Hi everyone,

I’ve got a query about calculation of heat transfer coefficient for natural convection inside floating roof storage tanks. Could you please help me to resolve this conflict?

In order to determine the overall heat loss of a single deck floating roof, I’m trying to calculate the heat transfer coefficients for natural convection of inside surface of the roof (hvr) and inside surface of the floor (hLB) as per article, “Predict Storage Tank Heat Transfer Precisely - By J.Kumana and S.Kothari”.

The article suggests applying equation 20 for facing down horizontal surfaces (Roof Inside), Nnu = 0.27 x (NGr NPr)^{0.25} and equation 19 for facing up horizontal surfaces (Floor Inside and Roof Outside), Nnu = 0.14 x (NGr NPr)^{0.33}. However, comparing these formulas and their applications with other heat transfer books like “Heat Transfer by Holman” – Refer table 7-1, P. 334, it is understood the application should be reversed. i.e. apply equation 20 to upper surface of a cooled plate (floor inside and top side of roof) and apply equation 19 to lower surface of cooled plate (roof inside). As the fluid temperature is always higher than roof and floor plate temperatures, the roof and floor plates are considered as cooled plate when calculating the heat transfer for inside of the tank, however roof plate could be considered as hot plate when we calculate roof outside coefficient as surface temperature higher than air temperature.

Since the single floating roof fully contacts the product, the heat loss through roof is significant and misunderstanding of application of these formulas obviously has an outstanding effect on total heat loss estimation.

Could you guys please clarify to me which formulation should be applied to roof underside and which should be applied to floor top side?

Many thanks,

smrastgou