Why are insertion type thermal gas mass flow meters less accurate than pipeline type?

Project Overview

When comparing different types of gas flow meters, we often find that the accuracy of insertion thermal gas mass flow meters is usually lower than that of pipe-type thermal gas mass flow meters. The reasons behind this involve multiple technical factors and practical application considerations. First, we need to understand the basic working principles of insertion thermal gas mass flow meters and pipeline thermal gas mass flow meters. Both measure gas flow based on the principle of thermal diffusion, that is, by measuring the effect of gas flow on the temperature of the sensor heating element to estimate the mass flow of the gas. However, there are significant differences in how they are installed and the environments in which they are used.

Insertion thermal gas mass flow meters measure by inserting one or more sensor probes into the pipe. Although this installation method has the advantages of easy installation and little impact on the pipeline system, it also brings some accuracy challenges. Since the sensor probes are directly inserted into the pipeline, the flow field environment in which they are located will be affected by the fluid dynamics characteristics in the pipeline, such as uneven flow velocity distribution, eddy flow, turbulence, etc. These factors can cause fluctuations in the temperature signal measured by the sensor probe, thereby affecting the accuracy of the flow calculation. In contrast, the pipeline thermal gas mass flow meter installs the entire flow meter on the pipeline to form a complete measurement unit. This installation method enables the flowmeter to more accurately measure the average flow rate and temperature of the fluid in the pipeline, thus improving the measurement accuracy. In addition, in-line flowmeters can further reduce the impact of fluid dynamics on measurement accuracy by optimizing flow channel design and sensor layout. In addition to the influence of the installation method, the accuracy of the insertion thermal gas mass flow meter is also restricted by other factors.

For example, parameters such as the material, size, and shape of the sensor probe will affect the heat exchange efficiency with the fluid, thereby affecting the accuracy of the measurement. In addition, factors such as the gap between the probe and the pipe wall, the insulation performance of the pipe, and the impact of the external environment on the fluid temperature in the pipe will also have a certain impact on the measurement accuracy. In practical applications, insertion thermal gas mass flow meters are usually used in situations where accuracy requirements are not particularly high, such as gas flow monitoring in some auxiliary systems or processes. In situations where precision is required, such as in key processes in the chemical, petroleum, natural gas and other industries, pipe-type thermal gas mass flow meters or other higher-precision measuring instruments are more likely to be used.