A gas mass flow meter measurement is based on the principle of thermal dispersion. The meter measures the mass flow rate of a gas by sensing the heat transfer from a heated surface to the fluid as it flows past it. The device typically consists of two temperature sensors, one that is heated and one that is not, and a flow channel where the fluid passes through.
Both the heated and reference sensors are located in the flow channel. The heated sensor temperature is kept constant by a heating element. The reference sensor measures the dynamic changes in the gas temperature. As the gas flows past the heated sensor, it carries away some of the heat, causing the temperature of the heated sensor to drop. The rate at which the temperature drops is proportional to the mass flow rate of the gas. The reference sensor measures the temperature of the surrounding environment and provides a baseline for comparison.
The temperature difference between the heated and reference sensors is then used to calculate the mass flow rate of the gas using a mathematical formula. This formula takes into account the physical properties of the gas, such as its density and specific heat capacity, as well as the design of the meter.
The accuracy of the mass flow meter measurement is affected by various factors, such as the calibration of the device, the gas properties, the temperature and pressure conditions, and the flow rate range. These dynamic changes vary from gas to gas and therefore it is crucial that gas flowmeters are calibrated in actual or equivalent gases as it is not possible to use the property changes of one gas in another. It is also essential to properly install, calibrate, and maintain the mass flow meter to ensure accurate and reliable data.
3 important things to know about mass flow meter measurement
What is a Coriolis Mass Flow Meter?
A Coriolis mass flow meter is a type of flow meter that measures the mass flow rate of liquids and some high-pressure gases by utilizing the Coriolis effect, which is the apparent deflection of an object’s path in a rotating reference frame. The meter consists of a vibrating tube that is placed in the fluid flow path. As the fluid flows through the vibrating tube, it causes the tube to vibrate at a specific frequency.
The Coriolis effect then causes a twisting or bending of the tube, which is proportional to the mass flow rate of the fluid. This bending is detected by sensors, and the data is used to calculate the mass flow rate of the fluid. Coriolis mass flow meters offer high accuracy, stability, and repeatability, making them suitable for use in a wide range of industries, including oil and gas, food and beverage, and chemical processing. Since about 90% of flow measurement consists of liquids Coriolis flow measurements are far more popular than thermal mass flowmeters.
Advantages of thermal mass flowmeters.
- No pressure drops as flow sensors are too small to cause a pressure drop in a pipe.
- Excellent flow sensitivity for gases, especially for low flows.
- Wide turn-down rations of better than 100:1
- Insertion style reduces installation costs by cutting a pipe only on the top or bottom
- No moving parts, no wear, and tearing
- Effective in both high- and low-pressure gases
Disadvantages of thermal mass flowmeters.
- Can only measure gases
- Accuracies at best are around 1%
- Moisture on the sensors if not blown away by the gas stream can affect their accuracy
- Debris and dirt must be cleaned for the sensors to operate effectively
- Cannot be used for custody transfer applications requiring high accuracies
Advantages of Coriolis mass flowmeters.
- Excellent accuracies of 0.1%
- Only a flowmeter can measure the mass of liquids. It can also high-pressure gases
- No straight run is required to install the meter, one can install it right after a valve bends, etc.
- Used for custody transfer
- Can measure density, mass, volume, and temperature with digital outputs
Disadvantages of Coriolis flowmeters
- Creates pressure drops and calculation of pressure drops across the pipe is needed for each flow point.
- The fluid mass be clean and therefore filters/strainers are needed to clean the fluid before it enters the meter
- Liquids must be free of bubbles or gases and therefore air eliminators are needed to knock off gases or bubbles before the fluid enters the meter
Overall, mass flow meter measurement is a critical process in various industries, such as food and beverage, chemical, and pharmaceutical, where precise control and monitoring of fluid mass flow rates are required for process optimization and quality control.
Do Mass Flow Meters contain mercury?
No, mass flow meters do not typically contain mercury. The most common types of mass flow meters, such as thermal and Coriolis meters, use non-toxic and non-hazardous materials, such as stainless steel, aluminum, and plastic, in their construction. These materials are chosen for their durability, resistance to corrosion, and ability to withstand the conditions of the fluid being measured.
Mercury is a toxic substance and is not commonly used in modern flow meter technology. In the past, some flow meters may have contained mercury switches or other mercury-containing components, but these have largely been phased out due to environmental and health concerns. If you have a specific flow meter in mind, it is always best to consult the manufacturer’s specifications to determine whether it contains any hazardous materials, including mercury.
Do Mass Flow Meters have hazardous chemicals?
Some mass flow meters may contain hazardous chemicals, depending on the type and application of the meter. For example, some mass flow meters that are used to measure the flow of corrosive or hazardous fluids may require the use of specialized materials or coatings that contain hazardous chemicals.
In general, however, mass flow meters are designed to minimize the use of hazardous materials and to ensure the safe handling of any chemicals that are used. Manufacturers are required to comply with local regulations and industry standards for the safe use and handling of chemicals, and they typically provide information on the materials and chemicals used in their products.
If you have concerns about the use of hazardous chemicals in a specific mass flow meter, it is best to consult the manufacturer’s specifications or contact the manufacturer directly for more information. It is important to ensure that any flow meter used in an application involving hazardous chemicals is properly installed, maintained, and operated to minimize the risk of exposure to workers and the environment.
