Multiphase Flow Measurement Study Based On Terahertz Technique

Multiphase flow phenomenon exists widely in nature and industrial processes. With the development of science and technology, understanding the phenomenon of multiphase flow becomes more and more important in chemical engineering, petroleum, power generation, nuclear energy, environment monitoring, metallurgy and so on. Therefore, fully understanding multiphase flow process is vital to the operation of industry and human lives. Meanwhile, due to the inherent complexity of multiphase flow system, it is difficult to measure the parameters of multiphase flow. Until very recently, most of the multiphase flow measurement techniques are still in labs, the urgent need of multiphase flow measurement from industries can hardly be satisfied. As a result, multiphase flow measurement techniques has already been an restriction for the further developing of multiphase flow research.Terahertz radiation is loosely defined by the frequency range of 0.1 to lOTHz (lTHz=1012Hz). Comparing with other region of the electromagnetic spectrum, the terahertz (THz) region of the electromagnetic spectrum has proven to be one of the most elusive. Terahertz radiation has attracted a lot of attention with its extremely safety radiation, non-absorbing in dry dielectric substances feature and high spectrum sensitivity. However, with the difficulties in the generation and detection of terahertz radiation, this region has been unexplored for a long time. From the late of 90s, the revolution in semiconductor industry and ultrafast laser technique welcome a prosperous era for the development of terahertz technique.As a rapid developing technique, terahertz technique have shown great potentials in fundamental science study, astronomy, safety insurance, medical biology, environment monitoring, telecommunication and so on. However, applications of terahertz technique in multiphase flow measurement are still in preliminary state, very limited research appears in scientific or engineering literature.The overall objectives of this thesis are exploring the possibility and practicability of terahertz technique to the measurement of multiphase flow. Three main applications have been under study:(1) Using terahertz time domain spectroscopy(THz-TDS) technique to investigate solids volume fraction in gas solids two phase flow measurement; (2) Using THz-TDS technique to reconstruct temperature distribution of combustion process; (3) Using THz-TDS technique to reconstruction of combustion temperature distribution and H2O concentration distribution. The main work of the dissertation includes:1) A new solids volume fraction measurement method of gas solids two phase flow based on THz-TDS technique have been proposed. This method overcomes the shortage of optical method which have limited optic depth in high concentration of particles(>1%). While this method can implement measurement of solids volume fraction of gas solids two phase flow in high concentration of particles. Static experiment have shown that both attenuation mode and time delay mode could implement the measurement of solids volume fraction with high concentration of particles. Meanwhile, experimental results show that he measurement of solids volume fraction with time delay mode is more accurate and with better linearity.2) Theoretical models of ISA, EFA and QCA have been investigated and compared with experimental results in dense gas solids two phase flow. Experimental results show that within three models, QCA is the best model to predict the propagation and scattering of terahertz wave in the gas solids flow, and this model is suitable for the analysis of gas solids flow with high concentration of particles.3) The effect of particle size and particle permittivity on the measurement of solids volume fraction have been investigated. Experimental results show that in high concentration of particles, particle size effect is not significant on both attenuation measurement mode and time delay measurement mode. But the permittivity of particles will affect both two measurement modes. If the imaginary part of the permittivity of particle is relatively large, the error of attenuation measurement mode will increase. On the contrary, if the real part of the permittivity of particle is larger, the error of time delay measurement model is smaller.4) With high spectra sensitivity of gas molecular, a new temperature measurement method based on THz-TDS have been proposed. This new method use two vibration and rotation spectra lines to obtain the temperature of gas molecular in combustion process. The method will not depend on component of combustion and not affect the combustion flow field. Base on the molecular spectra data from HITRAN database, the criterion of spectra line selection is setup. 5) Based on two spectra line temperature measurement, a new temperature distribution reconstruction method is established using THz-TDS technique. Applying ART reconstruction algorithm, three pairs of H2O spectra line are used to reconstruct the temperature field. The spectra line relative sensitivity and strength sensitivity are analyzed and the effective temperature sensing range is provided. Theoretical and experimental results demonstrate the proposed method of choosing large rotational quantum number and large differential molecular energy have been proved. The experimental results show that the proposed method based on THz-TDS is applicable for the temperature distribution reconstruction.6) A preliminary study on the temperature field reconstruction and chemical component concentration reconstruction are carried out based on THz-TDS technique. Experimental results show that based on THz-TDS the simultaneous reconstructing the temperature distribution and concentration distribution are possible. And application of terahertz technique in combustion temperature reconstruction and concentration reconstruction have a foreseen future.