Determination Of Liquid Holdup Research Articles

A noninvasive X-ray technique for determination of liquid holdup in a rotating packed bed

A rotating packed bed (RPB) has received considerable attention of many researchers due to its high mass transfer rate and mixing efficiency. In order to effectively promote and employ RPB in the chemical industry, it is necessary to have a better understanding of its flow characteristics. In this study, a noninvasive X-ray technique was employed for the first time to examine the hydrodynamics of RPB. Time-average tomographic cross sectional images showing the distribution of liquid in the packing zone under various operating conditions were captured. It was observed that high rotational speed improves the distribution of liquid in the packing. Additionally, quantitative analysis based on liquid holdup was made, and the effects of rotational speed, liquid flow rate, fluid viscosity, surfactant and two different kinds of packings on liquid holdup were evaluated. Results indicate that liquid holdup decreases with an increase in rotational speed and a reduction in both liquid flow rate and liquid viscosity. However, it was observed that surfactant has no significant effect on liquid holdup. Correlations to predict liquid holdup were developed, and the calculated values are in agreement with the experimental values with deviations within ±22%. Furthermore, the mean residence time in various conditions is calculated based on liquid holdup.

Holdup and Pressure Drop in Micro Packed‐Bed Reactors for Fischer‐Tropsch Synthesis

AbstractLow‐temperature Fischer‐Tropsch synthesis was investigated in micro packed‐bed reactors. Co/Re/γ‐Al2O3 catalysts with different particle shapes and sizes (60 to 580 μm) were employed. Tubular reactor geometry with lengths of up to 1 m was chosen. Pressure drop measurements in the absence of reaction and during reaction were carried out. For analysis of the experimental data a reactor model was developed, which was also used for the determination of liquid holdup. It could be observed that the liquid holdup is independent of conversion, reaction temperature, C5+ productivity, and reaction rate. For irregularly shaped catalyst particles, a liquid holdup in the range of 3 % was observed.

Mass transfer and liquid hold-up determination in structured packing by CFD

Mass transfer and liquid hold-up in structured packing geometry are investigated using the volume of fluid method. Numerical simulations of two-dimensional co-current gas–liquid flow on structured packing with interfacial mass transfer are performed. The volume of fluid method is used to capture the gas–liquid interface motion. The mass transfer is computed by solving the concentration equation with an adapted modeling of the solubility (Haroun et al., 2010b). The liquid hold-up and the mass transfer are studied as function of liquid flow rate and structured packing geometry. Results show how the liquid flow rate and the complex geometry affect the liquid film flow topology and the interfacial mass transfer. For a specified packing geometry, it is demonstrated that for low liquid flow rate, the liquid film remains uniform and follow closely the profile of the structured wall. For uniform liquid film flow along packing wall, it is found that the liquid hold-up is in good agreement with the model proposed by Billet and Schultes (1999) and Raynal and Royon-Lebeaud (2007). When increasing the liquid flow rate, the liquid film does not follow the shape of the structured wall anymore, a static hold-up (recirculation zone) form in the cavities and grows as the Reynolds number increases until covering most of the packing cavities. The present work gives the liquid hold-up evolution for each liquid film flow regime according to the Reynolds number and the dimensionless amplitude of the corrugation. Concerning the liquid side mass transfer, it is found that the liquid side mass transfer is well predicted by the Higbie (1935) theory provided that adequate velocity and length scales are considered for exposure time determination. The exposure time of fluid element at the interface corresponds to the ratio between the curvilinear distance between two periodic corrugation contact point and the interface velocity. An exposure time model is proposed taking into the account physical and geometric parameters.

Analysis of gas–liquid behavior in eccentric horizontal annuli with image processing and artificial intelligence techniques

In drilling operations estimation of gas–liquid behavior such as flow patterns and liquid holdup is beneficial in terms of cost, time and efficient usage of resources for the well to be opened. There is a lack of research for hydraulic behavior of two phase fluids in annular geometries. One of the aims of this study is to observe the flow patterns experimentally in two phase eccentric annulus. The second aim is to detect the liquid holdup of these flows using digital image processing techniques instead of emprical correlations or mechanistic models. The last aim is to estimate the flow pattern and liquid holdup for two phase (air and water) flow in horizontal eccentric annulus. This is conducted by using artificial intelligence techniques rather than conventional mechanistic models. In this study, nearest neighbor algorithm, backpropagation neural networks, and decision trees are used as the artificial intelligence techniques. Flow is generalized by representing the flow patternsas superficial Reynolds numbers for both liquid and gas phase. The results showed that the back propagation neural network model provided the best results as an estimation model for flow pattern identification whereas regression decision tree had the best performance for liquid holdup determination. In air and water flow, 7 observed flow patterns are classified correctly with an accuracy of 90.38% and liquid holdup is estimated with an average absolute percent error of 17.06%.

Determination of liquid hold-up and flow distribution inside modular catalytic structured packings

This paper presents the results of a study carried out to examine liquid hold-up and flow distribution in a 0.1 m internal diameter column filled with catalytic structured packing Katapak-SP. Information has been gathered at local scale by means of a non-intrusive high energy X-ray tomograph. Measurements have been carried out in a large number of packing cross sections situated at different heights between the top and bottom of the packed column, giving access to the evolution of axial profiles of liquid hold-up in the open channels (separation zone) and in the catalytic baskets (reaction zone) as a function of the liquid load. The total hold-up, evaluated by averaging local tomographic values over the packed volume, was compared with global hold-up data obtained by traditional methods, like draining and RTD measurements. A method was also proposed to deduce the distribution of liquid flowrate, between the reaction and the separation zones, from hold-up distribution measured by tomography. The methodology was validated by comparison with experimental data obtained by collecting separately the liquid flowing out of the two zones at the bottom of the packed bed. The obtained results are invaluable to improve the description of hydrodynamics in rate based performance models.

Estimation of Multiphase Flow Properties using Computational Intelligence Models

Estimation of flow properties is essential in terms of the efficient usage of resources in drilling operations. Meanwhile, hydraulic characteristics of two phase fluids in annular geometries are not studied thoroughly. In this study, the flow patterns and liquid holdup characteristics of liquid-gas flow is analyzed using experimental data obtained from an eccentric pipe configuration. A high speed digital camera is used for recording the flow; in addition liquid holdup values are calculated using digital image processing techniques instead of empirical correlations or mechanistic measurements. At the same time through the acquired images, corresponding flow patterns are observed. Using the acquired images, estimation models are developed for air-water flow in horizontal eccentric annulus. This is conducted by using computational intelligence rather than conventional mechanistic models. The chosen models are nearest neighbor, backpropagation, decision trees and SVM. Input attributes are superficial Reynolds numbers for both liquid and gas phase. The output is the classified flow pattern and the liquid holdup value. SVM model turned out to be the best estimator for flow pattern identification process (%92.49 success rate for classifying 7 different flow patterns) whereas regression decision tree had the best performance for liquid holdup determination (RMSE of 0.0777).

Liquid holdup and flow dispersion in zeolite packed beds

A simple tracing method, based on residence time distribution measurements, is presented for the evaluation of the liquid holdup and dispersion in zeolite packed beds. Two tracers and two different materials, one porous (zeolite clinoptilolite) and one non-porous (SiC), were used in experiments on seven packed beds of different dimensions, operating under downflow or upflow condition, in the range of superficial velocities from 0.04 to 0.61×10 −2 m/ s . The corresponding superficial Reynolds number is between 0.6 and 8.50. Drainage and tracing methods are experimentally compared. The tracing techniques tested are reliable and applicable for the determination of liquid holdup and dispersion in clinoptilolite beds. Liquid holdup, as % of void volume of the bed, is 90±10% for upflow condition, independent of the superficial velocity. For downflow condition it reaches 80% for superficial velocities greater than 0.4×10 −2 m/ s . Peclet numbers were determined, giving different trends for upflow and downflow conditions. For superficial velocity near 0.4×10 −2 m/ s (Reynolds number near 4) and greater, Peclet numbers are identical and in the vicinity of 0.12. A discussion is conducted in order to clarify this observation. Approximate correlations are proposed for liquid holdup and Peclet number in zeolite packed beds.

Gravimetric Method for the Determination of Liquid Holdup in Pressurized Trickle-Bed Reactors

A gravimetric method for the determination of liquid holdup was successfully employed in a high-pressure-operated trickle-bed reactor. The method has proven to be a reliable, fast, and relatively simple way of measuring liquid holdups under high pressures, despite opposite indications of previous works done in this field. A detailed description of the apparatus and measuring procedure is given.

Process intensification: operating characteristics of rotating packed beds — determination of liquid hold-up for a high-voidage structured packing

Measurements of electrical resistance across annular sections of a high-voidage rotating packed bed were used to determine liquid hold-up and residence time for a gas–liquid system. The results were compared with predictions based on established flow models. Differences between the results and similar studies conducted using lower porosity glass sphere packing were examined. The relationship between gas flow rate and rotational speed during flooding was discussed and compared for low and high porosity packing.

On dynamic liquid holdup determination by the drainage method

A careful examination of the liquid drainage in packed-bed reactors using liquid superficial velocities characteristic of trickle flow regime and no gas velocity is both experimentally and theoretically carried out. True free-flowing or dynamic liquid holdups are determined in two different reactors packed with porous and nonporous particles employing several liquids. Dynamic liquid holdups are shown to be higher than those determined directly from total liquid drained volumes, which are usually reported when the drainage method is applied. It is found that a model of laminar liquid films properly addresses the influence of liquid superficial velocities and of liquid viscosity on the dynamic liquid holdup within the experimental conditions studied. A simple quantitative phenomenological model to describe the drainage kinetics is developed and is independently verified from experimental data. Satisfactory agreement is found for all the examined conditions.

Liquid holdup in rotating packed beds: Examination of the film flow assumption

AbstractPossibilities of predicting liquid holdup in rotating packed beds are examined using the film flow theory. A hydrodynamic model based on film flow on the particle scale accommodates both laminar and turbulent films in the entry and developed regime. Conductance measurement was used for experimental determination of liquid holdup and estimation of the degree of anisotropy of liquid distribution. Experimental results represent the first data for liquid holdup in the rotating packed bed as a function of operating conditions and liquid properties. They indicate an anisotropic liquid distribution dependent on the operating variables. While the film model can be fitted to the experimental data, such a fit lacks a theoretical basis and the classical theory of film flow on the particle scale cannot explain the liquid flow in rotating packed beds. An empirical expression correlates well the holdup data with the operating parameters.

Liquid holdup determination in packed columns for sulfur dioxide absorption

Abstract Total, static and dynamic holdups have been measured for 0.012 m ceramic Raschig rings with air rates from 0 to 700 kg m−2 h−1 and sodium citrate solution rates from 2000 to 60 000 kg m−2 h−1 at 40°C using the draining method. Equations presented for estimating holdups are discussed.

Slug flow of air—water mixtures in a horizontal pipe: Determination of liquid holdup by γ-ray absorption

Two-phase pressure gradients and time-averaged values of liquid holdup have been measured for the co-current flow of air and water in a 42 mm bore horizontal pipeline. The majority of the data corresponded to the slug flow region, where rapid fluctuations in both wall pressure and holdup were observed. Instantaneous values of liquid holdup were also recorded by rapid scanning of a vertical cross-section of the pipe using the γ-ray absorption method, which enabled probability density functions (PDF) and power spectral densities (PSD) of holdup to be determined. From these functions, values of average film and slug holdups, average slug length and average slug frequency were estimated. These measurements facilitated the use of the Hubbard—Dukler slug flow model for two-phase pressure drop prediction which compared favourably with the Lockhart—Martinelli correlation over the X-parameter range 2–30.