Saturation pressure of water above the triple point temperature is computed from temperature.
Source: A Saul, W Wagner: "International equations for the saturation properties of ordinary water substance", equation 2.1
function saturationPressureLiquid_der extends Modelica.Icons.Function; input SI.Temperature Tsat "Saturation temperature"; input SI.TemperatureSlope dTsat "Saturation temperature derivative"; output SI.PressureSlope psat_der "Saturation pressure derivative"; end saturationPressureLiquid_der;