EBSILON®Professional Online Documentation
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Line connections |
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1 |
Inlet |
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2 |
Outlet |
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3 |
Necessary shaft power |
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4 |
Control inlet for efficiency (as H)
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5 |
Optional outlet for recirculation in case of flows below MINFLOW
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6 |
Shaft outlet
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General User Input Values Characteristic Lines Physics Used Displays Example
A pump can be modelled with the help of the Component 8. Different levels of detail are available here:
The simple mode (FCALC=0) is recommended if the purpose is to just model a pressure increase in a fluid. For a detailed modeling it is necessary to distinguish between a pump with fixed rotational speed (FCALC=1) and a pump with variable rotational speed (FCALC=2). The speed-dependency, however, is implemented in this component in a fixed way (via the laws of similarity). Component 83 has to be used to allow to consider a speed-dependent characteristic field.
FSPECP allows to set whether the component is to calculate the pressure increase or the mass flow, or none of these.
Which variants are available depends on the load case (design or off-design) and the calculation mode (FCALC). (see below)
The flag FSPECH allows to set whether the efficiency is to be used or calculated. Normally (FSPECH=0) the behaviour of the component is calculated by means of the efficiency. In identification mode (FSPECH<0), the current condition of the pump is identified, i.e. the efficiency is determined by specifying the output (FSPECH=-1) or the outlet temperature (FSPECH=-2) in order to be able to determine a performance factor for the pump.
The power intake is calculated on the basis of an isentropic compression as a rule. If this is not possible (e.g. in the case of oil), the calculation is effected from the density and the pressure difference.
Losses
Both constant and output-dependent mechanical losses can be considered. The specification value QLOSSM is used for the constant losses. The output-dependent losses result from the mechanical efficiency ETAMN.
The sequence in which the proportional and the constant fraction are considered depends on the direction of the energy flow.
If both a mechanical efficiency ETAMN and a constant loss QLOSSM are specified, the two are combined as follows:
Q_gross = ( Q_net + QLOSSM) / ETAMN
The result value QLOSS comprises the entire (load-independent and load-dependent) loss
QLOSS = Q_gross – Q_net
The result value ETAM contains both fractions (as in the case of Component 6), as ETAM is defined by
ETAM = Q_net / Q_gross
If a QLOSSM > 0 is specified, ETAM thus no longer equals ETAMN but is accordingly smaller (by QLOSSM/heat input).
Efficiency control
To make the efficiency (as variation quantity) accessible from the outside (for closed-loop control or reconciliation), it can be specified as enthalpy on the logic inlet (Pin 4).
To do so, the flag
• FVALETAI=2
has to be set.
The activation of this logic line can also be made conditional on the mode of calculation. This way, this feature can also be used for designs without having to switch manually all the time. For this, the flag FVALETAI features the settings
• FVALETAI=4: use logic line in design mode, use specification value in off-design
• FVALETAI=5: use specification value in design mode, use logic line in off-design
For reasons of compatibility, the obsolete setting FVALETAI=1 is still available, where an indexed measured value (specification value FIND) is placed on an auxiliary line and the same index must then be entered in the component as specification value IPS.
Shaft inlet (Pin 6)
Component 8 features a mechanical shaft as inlet (optional Pin 6). This allows to model the case that several pumps are located on one common shaft.
If this pin is used, the shaft power has to be specified on it. This power will then be added to the power required by the pump and the total will be output on Pin 3.
In default form, the optional shaft inlet is located in the same position as the likewise optional outlet for the recirculation (Pin 5). If both pins are to be used simultaneously, it is possible to shift the view to Form 2 where Pin 5 is located next to Pin 6.
Information for models created with Release 9 or older:
In this component, the flags FSPECP and FSPECH were introduced in Release 10 in order to harmonize the handling with other components. Previously there were the flags FCHR and FSPEC with other values and other meanings. For reasons of upward compatibility, these flags still exist, so that the old models continue to calculate. Therefore there is now a mode “-999” for FSPECP and FSPECH that is entered there when converting old models and tells Ebsilon that the old flags FCHR and FSPEC are to be used. By default, the old flags are set to -999. If, however, old EbsScripts where you accessed the numerical values of the old flags are to be used in new models, the following table specifies which numerical values have to be used for FSPECP and FSPECH in the case of which combination of FCALC, FCHR, and FSPEC:
FCALC FCHR FSPEC FSPECP FSPECH
0 -4 0 or 1 1 -2
0 -3 0 or 1 -1 -2
0 -2 0 or 1 1 -1
0 -1 0 or 1 -1 -1
0 0 0 or 1 -1 0
0 1 0 or 1 1 0
1 -4 or -3 0 1 -2
1 -4 or -3 1 2 -2
1 -2 or -1 0 1 -1
1 -2 or -1 1 2 -1
1 0 or 1 0 1 0
1 0 or 1 1 2 0
Simple Mode (FCALC=0 )
In simple mode, either mass flow and pressure (FSPECP=-1, default setting) or only the mass flow (FSPECP=1) can be specified in all load cases. The calculation of the mass flow from the pressure is not possible in simple mode.
To save users having to always specify the speed at the shaft connection, no error message is generated if the speed specification is missing, but instead a default value of 3000/min is set on the line.
FSPECP=-1
Of course, the possibility to specify mass flow and pressure at the same time independently of each other (FSPECP=-1) facilitates the modeling; however, in reality it can only be achieved by the fact that either the pump can be operated with variable rotational speed or it has a control valve downstream of the pump. The variant with the control valve, however, is unfavorable because thereby a part of the pump output has to be used for an unnecessary pressure increase that subsequently is throttled again. The advantage of the rotational speed control is that the efficiency of the pump changes only little across the entire load range as the rotational speed is always adjusted accordingly. Therefore the efficiency characteristic line CETA that is used in simple mode has been set to 1 by default.
If pressure and flow rate are set independently of each other in the off-design range and the efficiency is decreased at a lower flow rate M1/M1N<1, unrealistic values will result for the pump output. Only if a pump is operated at fixed rotational speed will the efficiency change with the flow rate; however, at a lower flow rate the pump with fixed speed will also develop a higher pressure in proportion to the head curve.
Thus an efficiency curve can only be applied together with a pressure – flow rate curve to correctly calculate the pump output in off-design. For the throttle control it is also important to set a control valve at the outlet.
FSPECP=1
In simple mode, the calculation of the pressure increase (mode FSPECP=1) is effected via the delivery head characteristic CP2. As CP2 is an absolute characteristic line (delivery head as a function of the volume flow) and does not refer to nominal values, the pressure increase can be calculated with it both in the design case and in off-design.
Advanced Modes (FCALC=1 and FCALC=2)
Design
As in these two modes only relative characteristic lines (CETAZHF and CHEADZHF) are used, both the mass flow and the pressure increase have to be specified from the outside in the design case, irrespective of the setting of the flag FSPECP.
In contrast to most other characteristic lines in Ebsilon, however, these characteristic lines are not normalized to the design values but to the operating limits
• ZHF (zero head flow = flow rate the pump can deliver without back pressure) and
• SOH (shut-off head = max. back pressure = pressure the pump can achieve against a closed slide valve)
In the case of the characteristic line CHEADZHF
• the volume flow is related to the max. possible volume flow ZHF (zero head flow) that can be achieved at a delivery head of 0
• the delivery head is related to the max. possible delivery head SOH (shut-off head) that can be achieved in the limit case of a volume flow of 0
In the design case, you are located on a certain point of this characteristic line, the design working point (VM1N, DHN). However, it is necessary to define at which position of the characteristic line this point is located. This can optionally be defined via the x-value or the y-value. This selection is effected by means of the flag FSPECD:
• At FSPECD=1, the x-value of the working point is defined. To do so, the flag FZHF allows to either
o directly enter this point as specification value SZHF (FZHF=0) or
o to define the ZHF via the mass flow (FZHF=1) or
o to define the ZHF via the volume flow (FZHF=2)
• At FSPECD=2, the y-value of the working point is defined. To do so, the flag FSOH allows to either specify
o the ratio between the (total) max. delivery head and the design delivery head (SOH/DHN) or
o the ratio between the still (additionally) available delivery head and the design delivery head ((SOH-DHN)/DHN) or
o the ratio between the design delivery head and the max. delivery head (DHN/SOH) or
o the max. delivery head (SOH).
In the case of the characteristic line CETAZHF
• the volume flow is related to the max. possible volume flow ZHF (zero head flow), as in the case of the characteristic line CHEADZHF
• the efficiency is related to the efficiency that exists at ZHF (which is why this characteristic line may exceed the value 1 as the max. efficiency normally does not exist at ZHF).
Mass flow, pressure increase, and rotational speed
In the advanced modes, two out of three of the variables mass flow, pressure increase, and rotational speed have to be specified at all times; the third one will be calculated.
For FCALC=1, a fixed rotational speed is used at all times, namely the specification value RRPM. The variant FSPECP=-1 (specification of mass flow and pressure increase) where the rotational speed would have to be variable is therefore unavailable for FCALC=1.
For FCALC=2, at FSPECP=1 (M given) and FSPECP=2 (P given) the rotational speed must be specified on the shaft from the outside in all load cases. At FSPECP=-1 (M and P given) the rotational speed is calculated by the pump. To do so, the specification value RRPM is resorted to in the design case; in off-design, the calculation of the rotational speed is carried out by means of the laws of similarity (see below).
In principle, it would have been possible to do without the specification of the rotational speed from the outside in the design case also at FSPECP>0 and to use the specification value RRPM. Then, however, double entries would have resulted when combining several pumps. Therefore the component has been implemented in such a way that a specification of the rotational speed from the outside is expected for FSPECP>0 in all load cases.
Information for models created with Release 13 or older:
Up to Release 13, the mode FCALC=2 (“variable speed (affinity laws)“) was not yet implemented for the setting FSPECP=1 (”M given“). Therefore the calculation was carried out with fixed rotational speed. Models where this combination of settings was used will therefore miss the specification of the rotational speed on the shaft. To make the model calculate again, the pump should be set to FCALC=1 (“fixed speed“) so the results are reproduced again.
Laws of similarity (for FCALC=2)
Component 8 offers the option to easily model a speed-controlled pump with the help of the laws of similarity.
These contain a proportional increase in the volume flow and a quadratic increase in the delivery head with rising rotational speed. The pump characteristic CHEADZHF defined for the design rotational speed can therefore also be used for other rotational speeds if you scale ZHF (”zero head flow“) with the rotational speed and SOH (“shut-off head“) with the rotational speed squared.
If a certain delivery head is to be achieved at a specified inlet volume flow, the rotational speed must thus be set in such a way that the pump characteristic shifts so far that the point of the desired combination of volume flow and delivery head gets to be located on the pump characteristic.
For this, the so-called similarity parabola is constructed through the operating point. On the similarity parabola, all equivalent points for different rotational speeds are located. The intersection point of this parabola with the pump characteristic (CHEADZHF) in the design case is the operating point corresponding to (“similar to”) the current operating point at the design rotational speed. Due to the law of similarity, the volume flow belonging to this operating point relates to the original ZHF like the current volume flow to the ZHF of the new pump characteristic. From this, the rotational speed ratio can be determined and thus also all other parameters of the pump characteristic for the current rotational speed:
• the rotational speed ratio (SPRAT)
• the current ZHF (ZHFOP)
• the current SOH (SOHOP)
• the current rotational speed (RRPMOP) as well as
• x- and y-values of the characteristic line (VM1ZHFOP, RHEADSOHOP)
are displayed as result values.
The rotational speed is also transferred to the mechanical shaft (Pin 3).
Minimum flow rate
By means of the specification value MINFLOW, a minimum flow rate can be defined. To prevent falling below this quantity, the flow rate is increased by routing a part of the outlet fluid back to the inlet, thus increasing the flow rate (recirculation). For this purpose, there is an additional Outlet 5 via which the recirculation flow is branched off. It must then be fed in again at an appropriate place in the model.
Please note: It must be considered that the recirculation can only be calculated if the mass flow is specified at the outlet of the pump. If it is smaller than the minimum mass flow, the inlet mass flow will be increased to the minimum mass flow and the difference will be extracted via Outlet 5. If a mass flow that is too small is specified at the inlet, the pump unfortunately has no possibility to increase it and will output an error message.
Information for models created with Release 12 or older:
As the minimum flow rate was only considered energetically in the past (for calculating the pump output, the calculation was indeed carried out with the increased flow rate but the mass flow remained unchanged), models using the minimum flow rate may now output error messages. In order to remedy those, Pin 5 must be added in the model.
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FVALETAI |
Validation of isentropic efficiency Like in Parent Profile (Sub Profile option only) Expression =0: ETAIN used without validation =1: (Deprecated) IPS used instead of ETAIN (validable) =2: ETAIN given by enthalpy on control inlet 4 =4: Enthalpy on control inlet 4 used in design, specification value ETAIN in off-design =5: Specification value ETAIN used in design, enthalpy on control inlet 4 in off-design |
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ETAIN |
Isentropic efficiency (nominal) |
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IPS |
Index for pseudo measurement point |
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ETAMN |
Mechanical efficiency (nominal) |
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QLOSSM |
Mechanical loss (constant fraction) |
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FCALC |
Flag for calculation mode Like in Parent Profile (Sub Profile option only) Expression =0: Simple mode (FZHF, SZHF, RRPM, FMINFLOW, MINFLOW are not used in the calculation) =1: Advanced mode |
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FSPECD |
Method for specification off design working point Like in Parent Profile (Sub Profile option only) Expression =0: By definition of zero head flow =1: By definition of shut-off head |
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FZHF |
Flag for specification of zero head flow Like in Parent Profile (Sub Profile option only) Expression =0: SZHF=rated zero head flow =1: SZHF=zero head mass flow =2: SZHF=zero head volume flow |
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SZHF |
Specified (related or absolute) zero head flow |
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FSOH |
Method for specification off shut-off head Like in Parent Profile (Sub Profile option only) Expression =0: SSOH = shut-off head / design head =1: SSOH = (shut-off head / design head) -1 =2: SSOH = design head / shut-off head =3: SSOH = SOH |
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SSOH |
Specification for shut-off head |
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RRPM |
Rated rotary speed |
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FMINFLOW |
Flag for specification of minimum flow Like in Parent Profile (Sub Profile option only) Expression =0: MINFLOW= rated minimum flow =1: MINFLOW= minimum mass flow =2: MINFLOW= minimum volume flow |
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MINFLOW |
(Related or absolute) minimum flow |
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FSPECP |
Flag for specification of mass flow or pressure: Like in Parent Profile (Sub Profile option only) Expression =-999: Unused (use deprecated FSPEC and FCHR instead) =-1: M1 and given externally (only for FCALC=0) =1: M1 given, P2 calculated (for FCALC=1, only in off-design) =2: P2 given, M1 calculated (for FCALC=1, only in off-design) |
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FSPECH |
Flag for specification of enthalpies and power: Like in Parent Profile (Sub Profile option only) Expression =-999: Unused (use deprecated FSPEC and FCHR instead) =0: Efficiency Characteristic used =11: Efficiency Characteristic used (validable) =-1: Power Specification =-11: Power Specification (validable) =-2: H2 Specification |
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FSPEC (obsolete) |
Flag for specification of mass flow or pressure in off- design (for FCALC=1 only): Like in Parent Profile (Sub Profile option only) Expression =-999 unused =0: M1 given, P2 calculated =1: P2 given, M1 calculated |
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FCHR |
Flag for using the characteristic lines and defaults Like in Parent Profile (Sub Profile option only) Expression =-999 unused =0: P2 given from outside, shaft power calculated via ETAIN =1: P2 calculated from the delivery head line, shaft power calculated via ETAIN = -1: P2 and shaft power given from outside (identification mode: ETAI is calculated) = -2: P2 calculated from the delivery head line,shaft power given from outside (identification mode: ETAI is calculated) = -3: H2 and P2 given = -4: H2 and delivery head given |
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FMODE |
Flag for calculation mode Design / Off-design =0: GLOBAL =1: local off-design i.e. always off-design mode, even when the model is calculated in the design mode. = -1: local design |
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FADAPT |
Flag for adaptation polynomial / adaptation function Like in Parent Profile (Sub Profile option only) Expression =0: Off =1: Correction factor P2=P1+9.81*head of delivery/V1*1.0E-5*polynomial =2: Replace P2=P1+polynomial =1000: Not used but ADAPT evaluated as RADAPT (Reduction of the computing time) = -1: Correction factor P2=P1+9.81*head of delivery/V1*1.0E-5*function = -2: Replace P2=P1+function = -1000: Not used but EADAPT evaluated as RADAPT (Reduction of the computing time) |
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EADAPT |
Adaptation function |
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FCHRX |
Flag for the interpretation of the x-axis of the efficiency and the pressure increase characteristics: Like in Parent Profile (Sub Profile option only) Expression =0: x-axis is interpreted as normalized volume flow at inlet =1: x-axis is interpreted as normalized reduced mass flow at inlet =2: x-axis is interpreted as normalized mass flow |
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M1N |
Mass flow (nominal) |
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DHN |
Rated delivery head (nominal) |
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VM1N |
Rated volume flow |
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ZHF |
Zero head flow |
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SOH |
Shut-off head |
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EFFZHF |
Efficiency at zero head flow |
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NS |
Specific speed (dimension less) |
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NSSI |
Specific speed (SI units) |
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NSUSCU |
Specific speed (US customary units) |
The quantities marked in blue are reference quantities for off-design mode. The actual off-design values refer to these quantities in the equations used.
Generally, all inputs that are visible are required. But, often default values are provided.
For more information on colour of the input fields and their descriptions see Edit Component\Specification values
For more information on design vs. off-design and nominal values see General\Accept Nominal values
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Characteristic line 1, CETA : isentropic efficiency ETAI/ETAIN = f (X/XN) Specification-value : FCHRX X/XN = M1/M1N or X/XN = VM1/V1MN |
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X-Axis 1 X/XN 1st point |
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Characteristic line 2, CP2 : Delivery head HEAD = f (VM1) |
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X-Axis 1 VM1 1st point |
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Characteristic line 3, CETAZHF: Related efficiency ETAI/EFFZHF = f (VM1/ZHF) |
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X-Axis 1 VM1/ZHF 1st point |
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Characteristic line 4, CHEADZHF : Related delivery head HEAD/SOH = f (VM1/ZHF) |
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X-Axis 1 VM1/ZHF 1st point |
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All cases |
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Fluid Water: S1 = f(P1,H1) Fluid Oil: DHS = 0.1*(P2-P1)/RHO For FCALC=1: For FCALC=0: For FCALC=1 and FSPEC=1: M2 = M1 For (FCALC=1 and FSPEC=0) or For FCHR >= -2: For FCHR >= 0 or FCHR <= -3:: |
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Display Option 1 |
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Display Option 2 |
Click here >> Component 8 Demo << to load an example.