Fluid mechanics terminologies

1.Kinematic viscosity of a fluid can be defined as proportion of dynamic viscosity of fluid to density of that fluid. It\'s unit is m^2/s

 2.Dynamic viscosity of fluid is defined as internal resistance to the flow of fluid between it\'s molecules in presence of some external force.

Dynamic viscosity is given by 

It\'s unit is Ns/m^2

3. Peclet number is ratio of advection transportation rate to that of diffusive transportation rate .

In thermal science,peclet number is ratio of heat energy given to fluid by convection to heat energy conducted within fluid

Since Peclet number is dimensionless,it is devoid of any unit 

Peclet number = advection transportation rate/diffusion transportation rate

 4.Nusslet number is ratio of thermal energy transferred by convection to thermal energy transferred by conduction in a given system .It is a dimensionless number and does not have any units.

 Nusselt number = hL/k

5.Momentum flux is rate of change of momentum of fluid per unit area . It acts in a direction perpendicular to fluid flow. It\'s unit is N/m2

6. Fourier law of heat conduction states that heat transfer by conduction in a material is directly proportional to thermal conductivity, heat transfer area and temperature gradient and inversely proportional to length or thivkness of the material

It\'s unit is W and is given by Q = -KAdT/dX

where K is thermal conductivity of a material is W/mK,A is the area in m^2 ,dT is temperature gradient in K,dX is length in m.

7. Ficks law of diffusion states that molar flux of molecules caused by diffusion is directly proportional to concentration gradient and the rate of change of concentration at a given point in space is proportional to second derivative of concentration with respect to space .

 8. Wall shear stress is the shear stress exerted by walls on layers of fluid adjacent to it. It\'s unit is N/m^2.

 9. Temperature gradient is a quantity that describes the rate of change of temperature at a given location. It\'s unit is celsius in degrees per unit length 

Temperature gradient = dt/dx where dt is change in temperature and dx is length over which temperature change occurs.

10. Divergence of velocity field represents the degree oof outward flow of velocity field from a particular point. If V is a velocity field then divergence of velocity field is given by nabla . V