scholarly journals Термокапиллярные структуры и разрыв нагреваемой пленки жидкости

2019 ◽  
Vol 45 (14) ◽  
pp. 44
Author(s):  
Е.А. Чиннов
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Type A ◽  
Vertical Surface ◽  
Film Rupture ◽  
Interaction Of Waves

The data of thermocapillary structures formation and breakdown of the heated liquid film flowing down on a vertical surface with the Reynolds number varied from 0.1 up to 500 are analyzed. It is shown that the interaction of waves with thermocapillary structures type A leads to an increase in critical heat flux, corresponding to the liquid film rupture, compared with literature data (regime B).

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

2006 ◽  
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%.

Study on Breakdown Features and Characteristics of Film at the Corrugated Plate Corner

2020 ◽  
Author(s):  
Bo Wang ◽  
Bowen Chen ◽  
Bingzheng Ke ◽  
Ru Li ◽  
Gongqing Wang ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Film Thickness ◽  
Liquid Film ◽  
Relative Position ◽  
Water Film ◽  
Theoretical Formula ◽  
Film Rupture ◽  
Water Separation ◽  
Water Film Thickness ◽  
Film Breakdown

Abstract Corrugated plate dryer is a extremely vital equipment for steam-water separation in the fields of heat transfer and nuclear engineering. The corrugated plate is also a commonly used steam-water separator in steam generators in nuclear power plants. It is meaningful to study the breakdown characteristics and mechanism of the water film on corrugated plate wall. Water film thickness of steady flow is measured based on plane laser induced fluorescence (PLIF) technique and time series and its fitted equation of water film thickness are obtained, respectively. Besides, fluctuation characteristics of water film are analyzed by probability density function (PDF). Based on the dimensionless approach, the water film breakdown model at the corner of the corrugated plate is established. And the calculation equation of the relative position of the water film breakdown at the corner is deprived. The specific conclusions are as follows. The theoretical equation agrees well with the relative position of the water film breakdown at the corrugated plate corner. The evolution of the surface wave of water film is carried out in time and space. The PDF curve have no significant peak characteristics. Therefore, the spectrum has no characteristic frequency, that is, the water film has multi-frequency characteristics. Gravity of water film can be ignored in the water film model. The thickness sequences for falling film is measured and fitted. The two-dimensional model of water film breakdown at the corner is set up. The equation for the film thickness when the water film is just ruptured is obtained. Relative position of the water film rupture at the corner of the corrugated plate is theoretically related only to the structural parameters of the corrugated plate, the parameters of the gas phase and the liquid phase, and the Reynolds number of the liquid film. However, in the low Reynolds number region, the airflow velocity is extremely large, which causes certain fluctuations and nonlinear characteristics of the water film boundary position. Therefore, the theoretical formula is not particularly good at predicting the relative position of the breakdown in this region. I think that this nonlinear feature has obvious chaotic characteristics. The study of the chaotic characteristics generated by shearing the liquid film by high velocity flow airflow at the corner of the corrugated plate may become a prospect for future research.

Paper 6: Effect of Vapour Drag on Laminar Film Condensation on a Vertical Surface

1965 ◽  
Vol 180 (10) ◽  
pp. 280-287 ◽  
Author(s):  
Y. R. Mayhew ◽  
D. J. Griffiths ◽  
J. W. Phillips
Keyword(s):  
Reynolds Number ◽  
Liquid Film ◽  
Atmospheric Pressure ◽  
Vertical Surface ◽  
Simple Theory ◽  
Experimental Results ◽  
Film Condensation ◽  
Laminar Film ◽  
Laminar Film Condensation

A simple theory is presented for laminar film condensation of a pure vapour on a vertical surface which takes account of the drag induced on the liquid film by the flow of the condensing vapour. Experiments were carried out with steam at atmospheric pressure condensing inside a vertical 1.824 in diameter tube 8 in high. The downward vapour velocity was varied from 5 to 150 ft/s, the corresponding range of the film Reynolds number at the bottom of the tube being 200-500. Experimental results agreed well with the theory.

H222 Critical Heat Flux of Counter-Current Two-Phase Flow : Effect of Subcooled Liquid Film

2011 ◽  
Vol 2011 (0) ◽  
pp. 371-372
Author(s):  
Ayaka Fujiwara ◽  
Takuya Suzuki ◽  
Takeyuki Ami ◽  
Hisashi Umekawa ◽  
Mamoru Ozawa
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Subcooled Liquid ◽  
Flow Effect ◽  
Counter Current

Simulation of Sweating/Evaporation Boosted Convective Heat Transfer Under Laminar Flow Condition

2017 ◽  
Author(s):  
Sudipta Saha ◽  
Rajib Mahamud ◽  
Jamil Khan ◽  
Tanvir Farouk
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Laminar Flow ◽  
Film Thickness ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Water Film ◽  
The Heat Transfer Coefficient

Phase change driven heat transfer has been the topic of interest for a significantly long time. However, in recent years on demand sweating boosted evaporation which requires substantially less amount of the liquid medium has drawn attention as a possible way of increasing/supplementing heat transfer under convective conditions where the convective heat transfer coefficient has already reached its maximum value as well as where dry cooling is a desired objective. In this study, a numerical study is conducted to obtain insight into the ‘hybrid’ system where evaporation and convection both contribute to the heat transfer effect. The system modeled consists of evaporation of thin liquid (water) film under a laminar flow condition. The mathematical model employed consists of coupled conservation equations of mass, species, momentum and energy for the convection-evaporation domain (gaseous), with only mass and energy conservation being resolved in the liquid film domain. The evaporative mass flux is obtained from a modified Hertz-Knudsen relation which is a function of liquid-vapor interface temperature and pressure. A two-dimensional rectangular domain with a pre-prescribed thin liquid water film representative of an experiment is simulated with the developed model. The thin rectangular liquid film is heated by uniform heat flux and is placed in the convection-evaporation domain with an unheated starting length. A moving boundary mesh is applied via the“Arbitrary Lagrangian-Eulerian” technique to resolve the receding liquid interface resulting from evaporation. The prescribed relative displacement of the moving interface is calculated from the net mass flux due to evaporation and is governed by the principle of mass conservation. Simulations were conducted over a range of Reynolds number, heat flux conditions and liquid film thickness. The numerical predictions indicate that under convective-evaporative conditions the overall heat transfer coefficient increases significantly (∼factor of a five) in comparison to the purely forced convection scenario. An increase in the heat transfer coefficient is observed with Reynolds number and vice versa for film thickness. A critical Reynolds number is identified beyond which the heat transfer coefficient does not continue to increase significantly rather tends to plateau out.

A Lower Bound for the Dryout Quality in Annular Flow

2014 ◽  
Author(s):  
J. P. Manning ◽  
S. P. Walker ◽  
G. F. Hewitt
Keyword(s):  
Heat Flux ◽  
Lower Bound ◽  
Liquid Film ◽  
Phenomenological Models ◽  
Flow Regime ◽  
Critical Heat Flux ◽  
Annular Flow ◽  
Large Fraction

The mechanism responsible for Critical Heat Flux (CHF) depends on the flow regime. In the annular flow regime it is normally assumed that CHF occurs when the liquid film dries out. The quality at the onset of annular flow varies, but is generally a few percent, and phenomenological models to predict CHF are routinely applied at qualities above this value. In this paper we will demonstrate that annular flow film dryout cannot occur until a quality significantly greater than this. This finding means that for a large fraction of the annular flow regime the film dryout mechanism cannot be responsible for CHF. This finding provides guidance as to under what circumstances such phenomenological models may properly be used.

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