This calculation mode computes the relative volume of a fluid over a specified pressure range at a specified temperature.
PRO/II produces tabular results and a printer plot of pressure versus the relative volume of the fluid with respect to a reference pressure. If the user provides experimental values, they appear in the table and plot, and PRO/II calculates the weighted sum of squares of the absolute errors (AERR) and the weighted sum of squares of the relative errors (RERR). These values are accessible by the MVC, OPTIMIZER, CALCULATOR, and CONTROLLER, allowing users to tune thermodynamic parameters to match experimental data.
If water is present in the system, PRO/II decants the free-water during each flash calculation. However, dissolved water still saturates the vapor and liquid phases, and this affects the value of the computed relative volumes.
Reference Temperature Reference temperature defaults to the merged feed stream temperature.
Reference Pressure Reference pressure typically corresponds to a saturation point (the bubble point in most cases).
End Pressure Specifies the lowest pressure for the relative volume calculations.
Start Pressure Specifies the highest pressure for the relative volume calculations. Typically, Start Pressure > Reference Pressure > End Pressure in order to be able to compute both sides of the curve.
Number of Points or Pressure Increment Specifies which pressure values PRO/II will use for the computation. The user may define either the number of points (N, where N <100) or a specific step size between consecutive pressure values (pressure increment).
Experimental Data Grid
Pressure / Relative Volume / Weighting Factor
User may provide optional experimental values for comparison purposes. A maximum of 100 experimental points may be entered (see Number of Points above) . The user may provide the experimental pressure, the corresponding relative volume with respect to the reference volume at reference conditions, and the weight assigned to each experimental data point (this value is optional and defaults to 1.0).
Based on these experimental data points, PRO/II computes the absolute and relative differences between the experimental and calculated value for each data point and reports the weighted sums of the squared absolute and relative errors as AERR and RERR, respectively. The user can specify the pressure unit of measure if different than its default unit.
When supplied, they appear in the table and plot, and PRO/II calculates weighted sums of squares of error. Both the absolute errors (AERR) and the weighted sum of squares of the relative errors (RERR) are computed.. These errors as well as the dew point pressure (PDEW) are accessible to the CALCULATOR, CONTROLLER, MVC, and OPTIMIZER, allowing the user to tune thermodynamic parameters to match the experimental data.