Abstract
This work involved the simulation of both a multiphase gas–liquid flow and the electromagnetic field representing a two-electrode capacitance sensor in a circular pipe. The simulation investigates in particular the sensitivity of the sensor orientation around the pipe (i.e., top-to-bottom or side-to-side) that best capture the induced flow patterns. The presented numerical work is a simplified simulation by COMSOL multi-physics which was validated by a systematic and an extensive experimental work, using (a) a specially designed simple capacitance sensor (i.e., concave two electrodes), (b) different gas–liquid superficial velocity combinations, (c) different flow section inclinations, and (d) high-speed camera images. The numerical modelling capacitance values were validated against the experimentally measured values which shows a satisfactory level of agreement with a deviation of less than ±2%. The quantity of finite points was between 280,000 and 340,000, which was influenced by the simulated flow pattern. The simulated cases captured the generated flow patterns and their variation inside the pipe, which was in a good agreement when compared to the experimental work as time-dependent values. It was found that the best orientation for the utilized two-electrode capacitance sensor was the top-to-bottom configuration. This is because the sensor’s electrical field distribution was more sensitive, and capable of detecting a greater range of capacitance values. The sensitivity of the top-to-bottom configuration was 1.25–1.64 times greater than that of the side-to-side configuration. Therefore, for design purposes and performance optimization, it is recommended to use the top-to-bottom configuration.
Highlights
IntroductionIn gas–solids two-phase flow systems (e.g., fluidized bed reactors), to optimize the system performance and reach a high chemical conversion rate, there are a number of variables that must be determined from the experimental measurements
A validation analysis was carried out by comparing the simulated sensor and its equivalent that is the designed capacitance sensor. This comparison was in terms of the time-dependent output of the capacitance sensor for selected samples of some of the generated flow pattern
The measured capacitance values as a function of time reflected a correct and descriptive visualization of the produced flow patterns when compared to the captured images and their scientific definitions
Summary
In gas–solids two-phase flow systems (e.g., fluidized bed reactors), to optimize the system performance and reach a high chemical conversion rate, there are a number of variables that must be determined from the experimental measurements. These variables are the solids holdup (including the resident time), the solids circulation rate, the flow regimes, and the pressure drop. Caution must to be taken when estimating the solids’ circulation rate from these sensors, because it was reported that the direct measurement of the solids circulation rate from the pressure sensors usually gives an overestimated value [1,9]
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