A nonintrusive flow-measurement system based on ultrasonics has been developed to replace a system based on turbine flowmeters. A turbine flowmeter must be mounted in line with a pipe; this raises the possibility of leakage at the flowmeter/pipe joints, and the flowmeter unavoidably perturbs the flow. Moreover, a turbine flowmeter is vulnerable to mechanical malfunction and can be vulnerable to corrosion or clogging, depending on the nature of the fluid. In contrast, the ultrasonic flow-measurement system does not contain any rotating or sliding mechanisms that could fail, and does not involve any penetration of the pipe, so that the flow is not perturbed and there is no risk of leakage, clogging, or corrosion.
The nonintrusive ultrasonic flow-measurement system includes two ultrasonic transducers that are clamped on the outside of a pipe, at positions upstream and downstream from each other (see figure). Each transducer serves as both a transmitter and a receiver of ultrasound. The transducers are connected to electronic signal-generating and -processing circuits and a digital data-acquisition and -processing subsystem.
The basic measurement principle is straightforward: ultrasonic signals are transmitted in both directions between the transducers. The intervals between transmission and reception (transit times) are measured for signals propagating both upstream and downstream. When the fluid in the pipe is not flowing, the transit times in both directions are equal. When the fluid is flowing, the upstream transit time exceeds the downstream transit time. The difference between the transit times is proportional to the flow velocity and the volumetric flow rate. Accordingly, the direction and magnitude of flow are determined by use of digital signal-processing techniques and software that utilizes the known proportionality between transit times and flow velocity for the given fluid, physical conditions, and pipe size.
Unlike turbine flowmeters, the ultrasonic transducers can be easily and quickly relocated, and can be used to measure flow rates over a wide range without loss of accuracy at high or low rates. An additional advantage afforded by the ultrasonic system is the ability to detect partial or total loss of fluid from a pipe.
This technique was employed to accurately determine hypergol oxidizer and fuel loading during preflight space-shuttle operations. Benefits of ultrasonics include flexibility, cost-efficiency, reliability, and hazard-free hyperol operation. This technology also proved valuable in the determination of extremely low flow rates through the space-shuttle water-coolant-loop floodlight cold plate used for cooling the crew compartment.
This work was done by Rudy J. Werlink of Kennedy Space Center and Ravi N. Margasahayam formerly of I-NET, Inc. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Mechanics category.
Inquiries concerning rights for the commercial use of this invention should be addressed to
the Technology Programs and Commercialization Office
Kennedy Space Center
Refer to KSC-11926.