### 12.2.2. Table Inversion

There are many cases where the flow solver must calculate one of the table independent variables when given the dependent variable and the other independent variable. For example, the flow solver calculates static enthalpy and pressure from the flow solution. To calculate static temperature, you take those values and invert the table. This is the most common example of table inversion used by the flow solver. The table inversion algorithm that includes saturation clipping, is similar to the interpolation algorithm. The `prop interp option` expert parameter also applies to table inversion.

The following two examples assume that and are given and you need to compute ( in this case is usually enthalpy).

: Supercritical table inversion

Option 2: Table inversion is performed in the same way as for below the critical point.

Option 3: Standard table inversion, without saturation clipping is used if . If then saturation clipping is used.

An example of standard table inversion is calculating the value of temperature, given enthalpy and pressure. First the location of the value of is located along the pressure axis. At that location, the solver searches along the two adjacent isobars for the enthalpy values that bound the given value of . Once the table location is found (both and ordinates) the temperature is backed out using bilinear interpolation.

: Vapor side table inversion

Option 2 and option 3 are equivalent in this region.

The recipe is slightly different when you include saturation clipping. First the flow solver looks up the table location where the value of occurs and calculates and . If then the flow solver searches for the table location where occurs starting at the saturation curve rather than at , ignoring the liquid region to the left. Once the flow solver finds both table locations ( and ordinates) the temperature is backed out using bilinear interpolation. Alternatively, if then temperature is simply set to . (Liquid side inversion works the same way but in the opposite sense.)

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