Clamp-on gas flowmeter

#1. Technical Field

#This invention is directed to a method and device for measuring flow rate of gas; in particular, a device and method for measuring gas flow in a pipe using a non-intrusive clamp-on flowmeter.

#2. Description of Related Art

#FIG. 1 shows a conventional transmit and receive transducer installed in a pipe;

#FIG. 2 shows the blowing effect on a narrow beam in the path of gas flow;

#FIG. 3 illustrates the differences in refraction angles for gas and liquids;

#According to a preferred embodiment of the invention, an energy absorbent material is placed in intimate contact with either the inside or outside wall of the pipe, or both, to absorb this energy. Since even a small gap between this material and the pipe wall itself will serve to preclude energy transfer, a true “molecular” bond between this material and the pipe wall is preferred. The material has high sonic impedance to accept this energy transfer efficiently. In addition, it is capable of converting the absorbed “coherent” sonic energy into “non-coherent” mechanical energy, or heat.

#FIG. 5 shows a clamp-on gas spool for use as a gas flowmeter according to a preferred embodiment of the present invention. The spool includes flanges 500, reducer 510 with precision machined pipe wall 520, on which is mounted transmit and receive transducers 560 and 570. According to this embodiment, liner 550 is bonded to the inside of the pipe wall 520. Materials suitable for the liner 550 should be viscous and have the ability to bond intimately to the pipe wall. Preferably, plastics including Tefzel, Polypropylene, and certain grades of Polyethylene is used. An intimate bonding is accomplished by melting the plastic onto the surface of the pipe, and by controlling the temperature decline slowly, while moving the assembly to assure a reasonably uniform thickness when cooled.

#Advantageously, it is found that the sonic impedance of the plastics lies between the high impedance of a metal pipe wall and the much lower impedance of gas. Therefore, the plastic can not only be used to dissipate the pipe wall transmit sonic energy, but also serves to improve the “impedance match” by being placed between the pipe wall and the gas, resulting in a greater amount of the available transmit sonic energy entering the gas itself, thereby substantially improving the signal to noise ratio.