An Empirical Modification of Nucleation Theory and Its Application to Boiling Heat Transfer Page: 29 of 38
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n C Added wetting agents
2 x 10~1 4.15 x 10-3 0.02% Mg., 0.0001% Ti
Due to the difficulty in evaluating the physical properties of sodium
and sodium-potassium alloy, comparison has not been made between cal-
culated and test results. The order of magnitude, however, can be easily
estimated from Eq. (24). Calculations have shown that the magnitude of the
exponential function in Eq. (21) does not vary too much for systems as dif-
ferent as organic liquids and mercury. The decisive factor in controlling
the magnitude of heat flux is the modulus in the rightside of Eq. (21), i.e.,
pc 0s(T3/C)1/Z, For a given superheat, such as 6s = 7 F, this quantity for
sodium is many times that for mercury, and hence the heat transfer by
boiling sodium should be several times larger than that by mercury.
10. HEAT TRANSFER DURING FEEBLE BOILING
At low superheat the bubble population is so low that the process of
heat transfer may be considered as that of simple convection. A great
number of formulae can be found in the literature about the heat transfer in
convection. The simplest ones, yet accurate enough, for free and forced
convection of ordinary fluids from a plane wall are probably of the type
indicated by Eqs. (25) and (26), respectively:
q = 0.145 G (GrLPr)" (25)
q= 0.034 G6 (Re L)f" Pr . (26)
For liquid metals which have very high thermal conductivity and
very low viscosity, Grosh and Cess(33) assumed potential flow and arrived
at the following equation for forced convection over a flat plate:
q = 1.00 k O0 (ReLPr)"/' (27)
In the range of feeble boiling, BC of Fig. 1, the transfer of heat by
eddy motion may be assumed to be of the same order of importance as by
molecular motion Thus the heat transfer rate can be readily written as:
q = 0.145 +-(1 +- 1 0 (GrL Pr) (28)
L \ c\
q = 0.03 L 1 + 6 (Re2Pr) 0
q = 1 00 1 ( - 9)e/0 (ReL Pr) (30)
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Chang, Y. P. An Empirical Modification of Nucleation Theory and Its Application to Boiling Heat Transfer, report, February 1, 1961; United States. (https://digital.library.unt.edu/ark:/67531/metadc863296/m1/29/: accessed May 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.