Flow meters play a crucial role in many industries and many processes. They form the basis for custody transfer in chemical plants and flow measurement in research laboratories. They also control the critical mixing of quantities in the pharmaceutical industry.

Figure 1: Flow meter being used in a research laboratory. Source: Bronkhorst USAFigure 1: Flow meter being used in a research laboratory. Source: Bronkhorst USA

Many flow meters with different technologies exist today, and statistics show that the projected flow sensor global market will be worth $8.49 billion by the end of 2020. The suitability of a flow meter technology for a particular application depends on several factors, such as accuracy, cost, flow rate range, head loss, operating requirements and maintenance. Flow meters operating based on the Coriolis principle are considered to be the most reliable flow devices in use today.

These flow meters are the preferred choice in industries and research laboratories where accuracy and fast processing are critical. The Bronkhorst mini CORI-FLOW Coriolis mass flow meter was particularly useful in a recent Oak Ridge National Laboratory (ORNL) project.

The ORNL Foam Fracturing Project

For many years, water has been used for hydraulic fracturing in the development of enhanced geothermal systems (EGS). It is a process that typically involves the injection of water under high pressure into a hot rock formation via a well, thus creating the fracture network required for the extraction of geothermal energy. Although this process produces clean and renewable energy, its water concerns and high cost make it unreliable.

The ORNL project, sponsored by the U.S. Department of Energy (DOE), focused on tackling these challenges. As part of a waterless stimulation initiative, the research scientists studied the suitability, stability and effectiveness of foam fluids for hydraulic fracturing.

Their experimental setup was comprised of a test line configured with three sections: liquid, gas and foam. The foam section contained foam fluids, which are a mixture of liquid and gaseous phases. Because of the complexity of the setup, there were some challenges associated with flow measurement.

The research scientists needed a flow meter technology suitable for extremely low flow rates at high pressure. They also needed a technology that handles two-phase flows and provides accurate measurements of mass flow rate and density of the mixture. Bronkhorst’s mini CORI-FLOW mass flow meter was selected for this project, and it played a crucial role in obtaining desirable results.

Mass flow measurement of an immiscible mixture of liquid and gaseous phases

A common limitation of most flow meters is the inability to handle two-phase flows. This limitation is not surprising as the fluid dynamic characteristics of these mixtures are extremely complex. Although the regular Coriolis flow meter easily outperforms many other flow meter technologies in this regard, their performance is still not good enough; not by Bronkhorst's standards and not by most research standards.

The mini CORI-FLOW mass flow meters by Bronkhorst are precise and compact mass flow meters. Although designed to address the challenges associated with the measurement of low flow rates, this flow device has also been successful in handling two-phase fluids. The M14-AAD-22-OH model allowed the research scientists to accurately measure mass flow rates of nitrogen-based foam. Unlike other flow meter technologies, the Bronkhorst compact flow device directly measures mass flow, eliminating the need for density, pressure or temperature corrections to compute mass flow.

Coriolis flow meters are only ever applied to medium to high flow rates, and rarely for low flow applications. The mini CORI-FLOW series by Bronkhorst was designed to cover the need for low flow markets. The M14-AAD-22-0H model accurately measured volume flow rates within the range of 10 to 30 ml/min in the ORNL project.

Measurement of foam quality

Density is an important fluid property, and it is either obtained directly or by inference from temperature and pressure measurements. The Coriolis flow meter is one of the few flow meter technologies that can be used as densitometers. This unique attribute makes it possible to monitor other parameters, such as foam quality.

In the ORNL project, foam quality describes the volumetric fraction of nitrogen gas in the two-phase mixture. The research scientists emphasized the importance of the foam quality for achieving desirable results. Therefore, they needed the measurement of fluid density to be accurate.

The Bronkhorst M14-AAD-22-O-H flow device allowed them to measure fluid density and subsequently monitor the foam quality. They were able to carefully control flow into a specimen once the target density of 300 kg/m3 and foam quality of 70% was reached.

Fast processing of data

Research projects featuring low flow rates are delicate. The slightest disturbance in process or change in fluid properties may produce staggering deviation from desired results. Hence, there is always a need for fast and accurate data acquisition. Flow meters operating based on the Coriolis principle are among the fastest flow meter technologies today. The ORNL research scientists benefited from using Bronkhorst’s compact flow device for the foam fracturing project.

Bronkhorst’s M14-AAD-22-O-H flow device features a highly stable control output with a fast response within 50 to 200 milliseconds. In addition, Bronkhorst FlowPlot was used for data acquisition, and it allowed ORNL scientists to quickly get sufficient data in a digital format. Not only were they able to quickly monitor the fluid flow rate, but the device also allowed them to monitor fluid density and temperature simultaneously.

The M14-AAD-22-O-H flow device belongs to the mini CORI-FLOW series by Bronkhorst. They are precise, compact and designed to cover the needs of the low flow market, common in research laboratories. These compact devices accurately provide data on flow rate, density and temperature regardless of the fluid mixture, phase, operating conditions or changes in fluid properties.

Figure 2: Bronkhorst mini CORI-FLOW mass flow meter. Source: Bronkhorst USAFigure 2: Bronkhorst mini CORI-FLOW mass flow meter. Source: Bronkhorst USA

Coriolis mass flow meters are better than many other flow meter technologies, but none matches the standards set by Bronkhorst’s flow devices. Contact Bronkhorst USA today to access the best flow measurement and control solutions.