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Orifice and Meter Sizing 

by Aasya Abdennour, Product Support Engineer at Engineered Software, Inc.

PIPE-FLO® Professional version 16.1’s new orifice and meter sizing functionality allows users to quickly determine the appropriate device size needed based on desired requirements. Meter and orifice calculations are performed in PIPE-FLO® in accordance to the following standards: ASME MFC-3M-2004 Measurement of Fluid Flow in Pipes Using Orifice, Nozzle, and Venturi, as well as ASME MFC-14M-2003 Small Bore Precision Orifice Meters 


Application 

Flow meters are used to measure and control the flow rate of a fluid, often in very hazardous processes. Sizing a meter for a particular application and range of flow rates is often time consuming and prone to errors. This becomes a quick and accurate process in version 16.1. Balancing and restricting orifices are sized to obtain a specific flow rate, pressure drop, upstream pressure, or downstream pressure in various applications, particularly when the siphon effect causes cavitation in control valves, pumps, or other areas of a piping system.


Sizing Examples in PIPE-FLO®


Resizing a Restricting Orifice  

The following system is comprised of a Cold Water Tank that supplies flow to multiple end users and for filling a Hot Water Tank. 

Figure 1. A gradient color legend colorizes model by elevation. 

The system is pumping over a high point, illustrated in Figure 1. The change in elevation and insufficient back pressure downstream to the valve attributives to the negative pressure and flashing conditions, typical for a siphon effect.

Figure 2. Due to the elevation differences, the system is experiencing a siphon effect. At the high point, the total and static pressure read to be -14.5 and -14.53 psig respectively, which is below the vapor pressure of water at these conditions (0.2564 psia). This is causing the fluid to change state. 

To mitigate these effects, a 2″ restricting orifice (modeled with Balancing Orifice device in PIPE-FLO®) was installed downstream. It was later discovered that the orifice was poorly sized, as while it successfully prevented the process water from changing state, at -14.29 psig, there still remained a severe vacuum at the high point.

Figure 3. The system after the 2" restricting orifice was installed.  

PIPE-FLO® orifice sizing capabilities can now be used to resize and replace the orifice.

  • The Balancing Orifice Diameter dialog window can be accessed via the Property Grid, or simply be right-clicking the orifice and choosing Change Diameter... from the drop-down selection list.
  • In order to use the sizing feature of the Balancing Orifice or one of the Flow Meters, the device must have an attached inlet pipe with an assigned Fluid ZonePipe Specification, and Pipe Size. The fluid density and inside diameter of the inlet pipe is used in the calculations.
  • If the model is calculated and a diameter was previously entered, the calculated results from the device and inlet pipe are used as the default values for the input fields. 

As the model is calculated and the 2″ diameter was already selected, the calculator will pull in the current values of Inlet Static PressureStatic Pressure Drop, and Flow Rate. These values can all be adjusted in order to determine the appropriate diameter size. 

The current pressure is -14.29 psig at the high point so there should be enough Static Pressure Drop across the orifice to ensure the back pressure will be sufficient in preventing severe vacuum conditions. 15 psi is specified for the Static Pressure Drop. Considering the downstream conditions of the Heat Exchanger and Hot Water Tank, an Inlet Static Pressure should also be specified. No changes are necessary for the Flow Rate

Figure 4. The system with the resized orifice. 

The calculated size of the new orifice is 0.8302 inches, as shown in Figure 4. The total pressure at the high point is now at 0.5014 psig.


Sizing a Flow Meter

With PIPE-FLO®'s flow meter sizing feature, users can size and evaluate flat plate concentric orifice meters, venturi meters, and nozzle meters.

For the following system, a VFD Pump needs to supply water to a VIM furnace's Cooling Jacket. As there are some particles in the cooling water, the VFD pump must also ensure that it supplies a flow rate high enough to the Cooling Jacket, in order that the fluid velocity does not fall below the particle settling velocity of 0.1 ft/s.

A flow meter needs to be sized and installed upstream to the Cooling Jacket for controls purposes and in order to for the VFD Pump to respond appropriately. 

Figure 5. A gradient color legend colorizes model by velocity. 

The flow meter will be modeled with an Orifice Meter device in PIPE-FLO® Professional, the maximum pressure drop across the meter is expected to be 1 psi. 

  • The Orifice Meter Diameter dialog window can be accessed via the Property Grid, or simply be right-clicking the orifice and choosing Change Diameter... from the drop-down selection list.
  • In order to use the sizing feature of the Balancing Orifice or one of the Flow Meters, the device must have an attached inlet pipe with an assigned Fluid ZonePipe Specification, and Pipe Size. The fluid density and inside diameter of the inlet pipe is used in the calculations.
     

The flow meter should be sized by the maximum allowable flow rate through the jacket which is 40 gpm.

By entering the Static Pressure DropInlet Static Pressure, and Flow Rate, PIPE-FLO® is able to determine the required diameter. 

Figure 6. The system with the sized flow meter.

The calculated size of the flow meter is 1.464 inches, as shown in Figure 6.


Summary

Using this sizing feature in PIPE-FLO® allows users to determine the optimum size for their meters and orifices. To help avoid over-sizing or under-sizing, user-defined inputs set sizing variables in accordance to parameters directly drawn from operating scenarios and unique demands of the system at hand. With the easy-to-use orifice and meter sizing functionality, equipment requirements can be efficiently implemented into a PIPE-FLO® model and quickly assessed.

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