Predict the nucleate-boiling heat transfer coefficient for water boiling at atmospheric pressure on the outside surface of a 1.5-cm-OD vertical copper tube 1.5-m-long. Assume the tube-surface temperature is constant at 10 K above the saturation temperature.
GIVEN
? Water boiling at atmospheric pressure on the outside surface of vertical copper tube
? Tube outside diameter (D) = 1.5 cm = 0.015 m
? Tube length (L) = 1.5 m
? Tube surface temperature above saturation temperature (?Tx) = 10 K
FIND
? The nucleate-boiling heat transfer coefficient (hb)
ASSUMPTIONS
? The water is at saturation temperature
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 13, for saturated water at 1 atm (Tsat = 100°C)
As stated near the end of Section 9.2.2, ‘the geometric shape of the heating surface has no appreciable
effect on the nucleate boiling mechanism’.
Assuming the boiling is nucleate boiling, the heat flux q", is given by Equation (9.2)
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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