In the paper Kandlikar, S. G., 2004, “Heat Transfer Mechanisms During Flow Boiling in Microchannels,” ASME J. Heat Transfer, 126(1), pp. 8–16, Kandlikar [(1)] derived two new nondimensional groups, K1 and K2, relevant to flow boiling phenomenon in microchannels as follows:
$K1=(qhfg)2DρGG2DρL=(qGhfg)2ρLρG$
1
$K2=(qhfg)2DρGσ=(qhfg)2DρGσ$
2
Kandlikar [(1)] mentioned that these two groups were able to represent some of the key flow boiling characteristics, including the critical heat flux (CHF). In his closing remarks, he mentioned that the usage of the new nondimensional groups K1 and K2 in conjunction with the Weber number (We) and the capillary number (Ca) was expected to provide a better tool for analyzing the experimental data and developing more representative models.
Similar to the combination of the nondimensional groups, K2K10.75 [(1)] that used in representing the flow boiling CHF data by Vandervort et al. [(2)], these two new nondimensional groups, K1 and K2, can be combined using Eqs. 1,2 as:
$K2K1=(qhfg)2DρGσ(qGhfg)2ρLρG=DG2ρLσ=WeLO$
3
i.e., the ratio of K2 and K1 is equal to the all liquid Weber number (WeLO). As a result, it is enough to use the new nondimensional groups K1 and K2 in conjunction with the capillary number (Ca) only to provide a better tool for analyzing the experimental data and developing more representative models for heat transfer mechanisms during flow boiling in microchannels because K2/K1 = WeLO.
Moreover, it should be noted that the ratio of K2 and K1 (K2/K1) and the Capillary number (Ca) can be combined as:
$K2/K1Ca=WeLOCa=ReLO$
4
i.e., the ratio of (K2/K1) and Ca is equal to the all liquid Reynolds number (ReLO).

## References

1.
Kandlikar
,
S. G.
, 2004, “
Heat Transfer Mechanisms During Flow Boiling in Microchannels
,”
ASME J. Heat Transfer
,
126
(
1
), pp.
8
16
.
2.
Vandervort
,
C. L.
,
Bergles
,
A. E.
, and
Jensen
,
M. K.
, 1994, “
An Experimental Study of Critical Heat Flux in Very High Heat Flux Subcooled Boiling
,”
Int. J. Heat Mass Transfer
,
37
(
Supplement 1
), pp.
161
173
.