I N I T I A L V A L U E S

Enter values or expressions for the initial value of the Velocity field u (SI unit: m/s), the Pressure p (SI unit: Pa), and the Temperature T (SI unit: K). The default values are 0 for the velocity and the pressure, and 293.15 K for the temperature.

In a turbulent flow interface, initial values for the turbulence variables are also specified. By default these are specified using the predefined variables defined by the expressions in Initial Guess.

The initial value for the surface radiosity J (SI unit: W/m2), for surface-to-surface radiation, has a default value of 0.

Pressure Work

The Pressure Work feature adds the following contribution to the right hand side of the Heat Transfer in Fluids equation:

The software computes the pressure work using the absolute pressure.

D O M A I N S E L E C T I O N

From the Selection list, choose the domains to add pressure work. By default, the selection is the same as for the Heat Transfer in Fluids feature that it is attached to.

P R E S S U R E W O R K F O R M U L A T I O N

select Full formulation or Low mach number formulation. The latter excludes the term u · p from Equation 12-3, which is small for most flows with low Mach number.

Viscous Heating

The Viscous Heating feature adds the following term to the right-hand side of the Heat Transfer in Fluids equation :S where is the viscous stress tensor and S is the strain rate tensor. Equation 12-1 represents the heating caused by viscous friction within the fluid.

D O M A I N S E L E C T I O N

From the Selection list, choose the domains to add pressure work. By default, the selection is the same as for the Heat Transfer in Fluids feature that it is attached to.

S H A R E D I N T E R F A C E F E A T U R E S | 391

D Y N A M I C V I S C O S I T Y

Specify the Dynamic viscosity (SI unit: Pa·s). The default setting is to use the value of the viscosity from the material. Select User defined to define another value for the viscosity.

The program uses the dynamic viscosity together with the velocity expressions to compute the viscous stress tensor, .

392 | C H A P T E R 1 2 : N O N - I S O T H E R M A L F L O W B R A N C H

In industrial applications it is common that the density of a process fluid varies. These variations can have a number of different sources but the most common one is the presence of an inhomogeneous temperature field. This Module includes the Non-Isothermal Flow predefined multiphysics coupling to simulate systems where density varies with temperature.

Other situations where the density might vary includes chemical reactions, for instance where reactants associate or dissociate.

The Non-Isothermal Flow interfaces contain the fully compressible formulation of the continuity equation and momentum equations:

where

• Cp is the specific heat capacity at constant pressure (SI unit: J/(kgK))

T H E O R Y F O R T H E N O N - I S O T H E R M A L F L O W A N D C O N J U G A T E H E A T T R A N S F E R I N T E R F A C E S | 393

•T is absolute temperature (SI unit: K)

•q is the heat flux by conduction (SI unit: W/m2)

•is the viscous stress tensor (SI unit: Pa)

•S is the strain-rate tensor (SI unit: 1/s)

are not included by default since they are commonly negligeable. These can, however, be added as subnodes to the Fluid node. For a detailed discussion of the fundamentals of heat transfer in fluids, see Ref. 3.

The interface also supports heat transfer in solids:

where

• E is the elastic contribution to entropy (SI unit: J/(m3·K)) As in the case of fluids, the pressure work term

394 | C H A P T E R 1 2 : N O N - I S O T H E R M A L F L O W B R A N C H