Search results
Results from the WOW.Com Content Network
The kinetic theory of gases allows accurate calculation of the temperature-variation of gaseous viscosity. The theoretical basis of the kinetic theory is given by the Boltzmann equation and Chapman–Enskog theory, which allow accurate statistical modeling of molecular trajectories.
The dilute gas viscosity contribution to the total viscosity of a fluid will only be important when predicting the viscosity of vapors at low pressures or the viscosity of dense fluids at high temperatures. The viscosity model for dilute gas, that is shown above, is widely used throughout the industry and applied science communities. Therefore ...
Elementary calculation of viscosity for a dilute gas Consider a dilute gas moving parallel to the -axis with velocity () that depends only on the coordinate. To simplify the discussion, the gas is assumed to have uniform temperature and density.
A gas is said to be in local equilibrium if it satisfies this equation. [4] The assumption of local equilibrium leads directly to the Euler equations, which describe fluids without dissipation, i.e. with thermal conductivity and viscosity equal to . The primary goal of Chapman–Enskog theory is to systematically obtain generalizations of the ...
The Vogel–Fulcher–Tammann equation, also known as Vogel–Fulcher–Tammann–Hesse equation or Vogel–Fulcher equation (abbreviated: VFT equation), is used to describe the viscosity of liquids as a function of temperature, and especially its strongly temperature dependent variation in the supercooled regime, upon approaching the glass transition.
β is the thermal expansion coefficient (equals to 1/T, for ideal gases, where T is absolute temperature). is the kinematic viscosity; α is the thermal diffusivity; T s is the surface temperature; T ∞ is the quiescent temperature (fluid temperature far from the surface of the object) Gr x is the Grashof number for characteristic length x
Consequently, if a liquid has dynamic viscosity of n centiPoise, and its density is not too different from that of water, then its kinematic viscosity is around n centiStokes. For gas, the dynamic viscosity is usually in the range of 10 to 20 microPascal-seconds, or 0.01 to 0.02 centiPoise. The density is usually on the order of 0.5 to 5 kg/m^3.
One possible way of assessing soil thermal properties is the analysis of soil temperature variations versus depth Fourier's law, Q = − λ d T / d z {\displaystyle Q=-\lambda dT/dz\,} where Q is heat flux or rate of heat transfer per unit area J·m −2 ∙s −1 or W·m −2 , λ is thermal conductivity W·m −1 ∙K −1 ; dT / dz is the ...