Supercritical fluid applications and numerical modeling

By 16.12.2019

Nowadays, the extensive role of supercritical fluids in different industrial applications from heat and electricity generation to food science is not inconsequential. The fluid is in the supercritical state when its temperature and pressure are above the critical values. As the operating conditions of a fluid approach the critical values, thermophysical properties change sharper and more non-linearly (see Figure 1). Consequently, the fluid behaves like a real gas and common ideal gas laws do not capture the fluid properties accurately.

Different numerical approaches have been investigated to compute the fluid properties in the vicinity of its critical point. There are well-founded real gas equation of states models which can predict the fluid properties in the supercritical region. However, in some applications where the fluid operating condition is located extremely close to the critical point, the accuracy of these models drops significantly. Furthermore, coupling the real gas equation of states model directly to the flow solver is costly in time and resource.

The well-stablished method which Stressfield has employed to overcome these difficulties is using a look-up table of fluid properties which can be coupled to the flow solver. By combining the fast numerical applicability of look-up tables with their easily adjustable resolution and range, simulations with high numerical accuracy can be performed within a short time frame.

By using the look-up table method, we can accurately model a wide range of fluid properties in the supercritical domain, metastable region and in the vicinity of the critical point. This method can be used to simulate supercritical turbomachinery, heat exchangers, pressurized valves and all other industrial equipment which operate in the supercritical region.

Figure 1. Isobaric specific heat of CO2 near the critical point.