The study of fluids and their motion and static behavior is known as fluid mechanics. An explanation of what we mean by “fluid” should come first. Fluids are substances that undergo continuous deformation when subjected to shear (tangential) stress, regardless of the magnitude of the applied force. Another way to characterize fluidity is to say that it is incompatible with shear stress in its resting state. Molecules make up fluids. However, the macroscopic or average influence of several molecules is of more importance in engineering applications. The macroscopic influence is what we often see and quantify. This means that we ignore the behavior of the individual molecules and instead think of the fluid as a continuum or endlessly divisible entity. The study of fluid mechanics encompasses a wide range of disciplines that are difficult to categories. Scientific studies have identified two distinct types of flows, laminar and turbulent, which researchers use to categories the degree of order and chaos present in a fluid. Single-phase flow and multiphase flow are two distinct phenomena in fluid physics. Since fluids may undergo a phase transition (condensation or evaporation) during the flow, changing from the single-phase flow to the multi-phase flow, the final boundary (like all the boundaries in fluid mechanics) isn’t crisp. In addition, two-phase (or multi-material) flows may be analyzed as if they were single-phase flows.