Heat Recovery Steam Generator (HRSG) Learning Center
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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 HRSG design. Other methods, such as HTRI, Maxwell, Dittus-Boelzer, or others may be more appropriate for a particular HRSG design. You will notice that we have not offered a method for film boiling coefficient. The reason for this ommision is that in the evaporator, when the hi is high, which it is for the boiling case, it does not have any significant effect on the calcuations. We would recommend that a value of 1,500 to 2,000 Btu/hr-ft2-°F be used for these cases.

Disclaimer:

The formulas and correlations presented herein are all in the public domain and are to be used only as a learning tool. Note that any product, process, or technology in this document may be the subject of other intellectual property rights reserved by sponsors or contributors to this site. This publication is provided as is, without any warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of fitness for a particular purpose, or non-infringement.

The formulas, correlations, and methods presented herein should not be considered as being recommended by or used by the sponsors of this site. The purpose of this site is educational and the methods may or may not be suitable for actual design of equipment. Only a fired heater design engineer is qualified to decide if a calculation or procedure is correct for an application.