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,
And for vapor flow with Re =>15,000,
Where the Reynolds number is,
And the Prandtl number is,
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,
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.
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.
T(2)
