Heat Transfer Coefficients

The inside film coefficient needed for the thermal calculations may be estimated by several different methods. The API RP530, Appendix C provides the following methods,

For liquid flow with Re =>10,000,
hl = 0.023(k/di)Re0.8*Pr0.33(mb/mw)0.14
And for vapor flow with Re =>15,000,
hv = 0.021(k/di)Re0.8*Pr0.4(Tb/Tw)0.5
Where the Reynolds number is,
Re = di*G/mb
And the Prandtl number is,
Pr = Cp*mb/k
Where,
hl = Heat transfer coefficient, liquid phase, Btu/hr-ft2-°F
k = Thermal conductivity, Btu/hr-ft-°F
di = Inside diameter of tube, ft
mb = Absolute viscosity at bulk temperature, lb/ft-hr
mw = Absolute viscosity at wall temperature, lb/ft-hr
hv = Heat transfer coefficient, vapor phase, Btu/hr-ft2-°F
Tb = Bulk temperature of vapor, °R
Tw = Wall Temperature of vapor, °R
G = Mass flow of fluid, lb/hr-ft2
Cp = Heat capacity of fluid at bulk temperature, Btu/lb-°F
For two-phase flow,
htp = hlWl + hvWv
Where,
htp = Heat transfer coefficient, two-phase, Btu/hr-ft2-°F
Wl = Weight fraction of liquid
Wv = Weight fraction of vapor
The following script will allow us to try these formulas out using our browser.
Tube diameter, in: Mass flow, lb/hr-ft2:
Percent vapor, %: Bulk Temp., °F:
Liquid PropertiesVapor Properties
Thermal cond., Btu/hr-ft-°F: Thermal cond., Btu/hr-ft-°F:
Visc. bulk, lb/ft-hr: Visc. bulk, lb/ft-hr:
Spec. Heat, Btu/lb-°F: Spec. Heat, Btu/lb-°F:
Visc. @ wall, lb/ft-hr: Temp. @ wall, °F:


hl Coefficient, Btu/hr-ft2-°F:
hv Coefficient, Btu/hr-ft2-°F:
htp Coefficient, Btu/hr-ft2-°F:
Reynolds number:LiquidVapor
It should be stressed at this time, that there are many ways to calculate the inside heat transfer coefficient, and a lot of care should be taken in the procedure selected for use in heater design. Other methods, such as HTRI, Maxwell, Dittus-Boelzer, or others may be more appropriate for a particular heater design.