Ultrasonic Flow MetersUltrasonic Flow MetersLimitations/DisadvantagesLimitations/Disadvantages

Fluid changes (% solids, bubbles, etc) Fluid changes (% solids, bubbles, etc) affect measurementaffect measurement

Proper installation is criticalProper installation is critical Longer upstream/downstream straight Longer upstream/downstream straight

piping requirementspiping requirements Minimum Reynolds number constraintMinimum Reynolds number constraint 4-wire operation (external power source)4-wire operation (external power source) Low user confidenceLow user confidence Only mixed success in industrial flow Only mixed success in industrial flow

applicationsapplications

Oscillatory FlowmetersOscillatory Flowmeters

Two types:Two types: Vortex SheddingVortex Shedding FluidicFluidic

Vortex Shedding Flowmeter

Fluidic Flowmeter

Vortex SheddingVortex Shedding Vortex shedding is caused by fluid flowing around an objectVortex shedding is caused by fluid flowing around an object Blunt object placed in the flowing streamBlunt object placed in the flowing stream The frequency of the vortices is measuredThe frequency of the vortices is measured The relationship between flow and frequency is: V = k*d*fThe relationship between flow and frequency is: V = k*d*f The frequency is directly proportional to the flow rate.The frequency is directly proportional to the flow rate.

Measuring the VorticesMeasuring the Vortices

Different objects manufactured to Different objects manufactured to produce stable vorticesproduce stable vortices

Vortices are measured by:Vortices are measured by: High frequency pressure transducersHigh frequency pressure transducers Measuring variations in heat transfer Measuring variations in heat transfer

from a heated resistorfrom a heated resistor UltrasonicsUltrasonics

Pros & ConsPros & Cons

ProsPros Good accuracy (+/- Good accuracy (+/-

0.5%) and rangeability 0.5%) and rangeability (40:1)(40:1)

No moving parts, less to No moving parts, less to breakbreak

Moderate costsModerate costs Can handle liquid, gas, Can handle liquid, gas,

and steamand steam Low pressure dropLow pressure drop Not affected by fluid Not affected by fluid

density changesdensity changes

ConsCons Intrusive, obstruct flowIntrusive, obstruct flow If using ultrasonics to If using ultrasonics to

measure the vortices, measure the vortices, straight runs of pipe straight runs of pipe are neededare needed

Re < 20,000 (high) for Re < 20,000 (high) for linear performancelinear performance

Sensitive to increasing Sensitive to increasing Viscosity Viscosity

Expensive in larger Expensive in larger sizessizes