Retention of Dissipation

The dissipation term is frequently neglected while solving the energy equation for incompressible flows. As the Mach number However, even at a low Mach number, can be important if is very small. Let us look at these aspects. Since

and

where R is the Gas constant and

Let the local acoustic velocity and Mach number

Then,

Hence,

or

In general for incompressible flows and Hence Ec is small. But for very small temperature difference, i.e., if is slightly larger than 1, Ec might assume a large value and importance of including dissipation arises. However, for computing incompressible convective flows, the viscous dissipation is neglected in this chapter and we continue with the steady state energy equation.