ACCURA-FLOW: Engineering for In-line Flow Monitoring

posted in: Flow Measurement Equipment | 0
By Kelly Hile and Craig Rood

Like all of the equipment we offer, the ACCURA-FLOW system means more than excellent instrumentation. It also means you have the support of industry-leading flow scientists and engineers.

The ACCURA-FLOW Averaging Pitot Tube is a real-time, pressure-based measurement system that measures gas flow rate in stacks or ducts. The ACCURA-FLOW combines state-of-the-art engineering with proven, reliable measurement techniques to offer superior flow monitoring.

ACCURA-FLOW Averaging Pitot Tube

The ACCURA-FLOW Averaging Pitot Tube

The probes rely on Bernoulli’s equation, which provides a way to convert a difference in pressure to fluid velocity. The pressure differential is measured between forward and rear-facing openings on the probe, which are averaged across the duct. This same methodology is the basis of the industry test protocol ASTM D3154, which details the flow measurement requirements for a stack, duct, or flue. Each probe is calibrated in our large in-house wind tunnel to ensure the highest level of accuracy.

The averaging pitot is an improvement over using standard L-shaped or S-type pitot tubes for in-line flow measurement. Instead of measuring flow velocity at one location in the flow stream, the averaging pitot measures flow across the entire duct profile. Velocity tends to be higher in the center of the duct and slower toward the walls. By averaging, the ACCURA-FLOW system establishes flow rate regardless of the shape of the velocity profile.

Instrumentation + Flow Analysis = Flow Rate Accuracy

Averaging pitot tubes offer incredible accuracy in determining real-time flow, as long as the flow is axial and not highly skewed. Knowing the flow patterns throughout the system is essential for reliable measurement results. That’s why we don’t just supply pitot tubes, but also supply the engineering work to ensure satisfactory flow conditions. For each project, our up-front analysis includes computational fluid dynamics (CFD). CFD modeling of the system allows insight into the flow field at any potential measurement locations. We look at the whole system and find places where the flow uniformity is suitable for maximum pitot tube accuracy. If the duct system is complex and flow patterns highly non-uniform, we implement design solutions to improve the flow.

flow comparison in overfire air duct

In this overfire air duct, the flow field was not straight enough for in-line flow monitoring (left). The existing plant set-up had no location with flow conditions that were suitable for probe installation. In this case, it was necessary to install flow control devices to properly align the flow (right). These devices, a combination of guide vanes and straightening baffles, were designed via CFD.

Flow monitoring that does not include this type of engineering analysis is easy to find, but is greatly inferior in quality of results. Inaccuracies can occur anytime the flow conditions at the point of measurement are angular or swirling. When this happens, the flow rate may be over- or under-estimated and cause flow imbalances, overworked fans, or inefficiencies in downstream processes. In a process like power plant combustion, inaccuracies in primary air flow rates can impact combustion ratios and cause sub-optimal boiler performance. In HVAC applications, measurement inaccuracies can affect system capacity and flow balance, resulting in performance degradation and inefficiency. All of these issues can be avoided with up-front engineering.

Flow instrumentation should be a perfect fit to your process.

At Airflow Sciences, we are masters of custom equipment, and nothing we build is a one-size-fits-all solution. Our products are specifically tailored to the process and facility. The averaging pitot tubes we supply as part of the ACCURA-FLOW system can be customized to any length, cross section, or application, ensuring that each probe is properly designed for the operation. If desired, we can configure the probes to connect into other real-time reporting systems that are already in place.

The ACCURA-FLOW has a wide range of applications. It can be used to monitor primary and secondary air flows for combustion processes, air flow in HVAC ducts, fan flow rate, and wind tunnel flow. Contact us today to find out more about how ACCURA-FLOW can be applied to your operation wherever you need real-time, reliable flow data.