 The behavior of the physical processes in actual problems is affected by so many physical quantities that a complete mathematical description thereof is usually very difficult and sometimes practically impossible due to the complicated nature of the phenomena.We know from experience that if two systems are geometrically similar there usually exists some kind of similarity under certain conditions, such as kinematic similarity, dynamic similarity, thermal similarity, and similarity of concentration distribution, and that if similarity conditions are satisfied we can greatly reduce the number of independent variables required to describe the behavior of the process.In this way, we can systematically understand.