Asymmetric annular flow in horizontal circular macro-channels: Basic modeling of liquid film distribution and heat transfer around the tube perimeter in convective boiling

2014 ◽  
Vol 77 ◽  
pp. 897-905 ◽  
Author(s):  
A.W. Mauro ◽  
A. Cioncolini ◽  
J.R. Thome ◽  
R. Mastrullo
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Annular Flow ◽  
Convective Boiling ◽  
Film Distribution

Measurement of Liquid Film Thickness in Micro Tube Annular Flow

2010 ◽  
Author(s):  
Hiroshi Kanno ◽  
Youngbae Han ◽  
Yusuke Saito ◽  
Naoki Shikazono
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Annular Flow ◽  
Liquid Film Thickness ◽  
Phase Flow ◽  
Two Phase ◽  
Micro Scale ◽  
Film Model ◽  
Annular Film

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.

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%.

Convective Boiling Heat Transfer and Pressure Drop Characteristics of R134a in a Microfinned Helically Coiled Tube

2005 ◽  
Author(s):  
Wenzhi Cui ◽  
Longjian Li ◽  
Mingdao Xin ◽  
Qinghua Chen ◽  
Quan Liao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Convective Boiling ◽  
Coiled Tube ◽  
Frictional Pressure Drop ◽  
Helically Coiled Tube

The main purpose of this paper was to experimentally study the heat transfer and pressure drop characteristics of refrigerant R134a boiling inside a new geometry microfin helically coiled tube. Experiments were performed in a range of mass quality from 0.05 up to 0.9, mass velocity 70 ∼ 380 kg/m2s and heat flux 2.0 ∼ 21.8 kW/m2. The local and average convective boiling heat transfer coefficients were reported in this paper, which were found to be dependent on both of mass flux and heat flux. Compared with corresponding smooth helically coiled tube, the microfin helically coiled tube could enhance the convective boiling heat transfer very well. The enhancement factor was up to 2.2 with the variety of mass flux and heat flux. Heat transfer in annular flow was specially studied. A flow boiling heat transfer correlation was presented for the annular flow regime, which had a mean deviation of 9.1%. The frictional pressure drop values were obtained by subtracting acceleration pressure drop and gravitational pressure drop from the measured total pressure drop. The frictional pressure drop data can be well correlated by Lockhart-Martinelli parameter. Considering the corresponding flow regimes, i.e., stratified and annular flow, two frictional pressure drop correlations were proposed, and showed a good agreement with the respective experimental data.

Analysis for the Fluctuation Characteristics of Annular Flow in the Oil-Air Lubrication System

2014 ◽  
Vol 487 ◽  
pp. 408-412
Author(s):  
Qi Guo Sun ◽  
Ali Cai ◽  
Zheng Hui Zhou ◽  
Zhi Hong Li ◽  
Xiong Shi Wang
Keyword(s):  
Pressure Drop ◽  
Film Thickness ◽  
Liquid Film ◽  
Annular Flow ◽  
Lubrication System ◽  
Air Velocity ◽  
Film Distribution ◽  
Air Lubrication ◽  
Calculation Results ◽  
Simulation Results

Fluctuation characteristics of the pressure drop distribution and liquid film distribution along a pipe of the oil-air annular flow in oil-air lubrication system are calculated respectively introducing Chisholm constant c base on the Chisholm theory and simulated by Fluent in this paper. The results show that the theoretical calculation results of the pressure drop and liquid film agree qualitatively with the simulation results, and the fluctuation characteristics of the pressure drop and liquid film thickness are augmented respectively when the air velocity increases. These conclusions will do favors for predicting and controlling the lubricant in the oil-air lubrication system.

Local Liquid Velocities in Horizontal, Annular Air/Water Flow

2003 ◽  
Author(s):  
Charles R. Kopplin
Keyword(s):  
Liquid Film ◽  
Water Flow ◽  
Measurement Method ◽  
Annular Flow ◽  
Current Data ◽  
Air Bubbles ◽  
Flow Modeling ◽  
Two Phase ◽  
Flow Rates ◽  
Film Distribution

A newly developed flow visualization method that utilizes a three color LED strobe has been used to study the axial and circumferential velocities of the liquid in horizontal, annular two-phase flow. This non-intrusive technique allows the tracking of naturally entertained air bubbles within the liquid film along the top, bottom, and sides of the tube. Sets of images have been obtained for multiple combinations of air and water flow rates ranging in quality from approximately 0.07 to 0.49. The bubble-tracking velocimetry measurement method is explained, and comparison of the current data with past results and their impact on annular flow modeling are discussed. The data do not support two of the four theories for liquid film distribution in annular, horizontal multiphase flow, while the two remaining theories cannot be directly examined using the three color LED strobe measurement technique.

Analysis of Annular and Stratified Flows for Vapor Condensation Heat Transfer in Horizontal Tubes

2013 ◽  
Vol 753-755 ◽  
pp. 2717-2721
Author(s):  
Jun Xia Zhang ◽  
Li Wang ◽  
Jian Wen Wang
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Annular Flow ◽  
Stratified Flow ◽  
Condensation Heat Transfer ◽  
Condenser Tube ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes ◽  
Annular Flows

The greater part of the horizontal condenser tube is occupied by the stratified and annular flows, which play important roles in condensation heat transfer coefficients. Both a volume of fluid (VOF) interface tracking method and k-ε two equations model was applied to analyze the characteristics of the stratified and annular flows for horizontal tubes, obtaining distribution of velocity, contours of both temperature and local condensation heat transfer coefficients. The computation shows that an annular flow having thinner liquid film attached on the inner surface of tubes appears at the inlet of the horizontal condenser tube because vapor exerts a higher interfacial shear stress on the gas-liquid interface, therefore, there are a higher local condensation heat transfer coefficients there. Next, as vapor quality decreases and condensate gravity increases along the condenser tube length, the condensation flow pattern transforms from the annular flow into the stratified flow in which local condensation heat transfer coefficients decreases and distributes unevenly along the circumference as liquid film at the bottom of the condenser tube become thicker. In addition, in the stratified flow, a wave structure is formed in the middle of the condensate pool at the bottom of the condenser tube because condensate on the top of the condenser tube slides into the bottom of the condenser tube and collapse each other. The heat transfer rate calculated by the present method is compared to those predicted from a Shah correlation, the agreement is found to be good, and both errors is within 7%.

Local Heat Transfer of Saturated Flow Boiling in Vertical Narrow Microchannel

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Junye Li ◽  
Yuhao Lin ◽  
Wei Li ◽  
Kan Zhou
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Liquid Film ◽  
Annular Flow ◽  
Flow Boiling ◽  
High Heat ◽  
Flow Patterns ◽  
High Heat Flux ◽  
Bubble Flow ◽  
Saturated Flow

Abstract An experimental study of saturated flow boiling in a high-aspect-ratio one-side-heating rectangular microchannel was conducted with de-ionized water as the working fluid. ZnO microrods with the average diameter of about 1 μm and length of about 7 μm were synthesized on the Ti wafer surface, which was used to fabricate the heated bottom surface of the microchannel. The ZnO microrod surface appeared to be hydrophobic and the capillary wetting effect on the surface was found after being wet. The heat transfer and pressure drop characteristics of saturated flow boiling in the microchannel were studied and the flow patterns were photographed with a high-speed camera. Almost all the flow patterns observed in this experiment featured the main annular flow and abrupt flush of bubbly flow. Because of the capillary wetting effect on the ZnO microrod surface, the local dryout and rewetting phenomenon did not appear in this study. However, due to the numerous nucleation sites on ZnO microrod surface, the abrupt bubble flow caused much more disruption to the liquid film of annular flow when compared to the regular silicon surface. The abrupt bubble flow flushed through the annular liquid film and caused the fluctuation and nonuniformity of the liquid film and heat transfer deterioration, which was severer in the high heat flux conditions. Otherwise, the capillary effect on the ZnO microrod surface was able to restrict the nonuniformity of the liquid film under high heat flux and low mass flux conditions; thus, the deterioration of heat transfer performances diminished.

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