The Dirty Air Probe is a reverse-impact probe used for measuring the air or gas flow rate in pneumatic conveying systems. These piping systems transport cement, pulverized coal, lime, or food products in pressurized air.
How does a Dirty Air Probe work?
Similar to an S-type probe, a Dirty Air Probe has two pressure measurement holes in the probe head, and the pressure difference between these holes is used to determine the velocity at that point in the flow stream.
The velocity (v) is calculated by solving the Bernoulli equation, where Cp is a calibration coefficient specific to the probe head geometry. The pressure Δp is the difference between the P1 and P2 pressure measurements and ρ represents the density of the duct air.
What makes a Dirty Air Probe unique is the placement of the holes on the inner sides of the tubes, making this probe very resistant to plugging and enabling it to be used in dense particle flows.
By performing multiple velocity measurements throughout the cross-section of the duct or pipe, the Dirty Air Probe can be used to establish the flow rate and average gas velocity in the duct. These traverse measurements are often combined with isokinetic sampling methods to gain an understanding of the mass flow rate of the particulate matter in the flow stream.
The ASE Dirty Air Probe collects data at multiple traverse points in a duct or pipe.
In isokinetic sampling, a velocity traverse is completed, to determine the velocity of the flow stream. While matching the flow stream velocity appropriately, a sample of the flow stream particulate is collected over a precisely measured time period and weighed to determine its total mass. The mass flow rate of particulate can then be calculated from this measurement.
What is the measurement range?
The ASE Dirty Air Probe can measure air velocities in the range of 17-160 ft/s (5-50 m/s) and is equipped also with a K-type thermocouple for temperature measurements in the range of 50-225 F (10-110 C).
What advantages and disadvantages should I consider?
The Dirty Air Probe is a highly accurate and compact probe for velocity measurement, with the distinct advantage of accurate flow measurement in particulate-laden flows. Even though the Dirty Air Probe is designed with particulate-laden flows in mind, the probe can also be used just as effectively to measure clean air streams or other gaseous flows, with similar performance to an S-type probe.
The Dirty Air Probe is most accurate when used in situations where the flow field is axial. This means it’s important to select a test port in a straight section of duct, away from elbows or other flow disturbances. The presence of swirling flow might affect the accuracy of the measurement. If you need flow measurements in a swirling, or complex flow stream with some particulate matter, a 3D prism probe might be more suitable. Our 3D probes can be paired with onboard purging to prevent pluggage.
How can I customize this probe?
ASE has been refining our Dirty Air Probe with technical improvements though over 30 years of coal pipe and particulate testing. Our system has top grade features to make testing operator-friendly, emphasizing safety and usability.
Every Dirty Air Probe has a built-in level and handle for accurate probe alignment and includes rugged tubing with protective nylon sleeves. We also provide a spreadsheet template that greatly simplifies the data analysis process and meets the requirements of ASME PTC4.2 and ISO 9931. A standard Dustless Connector is also included.
For a more efficient testing experience, you can choose to add the Mobile Seal Air Fitting to the base probe. This upgrade improves the accuracy, speed, and safety of a test. When testing in flow conditions with high positive static pressure, the seal air fitting keeps the air and particulate from leaking out of the pipe when the test port is opened. The Mobile Seal Air Fitting blows compressed air into the port, ensuring safe access and a much cleaner test. This feature also includes an integrated traverse rod that is color-coded with the insertion depths needed for proper traverse measurements (see image above). The traverse rod eliminates the need to manually mark the probe.
An additional upgrade from the standard Dustless Connector and Mobile Seal Air Fitting is the Fast-Lock system. In addition to providing seal air and a Traverse Rod, the Fast-Lock system speeds the testing process by allowing a quick connection to the Dustless Connector. A short turn of the Fast-Lock handles automatically connects and aligns the probe.
What data acquisition system should I use with this probe?
The Dirty Air Probe comes standard with a handheld meter that reads out pressure and temperature measurements. As an upgrade in both accuracy and usability for the Dirty Air Probe system, the standard meter can be replaced with an advanced meter that is programmable, logs data, takes time averages, and communicates with laptops via Bluetooth.
For the ultimate testing experience in coal optimization, we recommend using a Dirty Air Probe with our ACFM system. The Advanced Coal Flow Measurement system acts as an on-board data acquisition system but also facilitates mass sampling for determining mass flow easily. The complete test system contains everything you need for measuring and balancing pneumatic particulate flow.
Our flow testing experts look forward to hearing more about your technical needs and custom-building the best system for your budget. Contact us for a customized quote today!