Stirred Reactor Heat Losses

[TomX]

Hi guys,

Anybody has a way to estimate the heat loss of an insulated stirred reactor, or what is the same, the estimation of insulation thickness. (In this case is a batch process and I want to figure the need of heating coils out)
I have found an useful freeware program "3E Plus 3.2", and I have estimated the heat losses but without agitation, and I need to include the agitation factor, to see the change in the heat lost.

Thanks.

 

[StoneCold]

TomX
Agitation should not affect the heat loss of a reactor. The overall heat transfer coefficient should be controlled by natural convection on the outside. That is why the metal temperature is very close to the actual liquid temperature inside in most cases.
My opinion only.

StoneCold

 

[25362]

In heat transfer the driving force is the temperature difference. While the resistances to heat flow reside in the various "layers" on its path. Does the stirring action influence any of these in any manner ?

 

[m777182]

This is a remark on 25362's answer/question: The innermost layer is a layer of stagnant fluid and the thermal resistance of it depends on Reynolds number, that is on aggitation.With some deposits on the wall the stagnant layer and deposits resistance could be significant. The resistance of the vessel wall "layer" does not contribute much; it is given by the material (=steel)properties and thickness of the wall.However you can not change it very much.You can have effective control on heat losses with the application of thermal insulation that forms the outermost layer.As an approximation caculate with resistance factor 1 through the wall, 10 through the stagnant layer and 100 through the outer thermal insulation.
There is a great number of textbooks on heat flow through layers of different thermal conductivity, one of them is available as download version and mentioned here on engineering forum. With little effort you will do your calculations yourself.
m777182

 

[quark]

The internal heat transfer coefficient can't be ignored when contents in the vessel are stirred. Kern discussed it briefly but this topic is elaborately discussed with worked out examples in January01, 1999 issue of chemical engineering magazine. The topic is Heat Transfer In Agitated Jacketed Vessels

Regards,

 

[25362]

From ChE/January 1999, Heat Transfer In Agitated Jacketed Vessels by Robert F. Dream, P.E.:

But if during operation, the course of the process proves to be governed mainly by the heat transfer, then such variables as log mean temperature difference and heat-transfer surface area will usually take on more significance than the agitation variables.

...the mixing can affect only the heat-transfer resistance on the inner vessel wall, which is but one of the resistances that determine the overall heat-transfer coefficient.