the differences between flow patterns of the two cases were addressed.
It is noted from Triplett et al. [17,18] that based on different
channel cross-sectional shapes, the adiabatic two-phase air–
water flow characteristics in semi-triangular micro-channels were
similar to those obtained from circular channels. The heat transfer
of an air–water flow in parallel micro-channels of 0.1 mm in
hydraulic diameter was experimentally investigated by Hetsroni
et al. [19]. Their results showed a decrease in the Nusselt number
with an increasing gas flow rate, which was opposite to the results
obtained by Bao et al. [15]. Betz and Attinger [20] showed segmented
flow, an intermittent pattern of gas bubbles and liquid
slugs, resulting in the heat transfer enhancement up to 140% in a
micro-channel heat sink when compared with single-phase liquid
flow.
Heat transfer characteristics of a non-boiling two-phase flow in
micro-channels with different diameters were studied by Choo and
Kim [21]. Air and water were used as working fluids to examine the
dependence of Nusselt number on the channel diameter. They
found that with channel diameters of 0.506 and 0.334 mm, the
Nusselt number increased with the increment of gas flow rate,
but decreased with increasing gas flow rate when the channel
diameters of 0.222 and 0.140 were employed.
Marchitto et al. [22] studied two-phase flow distribution in parallel
upward channels. They reported that the phase distribution