Saturation Pressure

For a mixture at given temperature, the pressure at which a new infinitesimal (“incipient”) phase appears upon slight change in pressure. The mixture and its incipient phase are in thermodynamic equilibrium. If the incipient phase is lighter than the mixture phase, the saturation pressure is a bubblepoint and the incipient phase is a bubble appearing from the oil mixture. If the incipient phase is heavier than the mixture phase, the saturation pressure is a dewpoint and the incipient phase is a liquid (“dew”) appearing from the gas mixture. Petroleum mixtures will always exhibit lower dewpoints for the entire range of temperatures exhibiting two phases (i.e. less than the cricondentherm), while upper saturation pressures of both bubblepoint and dewpoint type are usually found in the range of relevant operational temperatures.

1. Generating a Saturation Pressure Calculation

To generate a Saturation Pressure Calculation, enter the temperature at which the components will be tested, along with the composition of each relevant component. The complete process is shown in the GIF below.

Normalization

Ensure the total composition equals 100%. If it does not, click the Normalize button to adjust it automatically. This will allow you to save changes.

2. Terminology

2.1. Bubble-Point

The state of a fluid mixture characterized by the co-existence of a liquid phase saturated with an infinitesimal quantity of equilibrium gas phase.

2.2. Dew-Point

The state of a fluid mixture characterized by the co-existence of a vapor phase saturated with an infinitesimal quantity of equilibrium liquid (condensate) phase.

2.3. Critical-Point

The state of a fluid mixture at which all properties of all coexisting vapor and liquid phases become identical (densities, viscosities, etc.), and the equilibrium ratios \(K_i=1\) for all components. The mixture is called a saturated critical fluid at its critical state (not a saturated bubblepoint oil or a saturated dewpoint gas).

2.4. Vapor Pressure

For a compound at a temperature below the critical temperature (\(T_c\)), down to the triple point \(T_t\), and further down to 0 degrees absolute (\(T_0\)), the vapor pressure defines where the compound exists in a multi-phase thermodynamic equilibrium with (a) saturated vapor and saturated liquid (\(T_t