Posted by: william
« on: May 11, 2012, 10:57:36 AM »When Viscous heating is turned on, Pressure work must also be turned on. We know h = u + P/rho. where h = specific enthalpy; u = specific internal energy; P = pressure; rho = density.Hence delta(h) = delta(u) + delta (p/rho) = delta (u) + P.delta(1/rho) + (1/rho).delta(P).
For incompressible liquids with constant density , P.delta(1/rho) = 0 but we need to account for (1/rho).delta(P). For gases both incompressible and compressible, depending upon whether it is constant volume or constant pressure process, the appropriate pressure work remains.
When viscous heating is turned on, the increase in enthalpy needs to be accounted for by the pressure work term. Otherwise, you will see a fictitious drop in exit temperature to satisfy the enthalpy balance.
Here is how you turn on Pressure Work?
In the text interface Define->Models->Energy; FLUENT will prompt you for inclusion of viscous dissipation term, pressure work term, kinetic energy term.
For incompressible liquids with constant density , P.delta(1/rho) = 0 but we need to account for (1/rho).delta(P). For gases both incompressible and compressible, depending upon whether it is constant volume or constant pressure process, the appropriate pressure work remains.
When viscous heating is turned on, the increase in enthalpy needs to be accounted for by the pressure work term. Otherwise, you will see a fictitious drop in exit temperature to satisfy the enthalpy balance.
Here is how you turn on Pressure Work?
In the text interface Define->Models->Energy; FLUENT will prompt you for inclusion of viscous dissipation term, pressure work term, kinetic energy term.