Vortex flow meters for accuracy in steam measurement

The problem

The heat is on. Many plant managers are in the hot seat to account for the energy going in and out of their facilities – no easy task. And this mandate includes steam flow.

Vortex flow meters remain the industry standard to measure steam flow accurately. However, which vortex meter should you use, mass or volumetric? Which offers the most accuracy and improves productivity best?

image ofVortex flow meters for accuracy
Courtesy of Sierra

Most steam meters measure volumetric flow. So many plant managers believe that they don’t need compensation because the pressure only varies by 10 percent. They use volumetric vortex meters with a constant density programmed for finding mass flow.

But physics tells us that when temperature and pressure change in the line, mass flow also changes. Let’s see why.

The math

Volumetric meters use density to find the mass flow, and density equals mass per unit volume. Therefore, mass equals density times volume. If the density changes, then the mass flow must change. And temperature and pressure can affect density. So if those change, then the mass flow changes, sometimes by a lot. Check out some typical values for saturated steam density:

    • 125 psig steam typically 0.3 lbm/ft3
    • 15 psig steam typically 0.07 lbm/ft3
    • 225 psig steam typically 0.52 lbm/ft3

You can see the importance of knowing the temperature and pressure of your steam. You can get notable errors in your data, which will cost you money. So for a good rule of thumb, remember that a 10 percent change in pressure equals a 10 percent error in the mass flow! And that means you lose 10 percent of your productivity and dollars in wasted energy.

The solution

For the best accuracy, you need a multi-variable device, one that measures  volumetric flow plus temperature and pressure. It should also maintain system accuracy with a single unit instead of multiple components.

Sierra’s new InnovaMass iSeries meter comes in both configurations, a low-cost volumetric flow meter and a multi-variable mass flow meter. You get an accuracy of one percent of reading and 30:1 turndown plus pressure and temperature compensation. This multi-meter provides accurate density calculations. And these calculations make your steam measurement accurate, which improves your productivity. So learn more about Sierra and our new InnovaMass meter here.

Original content is here.

Author: Scott Rouse, Product Line Director @ Sierra Instruments

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