21 July 2022

Rafiul K. Rasel, Shah M. Chowdhury, Qussai M. Marashdeh, and Fernando L. Teixeira

Abstract: Electrical Capacitance Volume Tomography (ECVT) has emerged as an attractive technology for addressing instrumentation requirements in various energy-related multiphase flow systems. ECVT can monitor multiple flow conditions and reconstruct real-time 3D images from capacitance measurements using a large set of electrode plates placed around the processes column enclosing the sensed flow system. ECVT is non-intrusive and allows the measurement of changes in mutual capacitance between all possible plate pair combinations. The objective of this paper is to provide a comprehensive review of recent advances in ECVT, enabling robust monitoring of multiphase flows, especially water-containing multiphase flows.


1 August 2022


ABSTRACT Electrical Capacitance Volume Tomography (ECVT) is a low-cost and high-speed sensing modality with great potential for industrial multiphase flow monitoring. In this work, we examine the use of the slope of the capacitance vector residual curve, as directly provided by the measurement data, to formulate a robust stopping criterion for the iterative image reconstruction in ECVT. The methodology is illustrated based on experimental data from a gas-solid fluidized bed. We show that the proposed stopping criterion can improve the performance of both the image reconstruction and the flow velocity profiling in ECVT applications. For concreteness, we focus on the popular Landweber iterative reconstruction algorithm although other reconstruction algorithms exhibiting semi-convergent behavior might benefit from the present analysis as well.


8 September 2021

Claas Spille, Vaishakh Prasannan Tholan, Benjamin Straiton, Monika Johannsen, Marko Hoffmann 1, Qussai Marashdeh, and Michael Schlüter

Abstract: Against the background of current and future global challenges, such as climate change, process engineering requires increasingly specific solutions adapted to the respective problem or application, especially in gas–liquid contact apparatuses. One possibility to adjust the conditions in this kind of apparatuses is an intelligent and customized structuring, which leads to consistent fluid properties and flow characteristics within the reactor. In the course of this, the interfacial area for mass
transfer, as well as residence times, have to be adjusted and optimized specifically for the respective application. In order to better understand and advance the research on intelligent customized additively manufactured lattice structures (AMLS), the phase distributions and local gas holdups that are essential for mass transfer are investigated for different structures and flow conditions. For the first time a tomographic measurement technique is used, the Electrical Capacitance Volume Tomography (ECVT), and validated with the volume expansion method and a fiber optical needle probe (A2PS-B-POP) for an air-water system for different modes of operation (with or without cocurrent liquid flow in empty or packed state). The ECVT proved to be particularly useful for both in the empty tube and the packed state and provided new insights into the phase distributions occurring within structured packings, which would have led to significantly underestimated results based on the visual reference measurements, especially for a densely packed additively manufactured lattice structure (5 mm cubic on the tip). Particularly for the modified structures, which were supposed to show local targeted differences, the ECVT was able to resolve the changes locally. The additional use of a pump for co-current flow operation resulted in slightly higher fluctuations within the ECVT data, although local events could still be resolved sufficiently. The final comparison of the empty tube at rest data with a fiber optical needle probe showed that the results were in good agreement and that the local deviations were due to general differences in the respective measurement techniques.


12 June 2021

Yan-Shu Huang, Sergio Medina-González, Benjamin Straiton, Joshua Keller, Qussai Marashdeh, Marcial Gonzalez, Zoltan Nagy, and Gintaras V. Reklaitis

Abstract: While measurement and monitoring of powder/particulate mass flow rate are not essential to the execution of traditional batch pharmaceutical tablet manufacturing, in continuous operation, it is an important additional critical process parameter. It has a key role both in establishing that the process is in a state of control, and as a controlled variable in process control system design. In current continuous tableting line operations, the pharmaceutical community relies on loss-in-weight feeders to monitor and understand upstream powder flow dynamics. However, due to the absence of established sensing technologies for measuring particulate flow rates, the downstream flow of the feeders is monitored and controlled using various indirect strategies. For example, the hopper level of the tablet press is maintained as a controlled process output by adjusting the turret speed of the tablet press, which indirectly controlling the flow rate. This gap in monitoring and control of the critical process flow motivates our investigation of a novel PAT tool, a capacitance-based sensor (ECVT), and its effective integration into the plant-wide control of a direct compaction process. First, the results of stand-alone experimental studies are reported, which confirm that the ECVT sensor can provide real-time measurements of mass flow rate with measurement error within −1.8 ~ 3.3% and with RMSE of 0.1 kg/h over the range of flow rates from 2 to 10 kg/h. The key caveat is that the powder flowability has to be good enough to avoid powder fouling on the transfer line walls. Next, simulation case studies are carried out using a dynamic flowsheet model of a continuous direct compression line implemented in Matlab/Simulink to demonstrate the potential structural and performance advantages in plant-wide process control enabled by mass flow sensing. Finally, experimental studies are performed on a direct compaction pilot plant in which the ECVT sensor is located at the exit of the blender, to confirm that the powder flow can be monitored instantaneously and controlled effectively at the specified setpoint within a plant-wide feedback controller system.



Shah Mahmud Hasan Chowdhury

Electrical Capacitance Volume Tomography (ECVT) refers to three-dimensional (3D) imaging of flow media exhibiting two or more material phases in a region of interest (RoI) based on electric permittivity variations. Such multiphase flows are commonly found in industrial settings such as gas-oil-water flow in oil pipelines, gas-solid flows in various chemical processes etc. An ECVT sensor is comprised of metal electrodes flush mounted on an insulating pipe wall surrounding the RoI. They are arranged in a multi-layer pattern being able to capture the 3D variation in permittivity, i.e. both the cross-sectional (xy) and the axial (z) variation. Because of the wall, there exists only capacitive coupling between the electrodes and the RoI, which makes the modality non-intrusive in nature. Other advantages include conformal sensor shape, cheaper electronics due to low-frequency operation, and fast acquisition rate suitable for capturing fast moving flows. The mutual capacitance measured among the electrodes is used, with the aid of an appropriate image reconstruction algorithm, to reconstruct a 3D image of the permittivity distribution corresponding to the actual material distribution in the RoI. A limitation of ECVT is the poor image resolution compared to other imaging modalities, e.g. X-ray, which originates from the ill-posed nature of the inverse problem associated with ECVT. Flow velocimetry has been a topic of interest for decades. A lot of information about a flow can be derived if the velocity profile can be determined. Although ECVT can perform flow imaging, there has not been a convenient way of determining the velocity profile.

Previous efforts include cross-correlating two successive images, which is computationally intensive and not robust as cross-correlation works in very simple cases only. Moreover, errors incurred in image reconstruction are compounded with cross-correlation which makes the situation worse. In this regard, a different velocimetry method is documented in this dissertation which is free of cross-correlation. The method exploits a mapping between the moving flow and the temporal change in capacitance. It formulates a new forward problem, which can be solved using the conventional image reconstruction methods used for imaging. This method overcomes the limitations with the previous cross-correlation based approach, however, it has its own shortcoming. It is more challenging than imaging as it deals with three unknowns, i.e. the velocity components in three axial directions, as opposed to only one unknown for imaging which is the permittivity. The number of known variables is, however, only one for both problems which is the capacitance. This difficulty often degrade the performance of velocimetry as compared to imaging in similar cases, which is documented in terms of simulation results. In addition to that, experimental results are included with various data conditioning methods such as data smoothing, outlier removal etc.

Another contribution documented in this dissertation is the electronic scanning for ECVT, which aims improving the image resolution. For electronic scanning, a high electrode density sensor is employed as compared to a conventional sensor. Then, the electrode segments are connected and reconfigured dynamically to mimic physical rotation and displacement of the sensor on its axis. It is shown that electronic scanning is capable of increasing the resolution over conventional ECVT, however, at the cost of additional acquisition time because of the scanning. In this regard, a number of scanning strategies are described featuring different synthetic electrode shapes, and the optimum one is pointed out considering different acquisition times. Also, the strategies are implemented in SPICE to evaluate their feasibility in circuit aspects, e.g. signal to noise ratio (SNR), as compared to a conventional ECVT sensor. The conclusions derived from this analysis would serve future hardware implementation and testing of electronic scanning with adaptive ECVT sensors. Lastly, a study is included for volume fraction estimation of a two-phase flow based on ECVT capacitance data. The estimated volume fraction is intended to be used as a stopping criterion for an iterative image reconstruction method used throughout this dissertation.


15 March 2021

Rafiul K. Rasel, Benjamin Straiton, Qussai Marashdeh, and Fernando L. Teixeira

Abstract—Real-time monitoring of water volume fraction in multiphase flows is an important problem for a number of industrial applications. The water phase in the multiphase flows may correspond to either the dispersed phase or the continuous phase. In the past, several low-cost and nonintrusive techniques based on the electrical capacitance tomography (ECT) has been developed to image and monitor in real-time multiphase flows containing water. However, such monitoring becomes increasingly challenging for high salinity levels, and no reliable ECT-based method is presently available which could work for obtaining water volume fraction in multiphase flows for all water salinity levels. In this paper, we propose a new approach based on the Hanai’s formula for complex dielectric constant and taking advantage of the Maxwell-Wagner-Sillars effect to obtain, to a good approximation, water volume fractions in multiphase flows containing water as either dispersed or continuous phase.