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joseph May 18, 2001 05:43

advection
 
hi everybody,

1.Could some one please tell me what is the meaning of Advection?

2.what is the difference between advestion and convection?

thank you soo much for your time.

Junseok Kim May 18, 2001 06:28

Re: advection
 
Convection is the transport of heat by large-scale movement of the fluid. For example when warm air flows in from the south St. Louis generally warms up.

The fluid flow can be vertical or horizontal. In meteorology, the responses to convection are quit different if the motion is vertical or horizontal. Therefore we define advection with horizontal motion, while convection will denote vertical motions.

Convection happens naturally in the atmosphere. During warm sunny days the sun warms the surface (by radiation the 3rd method) the surface warms the air touch the surface by conduction and the as the air warms it begins to rise. The warm air is replaced by cool air and the warm pool of air called a thermal continues to rise. This convection is actually warming the air away from the surface.

John C. Chien May 18, 2001 17:47

Re: advection
 
(1). In CFD, as in numerical analysis in fluid mechanics, "convection" is normally used and "advection" is just "convection". (2). In the momentum equations, you have "convection", "diffusion" and "pressure gradient" terms.

George Bergantz May 19, 2001 00:09

Re: advection
 
To add to the confusion, I often see advection reserved for 'forced' scalar transport, i.e. no body forces, and 'convection' used when body forces predominate.

But there is no rule for this, most will know what you mean. For those of us in earth science where buoyant flows are common, using 'convection' will usually call to mind buoyancy dominated flow. But again this is simply a matter of taste. For example, A. Bejan has a book titled "Convection Heat Transfer" that also includes a discussion of forced heat transfer.

joseph May 19, 2001 12:40

thank god
 
hi everybody,

I am really greatful to Junseok Kim,John C. Chien George Bergantz,thank you all for taking time out and answering this question of mine,I am also thank ful to god for good people like you.

I have now got some insight as to when to use convection or advection.

with lots of thanks,

joseph machnaim

Barney May 22, 2001 18:22

Re: advection
 
advection --- d/dx_j (\rho u_i u_j )

[term in momentum eqn.]

convection --- d/dx_j (\rho c_p T u_j)

[term in temperature eqn.]

De-Wei Yin May 27, 2001 01:13

advection, convection
 
advection: From Latin "advectio", which originally derives from Latin "advehere"; means transmission by horizontal movement. ("ad" = toward, "vehere", "vecto" = carry)

convection: From Latin "convectio", which originally derives from Latin "convehere"; means transmission by vertical movement. ("con" = "com" = with)

It seems more appropriate to prefer "convection" over "advection" in reference to general transport by fluid flow without regard to directionality. The Latin root of "advection" implies the need for an accusative object (i.e., the destination toward which the movement is made) whereas "convection" does not require such an accusative object. Both words include the concept of a dative object, i.e., the object being transported (e.g., heat).

John C. Chien May 27, 2001 15:37

Re: advection, convection
 
(1). It is interesting. (2). It is possible that the world was "perfectly flat" in those days. (3). Good Greif, as Charlie Brown used to say.


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