will pick up after that.

68.166.104.2 19:38, 23 February 2007 (UTC) JP

You're right, of course. I think it means to say "transferred away into the air by a mostly convective process". That first little bit where the air molecules hit the ground and come away faster isn't convection, nor is heating of air by radiation, but overall it's mostly a convective process, and not worth complicating here by going into it finely. I'll fix it. SBHarris 01:29, 24 February 2007 (UTC)

Oceanic Convection[edit]

On March 6th, someone changed the last word of the paragraph under Oceanic Convection from "heat" to "hell". I changed it back.

Was: "In this case it is quite possible for relatively warm, saline water to sink, and colder, fresher water to rise, reversing the normal transport of hell."

Is now:"In this case it is quite possible for relatively warm, saline water to sink, and colder, fresher water to rise, reversing the normal transport of heat." —The preceding unsigned comment was added by Doodit (talkcontribs) 16:40, 15 March 2007 (UTC).

Diffusion vs convection[edit]

Yesterday i added the comparism to diffusion in the article about convection. You edited my add. You 're right, "internal force" is misleading and "brownian motion" ist the correct discription of the physical process. But you also edited the term "caused by an external force such as gravity or heating" by "convection is a relatively large-scale effect, involving bulk fluid motion." I think yor 're right with the discription "how convection looks like" but you deleted what is the REASON for convection, and I think the reason is a (macroscopic) external force due to gravity, pressure difference, temperature difference and so on. For example in fuel cells technology forcing a liquid to move through a porous media is denoted by convection. —The preceding unsigned comment was added by 129.187.5.225 (talk) 08:54, 8 May 2007 (UTC).

(Above comment copied from my talk page) I don't disagree with your statements about the driving force for convection, but I feel it's covered sufficiently in the article text, and doesn't need to be discussed in that much detail in the introductory paragraph. What do the other editors think? --Slashme 10:31, 8 May 2007 (UTC)

Hmm... I don't know... I don't.... know... — Preceding unsigned comment added by 99.227.136.88 (talk) 01:30, 31 January 2014 (UTC)

Convection & Advection : Definitions[edit]

Reference : Wicktionary.

It appears to me that these two terms -- as they appear in this article and in the Wiktionary -- need to be harmonized. —Preceding unsigned comment added by 70.157.173.219 (talk) 06:34, August 30, 2007 (UTC)

I was very confused by this also. Many graduate texts on transport phenomena (at least in Chemical Engineering) define the flux of a quantity as a sum of convection and diffusion. This article uses convection as "flux" and then splits it into advection and diffusion. Is this due to the style of the article being formed from a heat transfer standpoint as opposed to transport phenomena in general? I believe this to be the case, as almost every talking point and section discusses heat transfer, many only discussing heat transfer. Some clarification should be added and convection should be expanded, as the scope of convection is very limited in this article to heat convection. For example, natural convection does NOT need to be created by temperature differences. It can also be caused by a constant temperature, variable density fluid, common in many heterogenous mixtures. 2001:1948:414:8:0:0:0:64 (talk) 20:06, 14 February 2013 (UTC)

Section on Natural Convection looks sabotoged[edit]

The section on Narural convection seems to be non-sensical. It talks about effects of gravity from Mars on Earth. It uses an Equation that has T to the fourh power which is for radiative cooling. —Preceding unsigned comment added by 71.206.168.67 (talk) 14:37, 25 November 2007 (UTC)

I have changed it, it was caused by vandalism. Seddon69 (talk) 16:40, 25 November 2007 (UTC)

I removed the whole chunk about radiative heat transfer. --Slashme (talk) 06:52, 26 November 2007 (UTC)

So were does conduction settle in this? —Preceding unsigned comment added by 76.226.233.73 (talk) 00:49, 12 March 2008 (UTC)

Could this image be used in the article?[edit]

Are there any objections to using this image in the article?
Hobo stove convection 2.jpg
image:Hobo_stove_convection_2.jpg
Description: Cutaway illustration of a hobo stove including air convection
--Dave (talk) 21:20, 16 May 2008 (UTC)

I think that's a good image for the article. It was already used in some of the other language versions of this article. -SCEhardT 13:03, 12 September 2008 (UTC)
Wasn't this used in the article at some other point? I swear I've seen it before. In any case, I think it's applicable. Go for it! --Wizard191 (talk) 13:21, 12 September 2008 (UTC)

Mantle Convection[edit]

In the mantle convection section, it says that movement of liquid metal in the outer core produces an electric current that in turn produces the Earth's magnetic field. This isn't quite true, as a physicist can tell you that moving metal is not sufficient to generate an electric current (it is if it's in a magnetic field, but that's circular reasoning in this case). As much as geologists are loath to admit it, we actually don't know what causes the Earth's magnetic field, just that it is probably driven by convection somehow. I think I'm going to go ahead and edit this, as I have some solid citations.--67.244.44.244 (talk) 17:57, 21 February 2009 (UTC)

Please do. As far as I remember (my thoughts usually don't go deeper than the asthenosphere), the idea is that the passage of a conductive fluid through other "loops" of conductive fluid induces a magnetic field. Awickert (talk) 06:54, 15 April 2009 (UTC)

There should be no mention of liquid metal convection in a section on the mantle. Liquid metal is found in the outer core only. The mantle is a solid, broadly ferro-magnesian silicate. cstarknyc (talk) 10:33, 12 August 2011 (EDT)

Of course you are correct. Will fix. SBHarris 23:28, 12 August 2011 (UTC)

Mechanics section[edit]

I'm thinking of making a mechanics section here. What do people think: should I present the Rayleigh number and explain its physical significance, or go through the entire mass/momentum/energy balance and its nondimensionalization (and then get to the Rayleigh number)? Awickert (talk) 06:55, 15 April 2009 (UTC)

I'm not sure you have to go into a full blown proof of the Rayleigh number, because that belongs in the Rayleigh number article, however having a section about dimensionless numbers that related to convection makes sense to me. Wizard191 (talk) 13:35, 15 April 2009 (UTC)
Thanks - that's where I was leaning. So I'll discuss the Rayleigh number and the onset of convection here, and then when I get a chance, I'll derive the Rayleigh number in its own article. Awickert (talk) 16:18, 15 April 2009 (UTC)
Sounds good! I look forward to seeing your edits. Wizard191 (talk) 19:56, 15 April 2009 (UTC)

Major cleanup[edit]

The current confusion of pages on convection, forced convection, natural convection and convective heat transfer prompted me to attempt a rewrite. This page will become a general overview of the mechanisms of convection both free and forced, but will direct most detail to pages on either forced or free, unless they relate to mixed or or other forms of convection. The mechanisms of convective heat transfer will be dealt with in the force and natural convection pages separately. The fact that there is no page about convective mass transfer gave me the confidence to attempt this merge; it should be possible to make these few pages more concise and less repetitive. Comments much appreciated. Jdpipe (talk) 15:49, 30 May 2009 (UTC)

Thanks for the boldness. This whole topic in general needs a lot of work. Your plan works for me. Wizard191 (talk) 16:13, 30 May 2009 (UTC)

Solar convection[edit]

I'd like to find out more about solar convection, and was surprised not to find info (or a handy pointer) here. 70.247.164.14 (talk) 01:52, 30 July 2010 (UTC)

Well, it's just ordinary natural convection, but occuring in the outer layers of the Sun. Nothing special about it but the location. SBHarris 21:42, 13 August 2010 (UTC)

Gravitational convection[edit]

One editor attempted to remove this, saying it was the same as natural convection. It isn't. Natural convection requires a heat source, since it is heat-induced expansion which causes the bouyancy changes. Gravitational convection works on any system where the materials have differing densities. It can both produce and transport heat, without being DEPENDENT on heat (the heat produced is due to gravitational potential being turned into heat, and is responsible for 1/3 to 1/2 of the heat coming from the interior of the Earth, and even more from Jupiter). In theory, this type of convection could transport mass-only, since the heat source isn't needed. SBHarris 21:44, 13 August 2010 (UTC)

Does convection mean conduction plus advection?[edit]

The discussion at the beginning of the article indicates that convection is usually viewed as the combination of conductive and advective transport. The reference is to Incropera et al. In the most recent edition of their book they state: "The convection heat transfer mode is comprised of two mechanisms. In addition to energy transfer due to random molecular motion (diffusion), energy is also transferred by the bulk, or macroscopic, motion of the fluid. This fluid motion is associated with the fact that, at any instant, large numbers of molecules are moving collectively or as aggregates. Such motion, in the presence of a temperature gradient, contributes to heat transfer. Because the molecules in the aggregate retain their random motion, the total heat transfer is then due to a superposition of energy transport by the random motion of the molecules and by the bulk motion of the fluid. It is customary to use the term convection when referring to this cumulative transport and the term advection when referring to transport due to bulk fluid motion."

I have also hear my colleagues indicate that convection is a composite term, derived by mixing the words conduction and advection. My reading in both the current and historic literature indicates to me that conduction and advection are equivalent terms, in the same way that thermal diffusion and conduction are also equivalent terms. Convection and advection are both derived from Latin words, meaning "to carry together" and "to carry", respectively. The term advective transport does not appear in the literature until the mid 1900's, whereas convection and convective transport are used much earlier. Furthermore, current standard texts, other than that of Incropera et al, tend to label the second term of the RHS of the heat equation as the convective term, which indicates those authors consider convection (aka advection) to be different from diffusion (aka conduction). --MuTau (talk) 00:49, 28 February 2011 (UTC)

Are you sure mean to to suggest that advection and conduction were once equivalent terms? At most, it is advection and convection that were once not separated. Convection and advection always had to do with bulk flows. In the last 50 years if has become conventional to separate convection into advective + diffusive terms. That might not have always been so in the past, but in the past, a "pilot" was a person who steered a boat on a river or in a port, and before that, even on the ocean. It didn't mean airplane pilot, because there were no airplanes. Electrocution referred specifically to electrical execution, not something your toaster might do to you. The language changes. Yes, "convection" is probably not built from conduction and advection. A historical section is appropriate (historically, advection was once used mainly for forced convection, not natural convection, and the diffusion was included because there was not way to separate it), but most texts use the words as they are defined here. ONE CAN have advection without diffusion-- though generally it's advection of mass in mass-transport, where the particles are too large to diffuse. SBHarris 06:56, 28 February 2011 (UTC)

Convection in solids[edit]

This page begins on a blatantly confusing premise by saying that convection cannot occur in solids while also saying it can occur in "rheids", which (according to the linked article) are solids that deform in a viscous fashion. For starters the term "rheid" is far too obscure for a first paragraph - geologists know the term "rheology" but they'd be hard pressed to define the term "rheid", and for lay readers it's wildly inappropriate. Such readers will look at the adjoining image of mantle convection and will likely leap to the incorrect conclusion that the mantle is liquid - a false premise so widely held that frequent explanations in the media of volcanic eruptions claim that the crust is floating on a molten liquid. In any case, convection can also occur in solids that deform plastically, in the sense that a yield stress need be exceeded before permanent strain can occur (viscous solids have zero yield stress). Cstarknyc 10:42, 12 August 2011 (EDT)

A bad 'good model'[edit]

'. A good model for convection is when you take a heat source (e.g. Bunsen burner) and place it at any side of a glass full of a liquid, you then can feel the different levels of heat in the glass..' The preceding line from the first section is disingenuous and should be removed by someone with more experience. The described set up is not a good model because it does not exclusively or predominantly explain or allow the visualization of convection. The described set up involved all three modes of heat transfer and fails to distinguish between any. 70.185.109.98 (talk) 01:19, 20 February 2013 (UTC) BGriffin

Bad Phrasing[edit]

"[...] you then can feel the different levels of heat in the glass [...]" is bad phrasing, as heat is not a state variable but a process variable, one cannot feel or see different levels of heat but the results from the heat flux. What one sees in the glass full of liquid when one puts a heat source on one side of the glass are the density gradients resulting from the temperature gradients in the water. (The density gradients are also what one sees using the Schlieren method.) — Preceding unsigned comment added by 143.107.45.103 (talk) 15:53, 25 September 2013 (UTC)

Incorrect scale bar?[edit]

It appears the scale bar in the following image (located in the Stellar Physics section) is incorrect:

here

According to WorldAtlas.com North America is 4,313 km East-West and 2,535 km North-South. The text in the section accompanying the image states solar granules are approximately 1,000 km in diameter. This appears to roughly match the image of North America, but not the scale bar.

The same image accompanies the article on solar granules. Perhaps this needs fixing...? — Preceding unsigned comment added by GDierk (talkcontribs) 03:38, 21 December 2013 (UTC)

Heat transfer[edit]

Added lede image at heat transfer. Prokaryotes (talk) 18:41, 5 April 2014 (UTC)