Prediction of the liquid film reversal of annular flow in vertical and inclined pipes

Heat transfer in micro scale two-phase flow attracts large attention since it can achieve large heat transfer area per density. At high quality, annular flow becomes one of the major flow regimes in micro two-phase flow. Heat is transferred by evaporation or condensation of the liquid film, which are the dominant mechanisms of micro scale heat transfer. Therefore, liquid film thickness is one of the most important parameters in modeling the phenomena. In macro tubes, large numbers of researches have been conducted to investigate the liquid film thickness. However, in micro tubes, quantitative information for the annular liquid film thickness is still limited. In the present study, annular liquid film thickness is measured using a confocal method, which is used in the previous study [1, 2]. Glass tubes with inner diameters of 0.3, 0.5 and 1.0 mm are used. Degassed water and FC40 are used as working fluids, and the total mass flux is varied from G = 100 to 500 kg/m2s. Liquid film thickness is measured by laser confocal displacement meter (LCDM), and the liquid-gas interface profile is observed by a high-speed camera. Mean liquid film thickness is then plotted against quality for different flow rates and tube diameters. Mean thickness data is compared with the smooth annular film model of Revellin et al. [3]. Annular film model predictions overestimated the experimental values especially at low quality. It is considered that this overestimation is attributed to the disturbances caused by the interface ripples.

Download Full-text

Effects of liquid viscosity on liquid film flow in gas-liquid two-phase annular flow

10.1117/12.852408 ◽

2009 ◽

Author(s):

Koji Mori ◽

Akio Nakata

Keyword(s):

Liquid Film ◽

Annular Flow ◽

Film Flow ◽

Liquid Viscosity ◽

Two Phase ◽

Liquid Film Flow

Download Full-text

Experimental Observation of Nucleate Boiling Entrainment in a Liquid Film

10.1115/icone28-63813 ◽

2021 ◽

Author(s):

Junpei Tabuchi ◽

Yuki Narushima ◽

Kenichi Katono ◽

Tomio Okawa

Keyword(s):

Liquid Film ◽

Forced Convection ◽

Vapor Bubble ◽

Water Surface ◽

Annular Flow ◽

Nucleate Boiling ◽

Vapor Bubbles ◽

Droplet Entrainment ◽

Bubble Bursting ◽

Filament Breakup

Abstract Many studies have been conducted on droplet entrainment in an annular flow regime, but little is known about droplet entrainment caused by nucleate boiling. In this report, visualization results of droplet entrainment caused by nucleate boiling are described. We observed two processes of droplet entrainment. The first one causes bubble bursting at a water surface. The second one causes filament breakup which occurs when the vapor bubble reaches and collapses at the interface between air and liquid. From comparison of the phenomena for the two processes, we found that the diameters of the droplets and vapor bubbles were considerably different. Using the results of this research allows the effect of forced convection to be taken into account. In the future, we plan to expand the amount of data and develop a boiling entrainment model under forced convection conditions.

Download Full-text

Measurement of Interfacial Structure on Liquid Film in Annular Flow Using Laser Focus Displacement Meter (2nd Report, Disturbance Wave Frequency and Local Minimum Film Thickness)

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.71.1272 ◽

2005 ◽

Vol 71 (705) ◽

pp. 1272-1277

Author(s):

Tatsuya HAZUKU ◽

Tomoji TAKAMASA ◽

Yoichiro MATSUMOTO

Keyword(s):

Film Thickness ◽

Liquid Film ◽

Annular Flow ◽

Local Minimum ◽

Interfacial Structure ◽

Wave Frequency ◽

Disturbance Wave ◽

Laser Focus ◽

Minimum Film Thickness

Download Full-text

Liquid film thickness in annular flow

Chemical Engineering Science ◽

10.1016/0009-2509(77)80016-x ◽

1973 ◽

Vol 28 (3) ◽

pp. 819-824 ◽

Cited By ~ 5

Author(s):

R.P.S. Srivastava

Keyword(s):

Film Thickness ◽

Liquid Film ◽

Annular Flow ◽

Liquid Film Thickness

Download Full-text

An Investigation of Slug Flow in Hilly Terrain Pipelines

Part B: Offshore and Arctic Operations; Pipeline Technology; Production Technology; Tribology ◽

10.1115/etce2001-17063 ◽

2001 ◽

Author(s):

Suat Bagci ◽

Adel Al-Shareef

Keyword(s):

Liquid Film ◽

Slug Flow ◽

Flow Characteristics ◽

Source Model ◽

Pipe Diameter ◽

Liquid Holdup ◽

Hilly Terrain ◽

Two Phase ◽

Flow Interactions ◽

Inclined Pipes

Abstract Two-phase flow in hilly terrain pipelines can cause significant practical operating problems. When slugs flow in a hilly terrain pipeline that contains sections of different inclinations they undergo a change of length and slug flow characteristics as the slug move from section to section. In addition, slugs can be generated at low elbows, dissipate at top elbows and shrink or grow in length as they travel along the pipe. A mathematical model and a computer program was developed to simulate these phenomena. The model was based on the sink/source concept at the pipeline connections. A connection between two pipeline sections of different slopes was conveniently called elbow. An elbow accumulates liquid as a sink, and releases liquid as a source. The sink/source has a characteristic capacity of its own. This capacity is positive if the liquid can indeed be accumulated at the elbow or negative if the liquid is actually drained away from the elbow. This type of treatment effectively isolates the flow upstream from an elbow from that downstream, while still allowing flow interactions between two detailed pipeline sections. The hydrodynamic flow model was also used to calculate the film liquid holdup in horizontal and inclined pipelines. The model can successfully predict the liquid film holdup if the liquid film height is assumed to be uniform through the gas pocket. Many other models were used to calculate all the needed parameters to perform the sink/source model. The overall effect of a hill or terrain on slug flow depends on the operating flow rates and pipeline configurations. For special case of near constant slug frequency corresponding to moderately high superficial liquid and gas velocities, this effect was found to be small. The changes in the film characteristics between two adjacent pipeline sections were found to be mostly responsible for the pseudo-slug generation, slug growth and dissipation in the downstream pipeline sections. The film liquid holdup decreased with increasing pipe diameter. The unit slug length increased at the upstream inclined pipes and decreased at the downstream inclined pipes with increasing pipe diameter. The possibility of pseudo-slug generation was increased at large pipe diameters even at high sink capacities. At low sink capacities, no pseudo-slugs were generated at high superficial velocities. The slug flow characteristics was more effected by low superficial gas and liquid velocities, large pipe diameters and shallow pipeline inclinations.

Download Full-text

An Investigation of Flow, Heat Transfer Characteristic of Annular Flow and Critical Heat Flux in Vertical Upward Round Tube

Volume 2: Thermal Hydraulics ◽

10.1115/icone14-89108 ◽

2006 ◽

Cited By ~ 2

Author(s):

Fan Pu ◽

Suizheng Qiu ◽

Guanghui Su ◽

Dounan Jia

Keyword(s):

Heat Transfer ◽

Experimental Data ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Liquid Film ◽

Critical Heat Flux ◽

Heat Transfer Characteristic ◽

Annular Flow ◽

Transfer Characteristic ◽

Round Tube

The term annular flow is used to describe the configuration of vapor-liquid flow in which part of the liquid travels as a film on the wall and the rest is entrained as drops by the vapor core in the center of the channel. The objective of this paper is to develop a hydrodynamic model for vertical upward annular flow. A separated flow model is developed and the conservations of Mass, Momentum, Energy, entrainment rate correlation in wide range of conditions and interfacial frictional correlation are used to research the flow and heat transfer characteristic of annular flow. The liquid film thickness, liquid film mass flow rate, two-phase heat transfer coefficient pressure along axial position, local velocity profiles along radial position are predicted theoretically. The influence of the mass flux, heat flux on liquid film thickness, heat transfer coefficient etc. are investigated in detail. The critical heat flux are also predicted in vertical upward round tube according to the theory that the dryout in vertical annular flow emerges at the point where the film is depleted due to the integrating result of entrainment, deposition and evaporation. The influence of mass flux, inlet mass quality and tube diameter on critical heat flux is also predicted in this paper. Finally the predicted result of critical heat flux is compared with experimental data, and the theoretical CHF values are higher than that of experimental data, with error within 30%.

Download Full-text