Fast and Precise Soft-Field Electromagnetic Tomography Systems for Multiphase Flow Imaging

Malte Mallach, Martin Gevers, Patrik Gebhardt, Thomas Musch
2018 Energies  
In the process industry, measurement systems are required for process development and optimization, as well as for monitoring and control. The processes often involve multiphase mixtures or flows that can be analyzed using tomography systems, which visualize the spatial material distribution within a certain measurement domain, e.g., a process pipe. In recent years, we studied the applicability of soft-field electromagnetic tomography methods for multiphase flow imaging, focusing on concepts
more » ... high-speed data acquisition and image reconstruction. Different non-intrusive electrical impedance and microwave tomography systems were developed at our institute, which are sensitive to the local contrasts of the electrical properties of the materials. These systems offer a very high measurement and image reconstruction rate of up to 1000 frames per second in conjunction with a dynamic range of up to 120 dB. This paper provides an overview of the underlying concepts and recent improvements in terms of sensor design, data acquisition and signal processing. We introduce a generalized description for modeling the electromagnetic behavior of the different sensors based on the finite element method (FEM) and for the reconstruction of the electrical property distribution using the Gauss-Newton method and Newton's one-step error reconstructor (NOSER) algorithm. Finally, we exemplify the applicability of the systems for different measurement scenarios. They are suitable for the analysis of rapidly-changing inhomogeneous scenarios, where a relatively low spatial resolution is sufficient. Therefore, modeling the electromagnetic behavior of the measurement domain, as well as image reconstruction are more complicated and computationally demanding. Furthermore, the achievable spatial resolution is significantly lower. However, soft-field methods are advantageous in terms of costs, instrument size and flexibility, and they avoid ionizing radiation, as well as radioactive sources. They include microwave tomography (MWT), magnetic induction tomography (MIT) and electrical impedance tomography (EIT). The latter comprises galvanically-coupled EIT and capacitively-coupled EIT. This paper focuses on the MWT and EIT methods, which enable one to determine an approximation of the cross-sectional distribution of electrical properties-electrical conductivity and permittivity-based on measurements of the electromagnetic fields at the boundary of the measurement domain. The distribution of the materials can be derived due to the contrast of their electrical properties. EIT utilizes electric fields, whose wavelengths are significantly larger than the instrument size, and thus, the electrostatic approximation is valid. In contrast, MWT is based on the propagation of electromagnetic waves, where the wavelength is typically in the same order of magnitude as the size of the measurement domain. Thus, modeling the electromagnetic behavior is more complex. Both methods have been investigated in conjunction with medical, biomedical, as well as agricultural applications [3-6] and, furthermore, as alternative techniques for industrial process monitoring and multiphase flow imaging [7] [8] [9] . The application of EIT and MWT for multiphase flow analysis is a difficult task [9,10], especially in terms of instrument integration, sensitivity, measurement rate, as well as reconstruction stability and rate. In recent years, we developed concepts and systems for EIT and MWT striving to overcome the following reported challenges [9,11]:
doi:10.3390/en11051199 fatcat:ijfvpergrne5patapac3luxupy