| Applies To | |||
| Product(s): | PlantFLOW | ||
| Version(s): | All | ||
| Environment: | N/A | ||
| Area: | General | ||
| Subarea: | |||
| Original Author: | Bentley Technical Support Group | ||
Item #1:
In regards to PlantFLOW and PlantFLOW Plus, what's the max Mach number that the flow can go in the pipe (for air and other gases)?
Answer:
Mach number should not exceed 1 for both STD and Plus versions.
Item #2:
Also if the pipe network is given fixed values such as pressure, flow, pipe length, can the program determine which pump would be the most effective in the system, (and report pump characteristics such as horse power, head loses etc
Answer:
From the output results one can see the effects of the pump curved used in the analysis has on the system. After some iterative changes and analysis results, a pump can be sized to produce the design requirements.
Item #3:
Does the program come with a pump database? i.e., can I look up a pump from Armstrong, or Goulds, to use in my pi ping system?
Answer:
At this point, because of the numerous amounts of companies that develop pumps with different configurations, flow curves, operating speeds, etc., PlantFLOW does not have a manufacture pump database. The application requires the user to enter specific pump data.
However, PlantFLOW does contain a comprehensive and extensible library of piping & components.
Pump curves are stored as a *.PMP file. You can create your own folder of pump curve and save time by reusing them in different projects.
Item #4:
I would also like to know, if the software calculates basic functions like NPSHa for pumps?
Answer:
Bentley apologizes for this inconvenience, however, the current version (06.02.00.05) does not calculate Net Positive Suction Head
Item #5:
How to you ignore tee losses?
Answer:
Analyze> run and check the option the ignore tee losses.
Item #6:
How does the program deal with using fixed pressure drops at the risers?
Answer:
Fixed pressure drop is prone to converge problems and it I do not think it matters if the pipe is horizontal or vertical.
Item #7:
The following was displayed when starting the program:
Forrtl: severe (47): write to readonly file, unit 72, file C:\Bentley\AutoPIPE\AutoPIPE.clr
How to fix and avoid?
Answer:
Increase the user's computer rights to have read / write access to the folder located on C drive "C:\Bentley\PlantFLOW V8i". Then it will work.
Item #8:
Model Does not converge:
I have modeled in 3 pumps. The system is a closed loop so fluid is constantly pumped around. Over this closed loop we need to calculate the total pressure drop (including running pumps). PlantFLOW requires 2 control points (inlet and outlet). I have located the 2 control point at the beginning of the pump discharge header and at the end of the pump suction header (see attached pdf file "control"). But when I doe the command "Analyze > Run" with the flow status of the pumps set "On" I get the Error "Solution not converging". Do you have any idea why this error appears?
Answer:
Updated the model to disable some segments where two of the pumps are present. Now it converges.
The original model is not a realistic one as the inlet and outlet should be part of the loop as in EX1.FDA (example model installed with the application). You would need to set pressures at inlet and outlet to KNOWN with same value, otherwise the cut is not valid.
In addition, using this particular model with settings to run three pumps together. The application did not converge. Update the model to provide more realistic flow scenario for it to converge.
Item #9:
The following were displayed when running the model:
E72-1: Unstable system
and / or
E72-30: Overspecified ctrl conditions
How to fix and avoid:
Answer:
There are a number of various circumstances that would cause these dialog to appear. One or more of the following may apply:
Reason #1:
In one particular model, noticed several valves with status set to off. This is one source of instability. First thing, select all items in the model or just the status off points and then turn them on. Use Select> points by flow status and then follow by Modify> Flow status.
Reason #2:
When working with heat transfer modeling, suggest the following.
1. Solve by turning off heat transfer during the analysis. That means you may need to specify the control points differently. After getting a convergence with that then you can turn on heat effects and add additional temperature control points (try not to remove the existing flow and pressure control points if possible).
2. I noticed that you have 35 combining tees as per the model input listing (control point data). Many of the tees where the status off valves are placed are dead end tees. The flow direction although does not matter, it actually matters a lot for heat transfer. So try to set the flow direction at these dead end tees so that they are NOT combining junctions (i.e. two flows in and one out). This will reduce the number of conditions you need to provide and will help keep the system stable.
Reason #3:
In another specific model, with 2 inlet control points with known Pressure and Consumption values, and 2 discharge control points with both unknown Pressure and Consumption settings, merely toggling the consumption setting from Known to Unknown are 2 different control points and the model analyzed without an issue. Thus proving that the issue is related to boundary conditions.
Note:
Please see the following PlantFLOW help:
Help > Contents> Contents Tab> Command Reference> Insert Menu> Control Point> Boundary Conditions, see the calculation for number of Boundary Conditions required in a given model.
Reason #4:
Check to make sure that all Tee connections are actual connected.
Item #10:
The following were displayed when running the model:
E72-2: Error in model connectivity
How to fix and avoid:
Answer:
This happens often when setting flow status to off as it could lead to discontinuity.
In a particular model, instead of setting the status to off for tees, suggest reversing the flow direction so that it would not be a combining tee and hence no need for an extra boundary condition.
Item #11:
Using Plantflow 6.1. i model a section of a system, the system is showing negative flow in a section where it is impossible for negative flow to occur as it is showing flow from a lower pressure to a higher pressure. see the attached file that represents the model. any help with this issue will be greatly appreciated ASAP.
I have looked at the model and highlighted the negative flow pipe:
I was looking at the the worksheet and did not see any double back pipe. What else should I look for to help resolve this model
Answer:
In this particular case:
It appears flow is impossible if flow rate is below 1.5 at the input. Suggest to disable the bypass loop if the flow is low and always give negative flow.
Yes it appears the pressure drop setting at 2 psi at K05 is not working. Recommend setting a large k-factor instead, e.g. 50. It may be 2 psi is a large pressure drop causing reverse flow, but this element pressure drop is not reversed when flow is reversed, for this reason a K-factor is more appropriate in this case.
Item #12:
Also, the project I'm working on has a pipe dumping ammonia vapor into a pipeline with coke oven gas. Is there a way for PlantFlow to handle more than one fluid?
Answer:
Bentley apologize for this inconvenience, however with PlantFLOW v. 06.02.00.05 this is a current limitation of the application.
Item #13:
In a model of Pumps and heat exchangers in basement, control point in the suction side of the points, then up to the system with a return. the following is being displayed when analyzing the model:
* * * W A R N I N G - MODEL * * *
W726-35: Inconsistent flow dirs at point K287
How to fix and avoid ?
Answer:
In this particular case:
The model had segments that start and stop at reducers, or have extra points at reducers ( i.e. L180 & L181). This confuse the direction of flow.
Suggested that start / stop segments at run points instead of reducers and examine all reducers to have only 2 node points that continue in the same direction.
Also, review the model to be sure that all bends are correctly shown (i.e. no 90 deg sharp corners) . Suggest that each sharp corner is confirmed as an OK bend.
Model analysis was able to converge if T-losses were ignored and with increased iterations to 100.
Item #14:
why isn't the Colebrook-White Equation used to calculate Darcy Friction Factor?
Answer
The online help shows the equation used.
Darcy friction is an iterative equation. This equation is used to speed calculations and have the same accuracy as Colebrook-White equation. We have no complaints about this equation as it gives very good values compared to moody diagram (which is based on Colebook-White). In PlantFLOW we do not have transition flow. It is laminar Re < 2000, otherwise turbulent.
The reference for friction factor equation is :
Miller, D.S., Internal Flow Systems. 2nd Edition, Gulf, 1990.
Item #15:
Gas Library. Their gas (COG) in this system includes the following composition. We’ve defined those in our Gas library, but not sure if it’s properly defined, especially we don’t know how to define CnHn 2.5%
Answer:
We do not know what CnHn stands for. Since this is a low percentage of 2.5%, suggest that is replaced with any gas that better matches its density. the development team suspects that n-pentane or n-Hexane would be a reasonable match. If you like to add this gas to the gas library you may do so in tools> library if you have the critical properties and conductivity values.
Item #16:
How can I build the air property with the attachment.(The yellow column in attachment)
Answer:
Unfortunately we do not have all the components of the mixture. For example the first two components are not part of AGA-8 or NIST.
There are two ways to do this.
Method #1:
User Pseudo gas as the fluid type and enter the MW, density and viscosity shown at the bottom. Some of the data is not shown and can be estimated by using AG8-8 (air) and checking model input listing as shown below. Add 0.1MPa to get absolute pressure (0.131 MPa).
FLUID PROPERTIES LISTING
Fluid type : AGA-8 Gas
Composition name: AIR
Initial pressure : 0.1310 MPa a
System temperature : 41.00 deg C
Gas Composition
---------------
Number of constituents: 3
Component Name I.D. # Mole %
-------------- ------ --------
Nitrogen 1 78.3000
Carbon-Dioxide 2 0.7000
Oxygen 18 21.0000
-------------- ------ --------
Total 100.0000
Molecular Weight : 28.9623 kg/kg-mol
Specific gravity : 1.0001
Gas Properties (@ above pressure and temperature)
Density : 1.4529 kg/m3
Specific volume : 0.6883 m3/kg
Absolute viscosity : 0.0191 E-3 Pa-s
Compress.factor, Z : 0.9998
Cp/Cv : 1.3986
Specific heat, Cp : 1.0130 kJ/kg-K
Specific heat, Cv : 0.7243 kJ/kg-K
Isentropic exp., K : 1.3983
Speed of sound : 355.0753 m/s
Thermal cond. : 0.0268 W/m-K
Method #2:
Add the missing fluids to the Usergas library. Consult the online help on how to add more components. You would need the critical pressure and temperature and also the thermal conductivity (conductivity is not as important if you are not doing heat transfer and may be able to set value as for some other component).
Note that Pseudo gas cannot be used for heat transfer and so method 2 is needed I that case
Item #17:
Standard pressure and temperature, what is the right values for both in their case?
Right now they just use our default which is 1 atm in pressure and 15 deg C in temperature.
Answer:
These values are not changed usually. They are slightly different in English units. They are the units used to enter flow rates or consumption. When using mass flow in General Model Options, these may not be used.
Item #18:
What does PlantFLOW calculate for straight pipe sections that do a 90 degree turn (no bend modelled)? It appears that there is no pressure loss apart from the loss due to the pipe length.
Answer:
Yes, the loss would be due to pipe loss only if the bend is not added.
Item #19:
Can AutoPIPE/PlantFLOW create 0 length pipe sections ? This would be very useful for accommodating actions like copying from bend to bend sections, inserting user loss sections after tees etc
Answer:
At this time, both AutoPIPE and PlantFLOW has the following error message appear when you try to copy any range with the starting and/or end point is an as any point on and Elbow, (ie. Near, Mid, or Far), “E521-25 Cannot copy range if either endpoint is a bend”.
One possible workaround is temporarily converter from a bend to a run point.
Copy the selections set and the convert the elbow, turned run, back into an elbow. I will send your suggestion to the CAE development group, where it will be logged for enhancement consideration.
A 0 length run can be created at any elbow, but it is not advisable. The program sometimes has difficulty calculating equations based on a 0 length node run. However if you must, place the cursor at the elbow tangent point, Insert run> Length = bend radius. Using the keyboard arrows, you could cycle from the bend tangent point to the near/far point. The next point should be the new run point you had just created. This point occupies the same space as the elbow point, thus creating a zero-length run.
Item #20:
I enclose a simple model. In all my trial I do not seem to be able to properly fix a bend with a radius (standard short/long versions are not a problem). Could you possibly take a look at the *.FDA and let me know what I am doing wrong ?
Answer:
Select the one of the elbows and then > Modify > Bend, the following dialog box appears.:
The radius of the elbow can be changed by selecting short or long from the drop down box. Or, you could enter the actual elbow radius in the field, as shown above in red. You can enter a bend radius value up the distance from the bend point to the nearest node point, which occurs from either direction. To illustrate this point, open your model, delete run point A01, A03, A04. Now, Select > Bend A02> Modify> Bend> Enter 326 mm in the Bend radius field , press OK
Notice the elbow is drawn, but A02f is very close to A07. Select the bend again, change the Bend radius from 326 mm to 327 mm, now notice what occurs. An error screen appears and the elbow is not drawn correctly. Thus, the largest bend radius is 326 mm.
Item #21:
In a model when I check the results report, I see some sections that I do not understand with a small length (0.63/0.64mm). I am only guessing that this is connected to the previous question.
Answer:
The values you saw were found on the General Report. Another source to view model / node data is from Tools> Model input Listing> Component Data Listing. The distance from the elbow tangent point to the next node point is modelled as 200 mm. However, remember that a bend node point are created with 3-4 points,( i.e. Near, Tangent, Far and sometimes mid points). The Far point of A02F was close to A03 and the near point A07N was very close to A04.Therefore you see the small values, as shown below:
G E N E R A L R E P O R T
From Press Temp * To Press Temp * Comp Flow Length I.D. Vel
Point (kPa ) (C) * Point (kPa ) (C) * Type (kg/s ) (mm) (mm) (m/s )
------ ------ ----- * ------ ------ ----- * ---- ------- ------- ------- ------
*** Segment A begin ***
A00 2000.0 100.0 * A01 1995.5 100.0 * RUN 1.00 400.00 23.37 2.434
A01 1995.5 100.0 * A02 N 1995.5 100.0 * RUN 1.00 0.64 23.37 2.434
A02 N 1995.5 100.0 * A02 F 1992.8 100.0 * BEND 1.00 23.37 2.434
A02 F 1992.8 100.0 * A03 1992.8 100.0 * RUN 1.00 0.00 23.37 2.434
A03 1992.8 100.0 * A04 1992.5 100.0 * RUN 1.00 126.00 23.37 2.434
A04 1992.5 100.0 * A07 N 1992.5 100.0 * RUN 1.00 0.63 23.37 2.434
A07 N 1992.5 100.0 * A07 F 1993.6 100.0 * BEND 1.00 23.37 2.434
A07 F 1993.6 100.0 * A08 1993.6 100.0 * RUN 1.00 0.63 23.37 2.434
A08 1993.6 100.0 * A09 1993.7 100.0 * RUN 1.00 20.00 23.37 2.434
*** Segment A end ***
C O M P O N E N T D A T A L I S T I N G
POINT ------COORDINATE(mm )------ DATA
NAME X Y Z TYPE DESCRIPTION
----- --------- --------- --------- ------ ------------------------------------
*** SEGMENT A
A00 0.00 0.00 0.00 CTRL Inlet
P = 2000.0 kPa a
C = 1.00 kg/s
A01 0.00 0.00 400.00
A02 N 0.00 0.00 400.64
A02 0.00 0.00 600.00 TI
A02 F 200.00 0.00 600.00
A03 200.00 0.00 600.00
A04 326.00 0.00 600.00
A07 N 326.64 0.00 600.00
A07 526.00 0.00 600.00 TI
A07 F 526.00 0.00 400.63
A08 526.00 0.00 400.00
A09 526.00 0.00 380.00 CTRL Outlet
P = ?
C = ?
Item #20:
In a model I can see positive changes to the pressure (positive DP). Is this correct ? (solve it to see)
Answer:
No, please analyse the model and review the output report, as shown below:.
T O T A L P R E S S / T E M P P R O F I L E S U M M A R Y
From Press Temp To Press Temp Del P Del T Flow Length I.D. Vel
Point (kPa ) (C) Point (kPa ) (C) (kPa) (C) (kg/s ) (mm) (mm) (m/s )
------ ------ ----- ------ ------ ----- ------ ----- ------- ------ ----- -----
*** Segment A begin ***
A00 2002.8 100.0 A01 1998.3 100.0 -4.5 0.0 1.00 400.00 23.37 2.434
A01 1998.3 100.0 A02 N 1998.3 100.0 0.0 0.0 1.00 0.64 23.37 2.434
A02 N 1998.3 100.0 A02 F 1995.6 100.0 -2.7 0.0 1.00 23.37 2.434
A02 F 1995.6 100.0 A03 1995.6 100.0 0.0 0.0 1.00 0.00 23.37 2.434
A03 1995.6 100.0 A04 1995.4 100.0 -0.2 0.0 1.00 126.00 23.37 2.434
A04 1995.4 100.0 A07 N 1995.4 100.0 0.0 0.0 1.00 0.63 23.37 2.434
A07 N 1995.4 100.0 A07 F 1996.4 100.0 1.0 0.0 1.00 23.37 2.434
A07 F 1996.4 100.0 A08 1996.4 100.0 0.0 0.0 1.00 0.63 23.37 2.434
A08 1996.4 100.0 A09 1996.6 100.0 0.2 0.0 1.00 20.00 23.37 2.434
*** Segment A end ***
Another key feature to use when looking at the results would be “Delta Mode”.. It is used to display the difference in the point results between any two points. It is active when the results are shown and would display a small window at the bottom of the screen with the following options:
Based on the displayed type, a message would appear at the top left corner of the screen. If the display is pressure, the message is: "CHANGE IN PRESSURE-psi.
Item #21:
When I use volume for flow type, consumption is in sm3/sec. What does the s stand for?
Answer:
Flow type allows you to select between volume or mass flow rate units. When the flow unit type is changed on an existing system, PlantFLOW model data is not automatically converted and therefore will need to be converted to the appropriate flow units.
The unit sm3/sec stands for standard cubic meters per second.
Item #22:
I had run a simulation on a steam piping model to analysis the temperature drop across the pipe. However, the results seem questionable. Thus, I did some manual calculations based on the heat transfer formula extracted from the software tutorial file and found that both results did not tally
Why?
Answer:
Heat transfer is also a function of the pressure drop. For smaller pipes there is more pressure drop and hence more discrepancy.
For example for 6” pipe when pipe roughness is decreased to 0.01mm Temperature is changed from 7.8 to 4.6 and pressure drop from 700 to 331.
Unfortunately there is no way to set pressure drop to zero in this case. See P2 and P1 in the equation below.
Note: The term e refers to internal energy.
Item #23:
What Gases and Liquids are available in the library?
Answer:
Per the online help:
This contains the fluid data for specified fluids. Default is PLANTGAS for "Gas Library" fluid, PLANTLIQ for "Liquid Library" fluid and "NISTLIB" for NIST fluids. PLANTLIQ contains temperature dependent liquid properties. PLANTGAS contains gas components properties (Molecular weight, Critical Pressure, Critical temperature, Accentric factor and temperature dependent Cp values) for Peng-Robinson equation of state for gas mixtures.
Fluid Properties
PlantFLOW contains an extensive list of fluids such as AGA-8 equation of state for natural gas mixtures, NIST hydrocarbon gas or liquid mixtures, Peng Robinson equation of state gas mixture library, generic liquid library and ASME steam tables. Some of these fluids are limited to PlantFLOW plus.
The dialog parameters displayed when the Edit/Fluid Properties option is executed depends on the current Fluid Type defined for the model.
The Fluid Type may be assigned/modified via the Tools/Model Options/General command. When you assign or modify the Fluid Type for a model using the General Model Options dialog, another dialog will display to enable you to define the properties of the selected type. The properties of the currently assigned Fluid Type may be modified directly using the Edit/Fluid Properties command.
The fluid types are listed below.
Fluid Types- PlantFLOW Standard Version
AGA-8 Gas:
AGA-8 Equation of state for natural gas mixtures. It includes 20 different user specified gas components. PlantFLOW standard sets the gas compressibility factor (Z) to one (Ideal Gas).
Default list of GASES available in the library:
Air
CARBON DIOXIDE
Methane
Water
Gas Library:
Gas mixture containing up to 20 user-specified gas components. The gas component data is stored in a user-defined library ( PLANTGAS.PFL). Peng-Robinson equation of state is used to compute gas mixture properties. PlantFLOW standard sets the gas compressibility factor (Z) to one (Ideal Gas). No phase information is available in this gas library
Default list of GASES available in the library:
Air
Default
Demo
Methane
With Components of:
NITROGEN CARBON DIOXIDE HYDROGEN SULFID
STEAM HELIUM METHANE
ETHANE PROPANE N-BUTANE
I-BUTANE N-PENTANE I-PENTANE
N-HEXANE N-HEPTANE N-OCTANE
N-NONANE N-DECANE OXYGEN
CARBON MONOXIDE HYDROGEN
Liquid Library:
Liquid with user-specified temperature dependent properties for flow and heat transfer analysis. The temperature-dependent properties are stored in a user-defined library (PLANTLIQ.PFL). Temperature dependent water properties are provided in this library.
Heat transfer not possible with this fluid type. Predefined properties include water, mercury, R-12 and ammonia.
Default list of LIQUIDS available in the library:
WATER 0-300C WATER-L 0-100C
Water-M 100C-200C Water-H 200C-300C
AMMONIA - NH3 -23C-126C REFRIG. - R-12 -23C-26C
MERCURY - HG -23C-526C DEMO LIQUID
Pseudo Gas:
Generic gas mixture for isothermal flow analysis, where user specifies actual gas properties.
User defined gas properties. Heat transfer not possible with this fluid type
Liquid:
Generic liquid for isothermal flow analysis where user specifies liquid density and viscosity.
Extra Fluids Available in PlantFLOW Plus
ASME Steam:
Uses ASME steam tables to evaluate properties of steam. Use the Liquid Library option for liquid water.
Superheated steam based ASME steam tables, sixth edition (1997), based on IFC 1967
NIST Gas:
Hydrocarbon gas mixtures based on National Institute of Standards and Technology, database 4 (SUPERTRAPP)
Use NIST hydrocarbon mixture database for specifying mixtures with up to 15 components. The components are selected from an NIST provided library of 192 components. The mixture should be gas at the pressure/temperature conditions provided in the model.
NIST Liquid:
Hydrocarbon liquid mixtures based on National Institute of Standards and Technology, database 4 (SUPERTRAPP)
Use NIST hydrocarbon mixture database for specifying mixtures with up to 15 components. The components are selected from an NIST provided library of 192 components. The mixture should be liquid at the pressure/temperature conditions provided in the model.
The Fluid library NISTLIB supplied by the program includes the 192 components provided by NIST. Users that have purchased SUPERTRAPP program directly from NIST, can update and append to this library as described in SUPERTRAPP User's Guide. SUPERTRAPP will create a new file PORTLIB that can be read into PlantFLOW using Tools/Make NIST Library file.
Conclusion:
PlantFLOW Plus supports all the above fluids. PlantFLOW STD limits the fluid type selection and sets compressibility factor to 1.0. Refer to PlantFLOW versus PlantFLOW plus for more information.
For those Gas / Liquids that are not available in the application see the online help for procedure to add user defined properties. Furthermore, PlantFlow doesn’t handle the following types of fluids: Non Newtonian fluids (similar to “Yogurt”) or 2 Phase. One of the assumptions in PlantFLOW, fluids are assumed to be newtonian.
Item#24:
Please provide details for "Pipe Eq: AGA".
Answer:
See the following from PLANTFLOW help:
"The implementation applies only to fully turbulent flow regime. "Steady Flow in Gas Pipelines", American Gas Association, IGT Technical Report 10, Chicago, 1965."
See Also
External Links
Bentley Technical Support KnowledgeBase
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