How To Draw Pump Performance Curve In Excel

Introduction

This article will demonstrate how you lot tin can balance a pump curve against a system curve to calculate liquid velocity with Excel.

First, nosotros'll develop the equations that make up one's mind the liquid velocity in a uncomplicated pump and pipe system.  Then we'll discuss how these equations exist solved using Excel's Goal Seek feature. Finally, we'll show Visual Basic code that can be used to automate Goal Seek and then that any parameter change volition automatically calculate the new liquid velocity.

The spreadsheet can be downloaded here, but read the rest of this article if you'd like to understand the theory.

Pump and Pipe System

Consider a centrifugal pump receiving liquid from a reservoir and forcing liquid through a pipage to a reservoir.

First consider the pump.  Its flowrate-head curve is can be described past a polynomial derived from empirical data, where a, b and c are best-fit coefficients, and Q is the volumetric flowrate

Equation 1

But the volumetric flowrate is

Equation ii

where A is the cross-exclusive surface area of the pipe and V is the liquid velocity through the piping.  Substituting Equation 2 into Equation ane to eliminate Q gives

Equation 3

This equation at present describes the caput produced by the pump as a function of the liquid velocity through the pipe.

Now consider the pipe.  Frictional head loss through the piping can be described by the Bernoulli equation and written as

Equation 4

We'll call Equation iv the Arrangement Curve. f is the friction factor, given by the Haaland Equation.

Equation 5

 where Re is the Reynolds Number.

Equation 6

The Haaland equation is only valid in turbulent flow, i.east. if the Reynolds Number is over 2500.

For our pump and pipe organization, the pump head is equal to the caput loss in the pipe.  Hence

Equation 7

We can now use Excel to detect the liquid velocity that satisfies Equation 7 (finer determining the intersection between the pump curve and the system curve).

Excel Implementation

The Excel spreadsheet uses this cell coloring convention.

Stride ane.  First define the parameters and summate the cantankerous-exclusive surface area of the piping.

Step 2. Now ascertain the coefficients of the pump curve

Pace 3. Set up the calculations required by Goal Seek

Step 4. Go to Data > What-If Assay > Goal Seek.  Brand the changes such that nosotros find the liquid velocity that makes difference betwixt pump bend and the system curve equal to aught.

You should now take the correct value of the liquid velocity.

Ensure that the Reynolds number is greater than 2500 so that our supposition of turbulent catamenia (and hence the use of the Haaland equation) is verified.

Visual Basic Macro to Automate Goal Seek

If you're really not bad, you lot can use Visual Bones to automate Goal Seek.

Individual Sub Worksheet_Change(ByVal Target As Range)

Dim bSuccess As Boolean
    On Error Resume Next
    bSuccess = Range("C23").GoalSeek(0, Range("c18"))
    On Error GoTo 0
    If Not bSuccess And so
        MsgBox "Goal Seek Failed"
    Finish If
End Sub

Whenever any value in the worksheet is inverse, the Worksheet_Change() effect is initiated .  The VB lawmaking then asks GoalSeek() to observe the liquid velocity ("C18") that makes the difference betwixt the pump and system curve ("C23") equal to zero.

Source: http://excelcalculations.blogspot.com/2011/05/balancing-pump-curve-against-system.html

Posted by: lynnfouty1959.blogspot.com

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