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Tank energy loss to surrounding
3

Tank energy loss to surrounding

Tank energy loss to surrounding

(OP)
I am looking for a way to calculate the heat loss of a tank to ambient temperature.
The tank is filled with a fluid:
Density = 910 Kg/m³
Specific Heat (cp) = 1,95 kJ/kg K
Ambient Temperature = 8 °C (46 °F)
Temperature Hold = 50 °C (122 °F)

The goal is to keep the temperature inside the tank at 50 °C. I don’t have any flows for the calculation.
The thickness (2 cm) of the wall is much much smaller than the diameter (60 m) of the tank. The tank is made of steel and is not insulated.

For the area I was thinking just to calculate A=pi*D²*H and not including the roof because the tank is filled only half way up and the air should be a good insulation. How about losing energy to the ground?

I know it should be easy using Q = k A (dT), but because the k-value is based on the ratio wall thickness and diameter I am rather sceptical concerning the calculated value.

I found a formula Q=h A dT
h = convection factor, which probably includes the heat capacity in an approximation

Anyway I tried a few ways and did not get results which do make sense.
I would be happy if anyone could help me.

RE: Tank energy loss to surrounding

my apology's for being direct, but this matter is a textbook example in most heat transfer books.

another consideration for determining heat loss is wind speed.

the website containing the 3eplus insulation calculation software should be adequate for this application. suggest conducting a search using google . . .

with that much of a temperature difference, it may be difficult to maintain the fluid temp without insulation or some heat addition.

the formulas you listed are appropriate for this application.

good luck!
-pmover

RE: Tank energy loss to surrounding

If you are interested in unsteady-state heat losses from the tank to the surroundings,

the heat lost in time t is Q = mCpo(T-To)

And the time/temperature relation:

t = [-mCpo/(UoAo)]* ln[(T-Ta)/(To-Ta)]

Ta = outside air temperature
To = Tank fluid temp. at time 0,
T = tank fluid temperature at time t
Uo = OHTC based on To
Ao = Tank surface area upon which Uo is based
m = mass of fluid in thee tank
Cpo = Heat capacity of the fluid at To

Be careful in using consistent units.

RE: Tank energy loss to surrounding

(OP)
Thank you guys!
I didn’t want to use programs to understand what’s behind the calculations.

"The only statistics you can trust are those you falsified yourself." Winston Churchill

So I tried a lot of equations and finally it was clear just to use the one given by “25362”. It was probably too obvious. The slope of t vs. ln(dT/dT) leads you to Uo which was the missing part all the time.
I wasted some time on some convection equations I found in Perry's Chemical Engineers' Handbook. The result was double as high as it is now.
Now I have nice diagrams which even show me the influence of the wind direction. In general I might say for non-insulated tanks, like the one above, you can use u0 or k-values from 5-7 W/m²K and you are on the safe side. I used roof and fluid level for area calculations.

RE: Tank energy loss to surrounding

2
Little late but this is a copy of a paper on calculating tank heat transfer coefficients.  For the external surface to air, Kern has some much simplier ones than the ones presented in this paper.

http://s17.yousendit.com/d.aspx?id=3V7OEZGNPCLK823CU2LS5A58UB

RE: Tank energy loss to surrounding

I hope this excellent paper didn't go unnoticed.

RE: Tank energy loss to surrounding

(OP)
No, it is really interesting. So far I had no time to check the equations for my case.
All that BTU/ft²H aso kills me. ;)
Another think is you need much more details like viscosity and this beta value which I do not have at hand.
I am going to check this paper please give me more time.
Thank you anyway for the paper.
Have a nice day folks.

RE: Tank energy loss to surrounding

is there anyway somebody cand send this to YSI again? The link is expired. Thanks!

RE: Tank energy loss to surrounding

Please post the paper again so that those of us who missed out previously can obtain a copy.  Thanks.

RE: Tank energy loss to surrounding

Track down a copy of ASTM C680, "Standard Practice for
Estimate of the Heat Gain or Loss and the Surface
Temperatures of Insulated Flat, Cylindrical, and Spherical
Systems by Use of Computer Programs".  It has good, consistent formulas for heat transfer and properties of air.

Larry

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