Need to know heat transfer coefficient/therm. conductivity of ss tank 2

[jesabell44]

I'm trying to compare an overall heat transfer coefficient I have calculated for a SS vessel, based on various assumptions. Does anyone know what the heat transfer coefficient or thermal conductivity of a bare 316ss vessel is? Thanks.

 

[StoneCold]

Jesabell44
If you are looking for a ball park number. I would say 70 Btu/hr*ft2*F or less. That would be for water flowing in the jacket and a liquid hydrocarbon in the tank. With the tank being agitated.

My gut feel only.

Regards
StoneCold

 

[jesabell44]

It's for a bare vessel, not jacketted.

 

[StoneCold]

Ok
In another recent thread someone quoted 0.5 BTU/hrft2F.

 

[panduru]

Apparently, we have a very important issue on hand here.

This factor needs to be addressed with a greater degree of seriousness and a reasonable correlation with the fluid(s), with as well as without agitation, found.

Is there any info available online on the topic?

Is there any published material where an attempt has been made to estimate or evaluate U for an SS vessel?

Any pointers are most welcome from forum members.

 

[jesabell44]

I have just found thermal conductivities for 316 SS but not necessarily on a tank from the web. Perry's has thermal conductivities for heat exchangers, not tanks. We are just assuming it is a water-like fluid in these tanks.

 

[25362]

From Perry VI, expressed in 9.5 Btu/(h.ft.^oF), it is 9.5 at 100^oC, rising to 12.4 at 500^oC

 

[panduru]

@25362:

Apart from the temperature, under what other conditions do you think are those figures of 9.5 / 12.4 applicable?

 

[25362]

Panduru, please note these values are thermal conductivities (see the units) and are not, repeat not, heat transfer coefficients.

 

[panduru]

@25362:
Of course, they are.

 

[corus]

The thermal conductivity is a material property and is unrelated to whether it's a tank, bucket, statue or whatever you can dream up. Heat transfer coefficients are unrelated to the material but are dependent on the fluid passing over the surface. If it's in free air then it will depend on the surface orientation, ie whether the surface is vertical or facing down. For natural convection and radiation then it will depend on the surface temperature.

corus

 

[panduru]

Very well stated, corus.
Now I suppose everyone is looking at the issue from the right perspective.

 

[jesabell44]

They are vertical "tanks" and filled with a "water-like" fluid. What I have calculated is for the fire case, so assuming the air is around 320C (608F).

 

[thermcool]

parameters like heat transfer coefficient are very much situational dependent and should be determined experimentally. Most of the available correlations are not able to give correct values for the Heat transfer coefficient (in most cases) due to the dependence of the HTC on the wide assortment of factors. I would suggest you to determine the HTC parameter by experiment rather than assuming or calculating some value.
Once you have experimented you can calculate and validate you calculation approach,

 

[panduru]

thermcool has stated it correctly. Empirical determination is the only right, reliable and reasonable alternative when it comes to the heat transfer co-efficient. Just make sure that all parameters are as close to the actual situation as possible.

@jesabell44: pl update us on your observations, thanks.

 

[corus]

You need two heat transfer coefficients, one to the air, and one to the water. To the air I'd assume radiation to an ambient 320C if I had no other data for the effect of fire. For the surface adjacent to the water you could assume that the surface was fixed at the water temperature, in effect an infinite htc. This ignores any convection you may have in the water and also any boiling that may occur at the surface but would give you the maximum delta T through the shell thickness if you were calculating stresses. In the worst case for boiling you could assume you have a zero htc and then the tank temperature would be at the outer ambient of 320C everywhere. This may also be a worst case for stress if the tank is restrained from expansion in some way.

corus