The Measurement Of Thermal Gas Flow And Development Of Flowmeter

The thermal gas flowmeter is used to directly measure the gas mass flow rate on the basis of heat transfer theory, which could be divided into heat distribution type and immersion type according to its structure. The heat distribution type is usually used to measure the small flow velocity; And the immersion type is mainly used in medium or large diameter pipes for high velocity measurement. To solve these problems, a new measuring method is proposed and a new thermal gas flowmeter has been designed.Firstly, a new method with the advantages of heat distribution type and immersion type has been proposed. Secondly, the influence of different sensor structures on flow field are studied. The Solidwords is used to establish the three-dimensional model and Fluent is adopted to numerical simulation. The weight method is used to determine the optimal sensor structure. A new type of sensor is employed and the temperature characteristic of the sensor are studied. The sensor circuit is designed according to the temperature experiments. The circuit can not only measure low flow but also high flow. The turndown ratio of flowmeter is improve.The sensor circuit can automatically realize the temperature compensation function, and can detect the direction of the flow velocity to judge whether there is the backflow in the pipe. The system of hardware and software is designed and the prototype is completed.At the end of article, the bell gas flow standard device and the standard meter prover are used for the prototype flow experiment. The influence of humidity to the measurement accuracy is studied and the error of the flowmeter is corrected based on the experimental data.