Fathom_Examples_Fat_002.pdf

Sizing a Pum

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Sizin g a Pump (SI Units) Sizing Sizi ng a Pump (English Units)

Summary  This exam example ple will will walk walk you you throu hrough gh a simp simple calcul calculat ation ion to size a pum pump. A pump is to be used to transfer water from a supply reservoir to a holding reservoir at the top of a hill. The system consists of a supply reservoir, a pump, a discharge reservoir, and two pipes.  The first pipe pipe fro from m the supp supply ly reser reservoi voirr to the pum pump is is 3 meter eters s long long,, and and the the secon second d pip pipe e lead leading ing from from the the pum pump to the the disc dischar harge ge reser reservo voir ir is 300 300 mete meters rs long. long. Both pip pipes es are are 4 inch inch (10.2 cm ID), Steel, Schedule 40 pipes. Constant fluid properties are assumed.  The suppl supply y reser reservo voir ir has has a sur surfa face ce pre pressu ssure re of 1 atm atm, and and the liq liquid uid surface face is at at an elevat elevation of 3 meter eters. s. The The disc discha harg rge e rese reserv rvoir oir has a surface rface pressure ssure of of 1 atm atm, and and the the liq liqui uid d surface is at an elevation of 60 meters. The pipes for both reservoirs connect to the reservoirs at a depth of 3 meters. What is the head requirement for a pump to supply flow in this system at 115 m3/hr?

Topics Covered ·

How to specify a pump in the P ump Specifications Spe cifications Window

·

Fittings and losses loss es lumped into a pipe

·

Sizing a pump

·

Entering pump curve data

Required Knowledge  This exam example ple assum assumes the user user has has alread already y work worked ed thro throug ugh h the theBeginner: Three-Reservoir Model example, or has a level of knowledge consistent with that topic.

Model File Sizing a Pump.fth

Step 1. Start AFT Fathom From the Start Menu choose choose AF T P roducts roducts and AFT Fathom. Fathom.  To ensu ensure re that that your your resul results ts are the same as as tho those se pre presen sente ted d in in this docu docum mentation ation,, thi this s exam exampl ple e should ould be be run run using using all defa defaul ultt AFT Fatho Fathom m setting tings, s, unless nless you are specif specifica ically lly instructed to do otherwise.

Step 2. Specify output Open the output control window by selecting Output Control in the Analysis menu. The window starts with a default set of outputs. Often the default output is sufficient. You may also specify the units for each output parameter. You may also s pecify a title for the model. Click on the "G eneral Output" tab and add a title of "Sizing a Pump".

Step 3. Specify System Properties 1.

Open the the System System Propertie Properties s window window by selecting System Properti Properties es in the the Analy Analysis sis menu menu

2.

On the Fluid Data Data Tab, select the AFT S tandard database database and then select select "wate "water at 1 atm" in the fluids available available window window

3.

Click "Add "Add to to Mode Model" l" to sele select ct wate waterr for for use use in in this this model odel

4.

Type Type in 21 degr degrees ees C in the the fluid tem temperatur ature e box box

5.

Click Click "Calcu Calcula latte Prope Propert rties" ies"

 This calcul calculat ates es the the flui fluid d pro proper perties ties to use in the the model. odel. For this model, odel, we will will not not model odel heat transf transfer er so "Const "Constant ant Fluid Fluid Proper Properties" ties" should should be select selected. ed. In order order to model odel heat heat transfe ransfer, r, one of the Heat Transfer options must be selected.

Step 4. Specify Cost Settings  The four fourth th Checkl Checklist ist item item,, Cost Cost Setti Setting ngs, s, is alwa always check checked ed when when you you start start AFT Fathom Fathom. When When used used with the the standa andard rd version sion of of AFT AFT Fathom Fathom, the the Cost Settings ings window indow provi provide des sa way to include energy costs. When used with the CST module it has additional features. By default the cost calculation is turned off, and hence nothing further is required for this Checklist item.

Step 5. Build the model At this point, the first four items items are completed on the analysis checklist. c hecklist. The only o nly remaining checklist item is to "Define "Define Pipes P ipes and J unctions". In the workspace window, use the toolbar icons to drag and drop two reservoirs and a pump onto the workspace window. Now connect these with the pipe drawing tool. The default flow direction will be from the first object you select to the second object. An arrow indicates the default flow direction. Now the workspace should look like this:

Figure 1:

Workspac e for Sizing a Pump Example

Sizing a Pum

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 The system is in place but now we need to enter the specifications of the objects. Double-click each junction and enter the following specifications in the Junction Specifications window. The required information is highlighted in blue. 1.

J 1 Reservoir a.

Name = Reservoir

b.

Elevation =3 meters

c.

Surface pressure =1 atm.

d. 2.

Pipe depth =3 meters (entered on the "Pipe Depth & Loss Coefficients" tab) J 2 Reservoir

a.

Name = Reservoir

b.

Elevation =60 meters

c.

Surface pressure =1 atm

d. 3.

Pipe depth =3 meters (entered on the "Pipe Depth & Loss Coefficients" tab) J 3 Pump

a.

Type =Assigned Volumetric Flow (for sizing)

b.

Flow rate =115 m3/hr

c.

Elevation =0 meters

 The pipe specifications are as follows: 1.

P1 a.

Material = Steel

b.

Size =4 inch (10.2 cmID)

c.

Type =STD (schedule 40)

d.

Friction model =Standard

e. 2.

L ength = 3 meters P2

a.

Material = Steel

b.

Size =4 inch (10.2 cmID)

c.

Type =STD (schedule 40)

d.

Friction Model =Standard

e.

Length =300 meters

 The pipe model also allows for fittings and losses like valves or elbows. Select the Fittings & Losses tab for P2, and type in 25 for the Total K Factor. Now close the pipe specification window to accept your changes.

Step 6. Run the model. Select Run Model in the Analysis menu. This will open the Solution Progres s window. This window allows you to watch as the Fathom Solver converges on the answer. This model runs very quickly. Now view the results by pressing View Output at the bottom of the solution control window.

Step 7. Examine output  The Output window contains all the data that was specified in the output control window. Because we were interested in the pump requirements for this system, select the Pump Summary tab in the General (top) window. The pump data can also be found in the J unction (bottom) window. We are primarily interested in the pump head (or pressure) requirement.  This information can be found in the Pump Summary window. For this system, the head requirement of the pump is 116.3 meters. Because the difference in elevation of the reservoirs was 57 meters this is the minimum head rise regardless of flow rate or pipe size. Coincidentally the friction loss was also approximately 57 meters. This can be seen in the dH column of the Pipe output window.

Figure 2:

Output window for Pump Sizing Example

Step 8. Add a pump cu rve Now that the pump head requirement has been identified as 116.3 meters at the design flow rate of 115 m3/hr, a pump of the correct size can be purchased to meet this requirement. Once the actual pump has been identified, the pump characteristics can be added to the pump component by adding the pump curve data to the pump junction. Open the Pump Specifications window. Change the Pump Model from Volumetric Flow Rate Fixed to Pump Curve. Then select the Enter Curve Data button. This will open the Pump Configuration window. Data for the pump curve is entered in the R aw Data table. After the data has been entered, a curve fit for the data must be created by selecting the Generate Curve Fit Now button. Enter the following pump curve data, as shown in Figure 2.3. 1.

Flow Parameter: Volumetric (m3/hr)

Sizing a Pum

2.

Pressure/Head Parameter: Head (meters)

3.

P ump C urve Data: a.

122 meters @ 0 m3/hr

b.

116 meters @ 115 m3/hr

c. 4.

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76 meters @ 230 m3/hr C urve F it Order: 2

After the curve data is entered, click the Generate Curve Fit Now button and then the OK button. Note: This is a situation where a user could create a new scenario using the Scenario Manager to examine a "what-if" situation, without disturbing the basic model. For an example that illustrates how to use the Scenario Manager, see the Water to Housing Project example.

Figure 3:

The Pump Configuration Window is used to enter pump curve data

Step 9. Re-evaluate the mo del Re-run this model. Examine the Pump Summary in the General O utput Section. The output (Fi gure 2.4) shows the pump operating at a flow rate of 114.7 m3/hr, and a head rise of  116.1 meters., which is acceptably close to the previous sizing calculation.

Figure 4:

Output when running with a pump curve.

Change to the Graph Results window (e.g., using the Windows menu), and choose Select Graph Data (Figure 2.5). Here you can specify that a pump vs. system curve be created as shown in Figure 2.6.

Sizing a Pum

Figure 5:

Select Graph Data for creating a pump vs. syst em curve.

Figure 6:

Pump vs. system curve using selected pump.

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Conclusion AFT F athom can be used to size pumps. Once the actual pump has been selected, the model can be modified to include the ac tual pump curve data. Then the actual s ystem properties and behavior can be calculated.