Best thermal mass flowmeter with features and installation requirements

Thermal gas mass flow meter principle

Thermal mass flowmeter, also known as calorimetric flowmeter, is an instrument that detects fluid mass flow.

It has two different measurement principles, but they are all boiled down to the word thermal. One of the principles is to heat the part of the pipeline through which the fluid flows, and use the change of the temperature field when the fluid flows through the heating pipeline to measure; the other One measurement principle is to heat the fluid itself, and use the relationship between the energy required for the fluid to heat up and the fluid mass to measure.

The sensor in a thermal mass flow meter usually consists of two reference-grade RTDs, one is a velocity sensor and the other is a temperature sensor that measures the change in gas temperature. When the two thermal resistors are placed in the gas to be measured in the pipeline, the speed sensor is heated, and the other temperature sensor is used to measure the temperature of the gas. As the flow rate of the gas increases, the heat taken away increases, and the temperature of the temperature sensor itself will decrease. The temperature change value before and after the temperature sensor and the mass flow of the gas passing through the pipeline are exactly linear proportions, and the mass flow of the gas can be calculated from this operating principle.

The working principle of thermal mass flow meters is based on Guin's law. An external heat source is used to heat the gas to be measured in the pipeline, and the heat energy moves with the gas. The mass flow of the gas is calculated by measuring the heat change in the pipeline due to the gas movement, that is, the temperature change before and after the gas passes through the pipeline. Another method is to calculate the mass flow rate of the gas by measuring the energy required for the gas temperature to rise to a certain point when heating the gas and the gas mass.

Thermal flow meter advantages and disadvantages

The thermal mass flowmeter is a flowmeter with an integral part. Its various parts cannot be disassembled. It is relatively simple in maintenance and maintenance, but if one of the small parts is broken, the entire thermal mass flowmeter must be replaced. , For many large-scale machinery and equipment, the use of thermal mass flow meters is not recommended, which is more troublesome in terms of maintenance and replacement.

The pressure loss of the thermal mass flowmeter is relatively small, and its use reliability is very high. It only needs to be used in conjunction with the flow sensor to form a fixed flowmeter. It has less damage or failure during the working process. It is a practical A relatively strong flowmeter, it can measure low flow rate or tiny flow rate. It doesn’t matter if there is dirt or impurities in the pipeline. Thermal mass flowmeter can accurately measure the flow rate, and the pressure loss is not very large and it is convenient and fast. When measuring a gas with a thermal mass flow meter, the specific heat capacity of the gas varies with pressure and temperature, but a small change around the temperature and pressure used can be regarded as a constant.

Although thermal mass flowmeter has many advantages, it also has many disadvantages. For example, it cannot be used in pulsating fluids, its response speed is slow, and it takes a period of time to respond to the results. For viscous liquid thermal mass flowmeters Flow is also limited, resulting in measurement errors and inaccuracies.

Thermal gas flow meter installation requirements

1. The installation of the thermal flowmeter requires that the resistance should not be greater than 10, and it cannot be shared with the grounding wire of other electrical equipment. If a good contact between the transmitter housing and the metal pipes cannot be guaranteed, metal wires should be used to connect them. And then reliable grounding.

2. Thermal mass flowmeter uses the temperature field change generated when the fluid flows through the pipeline heated by the external heat source to measure the fluid mass flow, or uses the energy required for the fluid temperature to rise to a certain value when the fluid is heated and the fluid mass. A flow meter used to measure the mass flow of a fluid.

3. The gas flow is measured by measuring the cooling effect of the gas flowing through the heating element in the flowmeter. There are two thermal resistance elements in the measuring section through which the gas passes, one of which is used as a temperature detection and the other as a heater. The temperature sensing element is used to detect the gas temperature, and the heater maintains a constant temperature difference between its temperature and the temperature of the gas being measured by changing the current. When the gas flow rate increases, the cooling effect is greater, and the current that must maintain a constant temperature between the thermal resistors is also greater. The heat transfer is proportional to the gas mass flow, that is, the supply current has a corresponding functional relationship with the gas mass flow to reflect the gas flow.