time constants for heat transfer?

Question

Are the characteristic time constants for heat convection always smaller than the heat conduction time constants for most of fluids? Why?

Answer 1

Practically Aplication: I worked in a steel foundry and I we would only have about 10 to 15 minutes once the steel once poured from the furnace into the ladle. The time contrast was that the air was cooling the steel. If we got the chemistry of the steel wrong and had to add alloy into the ladle and stir it. That would cool it further. If we have to add a lot, we'd have to pour from one ladle into another ladle, and that would really cool it. The boss would be yelling then.


However, one type of steel had a aluminum in it and the reaction was exothermic when we poured it. It actuacty gained heat when we poured it from the furnace into the ladle. And this one would sit on the floor for almost an hour. We'd have to purposely stir it to cool it down to get it down to pour temperature.

BTW, Silver is the best conducter of heat I'm told.

Answer 2

Not sure what you mean by time constants. Heat transfer by conduction depends on thermal conductivity of the material. Heat transfer by convection depends on a heat transfer coefficient which depends on temperatures,viscosity and density of the fluid are used to determine a fluid side transfer coefficient.

In general unless you're talking about insulators the heat transfer coefficient for convection in gases in the order of 2 BTU/ft^2*hr* F

And conduction transfer rates could be 20 times that rate or more.

Never heard these referred to as time constants.

Answer 3

Generally, fluids conduct heat better due to freer molecular interaction. Although, some metals and such can do this just fine depending on the initial form of the heat. It all depends on the materials and source/intention and specifications of use. But as a rule, molecules that can dance are better in this respect than the ones who just stand still.

Answer 4

Two different transfer mediums.

Convection travels by waves through open air.

Conduction occurs through water, a slightly and slower and more "demanding" process from the perspective of the heat in question.

-Daniel

Answer 5

Conduction is most efficient than convection and radiation. have you heard of "heat retentive plates" ?
A susceptor (material that absorbs or is susceptible to microwaves) in a cavity loses heat mostly by radiation. regulated by the stefan Boltzmann law

Answer 6

the fluids are contained inside..the heat varies on the outside because of temp

Answer 7

Your equation says that once 2 mols of Mg react, 1204 kJ of skill are released. you're asked for the skill whilst 2.6 g of Mg react. Your periodic chart will inform you the way plenty mass of Mg equals a million mol.

Answer 8

67