Chemical and industrial processes extending between polymerization to brewing rely on delivering precise quantities of liquids or gases. It’s feasible to measure delivery rates with regards to either volume or mass per unit of time, as well as selecting between them depends on the application.
Author: Sylvia Hopkins – (writer, blogger) in email marketing campaigns. Writes about flow measurement instrumentation, flow measurement application, and technology.
In many instances, volumetric flow measurement is enough and adequate, especially if the temperature and pressure are stable and known. But as mass flow measurement straightforwardly specifies the number of molecules available, it has the benefit of being resistant to density variation.
Most mass flowmeters have plenty of similarities. Each of them can be leveraged to measure mass flow, gas flow, or liquid flow. For a little help, we will walk you through how to choose the correct mass flowmeter for your application. So, take a read!
Types Of Mass Flowmeter and Its Operating Principles
For the most part, the commonly used mass flowmeter types are Coriolis, thermal, and differential mass flowmeter.
Coriolis Mass Flowmeter
This mass flowmeter type calculates mass via inertia. A dense liquid or gas traverse through a pipe which is, for the most part, vibrated through a tiny actuator. This speed produces a computable twisting force on the pipe proportionate to the mass.
Moreover, the mass flow rate is identified without needing any understanding of the fluid traversing inside. More advanced Coriolis mass flowmeters utilize dual-curved pipes for higher sensitivity and low-pressure drop.
Although this mass flowmeter type is loved by many, the price is usually a problem. Coriolis mass flowmeters are, believe it or not, the most costly flowmeter available, with regards to the average market price.
Its cost is usually between 5,000 dollars to 6,000 dollars. However, some offer inexpensive Coriolis meters in the 3,000 dollars range. But keep in mind that the performance specs for the inexpensive ones aren’t the same with the expensive Coriolis meters.
Nevertheless, these inexpensive meters can help users with their needs, especially those who’d want to enjoy the essential advantages of this technology yet don’t want to pay much.
Thermal Mass Flowmeter
This type of mass flowmeter is accessible in two designs: a heated sample tube and an inserted probe. Both designs obtain mass from the fluid’s particular heat capacity, nullifying density variations. Therefore, it’s crucial to know and understand this property.
Thermal meters are fitted for low gas flow rates. In the inserted probe mass flow meter design, it utilizes the same principle as the heated sample tube. However, it uses two resistance temperature detectors situated in the flow.
The first RTD probe calculates the fluid temp while the second one is, for the most part, heated to a temperature greater than the first RTD probe. The heat is then conveyed from the second RTD probe to the fluid at an acceleration proportional to the mass flow rate.
Differential Pressure Flowmeter
A blockage or impediment like round objects with a hole of distinguished diameter is mounted inside a section of the laminar flow. On each side, the fluid pressure is measured.
Take note that on the upstream side, the pressure will be greater, with the variability in readings proportional to the distance between the pipe diameter, volumetric flow rate, and viscosity, as stated on the Poiseuille’s equation. Then, adjustments or modifications are made for temperature and pressure to generate a normalized mass flow rate.
Determinants Affecting Accuracy
For the most part, the accuracy of the DP mass flowmeter is influenced by three factors.
- The calculation is surmised from temperature and pressure. Thus, inaccuracies in these manifest in the final result.
- There are assumptions about the degree and the viscosity wherein the laminar flow is obtained.
- The orifice might erode and be damaged, minimizing the pressure drop, and it can become bigger in the long run. Also, depending on the fluid flowing through, there’s a possibility of partial blockage.
On the other hand, when you use thermal flow meters, it’s critical to think about the potential effect of:
- Inaccuracies in particular heat capacity expectation: Originating from variation or inconsistencies in gas composition.
- Particulate buildup: More often than not, low readings might occur or happen if heat transfer is blocked by a buildup of residue on the sensor.
- Water vapor condensation on the temp detector: The gas saturation might cause moisture. Thus, it can lead to bad readings and eventually, corrosion.
In addition, thermal meters need ample time to achieve a steady and stable operating temp. Once the device is turned on, you must not take the readings yet.
Moreover, Coriolis meters, although regarded as the most precise, are susceptible to inaccuracies generated by bubbles in the liquid. These bubbles produce noise, allow splashing inside the tube, and altering the energy needed for tube vibration.
Huge spaces raise the energy needed for tube vibration to a large degree, resulting in absolute failure. Furthermore, the split-up of fluid into gas and liquid generates a damping effect on the tube vibration.
The three most common mass flowmeters are Coriolis, thermal, and differential pressure. Applications for Coriolis meters include, pulp and paper processing, wastewater handling, petroleum and oil, and chemical processing.
Applications for thermal meters include semiconductor process gas measurement, nuclear power facility air monitoring, filter and leak detection, and chemical processing. On the other hand, applications for DP meters must be anywhere where the fluid has good viscosity and where temp doesn’t change at all.