TOKYO GAS TOP > Technical development > For the stable production of city gas > Ultrasonic Flow Meter for Ultra-Low Temperature Fluids

Ultrasonic Flow Meter for Ultra-Low Temperature Fluids

Application


Tokyo Gas has developed an ultrasonic flow meter capable of measuring LNG, an ultra-low temperature (-162℃) flammable fluid. As it uses sensors on the pipe surface instead of the orifice normally used to measure the flow of LNG, there is zero pressure loss or leakage. As the price of the flow meter is virtually unaffected by the diameter of piping, moreover, it is widely used to measure flows in large-diameter pipes such as those used for filling LNG tanks.
 
Sensors attached to LNG tank filling pipe


 

How it works


When ultrasonic waves are propagated in a fluid, their speed of propagation changes with the flow of the fluid. As the change depends on the speed of the fluid, flow velocity can be determined by detecting the amount of change. The flow rate is calculated by multiplying the flow velocity by the cross-sectional area of the pipe. This flow meter measures the flow velocity by the propagation time lag method. In figure(Ultrasonic flow meter measuring principle), the propagation times for an ultrasonic wave propagated downstream t1 and upstream t2 are given by the following equations.


where

D:Piping Diameter (m)
V:Velocity of flow (m/s)

C:Acoustic velocity in in a static fluid (m/s)
θ:Angle between the direction of propagation of ultrasonic

wave and direction of flow

 

The difference between t1 and t2 is given by Fluid velocity V can therefore be obtained by measuring the propagation time lag Δt.
 
Ultrasonic flow meter measuring principle


 

Features


The materials and structure used for the sensors can be appropriately modified to allow even flows of ultra-low temperature fluids to be measured. As the sensors only have to be attached by stainless steel bands, they can be easily fitted to existing as well as new pipes.

 

Specifications


Flow meter specifications
Items Specification
Fluid temperature -185℃ to 65℃
Pipe diameter 200A to 1,000A
Accuracy of measurement ±1 to 3%FS
Explosion proof structure Exs IIT4
This product is only sold in Japan

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