A Comparison of Coriolis Flowmeters and Thermal Dispersion Flowmeters

The two leading methods for measuring mass flow rate of fluids in industrial control are the Coriolis flowmeter and the thermal dispersion flowmeter.

Thermal Dispersion (left) vs. Coriolis (right) Flow Technology
(click for larger view)

CORIOLIS FLOWMETER   

A Coriolis mass flowmeter measures mass flow rate of the fluid with a U-shaped tube that deflects or vibrates as the fluid flows through it. The operation of this type of mass flow meter is based on the conservation of angular momentum as it applies to the Coriolis acceleration of a fluid. Fluid flows through the oscillating tubes, twisting them slightly in proportion to the mass flow of the fluid and its inertia. Sensors are fixed at the inlet and outlet junctures of the tube, at equal distances from the central fixed point. When there is no fluid flowing through the tube, the amplitude is constant and the sensors at either end are in phase with one another.

Coriolis flowmeter (Tektrol)

While Coriolis flowmeters may be used for mass flow measurement in liquids as well as gases, they are prominently used for liquids as a high-density fluid is required to maintain the momentum of oscillation.

THERMAL DISPERSION FLOWMETER

Thermal flowmeter
(Tektrol)

Thermal Dispersion technology uses the principle of measuring the differential temperature between two temperature sensors and calculating mass flow based upon the cooling effect. Mass flow is based on the rate of heat dissipation per unit time. There are two types of thermal dispersion technology - Constant Temperature Differential Method and the Constant Current Method.

The Constant Current Method maintains a constant differential temperature and the current required to maintain the differential is used as the basis for determining the flow. The greater the mass flow rate, the greater is the cooling effect and the more current needed to maintain the same differential temperate.

The Constant Temperature Differential Method measures the differential temperature between sensors. A temperature difference between the two sensors is an indication of the mass flow rate of the fluid. The greater the mass flow rate, the smaller the temperature difference.

For any questions about measuring process flow, contact Hile Controls of Alabama by visiting https://hilealabama.com or by calling 800-536-0269.

Understanding How Flow is Measured by Differential Pressure

The differential flow meter is the most common device for measuring fluid flow through pipes. Flow rates and pressure differential of fluids, such as gases vapors and liquids, are explored using the orifice plate flow meter in the video below.

The differential flow meter, whether Venturi tube, flow nozzle, or orifice plate style, is an in line instrument that is installed between two pipe flanges.

The orifice plate flow meter is comprised the circular metal disc with a specific hole diameter that reduces the fluid flow in the pipe. Pressure taps are added on each side at the orifice plate to measure the pressure differential.

According to the Laws of Conservation of Energy, the fluid entering the pipe must equal the mass leaving the pipe during the same period of time. The velocity of the fluid leaving the orifice is greater than the velocity of the fluid entering the orifice. Applying Bernoulli's Principle, the increased fluid velocity results in a decrease in pressure.

As the fluid flow rate increases through the pipe, back pressure on the incoming side increases due to the restriction of flow created by the orifice plate.

The pressure of the fluid at the downstream side at the orifice plate is less than the incoming side due to the accelerated flow.

With a known differential pressure and velocity of the fluid, the volume metric flow rate can be determined. The flow rate “Q”, of a fluid through an orifice plate increases in proportion to the square root the pressure difference on each side multiplied by the K factor. For example if the differential pressure increases by 14 PSI with the K factor of one, the flow rate is increased by 3.74.

New Product Alert: ES-FLOW™ - The World's Smallest Ultrasonic Liquid Flow Meter/Controller

The new Bronkhorst ES-FLOW™ are Volumetric Liquid Flow Meters for very low flow ranges. The instruments operate on a innovative measuring principle, using ultrasound in a very small, straight tube. A wide range of liquids can be measured independent of fluid density, temperature and viscosity.

The ES-FLOW™ Ultrasonic Flow Meter was designed to measure tiny volume flows from 4 up to 1500 ml/min with high precision, high linearity and low pressure drop, using ultrasound in a small bore tube. Liquids can be measured independent of fluid density, temperature and viscosity. Thanks to the combination of a straight sensor tube with zero dead volume the flow meter is self-draining.

• The orbital TIG- welding allows hygienic connections so the instrument can be used for hygienic applications. 
• For non-hygienic applications, the flow meter can also be equipped with compression type fittings.
• Wetted parts are made of stainless steel, the exterior design is rated to IP67.
• The user interface is a capacitive touchscreen with a TFT display to operate and readout the instrument.
• The on-board PID controller can be used to drive a control valve or pump, enabling users to establish a complete, compact control loop.

Applications:

• Food & Beverage
• Pharma (e.g. additives, sterilization)
• Medical
• Chemical (e.g. catalysts, reagents)
• Many other markets which require precision fluid handling e.g. fuel consumption measurement and dosing of colorants or lubricants in many industries.

Download the ES-FLOW™ brochure here.