- What is a vortex flow meter?
- Vortex vs. Ultrasonic
Vortex flow meter vs ultrasonic flow meter
Vortex and ultrasonic flow meters are both great options for volumetric flow measurement. However, each of these solutions has benefits and limitations for different features and specifications.
In this article, we’ll compare the major distinctions between these two options. If you're looking for the best solution for your application, we have the information you need to make the most informed decision possible.
ifm specializes in vortex flow meters for water-based media along with various ultrasonic meters. This article provides a wider view of flow meters than our selection in order to provide a comprehensive guide.
ifm efector is a key player in the sensor and control technology market. As a subsidiary of the worldwide ifm electronic gmbh, we meet the demands of over 23,000 U.S. customers in varied fields like automotive and food and beverage, with annual sales reaching beyond $260 million. Globally, ifm efector has produced over 800,000 temperature and flow sensors and connectors.
Vortex meter: Overview
Vortex meters use the predictable patterns fluids take when they encounter an obstacle to calculate the rate of the flowing fluid.
Similar to how a rock in a stream will create vortices downstream, the bluff body in meters acts as a vortex generator. The amount of vortex shedding off the bluff body is proportional to the flow rate in the same way that higher velocity of a stream over rocks creates rapids.
A vortex meter measures the intensity of the vortices created in the system. That measurement reveals the velocity of the liquid, gas, or vaporous flow media in a system.
Ultrasonic meter: Overview
There are two types of ultrasonic meters - Doppler and transit time (time-of-flight). Here's how each one works.
Doppler
The Doppler type flow meter utilizes the Doppler effect, which Austrian physicist Christian Doppler discovered in 1842.
If you've ever heard an ambulance as it passed you, you have experienced the Doppler effect firsthand. In this example, the length of the sound waves shorten as the ambulance approaches and lengthen as the ambulance departs. This creates a distortion in the sound of the siren.
Ultrasonic flow meter use this change in sound waves to measure gas flow or the liquid flow. The meter emits an ultrasonic sound wave into the flowing pipe. The soundwaves then bounce off bubbles and particles in the flow and bounce back to the transducer.
The frequency shift in the sound waves is proportional to the flow of the fluid. The flow meter uses this change to measure the flow rate.
Transit Time
The transit time technology uses two transducers, off-set slightly, and on opposite sides of the pipe. The first transducer will emit an ultrasonic signal. That signal crosses the pipe twice, and the second transducer records it.
The sound waves speed up when they are moving with the flow. Then, they slow down when moving against the flow. The time between the bounces are proportional to the flow of the fluid.
This frequency shift is also proportional to the flow rate.
Vortex vs. ultrasonic flow meters: Main comparisons
Here's how to compare these two meters when choosing vortex flow meters vs. ultrasonic meters.
Allowable fluid characteristics
Vortex
These meters are suitable for liquids from clean to dirty, and for clean gases. Large particles can cause a potential for clogging across the meter. This type of meter only works with low viscosity liquids.
Ultrasonic
Transit time ultrasonic flow meters media work best with low-to-medium viscosity fluids. Doppler flow meters are much better for measuring fluids with bubbles or solids in them. However, they’re often not as accurate as transit time (time-of-flight) models.
Pressure Loss
Vortex
This type of flow medium has a medium pressure drop across the meter. Since the meter is placed directly in the flow path, the meter will cause an interruption in the flow.
Ultrasonic
These meters exhibit virtually no loss in pressure across the meter.
Initial setup and maintenance costs
Vortex
These meters are low cost solutions. However, they will need to be installed into the pipe. This could result in a temporary shut down when installed in an active system. Once installed, maintenance is low due to there being no moving parts.
Ultrasonic
This meter type is an expensive initial cost, but can have a lower setup cost than some other options. With no moving parts, maintenance is low and durability is high. Since most ultrasonic meters are inline, but some models clamp on to the outside of the pipe. Those models don’t require a system shutdown for installation.
Pipe Diameter Range and Straight Pipe Length
Most flow meters require a length of straight pipe before the meter to ensure accurate flow readings across the sensors.
Vortex
This type of meter has a pipe diameter range of 0.6” to 12” (0.015m to 0.3m.) The straight pipe length prior to the meter should be 15 to 25 times the diameter of the pipe.
Ultrasonic
This type of sensor has a much wider range of suitable pipe sizes. It can be suitable for pipes that are 0.” to 157.5” (0.025” to 4m) in diameter. The straight pipe length prior to the meter should be 5 to 20 times the diameter of the pipe.
Choosing the right flow meter for your needs
Vortex meters are ideal for water based systems such as cooling circuits. Since they don’t require conductivity of the fluid, these are a great option for deionized water systems. They are low cost, durable meters.
However, they produce medium pressure loss in the system and cannot handle high viscosity or low flow rates (see other vortex meter troubleshooting items).
Ultrasonic meters are great options for clean fluid or fluid with bubbles or particles in it, with low to medium viscosity. They are ideal for systems that require no pressure loss. Though initial cost can be high, setup and maintenance costs are low. Portable options are available to test flow at multiple locations.
Other types of flow meters
If a low cost meter that provides little pressure loss is required, an orifice flow meter would be a good option. This meter works by using the principles of differential pressure caused by constricting the pipe. However, this meter also has its limitations when it comes to viscous fluids.
Neither vortex, ultrasonic, nor orifice meters are suitable for very viscous fluids. An option for highly viscous fluids would be a positive displacement flow meter. This meter is a mechanical meter, which also has the advantage of not requiring an external power source. Some other mechanical flow meters are variable area flow meters and turbine flow meters.
Ultrasonic and coriolis meters are a great option for measuring reverse flow. Due to the unidirectional bluff body and location of the sensors in a standard vortex flow meter, bidirectional measurements aren’t ideal. Two vortex flow meters would need to be used to make this possible.