Kinematic Viscosity Coefficient

The kinematic viscosity coefficient is a convenient form of expressing the viscosity of a fluid. It is formed by combining the density p and the absolute coefficient of viscosity m, according to the equation:

(2.5)

The kinematic viscosity coefficient v is expressed as m2/s, and 1 cm2/s is known as stoke.

The kinematic viscosity coefficient is a measure of the relative magnitudes of viscosity and inertia of the fluid. Both dynamic viscosity coefficient m and kinematic viscosity coefficient v are functions of temperature. For liquids, m decreases with increase of temperature, whereas for gases m increases with increase of temperature. This is one of the fundamental differences between the behavior of gases and liquids. The viscosity is practically unaffected by the pressure.

2.2.4 Thermal Conductivity of Air

At high-speeds, heat transfer from vehicles becomes significant. For example, re-entry vehicles encounter an extreme situation where ablative shields are necessary to ensure protection of the vehicle during its
passage through the atmosphere. The heat transfer from a vehicle depends on the thermal conductivity к of air. Therefore, a method to evaluate к is also essential. For this case, a relation similar to Sutherland’s law for viscosity is found to be useful, and it is:

( T3/z

к = 1.99 x 10 3 ( ———— I J/(s m K),

T + 112y

where T is temperature in kelvin. The pressure and temperature ranges in which this equation is applicable are 0.01 to 100 atm and 0 to 2000 K, respectively. For the same reason given for viscosity relation, the thermal conductivity also depends only on temperature.