Correlation for boiling heat transfer to saturated fluids in convective flow
Chen, J. C.
It is postulated that two basic mechanisms take part in the heat transfer process for the boiling of saturated fluids with flow: the ordinary macroconvective mechanism of heat transfer which normally operates with flowing fluids, and the microconvective mechanism associated with bubble nucleation and growth. It is further postulated that these two mechanisms are additive in their contributions to total heat transfer.
h=h_macro+h_micro
Considering first the macroconvective mechanism, it was recognized that at the two limits of 0 and 100% quality, the macroconvective heat transfer should be described by the Dittus-Boelter type of correlation. It was then postulated that in the two-phase region where both liquid and vapor are present, the macroconvective heat transfer should still be described by a modified form of the Dittus-Boelter equation.
h_macro=0.023(Re)^0.8(Pr)^0.4(k/D)
In the case of ordinary fluids - i.e., not liquid metals - the Prandtl numbers of the liquid and of the vapor are normally of the same magnitude. The Prandtl number of the two-phase fluid should therefore also be of the same magnitude. Furthermore, since the heat is transferred through an annular film of liquid adhering to the wall (for annular flow), it is expected that the liquid properties would have the dominant effect.
Therefore, h_macro=0.023(Re_L)^0.8(Pr_L)^0.4(k_L/D)F
where F=(Re/Re_L)^0.8, Re is the effective Reynolds number for the two-phase flow.
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