In general, flow meters are separated into two main categories: volumetric flow meters and mass flow meters. The two types differ in the way that they measure flow and the way they represent flow rates. Volumetric flow meters measure the volume of the liquid passing through the system, while mass flow meters measure the mass of the fluid flowing through the system.
There are two main types of mass flow meters. The first type is called a Coriolis flow meter, or inertial mass flow meter, and draws its name from the fact that it utilizes the Coriolis effect to make mass flow measurements. As fluids flow through the Coriolis flow meter, it passes through a set of tubes which are constantly experiencing vibratory forces, causing the Coriolis effect. This effect causes oscillations in different parts of the tubes. Using sensors attached to the tube, the amplitude, frequency, and phase shift of these oscillations can be measured, and these measurements can be used to calculate the mass flow of the fluid.
Thermal mass flow meters are the second type of mass flow meters. These flow meters use heat transfer principles to determine mass flow rates. A thermal mass flow meter is comprised of a heating element and one or more temperature sensors located along the length of a tube. As the fluid passes by the heating element, it gains thermal energy, increasing the temperature of the fluid. The temperature sensor (or sensors) can then measure how much of the heat is dissipated, which can be used to calculate the flow rate. There are a variety of different methods to accomplish this task, but they all operate under the principle that faster moving flows have a greater cooling effect.
Both types of mass flow meters are commonly used across a broad range of industries. Some of these industries include chemical processing, oil and gas, food, beverage, pharmaceutical, power, water and wastewater, mining, and many others.
Obviously, this type of flow meter is more popular for applications where it is more important to know the mass of the fluid as opposed to the volume of the fluid. For example, mass flow is much more important for fluids used in the production of energy. In addition, both mass flow meter varieties offer high accuracy, reliability, and low maintenance. Thermal mass flow meters are especially low maintenance since they have no moving parts, and they also offer the benefit of having very limited obstruction to the fluid flow.