Pumping (by Vacuum Pump): Oper. Conds Tab

Variable Definitions, Ranges and Default Values

The following table shows a brief description of the variables appearing in this tab. The table also displays their default values and their generally acceptable range:

Variable	Default Value	Range

○ Power Consumption Set by User Check this box to specify a user-defined value for the power consumption (as specific power or total power or power per unit).If this box is not checked, then the power consumption will be calculated by the program by assuming either isothermal or isochoric compression.	No	Yes/No
○ Power Type Indicates the power type that is used by the operation. Click on the list box to bring up a list of available power types in order to select one.	<Std Power>	Any Power Type
◙ Specific Power (kW/(m³/h) The power consumption per unit of operating throughput for the operation. This is calculated by dividing the Power Per Unit by the Suction Rate (Per Unit).	0.0	Positive
◙ Total Power (kW) The total power consumption for the operation (per cycle, if the procedure is set to operate in batch mode).	0.0	Positive
◙ Power Per Unit (kW) The power consumption per equipment unit for the operation (per cycle, if the procedure is set to operate in batch mode).	0.0	Positive
○ Power Dissipation into Heat (%) The percentage of total power consumed for this operation that turns into heat, thereby raising the temperature of the material contained in the equipment.	0.0	[0,100)
○ Efficiency (%) The efficiency of the selected compression model (isothermal or isochoric). Usually, the efficiency of isothermal compression in liquid ring vacuum pumps is 25%-40%. A suitable efficiency for isochoric compression in a roots vacuum pump is 83%.	30.0	(0,100)
● Cooling Duty (kcal/h) The heat transfer rate of the cooling agent.	0.0	Positive
○ Cooling Agent Name Indicates the cooling agent used for the operation. Click on the list box to bring up a list of available cooling agents in order to select one.	<Cooling Water>	Any Cooling Agent
● Cooling Agent Inlet Temp. (^oC) The inlet temperature of the cooling agent.	25.0	Positive
● Cooling Agent Outlet Temp. (^oC) The outlet temperature of the cooling agent.	30.0	Positive
● Cooling Agent Rate (kg/h) The mass flow rate of the cooling agent.	0.0	Positive
● Suction Pressure (atm) The pressure at vacuum pump inlet. It is assumed equal to the pressure of the inlet stream.	0.0	Positive
● Suction Temp. (^oC) The temperature at vacuum pump inlet. It is assumed equal to the temperature of the inlet stream.	25.0	Positive
● Suction Rate (per Unit) (L/h) The volumetric flow rate of evacuated gas at each vacuum pump inlet. It is assumed equal to the volumetric flow rate of the inlet stream.	0.0	Positive
● Exit Pressure (atm) The pressure at vacuum pump outlet. It is assumed equal to the ambient pressure (specified at the flowsheet level).	1.0	Positive
○ Max Exit Temp. (^oC) The maximum allowable temperature at vacuum pump outlet. If the adiabatic temperature exceeds this value, then a cooling agent is used to cool down the gas.	40.0	Positive
○ Setup Time (min) The amount of time (per cycle) spent before each operation is carried in preparation for the actual execution of the operation. It may involve actions like cleaning, vacuuming, setting up of equipment, etc. which the user opted not to model explicitly.	0.0	Positive
◙ Process Time (min) The actual duration of the operation (per cycle).	240.0	Positive
○ Ignore Labor? Check this box to ignore labor for this operation. This option is used only if the process time is set by a master-slave relationship.	Yes	Yes/No

Symbol Key: ○ User-specified value (always input); ● Calculated value (always output); ◙ Sometimes input, sometimes output

Specification Choices / Comments

The following list describes the available specification choices in this tab; for more details on how these are implemented, see Pumping (by Vacuum Pump): Modeling Calculations.

•Power consumption...

Check this box to specify the total power or specific power (which is defined as the total power consumption divided by the total suction rate) or power per unit. If this box is not checked, then the power consumption is calculated based on the selected compression model (see below).

•Compression Model...

You may either select isothermal compression or isochoric compression. Compression in a liquid ring vacuum pump is isothermal, while compression in a roots vacuum pump is isochoric..

•Duration Options...

In Rating Mode, you can set the process time (and setup time) or allow the process time to be calculated based on the suction rate or allow the duration to match exactly the duration of another operation (either in the same procedure or in another procedure). In Design mode, you must either specify the process time (and setup time) or allow the duration to match exactly the duration of another operation (either in the same procedure or in another procedure), in order for the program to calculate the required power (per cycle and per unit).

If you choose to match the duration of this operation with the duration of another operation, you introduce a master-slave relationship between the two operations. The program will match the setup-time, the process time and the turnaround time of this operation (the ‘slave’) with the corresponding times of the reference operation (the ‘master’ operation). For more on master-slave relationship, see The Scheduling Tab.