Coriolis Flow Meters
Coriolis Flow Meter, is a device that measures how much liquid is flowing through a tube. It does not measure the volume of the liquid passing through the tube, it measures the amount of mass flowing through the device. Volumetric flow rate metering is proportional to mass flow rate only when the density of the fluid is constant. If the fluid has varying density, or contains bubbles, then the volume flow rate multiplied by the density is not an accurate measure of the mass flow rate. In a coriolis flow meter the fluid is contained in a smooth tube, with no moving parts that would need to be cleaned and maintained, and that would impede the flow.
Using the coriolis effect that causes a laterally vibrating tube to distort, a direct measurement of mass flow can be obtained in a coriolis flow meter. Furthermore a direct measure of the density of the fluid is obtained. Coriolis measurement can be very accurate irrespective of the type of gas or liquid that is measured; the same measurement tube can be used for hydrogen gas and bitumen without recalibration.Coriolis flow meters can be used for the measurement of natural gas flow.
Coriolis flow meters are relatively new compared to other flowmeters. They were not seen in industrial applications until 1980's. Coriolis meters are available in a number of different designs. A popular configuration consists of one or two U-shaped, horseshoe-shaped, or tennis-racket-shaped flow tube with inlet on one side and outlet on the other enclosed in a sensor housing connected to an electronics unit.
The flow is guided into the U-shaped tube. When an osillating excitation force is applied to the tube causing it to vibrate, the fluid flowing through the tube will induce a rotation or twist to the tube because of the coriolis acceleration acting in opposite directions on either side of the applied force. For example, when the tube is moving upward during the first half of a cycle, the fluid flowing into the meter resists being forced up by pushing down on the tube. On the opposite side, the liquid flowing out of the meter resists having its vertical motion decreased by pushing up on the tube. This action causes the tube to twist. When the tube is moving downward during the second half of the vibration cycle, it twists in the opposite direction. This twist results in a phase difference (time lag) between the inlet side and the outlet side and this phase difference is directly affected by the mass passing through the tube.
A more rescent single straight tube design is available to measure some dirty and/or abrasive liquids that may clog the older U-shaped design. An advantage of coriolis flow meter is that it measures the mass flow rate directly which eliminates the need to compensate for changing temperature, viscosity, and pressure conditions.