4 replies to this topic

[Jackwill]

Hello,

 

I am designing a shell and tube heat exchanger and I am not sure whether the sizing is correct. I have a duty of 100 kW, LMTD of 61 degrees C and estimated the overall heat transfer coefficient to be 400 W/m^2.C

 

This gives me an area of 4 m^2.

 

Can this be correct? It seems way too small.

 

I should add the fluids in the heat exchanger are saturated steam at 5.5 bar and dowtherm A. Is 400 a valid assumption for the overall heat transfer coefficient or is it way off?

 

 

Kind regards,

 

J. Will

[breizh]

https://durathermflu...CFQXHtAodFwoAeg

 

http://www.hcheattra....com/tools.html

 

Hi Jackwill ,

attached tools to support your work .

 

Good luck

 

Breizh

[srfish]

The overall heat transfer coefficient looks low for heating Dowtherm with steam if the allowable pressure drop is reasonable.

[Napo]

Jackwill,

Steam is 5.5 bar manometric, this is 6.5 bar absolute, from vapor tables the temperature is 162.1ºC (approximate).

If you are in design please take in count the “Dow Chemical Company suggest use of the fluid in the temperature range between 450º-750ºF” (232.2º-398.9ºC) (Geiringer P., Handbook of Heat Transfer Media, p. 77).

From your MLDT, the mean temperature of Dowtherm A is approximately 83.5ºC, from table V-4.3 Geiringer handbook, the viscosity is 2.1 cP --> Heavy hydrocarbon.

From Wuithier P., Raffinage et Génie Chimique, Vol . II, p. 1067, in French, for “Réchauffeurs” -->Vapeur d´eau (steam) and Hydrocarbures lourds (heavy hydrocarbon)--> U = 6-60 BTU/hr ft2 ºF. We can take Um = 66/2 = 33 BTU/hr ft2 ºF = 187,4 W/m2ºC. This value include fouling and pressure loss is between 0.35 to 0.7 kg/cm2.

Warning: Approximate overall heat transfer coefficient: Use as guide as to order of magnitude and not as limits to any value. Coefficients of actual equipment may be smaller or larger than the values listed (From Branan C., Rules of thumb for Chemical Engineers, Table 3 p. 33).

I Hope help you.

Napo.

Attached Files

•  Wuithier.jpg   127.4KB   1 downloads

[Jackwill]

Appreciate the help guys