scholarly journals Hydrodynamic behavior of liquid falling film over horizontal tubes: effect of hydrophilic circular surface on liquid film thickness and heat transfer

2020 ◽  
pp. 100821
Author(s):  
Zaher Ramadan ◽  
Chan Woo Park
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Liquid Film Thickness ◽  
Falling Film ◽  
Hydrodynamic Behavior ◽  
Horizontal Tubes ◽  
Circular Surface

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.

scholarly journals ANALYSIS OF INTERFACIAL AND MASS TRANSFER EFFECTS ON FORCED CONVECTION IN GAS-LIQUID ANNULAR TWO-PHASE FLOW

2004 ◽  
Vol 3 (1) ◽  
pp. 45
Author(s):  
E. Nogueira ◽  
B. D. Dantas ◽  
R. M. Cotta
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Liquid Film Thickness ◽  
Phase Flow ◽  
Transfer Effects ◽  
Two Phase ◽  
Transfer Rates ◽  
Interface Waves

In a gas-liquid annular two-phase flow one of the main factors influencing the determination of heat transfer rates is the average thickness of the liquid film. A model to accurately represent the heat transfer in such situations has to be able of determining the average liquid film thickness to within a reasonable accuracy. A typical physical aspect in gas-liquid annular flows is the appearance of interface waves, which affect heat, mass and momentum transfers. Existing models implicitly consider the wave effects in the momentum transfer by an empirical correlation for the interfacial friction factor. However, this procedure does not point out the difference between interface waves and the natural turbulent effects of the system. In the present work, the wave and mass transfer effects in the theoretical estimation of average liquid film thickness are analyzed, in comparison to a model that does not explicitly include these effects, as applied to the prediction of heat transfer rates in a thermally developing flow situation.

The Effect of Liquid Film Evaporation on Flow Boiling Heat Transfer in a Micro Tube

2010 ◽  
Author(s):  
Youngbae Han ◽  
Naoki Shikazono ◽  
Nobuhide Kasagi
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Flow Boiling ◽  
Liquid Film Thickness ◽  
Periodic Pattern ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Micro Channels ◽  
Measured Liquid

Flow boiling in micro channels is attracting large attention since it leads to large heat transfer area per unit volume. Generated vapor bubbles in micro channels are elongated due to the restriction of channel wall, and thus slug flow becomes one of the main flow regimes. In slug flow, sequential bubbles are confined by the liquid slugs, and thin liquid film is formed between tube wall and bubble. Liquid film evaporation is one of the main heat transfer mechanisms in micro channels and liquid film thickness is a very important parameter to determine heat transfer coefficient. In the present study, liquid film thickness is measured under flow boiling condition and compared with the correlation proposed under adiabatic condition. The relationship between liquid film thickness and heat transfer coefficient is also investigated. Pyrex glass tube with inner diameter of D = 0.5 mm is used as a test tube. Working fluids are water and ethanol. Laser focus displacement meter is used to measure the liquid film thickness. Initial liquid film thickness under flow boiling condition can be predicted well by the correlation proposed under adiabatic condition. However, measured liquid film thickness becomes thinner than the predicted values in the cases of back flow and short slugs. These are considered to be due to the change of velocity profile in the liquid slug. Under flow boiling condition, liquid film profile fluctuates due to high vapor velocity and shows periodic pattern against time. Frequency of periodic pattern increases with heat flux. At low quality, heat transfer coefficients calculated from measured liquid film thickness show good accordance with heat transfer coefficients obtained directly from wall temperature measurements.

Study on liquid film thickness and flow characteristics of falling film outside an elliptical tube

2019 ◽  
Vol 157 ◽  
pp. 1-7
Author(s):  
Xiaocui Zhang ◽  
Xiaojing Zhu ◽  
Qinggang Qiu
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Flow Characteristics ◽  
Liquid Film Thickness ◽  
Falling Film

scholarly journals Establishment of the falling film evaporation model and correlation of the overall heat transfer coefficient

2019 ◽  
Vol 6 (5) ◽  
pp. 190135 ◽  
Author(s):  
Jing Fang ◽  
Kaixuan Li ◽  
Mengyu Diao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Temperature Distribution ◽  
Film Thickness ◽  
Liquid Film ◽  
Velocity Distribution ◽  
Transfer Coefficient ◽  
Falling Film ◽  
Overall Heat Transfer Coefficient ◽  
Proposed Model

In order to study the heat transfer of the falling film evaporator with phase change on both sides, in this paper we built the mathematical model and the physical model where the liquid film inside the tube is laminar and turbulent. The film thickness of the condensate at different axial positions, total condensate volume and velocity distribution, and temperature distribution of condensate outside the tube can be obtained by calculating the proposed model. Meanwhile, the liquid film thickness, velocity distribution and temperature distribution inside the tube were obtained by numerical simulation by considering the influence of the liquid film with different compositions on the heat transfer during fluid flow. With ethanol–water as the system, the overall heat transfer coefficient and heat transfer quantity of the falling film evaporator were obtained by the calculation of the model. The accuracy of the proposed model was confirmed by experiments. The model and the calculation of heat transfer proposed in this paper have enormous significance for the basic data and theoretical guidance of the heat transfer performance prediction and operational optimization of the evaporator.

scholarly journals Analytical Solutions of Heat Transfer and Film Thickness with Slip Condition Effect in Thin-Film Evaporation for Two-Phase Flow in Microchannel

2015 ◽  
Vol 2015 ◽  
pp. 1-15 ◽  
Author(s):  
Ahmed Jassim Shkarah ◽  
Mohd Yusoff Bin Sulaiman ◽  
Md. Razali bin Hj Ayob
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Film Thickness ◽  
Liquid Film ◽  
Two Phase Flow ◽  
Current Model ◽  
Liquid Film Thickness ◽  
Phase Flow ◽  
Two Phase ◽  
Analytical Results

Physical and mathematical model has been developed to predict the two-phase flow and heat transfer in a microchannel with evaporative heat transfer. Sample solutions to the model were obtained for both analytical analysis and numerical analysis. It is assumed that the capillary pressure is neglected (Morris, 2003). Results are provided for liquid film thickness, total heat flux, and evaporating heat flux distribution. In addition to the sample calculations that were used to illustrate the transport characteristics, computations based on the current model were performed to generate results for comparisons with the analytical results of Wang et al. (2008) and Wayner Jr. et al. (1976). The calculated results from the current model match closely with those of analytical results of Wang et al. (2008) and Wayner Jr. et al. (1976). This work will lead to a better understanding of heat transfer and fluid flow occurring in the evaporating film region and develop an analytical equation for evaporating liquid film thickness.

Effect of Tube Geometry and Curvature on Film Condensation in the Presence of a Noncondensable Gas

2014 ◽  
Vol 7 (1) ◽  
Author(s):  
Huijun Li ◽  
Wenping Peng ◽  
Yingguang Liu ◽  
Chao Ma
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Liquid Film Thickness ◽  
Film Condensation ◽  
Tube Surface ◽  
Noncondensable Gas ◽  
Tube Geometry

Based on the double boundary layer theory, a generalized mathematical model was developed to study the distributions of gas film, liquid film, and heat transfer coefficient along the tube surface with different geometries and curvatures for film condensation in the presence of a noncondensable gas. The results show that: (i) for tubes with the same geometry, gas film thickness, and liquid film thickness near the top of the tube decrease with the increasing of curvature and the heat transfer rate increases with it. (ii) For tubes with different geometries, one need to take into account all factors to compare their overall heat transfer rate including gas film thickness, liquid film thickness and the separating area. Besides, the mechanism of the drainage and separation of gas film and liquid film was analyzed in detail. One can make a conclusion that for free convection, gas film never separate since parameter A is always positive, whereas liquid film can separate if parameter B becomes negative. The separating angle of liquid film decreases with the increasing of curvature.

Spray Cooling Modeling: Liquid Film Thickness Effect on Heat Transfer

2007 ◽  
Author(s):  
R. Panneer Selvam ◽  
Matthew Hamilton ◽  
Eric A. Silk
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Spray Cooling ◽  
Liquid Film Thickness ◽  
Thickness Effect
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