A

Which is faster conduction or convection?

10 Answers
Heat get transferred by conduction or convection
W

Firstly it is refreshing to encounter a debate that pitches good opinions against one another. Here are some rejoinders: In my example of a horizontal thread of mercury I argue that convection does occur owing to a temperature gradient vertically across the capillary. However because conduction occurs quickly this gradient is trivial and heat occurs mainly by conduction. If you heat a liquid in a container from the bottom then convection usually beats conduction but what if (i) the liquid has a high viscosity and does not flow freely under the small forces available, (ii) the liquid is in zero gravity (iii) the liquid has a very small coefficient of thermal expansion? How about finned tube heat exchangers? If convection, and forced convection if you like, dominated then there would be no need for the conductivity afforded by the fins. Again thanks for the stimulating discussion.

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M

I respect your opinions guys, but I stand by my original answer. I agree that there are many different circumstances where conduction contributes to heat transfer more than convection, but convection will always transfer heat more quickly in a particular substance than conduction IF convection occurs. The question did not stipulate any limiting circumstances, so we can only consider the general case.

Aside from forced convection (like in a convection oven), convection only occurs because of a temperature gradient that conduction is unable to resolve quickly enough. Therefore, convection must distribute heat more quickly than conduction.

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W

How about this then. Take a capillary tube filled with mercury, like a thermometer. Lay it horizontal and heat one end. Heat is conducted along the thread of mercury by conduction because mercury has a relatively high thermal conductivity. There is convection also but its contribution to overall heat transfer is small compared to conduction. As I say, it depends on the circumstances.

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W

Take a tank of water and put a steam pipe at the top just beneath the surface and apply heat. The water will get hot at the top but there will be almost zero heat transfer by convection to the rest of the water. In this case heat transfer to the rest of the water will be by conduction almost exclusively. Thus there is no universal rule for the superior mode of heat transfer.

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S

Which one operates "faster" as a mode of heat transfer will depend on the medium in question.

A metal pot will conduct heat faster than the atmosphere will convect.

However, a NuWave convection oven will convect heat faster than a metal pot will conduct it.

There is no general example that may stipulate one is faster than the other.

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M

Logically, convection must transfer heat more quickly than conduction.

Convection occurs when a fluid or gas is cooler in the upper portion and warmer in the lower portion. If conduction was able to transfer heat quickly enough, the temperature of the substance would be equalized, and convection would be prevented.

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M
Wristb34 your experiment would no doubt return the results you described. However, it is designed in a manner that prevents convection from occurring. The question was not under what circumstances will convection occur, but rather when it does occur how does the rate of heat transfer compare to that of conduction.

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C

Well conduction and convection are two diffrent things. if you are talking about weather then there is conduction. if your talking about fluids then there is convection. So fluids are convection and weather is conduction. pick your choice.

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S

Convection is more faster than conduction becuase molecules move more freely in convection.

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W

Too vague. You need to cite a specific example.

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