Pipe Main Window
This window is used to select the desired pipe calculation type and to supply the required pipe input data through its associated windows.
Calculation Type
PRO/II offers three types of pipe calculations. They are:
1. Fixed Line Diameter - Forward Calculations : Given the dimensions of the pipe, the pressure drop is calculated. The inlet conditions to the pipe must be provided and the pipe calculates the external properties for the fluid inside the pipe and at the exit.
2. Fixed Line Diameter - Backward Calculations : For this type, PRO/II calculates the pressure drop in the reverse direction. The feed conditions are taken as the outlet conditions, and the product is set to the computed inlet conditions. If heat transfer is to be considered, you can specify only a fixed duty for the entire pipe unit.
3. Line Sizing - Forward Calculations : This type of calculation selects the appropriate (nearest) pipe size from the given set of pipe sizes, in order to meet the desired pressure drop, minimum outlet pressure, or maximum velocity constraint. PRO/II provides a set of 10 sizes by default. If none of the allowable sizes are appropriate, a warning message is printed and the pipe size is rounded to the first allowable size. If you supply a line diameter in the "Line/Fitting Data" window (an optional entry), only those pipes which are equal to or larger than this size will be considered. Note that fittings cannot be included for this calculation type.
Calculation progress during negative pressure
When a negative pressure is encountered during calculation, or if the pipe unit fails to reach a solution, you can select either to continue or stop the flowsheet calculations. By default, PRO/II continues the calculations. To change the existing option, simply click on the highlighted text (Continue or Stop).
When the continue option is selected, a failed pressure drop calculation uses the best available solution or sets a negative outlet pressure to a low value. Similarly, a failed sizing calculation uses the line diameter that most closely satisfies the specification and prints a warning message. Also, a maximum of 3 consecutive failures is allowed if the failed pipe unit is inside a recycle loop. This allows negative pressures on intermediate iterations before ultimately solving to a valid solution. On the other hand, if you select to stop the calculations, all the flowsheet calculations will terminate.
Pressure Drop Method button
Push to display the Pipe Pressure Drop Method Window, where you can select a pressure drop correlation, and enter values for other parameters. The Briggs-Brill-Moody correlation is selected by default, and PRO/II provides default values for other parameters also.
Line/Fitting Data button
Push to display the Pipe Line/Fitting Data Window, where you can enter data for the pipe and/or fitting dimensions. Note that fitting data cannot be entered for sizing calculations.
Line Sizing button
Push to display the Pipe Line Sizing Window, where you can enter the constraints and select pipe sizes for line sizing calculations. Note that this button is available only when the sizing calculation option has been selected.
Heat Transfer button
Push to display the Heat Transfer Window, where you can select the heat transfer option and enter the necessary data. For backward calculations you can provide only a fixed duty for the entire pipe unit. By default, PRO/II considers no heat transfer (zero duty) during calculations.
Product Phases button
Push to display the Product Phases Window. If there are more than one product stream leaving the pipe unit, you must assign unique phases for each stream using this window.
Complete technical details may be found in topics under Pressure Calculations in the PRO/II Reference Manual.
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