Enhancement of Inter-Phase Transport in Mini/Micro-Scale Applications Using Passive Mixing

2011 ◽  
Author(s):  
Adam A. Donaldson ◽  
Patrick Plouffe ◽  
Arturo Macchi
Keyword(s):  
Mass Transfer ◽  
Pressure Drop ◽  
Scale Up ◽  
Interfacial Area ◽  
Flow Patterns ◽  
High Mass ◽  
Two Phase ◽  
Initial Flow ◽  
Micro Scale ◽  
Passive Mixing

Structured mini/micro-scale reactors continue to receive attention from both industry and academia due to their low pressure drop, high mass transfer rates and ease of scale-up when compared to conventional reactor technology. Commonly considered for heat and mass transfer limited reactions such as hydrogenations, hydrodesulphurization, oxidations and Fischer-Tropsch synthesis, the performance of these systems is highly dependent on mixing and the interfacial area between phases. While existing literature describes the initial flow patterns generated by a broad range of two-phase contactors, few studies explore the dynamic impacts of downstream passive mixing elements. Experimental and computational methodologies for characterizing two-phase flow pattern transitions, pressure drop, mixing and mass transfer are discussed, with relevant examples for serpentine and venturi-based passive mixing designs. The efficacy of these two configurations are explored in the context of pressure drop, conditions leading to significant interface renewal, and design considerations for optimizing mass transfer. Challenges associate with the characterization of multiphase flow through these systems are highlighted, and strategies suggested for both experimental and computational analysis of dynamic flow patterns and fluid-fluid interactions.

The effect of two-phase flow regime on hydrodynamics and mass transfer in a horizontal-tube gas-liquid reactor

1985 ◽  
Vol 50 (3) ◽  
pp. 745-757 ◽  
Author(s):  
Andreas Zahn ◽  
Lothar Ebner ◽  
Kurt Winkler ◽  
Jan Kratochvíl ◽  
Jindřich Zahradník
Keyword(s):  
Mass Transfer ◽  
Pressure Drop ◽  
Flow Regime ◽  
Liquid Flow ◽  
Horizontal Tube ◽  
Liquid Holdup ◽  
Two Phase ◽  
Flow Rates ◽  
Type Relation ◽  
Good Agreement

The effect of two-phase flow regime on decisive hydrodynamic and mass transfer characteristics of horizontal-tube gas-liquid reactors (pressure drop, liquid holdup, kLaL) was determined in a cocurrent-flow experimental unit of the length 4.15 m and diameter 0.05 m with air-water system. An adjustable-height weir was installed in the separation chamber at the reactor outlet to simulate the effect of internal baffles on reactor hydrodynamics. Flow regime maps were developed in the whole range of experimental gas and liquid flow rates both for the weirless arrangement and for the weir height 0.05 m, the former being in good agreement with flow-pattern boundaries presented by Mandhane. In the whole range of experi-mental conditions pressure drop data could be well correlated as a function of gas and liquid flow rates by an empirical exponential-type relation with specific sets of coefficients obtained for individual flow regimes from experimental data. Good agreement was observed between values of pressure drop obtained for weirless arrangement and data calculated from the Lockhart-Martinelli correlation while the contribution of weir to the overall pressure drop was well described by a relation proposed for the pressure loss in closed-end tubes. In the region of negligible weir influence values of liquid holdup were again succesfully correlated by the Lockhart-Martinelli relation while the dependence of liquid holdup data on gas and liquid flow rates obtained under conditions of significant weir effect (i.e. at low flow rates of both phases) could be well described by an empirical exponential-type relation. Results of preliminary kLaL measurements confirmed the decisive effect of the rate of energy dissipation on the intensity of interfacial mass transfer in gas-liquid dispersions.

scholarly journals Two-Phase Flow Mass Transfer Analysis of Airlift Pump for Aquaculture Applications

Fluids ◽  
2021 ◽  
Vol 6 (6) ◽  
pp. 226
Author(s):  
Rashal Abed ◽  
Mohamed M. Hussein ◽  
Wael H. Ahmed ◽  
Sherif Abdou
Keyword(s):  
Mass Transfer ◽  
Oxygen Transfer ◽  
Transfer Rate ◽  
Two Phase Flow ◽  
Oxygen Transfer Rate ◽  
Flow Patterns ◽  
Oxygen Mass Transfer ◽  
Phase Flow ◽  
Two Phase ◽  
Airlift Pump

Airlift pumps can be used in the aquaculture industry to provide aeration while concurrently moving water utilizing the dynamics of two-phase flow in the pump riser. The oxygen mass transfer that occurs from the injected compressed air to the water in the aquaculture systems can be experimentally investigated to determine the pump aeration capabilities. The objective of this study is to evaluate the effects of various airflow rates as well as the injection methods on the oxygen transfer rate within a dual injector airlift pump system. Experiments were conducted using an airlift pump connected to a vertical pump riser within a recirculating system. Both two-phase flow patterns and the void fraction measurements were used to evaluate the dissolved oxygen mass transfer mechanism through the airlift pump. A dissolved oxygen (DO) sensor was used to determine the DO levels within the airlift pumping system at different operating conditions required by the pump. Flow visualization imaging and particle image velocimetry (PIV) measurements were performed in order to better understand the effects of the two-phase flow patterns on the aeration performance. It was found that the radial injection method reached the saturation point faster at lower airflow rates, whereas the axial method performed better as the airflow rates were increased. The standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) were calculated and were found to strongly depend on the injection method as well as the two-phase flow patterns in the pump riser.

Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

2003 ◽  
Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase ◽  
Micro Channels

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406 × 2.032 mm cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal that the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Annual flow is identified as the dominant flow pattern for conditions relevant to two-phase micro-channel heat sinks, and forms the basis for development of a theoretical model for both pressure drop and heat transfer in micro-channels. Features unique to two-phase micro-channel flow, such as laminar liquid and gas flows, smooth liquid-gas interface, and strong entrainment and deposition effects are incorporated into the model. The model shows good agreement with experimental data for water-cooled heat sinks.

scholarly journals Boiling Flow Pattern Identification Using a Self-Organizing Map

2020 ◽  
Vol 10 (8) ◽  
pp. 2792
Author(s):  
Iwona Zaborowska ◽  
Hubert Grzybowski ◽  
Romuald Mosdorf
Keyword(s):  
Pressure Drop ◽  
Flow Patterns ◽  
Recurrence Quantification Analysis ◽  
Bubble Flow ◽  
Self Organizing Map ◽  
Two Phase ◽  
Recurrence Quantification ◽  
Quantification Analysis ◽  
Flow Pattern Identification ◽  
Self Organizing

In the paper, a self-organizing map combined with the recurrence quantification analysis was used to identify flow boiling patterns in a circular horizontal minichannel with an inner diameter of 1 mm. The dynamics of the pressure drop during density-wave oscillations in a single pressure drop oscillations cycle were considered. It has been shown that the proposed algorithm allows us to distinguish five types of non-stationary two-phase flow patterns, such as bubble flow, confined bubble flow, wavy annular flow, liquid flow, and slug flow. The flow pattern identification was confirmed by images obtained using a high-speed camera. Taking into consideration the oscillations between identified two-phase flow patterns, the four boiling regimes during a single cycle of the long-period pressure drop oscillations are classified. The obtained results show that the proposed combination of recurrence quantification analysis (RQA) and a self-organizing map (SOM) in the paper can be used to analyze changes in flow patterns in non-stationary boiling. It seems that the use of more complex algorithms of neural networks and their learning process can lead to the automation of the process of identifying boiling regimes in minichannel heat exchangers.

Experimental Investigation on Flow Patterns and Frictional Pressure Drop of Downward Air-Water Two-Phase Flow in Vertical Pipes

2013 ◽  
Author(s):  
Yuqing Xue ◽  
Huixiong Li ◽  
Tianyou Sheng ◽  
Changjiang Liao
Keyword(s):  
Pressure Drop ◽  
Flow Pattern ◽  
Oil Recovery ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Phase Flow ◽  
Vertical Pipe ◽  
Two Phase Flows ◽  
Two Phase ◽  
Frictional Pressure Drop

A large amount of air need be transported into the reservoir in the deep stratum to supply oxygen to some microbes in Microbial Enhanced Oil Recovery (MEOR). Air-water two-phase flows downward along vertical pipeline during the air transportation. Base on the experiment data described in this paper, the characteristics of air-water two phase flow patterns were investigated. The flow pattern map of air-water two phase flows in the pipe with inner diameter of 65 mm was drawn, criterions of flow pattern transition were discussed, and the dynamic signals of the pressure and the differential pressure of the two phase flow were recorded to characterize the three basic flow regimes indirectly. The frictional pressure drop of downward flow in vertical pipe must not be disregarded contrast with upward two phase flow in the vertical pipe because the buoyancy must be overcame when the gas flows downward along pipe, and there would be a maximum value of frictional when the flow pattern translated from slug flow to churn flow.

Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

2004 ◽  
Vol 126 (3) ◽  
pp. 288-300 ◽  
Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406×2.032mm2 cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Features unique to two-phase micro-channel flow were identified and employed to validate key assumptions of an annular flow boiling model that was previously developed to predict pressure drop and heat transfer in two-phase micro-channel heat sinks. This earlier model was modified based on new findings from the adiabatic two-phase flow study. The modified model shows good agreement with experimental data for water-cooled heat sinks.

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