Using image analysis in the study of multiphase gas absorption

Experimental determination of spatial distribution of granular fractions in flow of bimodal mixture

The contribution deals with the determination of the ratio of volumes of particles of individual fractions in flows transporting bimodal granular mixtures. The spatial distribution of the ratio is obtained by analyzing images collected by video recording. The measuring method and post-processing analysis are demonstrated on experiments in our new recirculating fluidization cell. The tested bimodal mixture is composed of two granular fractions of different colors – black and white. The analysis is based on a local identification of particles and their background in the collected images. More precisely, the identification of individual particles is based on the grayscale screening of the images. The method allows to identify both the instantaneous and time-averaged spacious distribution of the grain volume ratio. The experimental results reveal that the measuring method is successful if constant light condition is secured and the medium carrying particles is sufficiently transparent. The method is applicable to laboratory flows with sediment transport no matter whether sediment particles are transported as bed load or as suspended load.

Experimental Study on Bubble Size Distribution in Gas-Liquid Reversed Jet Loop Reactor

Bubble size distribution (BSD) is important for gas-liquid jet loop reactor (JLR)’s mass transfer performance of inter-phases. A self-designed reversed JLR was investigated with air-water system on the BSD. The CCD camera of particle imaging velocimetry (PIV) system and image processing technique were used to obtain the reliable photo. The influences of four parameters, gas phase flow rate, liquid phase flow rate, draft tube diameter and ejector mounting position, on the BSD were studied in detail. The results showed that the local BSD is accordance with log-normal distribution under the experimental conditions and the average diameter and BSD range increase with the increase of the gas phase flow rate, and decrease with the increase of the liquid phase flow rate, the downward movement of the nozzle installation position and the increase of the diameter of the draft tube.

Study of the Hydrodynamics and Mass Transfer Coefficient in a 2D Mimicked FT Slurry Bubble Columns for Alternative Clean Energy and Chemical Production

Bubble columns are widely used for contacting gas–liquid and gas–liquid–solid mass transfer/chemical reactions. Gas distributor is the most important accessory because it decides the bubble size/rise velocity and gas distribution. In this study, the effect of distributor design on hydrodynamics and mass transfer coefficient are studied at different operating conditions of height to diameter ratio, solid loading, and superficial gas velocity The overall gas holdup, is studied experimentally using a rectangular slurry bubble column operating at ambient temperature and pressure, using liquid paraffin (C9–C11), three heights to diameter ratios (6, 7.5 and 10) and silica as a solid phase (0 %, 9 % and 25 %) with oxygen as gas phase. Two types of distributor were used, perforated plate and ring type. The results showed that the overall gas holdup increased by increasing gas velocity and decreased by increasing height to diameter ratio and solid loading. Also, it is found that the perforated plate distributor gave a higher gas hold up than ring distributor at gas velocity higher than 0.03 m/sec. The following correlations are obtained:

Plate distributor at presence of silica particles: $$\eqalign{{{\rm{\varepsilon}}_{\rm{g}}} =& {\left({1.343{\rm{U}}_{\rm{g}}^{0.0612} - 0.00891{\rm{\varepsilon}}_{\rm{s}}^{- 0.374} - 0.702{{\left({{{\rm{L}} \over {\rm{D}}}} \right)}^{0.041}}} \right)^{4.904}}\cr& - 0.0251}$$

Ring distributor at presence and absence of silica particles: $$\eqalign{{{\rm{\varepsilon}}_{\rm{g}}} = &{\left({0.216{\rm{U}}_{\rm{g}}^{0.297} - 0.354{\rm{\varepsilon}}_{\rm{s}}^{1.4671} - 0.127{{\left({{{\rm{L}} \over {\rm{D}}}} \right)}^{0.147}}} \right)^{1.1206}} \cr&+ 0.058}$$

There is a good agreement between experimental and predicted values with a percent of error less than 2 %.

It has been found that the mass transfer coefficient is higher for ring distributor than the perforated plate and growing higher for heterogeneous flow regime and higher solid loading.

Chemical Reaction Effect upon Gas–Liquid Interfacial Area in a Bubble Column Reactor

This work analyses the influence of different experimental conditions over important hydrodynamic parameters of a bubble column reactor, such as bubble size distribution, gas hold-up and the gas–liquid interfacial area. The influence of gas flow-rate (18–40 L h–1) and reagent concentration (0–0.5 mol L–1) in the liquid phase upon these hydrodynamic parameters have been studied. The influence of experiment time must also be taken into account due to non-steady-state regime. Under these considerations, the chemical absorption rate changes throughout time, and it produces important changes upon the global absorption process, due to modifications in the gas–liquid interfacial area. The presence of a fast reaction in the liquid bulk has the highest influence upon interfacial area.

Fiber-Optical Sensors: Basics and Applications in Multiphase Reactors

This work presents a brief introduction on the basics of fiber-optical sensors and an overview focused on the applications to measurements in multiphase reactors. The most commonly principle utilized is laser back scattering, which is also the foundation for almost all current probes used in multiphase reactors. The fiber-optical probe techniques in two-phase reactors are more developed than those in three-phase reactors. There are many studies on the measurement of gas holdup using fiber-optical probes in three-phase fluidized beds, but negative interference of particles on probe function was less studied. The interactions between solids and probe tips were less studied because glass beads etc. were always used as the solid phase. The vision probes may be the most promising for simultaneous measurements of gas dispersion and solids suspension in three-phase reactors. Thus, the following techniques of the fiber-optical probes in multiphase reactors should be developed further: (1) online measuring techniques under nearly industrial operating conditions; (2) corresponding signal data processing techniques; (3) joint application with other measuring techniques.