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

This topic 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 = U_o*A*ΔT

or

A = Q /( U_o*ΔT)

where:

A = Steam Coil surface area, m² or ft²

Q = Heat Loss Rate from tank, W or Btu/hr

U_o = 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, U_o

United States Customary Units:

U_o = 30*(T_c - T_f)^0.14 / (µ_f)^0.4

Metric Units:

U_o = 11.7*(T_c - T_f)^0.14 / (µ_f)^0.4

where:

T_c = Temperature of the steam, ⁰F, ⁰C

T_f = Bulk Temperature of the process fluid, ⁰F, ⁰C

µ_f = The absolute viscosity of the process fluid at the average film temperature ((T_f + T_i) / 2), cP, Pa.s

where:

T_i = Temperature of the coil surface in contact with the fluid, ⁰F, ⁰C

Generally T_i is 10-15⁰C 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.