New Method for Treatment of Variable Physical Properties

Abstract

The advanced method reported in this chapter for treatment of fluid variable physical properties involves temperature parameter method for treatment of temperature-dependent physical properties of gases, theoretical equation method for treatment of concentration- and temperature-dependent density of vapour-gas mixture, weighted sum method for treatment of other concentration- and temperature-dependent physical properties of vapour-gas mixture and polynomial method for treatment of temperature-dependent physical properties of liquids. These methods are taken as a theoretical foundation of this book for extensive investigation of hydrodynamics and heat transfer of free convection of gases, free convection of liquids, free convection film boiling of liquid and free convection film condensation of pure vapour or vapour-gas mixture with consideration of coupled effects of variable physical properties. For the temperature parameter method based on the simple power-law of the temperature-dependent physical properties of gases, a system of the temperature parameters such as \(n_\mu \), \(n_\lambda \) and \({n_{c}}_{p}\) are reported. From these temperature parameters, it is seen that the specific heat parameter is much small, and then, it follows that the variable temperature will have more obvious effects on viscosity, thermal conductivity and density of gases than that of the specific heat. Since the determination of the temperature parameter is based on the typical experimental data, with the provided temperature parameters, the temperature-variable physical properties of gases can be stimulated very well by using the temperature parameter method. Furthermore, with the temperature parameter method the treatment of variable physical properties of vapour or gas becomes very simple and convenient. Taking water as an example, the temperature-dependent polynomials of the density, thermal conductivity and viscosity are introduced for liquid variable physical properties, while the specific heat at constant pressure is so small that it can be disregarded generally with variation of temperature. These polynomials are reliable, since the related typical experimental data. The concentration-dependent density equations of vapour-gas mixture are reported through the rigorously theoretical derivation, while the other concentration-dependent physical properties of vapour-gas mixture are expressed as the weighted sum of the physical properties of the involved vapour and gas with their concentrations (mass fraction). Since the involved vapour and gas are temperature-dependent, the physical properties of the vapour-gas mixture are concentration- and temperature-dependent.