Calculate the heat transfer coefficient for film boiling of water on a 1.3 cm horizontal tube if the tube temperature is 550°C and the system is placed under pressure of 50 kPa.
GIVEN
? Film boiling of water on a horizontal tube
? Tube outside diameter (D) = 1.3 cm = 0.013 m
? Tube temperature (Tt) = 550°C
? Pressure = 50 kPa = 50,000 N/m2
FIND
? The heat transfer coefficient (hc)
ASSUMPTIONS
? Steady state
? Tube temperature is uniform and constant
? The viscosity, specific heat, and thermal conductivity of the vapor can be approximated by those
of steam at 1 atm pressure
? Radiation across the vapor film is negligible
SKETCH
PROPERTIES AND CONSTANTS
Extrapolating from Appendix 2, Table 35, for steam at 1 atm and 81.5°C
The heat transfer coefficient for film boiling on tubes is given by Equation (9.6)
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