Heat losses through a floor of a tank

[TerenceA]

Hello everyone!

This is my first post on EngTips. I am a mechanical engineer from France, and these days working on heat losses in a tank.

I already have calculated heat losses due to convection / conduction for the roof and "walls" (thanks to Lienhard's free textbook and its recent correlations for the Nusselt number...), but I am not sure about the calculation of heat losses through the "floor".

"My" tank is a big one (about 20m in diameter) made in metal, and put on a concrete floor. It contains hot liquid.

As the global heat transfert coefficients are calculated with two fluids "separated" by several "conductive" layers, I don't know how to handle the problem with my tank bottom.
Indeed, I can calculate the convection coefficient for the liquid in the tank, the conduction coefficient for the metal, but what do I need to add in order to take into account the concrete floor and soil?

I saw some answers on the Net telling about some "linear" coefficients (in W / m K instead of W / m2 K) but I would like to be sure these are correct before using them.

Thank you in advance for your answers, and I hope my "technical" english will be easily understood...

 

[IRstuff]

This subject has been discussed here. You might try to do a search

TTFN

Eng-Tips Policies FAQ731-376

 

[TerenceA]

I did a search on EngTips forums, but I couldn't find the answer for my question.
This is probably due to the difficulties I have to clearly describe it, or the difficulties I have to clearly understand technical english in threads.

In fact, I saw on others forums that a way to calculate heat losses to the ground can be:
- convection from fluid to tank "bottom wall"
- conduction through multiple layers of insulation (if exists) until the fixed temperature considered in soil.

As I am not able to estimate the soil characteristics or a fixed temperature, I was asking me if it is possible to calculate the global heat transfert coefficient as follows:
- convection from fluid to tank "bottom wall" (downwards)
- conduction through multiple layers of insulation (downwards)
- conduction through the soil until the surface with ambient air (upwards)

I saw this kind of coefficients on this site (sorry it's in french):

http://www.thermexcel.com/french/ressourc/deperdit.htm

My question is: does anyone has ever heard about some heat losses calculation of this kind (i.e. going from the fluid to the ambient air, through the soil under the tank)? And in this case, could it be possible to explain me how does it works?

My apologies if this subject has really already been discussed in other threads, I would be very happy to know which thread is it.

Thank you for your patience with a new and foreign user of EngTips!

 

[quark]

thread391-175521 can be of help to you.

 

[CarlB]

And this thread thread194-179435

 

[TerenceA]

Well, thank you both for the links.
I'll try to do with it!