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# Overall Heat Transfer Coefficient For Tank Heaters (Steam) Heating Hfo / Asphalt

Dear All,

Today's blog entry provides an equation for Overall Heat Transfer Coefficient for storage tanks handling Heavy Fuel Oil (HFO) / Asphalt and provided with tank heating coils using steam as a heating medium.

If the heat loss rate Q (W or Btu/hr), from the tank is known, then the steam coil surface area can be calculated and thus the coil geometry fixed. The general equation for sizing heat exchange equipment can be utilized for this:

Q = Uo*A*ΔT

or

A = Q /( Uo*ΔT)

where:
A = Steam Coil surface area, m2 or ft2
Q = Heat Loss Rate from tank, W or Btu/hr
Uo = Overall Heat Transfer Coefficient, W / m2.⁰C, Btu / hr.ft2.⁰F
ΔT = Temperature difference between steam supply temperature and bulk process fluid temperature in tank, ⁰C, ⁰F

For heat loss rate from storage tanks, refer this very well known post on "Cheresources":

http://www.cheresour...icle/?hl=kumana

Now for the equation for the equation for the Overall Heat Transfer Equation, Uo

United States Customary Units:

Uo = 30*(Tc - Tf)0.14 / (µf)0.4

Metric Units:

Uo = 11.7*(Tc - Tf)0.14 / (µf)0.4

where:

Tc = Temperature of the steam, ⁰F, ⁰C
Tf = Bulk Temperature of the process fluid, ⁰F, ⁰C
µf = The absolute viscosity of the process fluid at the average film temperature ((Tf + Ti) / 2), cP, Pa.s

where:
Ti = Temperature of the coil surface in contact with the fluid, ⁰F, ⁰C

Generally Ti is 10-15C more than the bulk process fluid temperature

Once the steam coil surface area A is calculated, the length of the coil can be calculated after fixing a NPS or OD of the steam coil pipe.

That is it for today's blog entry. I look forward to comments from the members of "Cheresources" on this blog entry.

Regards,
Ankur.

jfuhr

How does this change if using hot oil instead of steam?

ankur2061

How does this change if using hot oil instead of steam?

I don't know the answer to your question. You will have to do your own research to arrive at an answer.

Regards,

Ankur

breizh

https://durathermflu...-calculator.php

Jifuhr , to support your work .

All vendors are providing similar calculator !

Breizh

Art Montemayor

Ankur:

This could be a very useful correlation for the Overall Heat Transfer Coefficient.  What is the source and the derivation of the given equation for Uo?  Is it an empirical relationship or is it mathematically derived?  If derived, what are the assumptions and the bases for the derivation?  If empirical, has the equation been tested in the field for successful results?

Art.

ankur2061

Ankur:

This could be a very useful correlation for the Overall Heat Transfer Coefficient.  What is the source and the derivation of the given equation for Uo?  Is it an empirical relationship or is it mathematically derived?  If derived, what are the assumptions and the bases for the derivation?  If empirical, has the equation been tested in the field for successful results?

Art.

Art,

This correlation is mentioned in Exxon Design Practices and probably an empirical correlation based on their own experience of storing and handling heavy fuel oil / asphalt.

Regards,

Ankur.

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