### 1.5.6. Energy Equation

Recall that Equation 2–5 is the Reynolds-averaged conservation equation for energy of a single component fluid. Extending this equation for multicomponent fluids involves adding an additional diffusion term to the energy equation:

| (1–157)

For turbulent flow, this term is Reynolds-averaged (see Turbulence Models) giving:

| (1–158)

This expression introduces several terms involving the fluctuations of diffusion coefficient, component enthalpy and species concentration. Under certain circumstances, the fluctuating components could be an important component of the diffusion process. However, adequate models are not available within the existing turbulence model to account for these effects. Thus, only the mean component is retained in the current version of ANSYS CFX.

The implemented conservation of energy equation for multicomponent fluids involves only mean scalar components and is expressed as:

| (1–159)

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