Ghajar et al. [12] also reported th

Ghajar et al. [12] also reported that the effect of superficial gas
velocity on heat transfer depended on flow pattern and showed its
own distinguished trend. In the range of ReGS = 800–1800 heat
transfer coefficient increases with increasing ReGS. Bao et al. [11]
also reported that the measured heat transfer coefficients for the
air–water system are always higher than would be expected for
the corresponding single-phase liquid flow, so that the addition
of air can be considered to have an enhancing effect. This paper reports
an experimental study of non-boiling air–water flows in a
narrow horizontal tube (diameter 1.95 mm). Results are presented
for pressure drop characteristics and for local heat transfer coefficients
over a wide range of gas superficial velocity (0.1–50 m/s),
liquid superficial velocity (0.08–0.5 m/s) and wall heat flux
(3–58 kW/m2). From Eqs. (11) and (12) one may conclude that
for micro-channels of dh = 130 lm in the range of ReLS = 4–56 and
ReGS = 4.7–270 an increase in ReGS leads to a decrease in the heat
transfer coefficient as opposed to results [11,12] reported for the
channels of 1.95–25 mm.