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)

Physics & Space Science

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