u/g tank heat loss calculation
u/g tank heat loss calculation
(OP)
I need to evaluate heat loss in an uninsulated underground (1 m) tank (20 m3) due to freezing problems.
I have some values for apparent thermal conductivity for different soils based on soil type and moisture content, but I don't know how to estimate the equivalent thickness to calculate the overall heat transfer coefficient.
Any idea?
thanks
j
I have some values for apparent thermal conductivity for different soils based on soil type and moisture content, but I don't know how to estimate the equivalent thickness to calculate the overall heat transfer coefficient.
Any idea?
thanks
j





RE: u/g tank heat loss calculation
RE: u/g tank heat loss calculation
i'll drop you a later at night
j
RE: u/g tank heat loss calculation
RE: u/g tank heat loss calculation
i've already take it into account in my calculations, i fixed constant inner temperature, evaluating heat conduction across inox wall, intermediate natural turbulent convection (air chamber) and conduction across carbon steal and coating.... and now the soil, my problem
thanks
j
RE: u/g tank heat loss calculation
Since I have a problem similar to yours, would you please specify how did you treat the air resistance and what is the gap thickness ? Apart from the soil, I think that the air chamber has a significant heat resistance.
Thanks, Roal
RE: u/g tank heat loss calculation
i looked for natural-convection coefficients in enclosed spaces (Perry 7th 5-13) but my case was out of range...
so i use a 50 W/m2K coefficient as a very conservative value (between 10-50W/m2K are reasonable values, i think :P)
however the heat resistance in the soil is the most significant
j
p.d.: 8mm is the gap tickness in my case
RE: u/g tank heat loss calculation
I think you are wrong.
If gap thickness is only 8 mm, I should consider only air conductivity, so the coefficient is much lower. Unfortunately, I have Perry 6th and cannot check your reference.
RE: u/g tank heat loss calculation
i've also considered only heat conductivity and numerical results (inox-air-c.steel) differed less than 10% with a deltaT= 25ºC as i really considered h(air)=17 W/m2K
j
RE: u/g tank heat loss calculation
Assuming 10 mm SS wall: 0.01/15 = 0.00067
8 mm air gap: 0.008/0.025 = 0.32
Assuming 10 mm CS wall: 0.01/40 = 0.00025
1/K = 0.00067 + 0.32 + 0.0025 = 0.32092
K = 3.12 W/sqm°C
This figure differs from that calculated by you (17).
Am I wrong ?