Before mass flow metres came into play, measuring mass flow was like solving a puzzle with volumetric flow meters and densitometers. These gadgets juggled density calculations, sometimes by directly measuring it, other times by tapping into the temperature and pressure transmitter outputs of a process.

But let's face it, it was like trying to hit a target blindfolded, with each sensor adding its own twist to the mix. Then came the mass flow meter, and a new era of precision started. So, what's the deal with these precision pioneers?

In this article, we will delve into precisely that and understand what a mass flow meter is, its types, how it works, its history, and other detailed information regarding this device. So, stick around.

What is a Mass Flow Meter?

A mass flow meter, also known as a mass flow sensor or an inertial flow meter, is a device that measures fluid flow by assessing its mass, rather than using traditional volume-based methods. It works by calculating the difference between the mass of fluid entering the pipe and the mass exiting the pipe, thus determining the flow rate.

Now, let's talk about the different types—like Coriolis and thermal mass flow meters. They function on the fundamental principle of measuring mass to determine flow. It is noteworthy to highlight their exceptional accuracy, a result of prioritizing mass over volume. This characteristic renders them less susceptible to errors compared to earlier flow meter devices, where inaccuracies often stemmed from fluctuations in temperature and pressure.

The super-accuracy of mass flow meters makes them a must-have tool in industries where precision is everything, especially in fields like chemicals and pharmaceuticals. Here, where every tiny detail matters, mass flow meters are like trusted companions, ensuring that fluid flow measurements are bang-on accurate. They're basically the backbone of these industries, guaranteeing that everything runs smoothly and precisely.

How have Mass Flow Meters Evolved?

Over time, mass flow measurement has come a long way, with significant improvements in accuracy and efficiency. In the early days, mass flow meters worked on angular momentum principles, using motor-driven impellers to measure fluid density. They did the job, but they had lots of moving parts and complicated mechanisms, making maintenance a hassle.

As technology advanced, new methods popped up, like batch weighing and combining level sensors with densitometers. There were even clever ideas using differential pressure transmitters for density determination, especially in measuring slurry mass flow.

While the old-school designs had their perks, modern mass flow meter solutions are way more reliable and need less maintenance. It shows how measurement technology keeps getting better and better.

Also Read: Mechanical Flow Meter: Meaning, Pros & Cons, Selection Process

How Does a Mass Flow Meter Work?

While all mass flow meters serve the purpose of measuring flow rates, they employ different methods depending on the materials, conditions, and required accuracy. The working principle of a mass flow meter is rooted in inertia, enabling it to measure both mass flow and density effectively. With their unobstructed, open-flow design, these meters accurately determine flow rates by directly assessing fluid mass across different temperature ranges.

As fluid flows through the sensor tubes, the forces generated by the mass flow cause twisting motions in the tubes, which are directly proportional to the mass being measured. To grasp their functions better, let's take a quick look at how some flow meters operate. Each method offers a unique approach to mass flow measurement, catering to various application needs.

Direct Mass Flow Measurement:

It eliminates inaccuracies tied to fluid properties like mass and volumetric flow differences. It remains unaffected by changes in pressure, temperature, viscosity, and density, a crucial advantage for mass flow meters. Volumetric devices, like variable area meters, lack sensitivity to temperature and pressure changes, bettering flow rate accuracy.

The Coriolis principle:

This mass flow meter principle is a fundamental yet practical concept that powers Coriolis flow meters. The method involves a vibrating tube influenced by fluid mass flow, generating a phase shift proportional to flow. Coriolis meters offer direct, high-flow measurements with minimal pressure loss, which is independent of any material type.

Indirect Mass Flow Measurement:

It employs alternate methods for infeasible direct measurements. Methods like magnetic, ultrasonic, and turbine meters, though volumetric, integrate pressure and temperature sensors with flow computers.

Differential Pressure (DP) Methods:

It uses Bernoulli's law to gauge velocity by measuring pressure changes in a narrowing pipe.

Thermal Mass Flow Meters:

They employ convective heat transfer, with two RTD (Resistance Temperature Detector) sensors detecting temperature changes for gas mass flow measurement.

Turbine Flow Meters:

They measure flow energy through rotating blades, providing accurate readings regardless of flow direction. 

What are the Types of Mass Flow Meters?

A mass flow meter has various applications, and each industry might prefer different types of mass flow meters to measure mass. Here is the low-down of the different mass flow meter types.

Coriolis Mass Flow Meter

This meter relies on inertia, vibrating a tube as dense gas or liquid passes through. The twisting force on the tube, proportional to mass, determines the measurement. Dual curved tubes enhance sensitivity and reduce pressure drop. While highly accurate, they may encounter errors with bubbles in liquids, causing noise and altering energy needs.

Thermal Mass Flow Meter

Measuring flow based on convective heat transfer to a heated surface, this type directly assesses the mass flow rate for liquids and gases. Unaffected by changes in viscosity, pressure, temperature, or density, it's ideal for mass-dependent processes like chemical reactions.

Impeller Turbine Mass Flow Meter

This meter uses a turbine and an impeller to impart angular velocity to the fluid via a constant-speed impeller. Torque on the downstream turbine, proportional to angular momentum, is restrained by a spring, providing a measure of mass flow.

Twin Turbine Mass Flow Meter

Operating on fluid inertia, this meter features two turbine wheels with different blade pitches coupled within the tube. Fluid inertia causes a torque differential between the wheels, with greater mass flow rates leading to increased angular displacement.

Also Read: Vortex Flow Meter - Meaning, Principle, Usage & More

What are the Mass Flow Meter Applications?

Mass flow meters are pivotal in monitoring and controlling mass-related processes, particularly those dependent on the relative masses of unreacted ingredients. Their application extends to tasks such as recipe formulations, material balance determinations, and billing/custody transfer operations. Given their critical role in processing plants, the reliability and accuracy of mass flow measurements are paramount for optimal operational efficiency. Here is a small mass flow meter selection guide for you to decide which thermal mass flow meter vs. Coriolis mass flow meter is best suited for your application.

Applications of Coriolis Mass Flow Meters

Coriolis mass flow meters have diverse applications in both industrial and scientific spaces. They excel in measuring corrosive and clean gases and liquids, providing high accuracy not only in mass flow but also in density, temperature, and viscosity measurements. Widely used across various industries, Coriolis mass flow meters are indispensable for ensuring precision in complex and demanding processes.

Applications of Thermal Mass Flow Meters

Thermal mass flow meters offer versatile applications, especially in processes reliant on chemical reactions and relative masses of unreacted ingredients. In gas-flow scenarios, they prove valuable for combustion air measurement in large boilers, semiconductor process gas measurement, research and development applications, gas chromatography, and filter and leak testing. Additionally, these meters excel in detecting the mass flow of compressible vapors and gases, providing accurate measurements even at low flow rates or velocities below 25 ft. per minute. In addition to that, operating in a constant-temperature-difference mode, thermal mass flow meters exhibit high rangeability (10:1 to 100:1), showcasing their adaptability to diverse industrial settings.

While thermal mass flow meters offer exceptional capabilities, it's essential to note that their precision and rangeability may decrease with constant heat input. At normal flows, these meters typically exhibit measurement errors in the 1-2% full-scale range. Understanding these considerations ensures effective and reliable  usage in various applications.

What are the Advantages of Mass Flow Meters?

Mass flow meters have many advantages that make it more reliable than other measurement tools, depending on their applications. Some of these advantages are as follows.

Precision for Enhanced Process Performance:

Mass flow meters offer precise measurements, enhancing process throughput, quality, profitability, and safety. The accuracy they provide is crucial for optimizing various aspects of industrial processes.

Comprehensive Measurement Capabilities:

These meters boast the impressive ability to simultaneously measure true mass flow and density readings. Additionally, they excel in handling complex scenarios, such as measuring fluids with two liquids or a liquid with suspended solids, allowing for the derivation of concentration and mass for each fluid.

Robust and Low-Maintenance Design:

Characterized by a durable and unobstructed, open-flow design, mass flow meters incorporate no moving parts. This design minimizes maintenance requirements, ensuring reliable and efficient operation over an extended period.

Suitability for Hazardous Environments:

Built with the capability to measure a variety of viscous, nonconductive fluids, mass flow meters extend their utility even to hazardous locations. Their versatility and robust construction make them suitable for a wide range of industrial applications, contributing to overall operational safety and efficiency.

What are the Limitations of Mass Flow Meters?

As discussed above, mass flow meters boast a notable combination of high rangeability and accuracy, making them valuable instruments for diverse applications. However, these meters encounter significant limitations that can impact efficiency, potentially harm equipment, and result in reduced accuracy. Environmental variables, along with errors in reading, calculation, and adjustment, contribute to these challenges. Some of the limitations in Coriolis and thermal mass flow meters are given below.

Coriolis Mass Flow Meters

• High Flow Velocities Required: Coriolis mass flow meters demand high flow velocities for effective detection, resulting in elevated pressure drops.
• Cost and Size Limitations: These meters, while accurate, tend to be expensive compared to other flow meters and are not readily available for larger-sized pipes.

Thermal Mass Flow Meters

• Condensation Impact: Thermal mass flow meters are susceptible to condensation of moisture in saturated gases on the temperature detector, causing low readings and potential corrosion.
• Effect of Coating or Material Build-Up: Coating or material build-up on the sensor impedes heat transfer, leading to inaccurate readings.
• Specific Heat Variations: Variations in specific heat due to changes in the gas's composition further pose challenges for thermal mass flow meters.

What are the Types of Readings in Mass Flow Meter?

Mass flow measurement encompasses both mass and volumetric approaches. Volumetric flow rate specifically evaluates the three-dimensional space occupied by a gas as it passes through the instrument under the measured pressure and temperature conditions, representing the actual flow rate.

On the other hand, mass flow meters gauge the flow of molecules through the instrument, quantifying it as a volumetric flow rate. This rate signifies the space occupied by molecules under standard temperature and pressure conditions. Mass flow meters provide data through various measurements, relying on the force generated by the flowing stream when encountering an obstruction. This force can also yield velocity measurements. Let’s understand a few important terms related to the readings in the mass flow meter.

Units of Measurement for Gases and Liquids

Gas and liquid flow rates are typically measured in units such as liters or kilograms per second, reflecting density. A liquid’s density is unaffected by surrounding conditions, unlike gases, which are influenced by pressure and temperature variations.

For energy-related applications, the flow rate of gases or liquids is measured in gigajoules per hour or BTUs per day. Flow computers utilize mass and volumetric flow rates to determine energy flow rates.

Gas flow rates, prone to volume changes under different conditions, are expressed in various units, such as actual or standard cubic meters per hour or million standard cubic feet per day. Thermal, Coriolis, or controllers are recommended for accurate gas flow measurement. Meanwhile, liquid flow rates vary based on the application and industry, often measured in liters per second, gallons per minute, bushels per minute, or cubic meters per second.

Venturi Effect

The Venturi effect describes fluid pressure reduction in a constricted space, with a corresponding increase in fluid velocity. This principle is utilized to measure fluid velocity in pipes, typically expressed in liters per second, gallons per minute, or cubic meters per second.

Accuracy

A flow meter's accuracy and precision determine its performance, which is evaluated in terms of error and measurement reliability. Mass flow meter accuracy is expressed as percentages of flow rate, full scale, calibrated span, and upper range limit, aiding in selecting suitable mass flow meters for specific operations.

Conclusion

In conclusion, investing in a reliable mass flow meter is crucial for precise fluid flow monitoring in industries. Understanding potential challenges and factors affecting readings helps make informed decisions, reducing risks and enhancing performance. With capabilities including accurate measurement in tough environments, mass flow meters are vital for productivity and downtime reduction. However, proper installation is critical, following manufacturer guidelines ensures optimal performance and accuracy.