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Abstract
Metering the mass flow rate of bulk solids is becoming increasingly important in
chemical production, coal transportation, food processing. Although there are many
measurement methods of solid mass flow rate both at home and abroad, such as direct
measurement, capacitance method, acoustic sensing method, tomography method.
However, these methods lack either precision or real-time performance. As a new
measurement method, Microwave sensor is becoming more and more popular in the
world because of its strong penetrability, quick response, easy installation, low cost.
But there are still some technical problems, the limit of moisture in measurement
precision, the extraction and processing of signal for large number of particles. To
resolve these problems, based on the principle of microwave method in measuring the
speed of solid particles, this thesis studies the core issue of metering the mass flow
rate of bulk solids. The main research work and the results are as follows:
1. Aiming at the measurement method of volumetric concentrations of solids,
this thesis puts out two defects, which are poor accuracy, humidity influence. To
resolve these problems, we start from wave propagation equation, combine
attenuation coefficient and phase shift coefficient with concentrations of water, air,
solid, get each phase concentrations of mixture through simulation with C++. This
algorithm solves the problem of humidity influence in concentration measurement. In
addition, when water concentration is fixed as 0.283, the volume fraction of solids
and gases can be determined by microwave amplitude and phase information;
2. It is difficult to get the average velocity of solid particles from the Doppler
principle. As the number of particles increases, there will be different frequency
components in Doppler signals, which could not reflect the rate of movement of the
particles. To resolve this problem, this thesis adopts fast Fourier transform,
discretizes time domain signal, averages the weighting signal amplitude in frequency
domain. In this way, we get the average velocity of solid particles. In the experiments,
average velocities of mass solid particles are found much smaller than theoretical
velocity. To analyze the influence factors on velocity, we change signal in time
domain to signal in frequency domain, extract the frequency shift of single particle,
obtain the velocity from Doppler’s principle. Through the experiments, interaction is
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