84680066-Stahdard-Chapter1

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 1 OF 44 REVISION 2.01, MAY 2009

PIPENET STANDARD MODULE

CHAPTER 1

THE BASICS AND INTRODUCTORY EXAMPLES

1. Introduction:

In this section, the concepts used in the PIPENET VISION Standard Module are described briefly. The modelling concepts and the design concepts are covered under this category. PIPENET VISION Standard Module uses the contemporary equations for all the models like pipe, ducts, pumps, valves, filters, etc.

In the past, the fluid flow analysis was done by the engineers with manual calculations. To do such analysis for large networks takes a real time effort. Now PIPENET VISION Standard module helps the user, providing faster and reliable solutions.

It is important that the reader of this chapter is familiar with the contents of USER INTERFACE – CHAPTER 1. It is highly recommended that the reader is at least familiar with the main aspects discussed in that chapter. 2. Concepts:

2.1. Pressure drop Model

Pressure loss in a pipe is described below:

Where:

platelevfric PPPP ++=

Pfric = Pressure loss due to friction and fittings.

Pelev = Pressure loss due to elevation change.

Pplat = Pressure loss due to any orifice plate fitted.

The full details of the equations used to calculate these pressure losses are described below.


2.2. Frictional Losses in Pipes – Darcy Equation

Pfric is found using the Bernoulli equation method. The Bernoulli equation is a theoretical equation which gives the pressure in pipes, ignoring frictional effects. By comparing the theoretical results obtained using the Bernoulli Equation with those obtained in experiments the pressure drop due to friction effects can be found. Based on the work of the French engineer Henri Darcy (1803–58) the following equations are obtained:

D

ufLPfric

22 ρ=

Where:

D is the internal diameter of the pipe,

L is the pipe length,

f is the Fanning friction factor,

u is the fluid velocity and

ρ is the fluid density.

The Fanning friction factor depends on Reynolds’s number (Re= ρρρρuD/µ where µ is the fluid viscosity) and the relative roughness of the pipe (pipe roughness/pipe diameter). The standard values for f can be obtained from a graphical representation known as the Moody diagram. This is represented in PIPENET VISION by the following empirical formulae (where r is the surface roughness of the pipe):

Laminar flow (Re < 2000):


Re16=f

Transitional flow (2000<Re<3000):

f is found by interpolating between laminar value for Re=2000 and turbulent value at Re=3000.

Turbulent flow (Re >3000):

+−=

fD

r

f Re

252.127.0ln768.1

1

PIPENET VISION can also optionally use an alternative formulation of the latter (Colebrook equation ):

+−=

fD

r

f Re

256.1

7.3log4

1

The pressure loss due to fittings is given by the following formula:

2

2ukPfittings

ρ=

Where k is the K-factor of the fitting.

2.3. Pressure Loss due to elevation change

The pressure drop caused by the difference in elevation of the two ends of the pipe is given

by:

gZPelev ρ=

Where:

g is the acceleration due to gravity.

Z is the change in elevation.


2.4. Frictional Losses in Ducts

Ducts are very similar to pipes except for the obvious difference that ducts have a rectangular cross-section. Ducts can be used only when the fluid used in the network is gas. If the user wishes to use Rectangular ducts and use any liquids, then the hydraulic radius is derived from the duct dimensions and model the same as pipes. Ducts are modelled using the same equations as pipes. In order to do this PIPENET VISION calculates a mean hydraulic diameter, DH, for the duct using:

( )WH

HWDH +

= 2

Where: H is the duct height and W is the duct width.

2.5. Treatment of Elevation Differences

2.5.1. Pipe/duct elevations Each pipe or duct is assigned a change in elevation from its input to its output. PIPENET also assigns a reference node. The height of each node is calculated with respect to the reference node. This pipe/duct elevations option can result in height inconsistencies if a network contains one or more loops. In a loop, the sum of the elevation changes must be zero. However, if a pipe/duct elevation has been incorrectly entered, the sum will not be zero and an elevation error will be reported. Elevation errors can be difficult to locate in network systems with many complex loops. PIPENET provided tools for locating elevation errors quickly.


2.5.2. Node elevations The elevation of each node is directly entered as an attribute of the node - elevation errors cannot occur with this method. On the other hand, if a mistake is made while inputting a node elevation, PIPENET will not detect it.

2.6. User-defined fluids

2.6.1. User defined liquids:

For a user-defined liquid, the density and viscosity must be defined. For the following three classes, the density and viscosity can be defined as follows:

• Liquid direct specification - They are given as constants.

• Liquid property correlations - They vary with temperature and can be obtained using the following correlation formulae:

Density

( ) 7

2

1

−−= CT

TBAρ

Viscosity

MCT=µ

Where:

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 6 OF 44 REVISION 2.01, MAY 2009 T is the temperature (K),

Tc is the critical temperature (K) and

A, B, C and M are constants for the liquid. Besides the temperature T, the user must also give values for A, B, C, M and Tc.

• Liquid variable properties - From a given set of tabular data for density and viscosity against temperature, the density and viscosity at time T are calculated using linear interpolation.

2.6.2. User-defined gases

The gas may be defined by the user either as a Van der Waal’s gas (class 3) or as an Ideal gas (class 4). In either case, the user must supply the following information: Molecular Weight, Critical Properties (temperature, pressure and volume) and Ratio of specific heat capacities (Gamma).

2.7. Control Valves

The valve may be characterised by one of three built-in models which require either a K-factor and a port area, or a flow coefficient, or by a control valve type. Select the appropriate choice from the Valve type combo-box and radio buttons and enter the required data, if any, in the valve characteristics boxes below. Note that the flow coefficient is that for water at 20ºC.

Modelling Equation:

( )2

2

sC

QP

voρρ=

Or:

22

2

2 As

QKP

ρ=

Where:

P is the pressure drop across the valve,

Q is the (volumetric) flowrate through the valve,

ρ is the fluid density,


ρ0 is the density of water at 20ºC.

s is the valve setting, 0 < s < 1,

K is the K-factor for the valve,

A is the cross-sectional area of the valve port and

Cv (s) is the valve flow coefficient for water at 20ºC.

Control Valve Considerations

A control valve regulates flow or pressure in a network. The pressure drop across the control valve is dependent on the valve setting, s, and its physical characteristics.

The valve setting can either be specified directly by the User, or be determined by PIPENET VISION such that a particular sensor reading is satisfied. Three sensor types are available:

• Pressure at a node - Pressure control

• Flowrate Q through a particular pipe - Flow control

• Pressure Difference between two nodes - Differential pressure control

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 8 OF 44 REVISION 2.01, MAY 2009 PIPENET VISION calculates a control valve's setting such that the associated sensor reading is attained. In some scenarios this is not possible. For example, a control valve monitoring flowrate in an adjacent pipe may be unable to achieve the sensor reading even with a fully open setting. In such cases the valve setting will be fully open or closed, whichever gives the closest result for the sensor reading.

Some care is required when using control valves that use a sensor to calculate the valve position. A fully closed control valve behaves like a closed non-return valve and can isolate parts of the network resulting in an unsolvable system. In particular, this can sometimes occur if blocked pipes and control valves are both present in a scenario.

Three built in control valve characteristics are available: Linear, Equal Percentage or Quick opening. Alternatively a library control valve type can be created by specifying the valve characteristic curve of K-factor or flow coefficient against ‘s’. PIPENET VISION then uses cubic interpolation to determine intermediate points on the characteristic curve.

The linear control valve option provides the same model as used in earlier versions of PIPENET VISION, which did not offer equal percentage or quick-opening valves.

2.8. Pumps

A simple pump model uses the pump performance curve. The user inputs the flowrate against head data at 100% rpm. PIPENET VISION can calculate the performance curve at other speeds using the homologous relationships for pumps. This is normally intended only for use in the positive quadrant, in other words when the flow and the head are positive.

Data required in-order to build the pump Pumps - Coefficients Unknown

In PIPENET VISION Standard module, data for pumps and fans can be created into a library. PIPENET VISION also does a curve fit and uses the coefficients in the calculations. The input data must be in the form of data pairs taken from the performance curves.

Typically, the pump curves are not supplied in the same units as the units in which pressure drop calculations are going to be made. For example, it is usual to specify the pump curve in head of fluid, rather than psi. For this reason, the pump/fan module accepts data in its own units.


The dialog box for inputting a pump curve is shown below:

PIPENET VISION would take into account the fact that the head generated by a pump is independent of the density of the fluid, and make an appropriate density correction in converting it to a pressure. Similarly, the pressure generated by a pump would depend on the fluid, and when the pump curve is defined in pressure terms a density correction as

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 10 OF 44 REVISION 2.01, MAY 2009 appropriate is applied. This is the reason why the performance curve is interpreted to be that of water when it is defined in terms of pressure.

Creating a new pump

1. Select the NEW button and provide a name and description

2. Select the desired flowrate and pressure units from the drop-down lists provided

at the top left-hand corner of the dialog

3. Provide a minimum and maximum flow rate

4. Provide a minimum of three points for the curve in the bottom left-hand corner

window

5. Select the type of curve to be fitted – three are available, quadratic, cubic and cubic spline.

6. Select Apply to add the pump to the library

7. The coefficients are calculated and displayed, along with the pump curve.

Note that the definition of the pump curve will only be accepted if at least three points are provided and the slope of the calculated curve is negative everywhere between the minimum and maximum values.


Editing an existing pump

1. Select the pump from the drop-down list presented in the pump name box

2. Make any changes required to the pump parameters;

3. Select Apply to commit the changes.

Deleting a pump

1. Select the pump from the drop-down list presented in the pump name box;

Type of curve fitted


2. Select the Delete button.

Pumps Coefficients Known

This capability is hardly ever used. Unless there is a compelling reason it is better to use the coefficients unknown option.

In case, the pump coefficients defining the performance curve are provided by the manufacturer, then using ‘Pump Coefficients Known ’ dialog box.

Pump Input Data in Network

1. The pump label

2. Input and output nodes

3. Pump efficiency

4. Name of pump in library

Some useful tips

If the user knows the performance coefficients for a pump and does not want to use a pump library, then the pump can be defined as a non-library pump by giving the values of A, B, C, Qmin, Qmax.


In order for the calculator to function correctly, it is necessary to ensure that there is only one flowrate corresponding to each pressure gain, and so the following restrictions are applied:

• For flow rates between Qmin and Qmax, the slope of the performance curve must be negative or zero.

• For flow rates between Qmin and Qmax, there must be no flowrate that gives no pressure change. (That is, the performance curve must not cross the horizontal axis.)

For flow rates outside the range Qmin to Qmax, PIPENET VISION extrapolates the performance curve using the tangent to the curve at the minimum or maximum flowrate, and issues an appropriate warning message.

PIPENET VISION will calculate the power required by a pump based on a supplied efficiency. This need not be supplied, in which case the power calculation will assume that the pump is 100% efficient.

2.9. Introduction to Specifications

In order to solve a network, boundary conditions must be provided in the form of flow or pressure specifications on input and output nodes or pressure specifications on internal nodes (i.e. any node which is not an input or output node). These specifications must obey the rules described more formally in the following:

Assumptions

1. Input and output nodes correspond to those points in the network where fluid enters or leaves the network

2. Internal nodes are those nodes, which are not inputs or outputs

3. Sub-networks may be created by the presence of breaks and blocks

4. If a node is at one end of a break then it is considered to have an attached pressure specification

5. If a node is at one end of a block then it is considered to have an attached flow specification

Rules Governing Specifications

The specification rules can be summarised as follows:

Let Np be the number of pressure specifications.

Let Nf be the number of flowrate specifications.


Let Nio be the number of I/Onodes.

In all cases, the basic rules regarding specifications which must be satisfied are the following: Np + Nf = Nio

Np ≥ 1

Design Case

In the design case one or more pipe sizes would be left unset. PIPENET will determine the pipe sizes based on either the maximum allowable pipe velocity or pressure drop per unit length. In the design case two sets of specifications need to be given. One set is for pipe sizing and the other is for the final analysis calculation. There are three reasons why two sets of specifications are needed.

• The conditions for pipe sizing may be different from the conditions for analysis. For example, pipe sizing may be based on the summer operating conditions on the plant, whereas the analysis may be based on the winter operating conditions.

• Pipe sizing may take into account a future expansion in mind, whereas the analysis may be based on operating conditions of today.

• Pipe sizes depend mainly on the flowrates the system needs to handle. All but one specification must be flowrates in the design phase. In the analysis phase pressures and flowrates may be given in any reasonable combination as long as there is one pressure.

In the pipe sizing case where the design phase is used, Np and Nf must satisfy the constraints given in the following table:

Phase Np Nf

Design 1 Nio - 1

Analysis Np >= 1 Nf = Nio - Np

This means the following:

Design phase – give one pressure specification and flowrate specification to all but one input/output node.

Analysis phase – give appropriate pressure and flowrate specifications so that the total number of specifications is equal to the number of input + output nodes.

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 15 OF 44 REVISION 2.01, MAY 2009 The design option must be switched on if pipe sizes are to be determined by PIPENET as shown below.

A typical specification in the design case is shown below.

Design Case

Two sets of specification must be given, namely, design phase and analysis phase specifications.

The design phase specifications are used for pipe sizing. The analysis phase specifications are used for modelling the actual operating case.

There are two reasons why the design phase specifications may not be the same as analysis phase specifications.

In the design phase all except one specification are flowrates. In the analysis phase they can be given in any reasonable combination as long as at least one of them is a pressure specification.

Design Option Button


The pipe sizing may be based one set of operating conditions and the analysis case on another. For example, pipe sizing may be carried out with a future expansion in mind whereas the analysis specifications may be based on the current operation.

Nodes 1, 3 and 4 are I/O nodes. Thus we have Nio = 3.

For the Design phase:

Np = 1, and

Nf = Nio - Np = 3 - 1 = 2.

For the Analysis phase:

Np >= 1, and

Nf + Np = 3.

Suppose the pressures at nodes 1, 3 and 4 are all set. Then Np = 3, so Nf = 0.

In a Tabular form, this can be summarised as follows:

PHASE Np Nf

DESIGN 1 2

ANALYSIS 3 0

Analysis Case

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 17 OF 44 REVISION 2.01, MAY 2009 If pipe sizing is not required then Analysis specifications are all that are needed.

3. Introductory Examples:

In this chapter we consider a number of examples which would enable users to become familiar with the use of PIPENET. Standard Module. Some of the examples are very simple and others are closer to real applications. In order to keep the input simple several section are skipped and they are indicated in the text.

3.1. Steady State Single Pipe Problem

The problem

Calculate the pressure loss in a single pipe with an inner diameter of 1.61 in., length 10 ft., elevation change of 2 ft., pipe roughness of 0.0018 in. and 3 x 90 deg bends. The inlet

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 18 OF 44 REVISION 2.01, MAY 2009 pressure is 20 psi G and the outlet pressure is 10 psi G. Fluid is water at 20 deg C. Use the orthogonal schematic option. Note: The elevation of a pipe is +ve if the output node is higher than the input node, and is –ve if the output node is lower than the input node. Elevation in PIPENET VISION terminology means the difference in the height between the input and output nodes of a pipe.

3.1.1. Initialisation Data To start with initialisation, click on Init or Options (The 'Init' menu is shown in case the module uses ‘PIPENET VISION menu style’ and Options menu is shown in case the module uses ‘Window menu style’. This accessed from the pull down menu ‘Window’. The menu bar arrangement under the two options, namely Windows style and PIPENET style, are shown below. These can be selected under the Window pull down menu.

• Windows menu style

• PIPENET menu style

Title Any four line title can be provided. In order to register the data click Apply and click Cancel to undo changes. The ‘OK’ button registers the data in the dialog box leaving the initialization menu unlike ‘Apply’. This is applicable to all.


Standard options Choose Colebrook-White for Pressure Model and Pipe/Duct elevation for elevations. Make sure that under Warnings Control the ‘Ignore-Proceed with Calculation’ option is chosen. Always choose Crane for Orifice plate Model.

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 20 OF 44 REVISION 2.01, MAY 2009 Units – Choose U.S. Units

Fluid Type

Water at 68 deg F.


Pipe Type – skip Display – For Labels select all the Options, for Grid option select ‘orthogonal’ for style and ‘lines’ for gird. Make sure ‘Display Grid’, ‘Snap Grid’ and ‘Results/Arrows indicating Flow’ are checked on.


Calculation – skip Defaults – skip Libraries - skip section for the time being Calculation - skip section for the time being Colouration - skip section for the time being

3.1.2. The network Go to the tools palette and select the pipe tool. Move the cursor to a grid point and click. Move the cursor to another grid point and click. You would have created a line, with two nodes. The grid would be orthogonal and the network would be a single pipe with the node numbers and the pipe label shown.


Input attributes data Pick up the arrow cursor from the tools palette. Point it at the pipe and the pipe turns red. The attributes for the pipe can be entered through the ‘Properties Window'.

Pipe tool

Pipe tool


The Additional k-factor box is for inputting a k-factor, which you do not wish to set up in a library.

In order to enter fittings select the ‘Fittings’ option. This switches from the ‘Properties’ to the ‘Fittings’ table. Then select the fitting from the available fittings and press the Add button the appropriate number of times (in the above example it’s three 90 deg bends).

Flow Status can be normal, blocked or broken. A blocked pipe is one which might have an isolation valve closed or a blocked filter. A broken pipe is one which might have ruptured.

Pipe Type shows the pipe schedule which is used for the pipe and is not relevant for this particular problem.

The Input attribute data can be also entered through the ‘Data window’ which can be accessed from the ‘View’ menu. Changing the attributes in the Data Window will be reflected in the schematic. Through the browse menu, the attributes for node and any other component used in the network can be accessed.

Input Specifications:

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 25 OF 44 REVISION 2.01, MAY 2009 Specifications are operating conditions specified by the user to enable PIPENET VISION to perform calculations.

The number of specifications is equal to the number of I/O nodes.

Make sure that the arrow cursor is active. Point the cursor to node 2 and click. The ‘Properties Window’ will display the table for entering the specification. Set the Input/Output node type to Output, then select ‘YES’ to Analysis Spec. and set the pressure to 10 psi G. See below.

Point the cursor to node 1 and click. The ‘properties Window’ for node 1 will open. Set the Input/Output node type to Input, then select ‘YES’ to the Analysis Spec. and set pressure to 20 psi G. See below.

Design specifications are for the specifications for pipe sizing if required. It is not required in this problem.

Analysis phase specifications are for the specifications for the hydraulic calculation. These must always be specified, whether or not pipe sizing is required.

3.1.3. Saving the data Click on file and select Save As… Give a file name for the .SDF file and click on Save. Make sure that the path name is what you intend and the file type is .SDF


Checking input data The network generated and the specification input is checked for its validity. This can be done by clicking on the Check icon or by accessing the Check option through the calculation menu.

Check tool

Menu bar check

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 27 OF 44 REVISION 2.01, MAY 2009 Performing the Calculation Once the validity of the system is confirmed, the calculation is performed. The calculation can be performed by clicking the Calculate icon or by accessing the Calculate option in the calculation menu.

Looking at the Results

Display node results

Display link results

Menu of node items


It is possible to take a look at the results on the Schematic itself, through the Data Window or the Properties Window. A more detailed result can be viewed through the output browser or word processor. The display options tag, as shown below is used for displaying the result in the schematic window.

In order to look at the results on the schematic itself, click on results-related options. Display

node colouring legend button - if this is selected, a node colour coding legend is displayed in the schematic window. A drop-down box from which can be selected the parameter to be displayed on nodes, for example elevation and pressure.

Display pipe/duct colouring legend button - if this is selected a link colour coding legend is displayed in the schematic window. A drop-down box from which the parameter to be displayed on pipes can be selected. For example, flow rate and velocity. Arrows indicate flow

direction . Results through the Schematic:

Menu of link items


The above picture shows the results for the given network in the schematic. The result-related options are used to provide the results with distinct colours. As in this case the legends are also provided for Pressure (Node result) and Pipe vol. flow (Pipe result) with their respective units. The colouration is covered completely in the colour schemes that would be given in the next topic. Results through the Data Window:

The results can be viewed through the ‘Data Window/Results’ as shown above. The Data Window displays the result in the Excel format. The details from the data window can be directly copied to an Excel sheet using the copy/paste commands. Results through the Properties Window:

Results button

FlowrateUSgpm

Pressure psig


The result can be viewed through the ‘Properties Window’ as shown above. To view the result of any component, in this case the pipe or a node, click on the item which needs to be examined, and PIPENET VISION will display the appropriate data and results in the ‘Property Window’.

In order to look at the output file, click on Calculation|Browser and then select the relevant option.

3.2. Simple Three Pipe Problem:

In this example we consider a three pipe problem handling water at 20 deg C. A number of cases are considered in particular the following:

Results for pipe 1

Results


• Three pressure specifications. • One pressure and two flowrate specifications. • Pump selection. • Using a device to balance the flowrate. • Inputting vendor’s pump curve and performing final calculation

The network is shown on the next page. The input of data begins from section 3.1.

Objectives Perform calculations with several combinations of specifications. Perform calculations in order to find the duty point of the required pump. Standard options Use the Colebrook - White Equation for Pressure Drop model.


Units

Variable Unit Length m Diameter mm Velocity m/sec Temperature Celcius Density Kg/m3 Viscosity cP Pressure bar Gauge Flow rate type Volumetric Flow rate m3/hr

. Fluid Data The fluid is water at 20°C

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 33 OF 44 REVISION 2.01, MAY 2009 Pipe Data Use a roughness of 0.0457 mm for all pipes.

Pipe Label

Input Node

Output Node

Diameter mm

Pipe Length, m

Elevation, m

Fittings

1 1 2 25 25 0 2 x 90

2 2 3 25 12 0 1 x90 2 x 45

3 2 4 25 18 0 1 x 90 1 x ball valve

Case 1: Set the specifications as below. All press ure specifications.

Node Number Pressure, bar G Flow rate, m 3/hr

1 2 Unset

3 1 Unset

4 1 Unset

This box can be displayed by clicking on the node of interest and selecting the properties tab in the bottom left corner of the screen.


Case 2: Set a Mixture of flow and pressure specifi cations. Note that the specification must indicate whether it is an input or an output node with a flow specification. However, with a pressure specification this is not necessary. Node Number Pressure, bar G Flow rate, m 3/hr

1 2 Unset

3 Unset 3 (out)

4 Unset 2.4 (out)

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 35 OF 44 REVISION 2.01, MAY 2009 Case 3: Pump selection case. In this case we will assume that the flow rate and pressure requirements are given at both outputs. However, nothing is specified at the inlet. In fact, our aim is to find the pressure and the flow rate at the inlet. Furthermore, we would regard the flow rate requirements as exact, but the pressure requirements as minimum values. Note that no more than three specifications can be made at any one time. The calculation will be done by making an assumption as to which is the critical pressure, and setting that as a specification. After the calculation, we check to see if the other pressure is more than the required value. If it is, a further calculation will not be necessary. If it is not, then we change the node on which the pressure specification has been made and perform another calculation. Let us assume the following requirements.

Node Number

Pressure, bar G

Flow rate, m3/hr

1 Unset Unset 3 > 4.5 3 (out) 4 >5.0 2.4 (out)

As we are only allowed three specifications, in the first instance we use the following combination. We expect this to be the critical case.

If this turns out to be not the critical case then a pressure of 4.5 barg should be specified on node 3 and the pressure specification on node 4 should be dropped.

Node Number

Pressure, bar G

Flow rate, m3/hr

1 Unset Unset 3 Unset 3 (out) 4 5.0 2.4 (out)


As the pressure on node 3 is 4.9857 bar G, which is more than the required 4.5 bar G, we conclude that our choice of the critical node is correct. If our choice had not been correct we would have to use specifications according to the table below.

Node Number Pressure, bar G Flow rate, m 3/hr 1 Unset Unset 3 4.5 3 (out) 4 Unset 2.4 (out)

As our choice of the critical node is correct, we can determine that the excess pressure on node 3 is 4.9857 – 4.5 = 0.4857 bar G. Therefore, in order to achieve the required pressure, we can create and introduce a ‘device’ type user-defined fitting. Case 4: Introduce a device type fitting (0.4857 bar G @ 3 m3/hr) on pipe 2 and repeat the calculation.


In the properties window, the fittings option is selected and the fittings are added.



The outlet nodes meet the required user demands exactly. Therefore we conclude that the duty point of the pump needs to be 5.40 m3/hr @ 6.34 bar G. Case 5: Select and input a suitable pump into the pump library. Then insert the pump into the network and perform a calculation. We will assume that the flow rates at the outlets are kept at their required values. We are therefore intending to calculate the delivery pressure achieved. In general, the pump curve would be more than adequate to meet the requirement and we would expect the pressures achieved to be more than the required values.

Flow rate, m 3/hr Pressure, bar G 4.00 6.9 5.00 6.7 6.00 6.4 7.00 6.0

The above points are input to the pump/fan module as follows. Note that the minimum and maximum flowrates are given. To open the fan module, go to the libraries menu and select “Pumps – Coeffs. unknown.


Insert the pump into the network and select the pump curve, as shown in the dialog box below:

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 41 OF 44 REVISION 2.01, MAY 2009 Select the pump type

Remove the specification on Node 1.

Apply a specification of 0 barg to the inlet o the pump.

PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 42 OF 44 REVISION 2.01, MAY 2009 The results are shown below.

.


PIPENET VISION TRAINING MANUAL STANDARD: CHAPTER 1 PAGE 44 OF 44 REVISION 2.01, MAY 2009 It can be seen that the pressures at the outlet nodes are more than what is required. This completes the calculation.

This example shows the main steps in the complete design cycle covering pipe sizing, pump selection, flow balancing and final calculation using the chosen pump.

Documents

84680066-Stahdard-Chapter1