The scale effect in two-phase flow and the classification of channel sizes were discussed in Section 3.6.2. The discussions in this chapter will primarily deal with channels with hydraulic diameters in the range 10 μm ≲ DH ≲ 1mm, where the limits are understood to be approximate magnitudes. For convenience, however, channels with 10 μm ≲ DH 100 < μm will be referred to as microchannels, and channels with 100 μm ≲ DH ≲ 1mm will be referred to as minichannels. The two categories of channels will be discussed separately, furthermore, because as will be seen there are significant differences between them.

Single-phase and two-phase flows in minichannels have been of interest for decades. The occurrence of flashing two-phase flow in refrigerant restrictors formed the impetus for some of the early studies (Mikol, 1963; Marcy, 1949; Bolstad and Jordan, 1948; Hopkins, 1950). The number of investigations dealing with two-phase flow in minichannels is relatively large, but two-phase flow in microchannels is a more recent subject of interest.

Two-phase flow in mini- and microchannels comprises a dynamic and rapidly developing area. Some attributes of two-phase flow in mini- and microchannels are not fully understood, and there are inconsistencies among experimental observations, phenomenological interpretation, and theoretical models. This chapter is therefore meant to be an outline review of the current state of knowledge.

Two-Phase Flow Regimes in Minichannels

Two-phase flow regimes in minichannels under conditions where inertia is significant have been experimentally investigated rather extensively. Table 10.1 summarizes some of the published studies.