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STANDARD: CHAPTER 1 REVISION 2.01, MAY 2009
PIPENET STANDARD MODULE CHAPTER 1 THE BASICS AND INTRODUCTORY EXAMPLES1. 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:
P = Pfric + Pelev + PplatPfric = 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.
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STANDARD: CHAPTER 1 REVISION 2.01, MAY 2009
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 (180358) the following equations are obtained:
PfricWhere:
2 fLu 2 = D
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
is the fluid density.The Fanning friction factor depends on Reynoldss number (Re= uD/ where 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):
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STANDARD: CHAPTER 1 REVISION 2.01, MAY 2009
f =
16 Re
Transitional flow (2000 4.5 >5.0 Flow rate, m3/hr Unset 3 (out) 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. Node Pressure, bar Flow rate, Number G m3/hr 1 Unset Unset 3 Unset 3 (out) 4 5.0 2.4 (out) 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.
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STANDARD: CHAPTER 1 REVISION 2.01, MAY 2009
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 1 3 4 Pressure, bar G Unset 4.5 Unset Flow rate, m3/hr Unset 3 (out) 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.
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STANDARD: CHAPTER 1 REVISION 2.01, MAY 2009
In the properties window, the fittings option is selected and the fittings are added.
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STANDARD: CHAPTER 1 REVISION 2.01, MAY 2009
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, m3/hr 4.00 5.00 6.00 7.00 Pressure, bar G 6.9 6.7 6.4 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.
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STANDARD: CHAPTER 1 REVISION 2.01, MAY 2009
Insert the pump into the network and select the pump curve, as shown in the dialog box below:
PIPENET VISION TRAINING MANUAL PAGE 41 OF 44 Select the pump type
STANDARD: CHAPTER 1 REVISION 2.01, MAY 2009
Remove the specification on Node 1.
Apply a specification of 0 barg to the inlet o the pump.
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STANDARD: CHAPTER 1 REVISION 2.01, MAY 2009
The results are shown below.
.
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STANDARD: CHAPTER 1 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.