Physical Properties and Characteristics Dimensionless Groups
All fluid properties, unless otherwise specified, are expressed using the International System of Units; in such a system, the four fundamental magnitudes, whose combination leads to the units of all transport and physical properties of interest in thermohydraulics, are length, L (m); mass, M (kg); time, t (sec); thermodynamic temperature, T (K; degrees Kelvin). In two-phase mixtures heat transfer problems, physical properties and transport parameters of the two single phases are not sufficient, the introduction of parameters characterizing the interaction between the phases being necessary. Vapor quality is defined as the ratio between the gaseous mass flow rate and the total mass flow rate. Properties and parameters representing the average characteristics of the mixture, the mechanical, or thermal interactions between the two phases are considered. Some of them are representative of a system dimension scale, while others refer to a fluid-particles-dimension scale.