Quantitative Visualization of Vapor Bubble Growth in Diabatic Vapor-Liquid Microchannel Slug Flow

2015 ◽  
Author(s):  
Todd A. Kingston ◽  
Justin A. Weibel ◽  
Suresh V. Garimella
Keyword(s):  
Flow Regime ◽  
Vapor Bubble ◽  
Slug Flow ◽  
Flow Boiling ◽  
Flow Behavior ◽  
Circular Cross Section ◽  
Vapor Flow ◽  
Liquid Slug ◽  
Two Phase ◽  
Vapor Liquid

Slug flow is a commonly encountered flow regime in microchannels due to the influence of surface tension and vapor confinement at small length scales. Few experimental studies have considered diabatic vapor-liquid slug flow, owing to difficulties in generating a well-controlled and repeatable slug flow regime; generation of vapor by wall heating typically leads to large, stochastic variations in the vapor bubble characteristics. To facilitate the study of flow behavior and vapor-liquid interfaces under precisely controlled conditions, a diabatic, one-component, two-phase microchannel flow was generated by separately injecting HFE-7100 vapor and liquid into a T-junction. Injection at independently controllable liquid and vapor flow rates allows the creation of vapor-liquid slug flow patterns in a downstream borosilicate microchannel of circular cross-section with a 500 μm inside diameter. The outside surface of the microchannel was coated with a 100 nm-thick layer of indium tin oxide (ITO) to generate a uniform wall heat flux via Joule heating while allowing full optical access for flow visualization. The growth of individual vapor bubbles was quantitatively visualized at different imposed heat fluxes, in terms of the percentage change in vapor bubble length along the heated microchannel. The results demonstrate the ability of the T-junction to generate diabatic, one-component, two-phase microchannel slug flow that is suitable for generating results for the validation of flow boiling models.

Two-Phase Flow Induced Force Fluctuations on Pipe Bend

2014 ◽  
Author(s):  
Shuichiro Miwa ◽  
Yang Liu ◽  
Takashi Hibiki ◽  
Mamoru Ishii ◽  
Yoshiyuki Kondo ◽  
...  
Keyword(s):  
Flow Regime ◽  
Slug Flow ◽  
Two Phase Flow ◽  
Pressure Fluctuations ◽  
Flow Regimes ◽  
Phase Flow ◽  
Liquid Slug ◽  
Two Phase ◽  
Pipe Bend ◽  
Force Fluctuation

In this study, fluctuating force induced by both upward and horizontal gas-liquid two-phase flow on 90 degree pipe bend at atmospheric condition was investigated. First, the database comprised of dynamic force signals and two-phase flow parameters such as volumetric fluxes, area averaged void fraction and pressure fluctuations covering entire two-phase flow regimes was developed for both flow orientations. Then, study was conducted to develop a model which is capable of predicting the force fluctuation frequency and magnitudes particularly for the slug flow regime. The model was fundamentally developed from the local instantaneous two-fluid model which was applied to the control volume around the elbow test section. Main contribution of the force fluctuation of two-phase flow is from the momentum and pressure fluctuations for most of the flow regimes. For slug flow regime, however, water-hammer like impact was produced by the collision of liquid slug against the structure surface. In order to consider that effect, the liquid slug impact force model was developed. The model utilizes two-group interfacial area concentration correlation to treat the flow regime transition without an abrupt discontinuity. It was found that the newly developed model is capable of predicting two-phase flow induced force fluctuation and dominant frequency range with satisfactory accuracy for flow regimes up to churn-turbulent.

Flow Regime Classification and Transition of Flow Boiling Through Porous Channel

2009 ◽  
Author(s):  
Bofeng Bai ◽  
Xiaojie Zhang ◽  
Maolong Liu ◽  
Wang Su
Keyword(s):  
Heat Flux ◽  
Flow Regime ◽  
Mass Flux ◽  
Slug Flow ◽  
Flow Boiling ◽  
Particle Diameter ◽  
Experimental Parameter ◽  
Flow Regimes ◽  
Two Phase ◽  
Porous Channels

In the present research, a visual experiment was carried out on the flow regimes of the porous channels in the spherical fuel element nuclear reactor. Boiling two-phase flow in different porous channels composed of particles with diameters of 4mm, 6mm and 8mm were studied respectively, and four different flow regimes occur within the experimental parameter range: bubbly flow, bubbly-slug flow, slug flow and slug-annular flow. The effects of heat flux, mass flux and particle diameter on the flow regimes were obtained. Bubbles and slugs deform, coalesce and break up more frequently, and increase in both number and size with the increase of the heat flux; bubbles and slugs tend to decrease in number and size with higher mass flux and particles of smaller diameters. At higher mass flux, a higher heat flux is needed to get the same flow regime that occurs at lower mass flux; with particles of smaller diameter, a higher heat flux is needed to get the same flow regime as that of particles of larger diameter. The flow regime map and flow regime transition have been proposed by modifying the void fractions of Tung/Dhir model.

An Experimentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Circular Microchannels

2001 ◽  
Vol 124 (1) ◽  
pp. 205-214 ◽  
Author(s):  
S. Garimella ◽  
J. D. Killion ◽  
J. W. Coleman
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Vapor Bubble ◽  
Total Pressure ◽  
Measured Data ◽  
Unit Cell ◽  
Intermittent Flow ◽  
Liquid Slug ◽  
Two Phase ◽  
Phase Pressure

This paper reports the development of an experimentally validated model for pressure drop during intermittent flow of condensing refrigerant R134a in horizontal microchannels. Two-phase pressure drops were measured in five circular channels ranging in hydraulic diameter from 0.5 mm to 4.91 mm. For each tube under consideration, pressure drop measurements were first taken over the entire range of qualities from 100% vapor to 100% liquid. In addition, the tests for each tube were conducted for five different refrigerant mass fluxes between 150 kg/m2-s and 750 kg/m2-s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were then used to identify data that corresponded to the intermittent flow regime. A pressure drop model was developed for a unit cell in the channel based on the observed slug/bubble flow pattern for these conditions. The unit cell comprises a liquid slug followed by a vapor bubble that is surrounded by a thin, annular liquid film. Contributions of the liquid slug, the vapor bubble, and the flow of liquid between the film and slug to the pressure drop were included. Empirical data from the literature for the relative length and velocity of the slugs and bubbles, and relationships from the literature for the pressure loss associated with the mixing that occurs between the slug and film were used with assumptions about individual phase friction factors, to estimate the total pressure drop in each unit cell. A simple correlation for non-dimensional unit-cell length based on slug Reynolds number was then used to estimate the total pressure drop. The results from this model were on average within ±13.4% of the measured data, with 88% of the predicted results within ±25% of the 77 measured data points.

On Instabilities in Horizontal Two-Phase Flow

1994 ◽  
Vol 59 (12) ◽  
pp. 2595-2603
Author(s):  
Lothar Ebner ◽  
Marie Fialová
Keyword(s):  
Differential Equation ◽  
Flow Regime ◽  
Slug Flow ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Annular Flows ◽  
Flow Regime Maps

Two regions of instabilities in horizontal two-phase flow were detected. The first was found in the transition from slug to annular flow, the second between stratified and slug flow. The existence of oscillations between the slug and annular flows can explain the differences in the limitation of the slug flow in flow regime maps proposed by different authors. Coexistence of these two regimes is similar to bistable behaviour of some differential equation solutions.

Prediction of High Viscosity Liquid/Gas Two-Phase Slug Length in Horizontal and Slightly Inclined Pipelines

2021 ◽  
Author(s):  
Omar Shaaban ◽  
Eissa Al-Safran
Keyword(s):  
Numerical Optimization ◽  
Flow Behavior ◽  
Mechanistic Model ◽  
High Viscosity ◽  
Oil Well ◽  
Liquid Slug ◽  
Two Phase ◽  
Proposed Model ◽  
Wide Range ◽  
Flow Closure

Abstract The production and transportation of high viscosity liquid/gas two-phase along petroleum production system is a challenging operation due to the lack of understanding the flow behavior and characteristics. In particular, accurate prediction of two-phase slug length in pipes is crucial to efficiently operate and safely design oil well and separation facilities. The objective of this study is to develop a mechanistic model to predict high viscosity liquid slug length in pipelines and to optimize the proper set of closure relationships required to ensure high accuracy prediction. A large high viscosity liquid slug length database is collected and presented in this study, against which the proposed model is validated and compared with other models. A mechanistic slug length model is derived based on the first principles of mass and momentum balances over a two-phase slug unit, which requires a set of closure relationships of other slug characteristics. To select the proper set of closure relationships, a numerical optimization is carried out using a large slug length dataset to minimize the prediction error. Thousands of combinations of various slug flow closure relationships were evaluated to identify the most appropriate relationships for the proposed slug length model under high viscosity slug length condition. Results show that the proposed slug length mechanistic model is applicable for a wide range of liquid viscosities and is sensitive to the selected closure relationships. Results revealed that the optimum closure relationships combination is Archibong-Eso et al. (2018) for slug frequency, Malnes (1983) for slug liquid holdup, Jeyachandra et al. (2012) for drift velocity, and Nicklin et al. (1962) for the distribution coefficient. Using the above set of closure relationships, model validation yields 37.8% absolute average percent error, outperforming all existing slug length models.

Compact Model of Slug Flow in Microchannels

2007 ◽  
Author(s):  
Dong Rip Kim ◽  
Jae-Mo Koo ◽  
Chen Fang ◽  
Julie E. Steinbrenner ◽  
Eon Soo Lee ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Liquid Water ◽  
Slug Flow ◽  
Flow Behavior ◽  
Contact Angles ◽  
Proton Exchange ◽  
Force Balance ◽  
Compact Model ◽  
Two Phase ◽  
Coverage Ratio

This paper presents a theoretical investigation of the movement of liquid droplets and slugs in hydrophobic microchannels and develops a compact model for this type of two-phase flow. This model is used in the prediction of pressure drop and liquid water coverage ratio, key parameters in the operation of Proton Exchange Membrane Fuel Cells (PEMFC), the primary motivation for this work. A semi-empirical, periodic-steady two-phase separated flow compact model is formulated to characterize the slug flow behavior. The momentum equation includes the effects of acceleration, friction and surface tension on the pressure drop. The model considers spatial changes in slug velocity through the use of a force balance formulation. The model uses a departure scheme that computes slug size and shape at entrainment. The steady state slug flow compact model is capable of predicting liquid water coverage ratio and pressure drop using liquid and gas flow rates and advancing/receding triple point contact angles as its only inputs. The results indicate that the pressure drop increases as the droplet formation frequency increases.

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