Water at atmospheric pressure is boiling in a pot with a flat copper bottom on an electric range which maintains the surface temperature at 115°C. Calculate the boiling heat transfer coefficient.
GIVEN
? Water at atmospheric pressure boiling in a copper bottom pot
? Surface temperature of the pot bottom (Ts ) = 115°C
FIND
? The boiling heat transfer coefficient (hb)
ASSUMPTIONS
? Temperature of the pan bottom is uniform
? The copper is polished
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 13, for saturated water at 1 atm (Tsat = 100°C)
Assuming the boiling is nucleate boiling, the heat flux, q" , is given by Equation (9.2)
where
??Tx = Ts – Tsat = 115°C – 100°C = 15°C
gc = 1.0 (in the SI system)
n = 1.0 for water
g = 9.8 m/s2
Rearranging
The critical heat flux for nucleate boiling is given by Equation (9.4)
Since q"< q?c, the nucleate boiling assumption is valid.
By definition
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