In the modern industrial production process, in order to effectively carry out the production operation and control, the need to measure the physical parameters of various media in the production process. The flow of fluid is one of the important parameters which are often measured and controlled. Due to the complexity of the flow measurement, the flow meter has become the most various kinds of instruments in the process of testing and controlling instrument. Heat flow meter is a meter that uses heat transfer principle to directly measure the mass flow of fluid. It is widely used at present. The heat flow meter can measure the micro flow with very low flow rate, the pressure loss is small, and the reliability is high because there is no movable component.
In this paper, the flow gas is heated by the intrusive heating resistance element, and the gas mass flow in the pipe is measured by the change of temperature difference. In order to make the heat flow meter be used in the measurement of the flow rate of easy vaporization liquid, the refrigeration type heat type liquid mass flowmeter is studied in this paper. The main research work is summarized as follows:
1, based on the detailed reading of the relevant literature, summed up the development process of the flowmeter, focus on the type of thermal mass flowmeter and its measurement principle.
2, describes the basic concepts and analysis methods of fluid mechanics, the measuring principle of thermal flowmeter of convective heat transfer and cooling, and the physical phenomena of the mathematical description; flow equation of constant power heat dissipation thermal flowmeter and cold type liquid flow meter is deduced and proved the feasibility of the two flow measurement method.
3. In this case, the fluid simulation experiment is carried out on the case that the air flows through the cylindrical constant power heating resistance element in the circular pipe. The simulation results given the velocity and temperature distribution of heating elements of different air mass flow under the surrounding fluid, reflect the impact of the convection heating element on the surface of the heating element; the fluid velocity distribution, reveal the effect of natural convection caused by buoyancy on the flow measurement, the measurement of the lower limit value of the simulation results are given and the constant power flow equation; heat dissipation thermal flowmeter is verified by simulation data.
4. The measurement circuit of temperature signal is designed for the constant power dissipation heat type gas flow meter and the refrigeration type heat type liquid flowmeter. The combination of statistical method and mean filter method is proposed, and the software is used to filter the sampled data. By dynamically changing the power saving management mode and the system clock frequency, the system can effectively reduce the power consumption of the system.