CO2 mass flow meter

Challenges in Measuring CO2 Volume Flow

Most Co2 flow meters in common use today are designed to measure volume gas flow. However, since the volume of a CO2 gas is influenced by its temperature, pressure, and other parameters, any changes in these conditions require the measured volume flow to be adjusted to a corresponding value under standard or agreed-upon conditions. In practice, frequent fluctuations in temperature and pressure make it challenging, and at times impossible, to perform these conversions in a timely manner. Consequently, there is a growing preference for using mass flow meters for CO2 gas measurement.

The Importance of CO2 Mass Flow Meters in Industrial ProductionIn

industrial production, CO2 mass flow meters are essential for controlling product quality, determining the mixing ratios of various materials during production, conducting cost accounting, and enabling automatic adjustments to the production process. As industrial production technology advances and process automation increases, the importance of CO2 mass flow measurement continues to grow.

Relationship between Volume Flow Rate and Mass Flow Rate

The relationship between volume flow rate qv and mass flow rate qmis given by:

(1-1)

or

(1-2)

Where:

• ρ is the density of the fluid being measured, in kg/m³;
• A is the cross-sectional area of the flow (usually the pipeline cross-section), in m²;
• V is the average flow velocity at section A, in m/s.

Indirect Mass Flow Meters and Their Limitations

CO2 Mass flow meters can be classified into two categories: indirect (or derivative) and direct. Indirect mass flow meters first measure the CO2 volume flow and then multiply it by the density of the fluid, achieved through a densitometer and a multiplier. Due to the limitations of their structure and components, densitometers cannot operate effectively under high temperature and pressure conditions, and therefore rely on a fixed density value to calculate the mass flow. However, since fluid density varies with pressure and temperature, using a fixed density value under varying conditions results in significant mass flow measurement errors, necessitating parametercompensation. This led to the development of temperature and pressure-compensated flow meters, which detect the fluid's temperature and pressure and automatically convert these into the corresponding density value using a mathematical model. The product of this density value and the volume flow provides the mass flow measurement. This type of meter is thus referred to as a temperature and pressure-compensated mass flow meter and is widely used in industry.

Direct Mass Flow Meters: Accurate Measurement without Parameter Compensation

Direct mass flow meters, on the other hand, measure quantities directly related to the mass flow, ensuring that the output signal representing mass flow is independent of the medium’s pressure, temperature, and other parameters. This approach addresses the complexities and inaccuracies associated with the linearity assumptions between density, temperature, and pressure under varying conditions, and the cumbersome nature of temperature and pressure compensation.

Types of Direct Mass Flow Meters for CO2 Measurement

Direct mass flow meters detect mass flow directly through their measurement elements. There are several types of direct mass flow meters, including momentum and momentum moment types, inertial force types, Coriolis mass flow meter, differential pressure types, vibration types, and thermal mass flow meter.

Thermal mass flow meter for CO2 gas flow measurement

How thermal mass flow meter work for CO2 ?

Thermal mass flowmeter, a type of direct mass flowmeter, has seen rapid development in recent years. Its basic operating principle involves using an external heat source to heat the CO2 being measured and then detecting changes in the temperature field caused by the CO2 flow to determine the CO2 mass flow. This change in the temperature field is indicated by the temperature difference between the upstream and downstream ends of the heater. The relationship between the mass flow rate qm of the fluid and the temperature difference across the heater is given by:

(1-3)

Where:

• P is the heater power,
• J is the heat equivalent,
• Cp is the specific heat at constant pressure of the fluid,
• Δt is the temperature difference between the front and rear ends of the heater.

From this equation, it can be observed that in the constant power method, the temperature difference Δt is inversely proportional to the CO2 mass flow rate qm. By measuring the temperature difference Δt, the mass flow rate qm can be determined. Conversely, in the constant temperature difference method, the heater input power P is directly proportional to the mass flow rate qm. By measuring the heater input power P, the value of qm can be obtained. The constant temperature difference method is generally preferred in practice due to its simpler relationship and easier measurement process; the co2 mass flow rate qm can be directly determined by reading the power P from a power meter, making it widely used.

Advantages of using thermal mass flow meter for CO2 mass flow measurement

√  It can directly measure the mass flow of CO2 gas, which is of great significance to the process gas input quantity control and manufacturing process.
√ The thermal gas flowmeter sensor has no moving parts when taking gas flow measurement, so there is no mechanical wear and maintenance.
√ It can measure the instantaneous flow of CO2, and the response speed is fast.
√ Wide measurement range: The ratio of the maximum flow rate to the minimum measurement range can reach 100:1, which has a very wide measurement range compared with gas turbine flowmeters and gas vortex flowmeters.
√ There are inline gas flowmeter or insertion thermal gas flow meters, which can be used for CO2 flow measurement of large pipeline gas.

Coriolis mass flow meter to measure CO2

How Coriolis mass flow meter work for Co2 mass flow measurement.

The Coriolis mass flowmeter reflects the size of the mass flow rate by measuring the change of the Coriolis force. The so-called Coriolis force refers to the fact that, for an object in a reference frame rotating at a uniform angular velocity, in addition to the inertial centrifugal force, it is necessary to add another inertial force to the observer in the rotating reference frame in order to use Newton's second law to describe the state of motion of the object. This force is the Coriolis force, or Coriolis force for short. For example, if a disk is used as a rotating reference frame, and the disk rotates around the central axis at an angular velocity of, an object is assumed to move in a uniform straight line relative to the disk along the radius of the disk at a speed from the center of rotation. In addition to the inertial centrifugal force, the object is also affected by the Coriolis force. The size of the Coriolis force is determined by the angular velocity of the disk and the radial velocity of the object. Assuming that the Coriolis force is represented by f, its expression is:

(1-4)

In the formula:

m—the mass of the moving object
v- The speed of an object in a rotating reference frame
`w- Angular velocity of the rotating reference frame.

As indicated by the equation, the existence of the Coriolis force depends on the simultaneous presence of radial velocity and angular velocity; if either velocity is zero, no Coriolis force will be generated.

From equation (1-4), it is evident that when the angular velocity of rotation is constant, the Coriolis force fc is directly proportional to theCO2  of the mass and velocity of the object. This principle forms the fundamental theoretical basis for using the Coriolis force to measure mass flow. In flow measurement, the CO2 being measured is made to flow through a movable pipe, which rotates at a certain angular velocity, thereby achieving the simultaneous existence of flow velocity and angular velocity. This movable pipe is referred to as the flow measuring tube. The measuring tube can achieve the necessary conditions by rotating or vibrating periodically. When the fluid flows through the measuring tube, it experiences the Coriolis effect due to the periodic changes in angular velocity, albeit with a relatively simple structure.

Features of CO2 mass flow meter

↗ Designed for gas flow sizes ranging from micro CO2 mass flow meter DN1.5 to DN200 (8 inches)
↗ Direct measurement of gas mass flow for high-density gases
↗ Equipped with electronic displays, 4-20mA, RS485, and batch control options
↗ High accuracy in measuring gas mass flow
↗ Ideal for high-pressure gas flow applications such as monitoring CO2 or LPG gas flow
↗ Can also measure ultralow temperature CO2 mass flow
↗ Digital readings of the gas flow rate in kilograms per second (kg/s) or kg/h, t/h ,mass flow unit

Coriolis flow meter for cryogenic CO2 flow measurement

Coriolis flow meters are highly effective for measuring cryogenic CO2, especially in applications requiring precise mass flow measurement at extremely low temperatures. These meters utilize the Coriolis effect, where the fluid's mass flow rate is determined by measuring the induced Coriolis force as the CO2 flows through vibrating tubes. The key advantage of using Coriolis flow meters for cryogenic CO2 lies in their direct mass measurement capability, which remains highly accurate even at ultra-low temperatures. Additionally, they provide excellent repeatability and reliability without the need for flow straighteners or temperature compensation. This makes them ideal for applications such as cryogenic storage, transportation, and precise dosing in industrial processes where maintaining CO2 in its supercritical or liquid state is crucial.

Micro CO2 mass flow meter

We also offer micro mass flow meters for CO2, primarily including thermal gas micro flow meters and Coriolis flow meters.

Thermal Gas Micro Flow Meters/Flow controllers

Thermal meters/flow controllers are designed to measure extremely low flow rates with high precision. The min flow we can detect is as low as 2 ml/min, but it can still keep high accuracy of ± 1% F.S , They operate by detecting changes in temperature as CO2 passes through a heated sensor. The advantages include high sensitivity to low flow rates, no moving parts (which means minimal maintenance), and quick response times. These meters are ideal for applications requiring precise control of small gas quantities, such as in laboratory research, medical devices, and environmental monitoring.

Coriolis Micro Flow Meters,

on the other hand, directly measure the mass flow by detecting the Coriolis force generated as CO2 flows through vibrating tubes. These meters provide highly accurate and reliable mass flow measurements, independent of pressure and temperature variations. They are particularly suited for applications where precision is critical, such as in pharmaceutical manufacturing, chemical processing, and food and beverage industries. Both types of meters are essential in processes where accurate CO2 mass flow measurement is crucial, each offering unique advantages depending on the application needs.