The flow pattern maps available in literature were first developed for the petrochemical industry (Baker, 1954) for flow of oil and gas in large diameter pipes. Subsequently, the adiabatic flow pattern maps were developed as general flow pattern maps (for example, Hewitt and Roberts, 1969; Taitel et al., 1980). In recent years, a number of flow pattern maps have been developed for specific conditions such as small diameter tubes, evaporation or condensation, and compact heat exchanger geometries. The main task is to group together the basic flow structures and define a few basic patterns. This is by no means well defined and indeed many flow patterns exist as individual researchers group the flow patterns somewhat differently depending on their own interpretations. Basically the attitude of most practitioners is to minimize the number of flow pattern groups and to group together the flow structures that has basically the same character pertaining to the distribution of the interfaces. When designing devices in which a two-phase flow occurs, the determination of a flow regime is one of the most essential problems. Different flow regimes may arise, which are depending on the flux of both phases, properties of various factors as well as dimensions and location of a channel. The ranges of occurrence of particular two-phase flow regimes are generally presented in diagrams, called flow regime maps, in the form of areas divided by transition lines. In the literature there is a large number of such works which vary considerably and there are only quite a few