Rupture of thin liquid film based premature critical heat flux prediction in microchannel

2018 ◽  
Vol 125 ◽  
pp. 933-942 ◽  
Author(s):  
Hui He ◽  
Liang-ming Pan ◽  
Hao-jie Huang ◽  
Run-gang Yan
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Thin Liquid Film

scholarly journals Liquid film–induced critical heat flux enhancement on structured surfaces

2021 ◽  
Vol 7 (26) ◽  
pp. eabg4537
Author(s):  
Jiaqi Li ◽  
Daniel Kang ◽  
Kazi Fazle Rabbi ◽  
Wuchen Fu ◽  
Xiao Yan ◽  
...  
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Thin Liquid Film ◽  
Bubble Formation ◽  
Contact Lines ◽  
Bubble Behavior ◽  
Two Phase ◽  
Structured Surfaces ◽  
Bubble Evolution

Enhancing critical heat flux (CHF) during boiling with structured surfaces has received much attention because of its important implications for two-phase flow. The role of surface structures on bubble evolution and CHF enhancement remains unclear because of the lack of direct visualization of the liquid- and solid-vapor interfaces. Here, we use high-magnification in-liquid endoscopy to directly probe bubble behavior during boiling. We report the previously unidentified coexistence of two distinct three-phase contact lines underneath growing bubbles on structured surfaces, resulting in retention of a thin liquid film within the structures between the two contact lines due to their disparate advancing velocities. This finding sheds light on a previously unidentified mechanism governing bubble evolution on structured surfaces, which has notable implications for a variety of real systems using bubble formation, such as thermal management, microfluidics, and electrochemical reactors.

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%.

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).

Temporal Effect and Transient Simulation of Thin Liquid Film in Micro Channels

2013 ◽  
Author(s):  
Yu-Yan Jiang ◽  
Da-Wei Tang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Liquid Film ◽  
Flow Boiling ◽  
Thin Liquid Film ◽  
Liquid Films ◽  
Transient Simulation ◽  
Governing Equations ◽  
Flash Evaporation ◽  
Micro Channels

The evaporation and heat transfer of thin liquid film are crucial factors affecting on the heat transfer performance of boiling bubbles or slugs. For boiling in micro-channels, the flash evaporation of the liquid film may give rise to boiling instability, and the dry-out of the film leads to serious deterioration of the heat transport. The thin liquid film has multi-scale transitions, and hence the phase change and fluid dynamics need to be solved by special governing equations and numerical algorithm. The numerical studies to date have solved the steady state distribution of the film, but the difficulty consists in the transient simulation of time-variant liquid films. In the present study, unsteady form governing equations are developed. With inclusion of the temporal terms, we conducted transient simulations for flat liquid films formed during the flow boiling in micro-channels. The model predicts the developing of drying spot during growth of elongated bubbles. The results show that the film thickness and distribution change quickly in a growth period, which are functions of the heat flux, mass flow rate and the other parameters. The quantitative assessment of these effects helps to clarify the mechanism of boiling instability and the conditions for the occurrence of critical heat flux (CHF). The simulation needs special numerical scheme for time marching and stabilization treatment for the nonlinear terms, where the numerical accuracy and the significance of the temporal effects are also discussed.

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

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.

Effect of Hydraulic Jump on Hydrodynamics and Heat Transfer in a Thin Liquid Film Flowing Over a Rotating Disk Analyzed by Integral Method

2006 ◽  
Vol 129 (5) ◽  
pp. 657-663 ◽  
Author(s):  
S. Basu ◽  
B. M. Cetegen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Liquid Film ◽  
Hydraulic Jump ◽  
Thin Liquid Film ◽  
Rotating Disk ◽  
Disk Surface ◽  
Constant Heat Flux ◽  
Heat Transfer Analysis ◽  
Scaling Analysis

Flow and heat transfer in a liquid film flowing over the surface of a rotating disk was analyzed by integral technique. The integral analysis includes the prediction of the hydraulic jump and its effects on heat transfer. The results of this analysis are compared to the earlier results that did not include this effect. At low inlet Reynolds numbers and high Rossby numbers, corresponding to low film inertia and low rotation rates, respectively, a hydraulic jump appears on the disk surface. The location of the jump and the liquid film height at this location are predicted. A scaling analysis of the equations governing the film thickness provided a semi-empirical expression for these quantities that was found to be in very good agreement with numerical results. Heat transfer analysis shows that the Nusselt numbers for both constant disk surface temperature and constant disk surface heat flux boundary conditions are lowered in the vicinity of the hydraulic jump due to the thickened liquid film. This effect can be more pronounced for the constant heat flux case depending on the location of the hydraulic jump. The Nusselt number exhibits a turning point at the jump location and can have higher values downstream of the hydraulic jump compared to those obtained from the analysis that does not include the gravitational effects.

scholarly journals Analysis of Hydrodynamics and Heat Transfer in a Thin Liquid Film Flowing Over a Rotating Disk by the Integral Method

2005 ◽  
Vol 128 (3) ◽  
pp. 217-225 ◽  
Author(s):  
S. Basu ◽  
B. M. Cetegen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Rotating Disk ◽  
Disk Surface ◽  
Experimental Results ◽  
Rotation Rates

An integral analysis of hydrodynamics and heat transfer in a thin liquid film flowing over a rotating disk surface is presented for both constant temperature and constant heat flux boundary conditions. The model is found to capture the correct trends of the liquid film thickness variation over the disk surface and compare reasonably well with experimental results over the range of Reynolds and Rossby numbers covering both inertia and rotation dominated regimes. Nusselt number variation over the disk surface shows two types of behavior. At low rotation rates, the Nusselt number exhibits a radial decay with Nusselt number magnitudes increasing with higher inlet Reynolds number for both constant wall temperature and heat flux cases. At high rotation rates, the Nusselt number profiles exhibit a peak whose location advances radially outward with increasing film Reynolds number or inertia. The results also compare favorably with the full numerical simulation results from an earlier study as well as with the reported experimental results.

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