Evaporating Liquid Film Flow in the Presence of Micro-Encapsulated Phase Change Materials: A Numerical Study

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Yasmin Khakpour ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Phase Change ◽  
Film Flow ◽  
Operating Conditions ◽  
Liquid Film Thickness ◽  
Pure Liquid ◽  
Heated Plate ◽  
Liquid Film Flow

This paper numerically investigates the heat transfer characteristics of a mesoscale liquid film slurry flow containing micro-encapsulated phase change material (MEPCM) in the presence of evaporation. The two-phase evaporating liquid film flow is modeled using one-fluid volume-of-fluid (VOF) formulation. During the evaporation process of the base fluid, the concentration of MEPCM in the slurry film increases as it flows along a heated plate, resulting in a continuous variation of its effective thermal properties. The effect of MEPCM on the evolution of the liquid film thickness under different operating conditions is presented. It is shown that the MEPCM suppresses the rate of decline in the liquid film thickness, which results in a higher heat transfer coefficient compared to that of pure liquid film under similar operating conditions. This study also provides an understanding towards delaying of the dry-out condition in slurry liquid film flow evaporation compared to that of the pure fluid.

Measurement of Liquid Film Thickness around Horizontal Tube Bundle by Optical Technique for Optimizing Evaporator Design and Manufacturing

2014 ◽  
Vol 974 ◽  
pp. 220-224
Author(s):  
Karim Bourouni ◽  
Ali L. Taee
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Film Flow ◽  
Tube Bundle ◽  
Horizontal Tube ◽  
Falling Film ◽  
Optical Technique ◽  
Design And Manufacturing ◽  
Liquid Film Flow

This paper proposes the improvement of design and manufacturing of Falling Film Horizontal Tube Evaporators (FFHTE) through optimizing different parameters such as tubes pitch, tubes diameter and material and liquid film flow rate. These design and operational parameters have a significant influence on the hydrodynamic of the liquid film (eg: wetability of the tubes, scale deposition, heat transfer coefficient, etc.). Due to the complexity of the liquid film flow around the horizontal tube bundle, the experimental approach is preferred than modeling because it gives a better understanding of the phenomena occurring in the heat exchanger. In this paper one experiment was carried out to investigate liquid film flow around a single horizontal tube. A particular attention was taken for the measurement of liquid film thickness around the tube using a novel optical technique based on light reflection. The influence of the tubes pitch, tube diameter, height of the liquid distribution system and the liquid mass flow on the transitions between falling-film modes and film thickness is investigated and the results are compared to other data obtained from the literature. It was found that tubes wetability and heat transfer increased with increasing the vertical tube pitch. To account for fouling and heat transfer performance, a tube spacing value of 1.3 was recommended.

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.

Measurement of Liquid Film Thickness for Annular Two-Phase HFC134a Gas-Liquid Ethanol Flow in the Vertical Tube

2021 ◽  
Author(s):  
Huacheng Zhang ◽  
Tutomo Hisano ◽  
Shoji Mori ◽  
Hiroyuki Yoshida
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Atmospheric Condition ◽  
Heating Surface ◽  
Operating Conditions ◽  
Liquid Film Thickness ◽  
Two Phase ◽  
Disturbance Waves ◽  
Analytical Approaches

Abstract Annular gas-liquid two-phase flows, such as the flows attached to the fuel rods of boiling water reactors (BWR), are a prevalent occurrence in industrial processes. At the gas-liquid interface of such flows, disturbance waves with diverse velocity and amplitude commonly arise. Since the thin liquid film between two successive disturbance waves leads to the dryout on the heating surface and limits the performance of the BWRs, complete knowledge of the disturbance waves is of great importance for the characterized properties of disturbance waves. The properties of disturbance waves have been studied by numerous researchers through extensive experimental and analytical approaches. However, most of the experimental data and analyses available in the literature are limited to the near atmospheric condition. In consideration of the properties of liquids and gases under atmospheric pressure which are distinct from those under BWR operating conditions (7 MPa, 285 °C), we employed the HFC134a gas and liquid ethanol whose properties at relatively low pressure and temperature (0.7 MPa, 40 °C) are similar to those of steam and water under BWR operating conditions as working fluids in a tubular test section having an inside diameter 5.0mm. Meanwhile, the liquid film thickness is measured by conductance probes. In this study, we report the liquid film thickness characteristics in a two-phase HFC134a gas-liquid ethanol flow. A simple model of the height of a disturbance wave was also proposed.

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.

Theoretical and Experimental Analysis of Turbulent Liquid Film Flowing down a Vertical Surface

2009 ◽  
Vol 15 ◽  
pp. 3-8
Author(s):  
Stasys Sinkunas ◽  
Jonas Gylys ◽  
Algimantas Kiela
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Analytical Study ◽  
Film Flow ◽  
Convex Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Vertical Surface ◽  
Momentum And Heat Transfer ◽  
Liquid Film Flow

The purpose of the present study is to obtain a comprehension for the momentum and heat transfer developments in gravitational liquid film flow. Analytical study of stabilized heat transfer for turbulent film was performed. A calculation method of the local heat transfer coefficient for a turbulent film falling down a vertical convex surface was proposed. The dependence of heat flux variation upon the distance from the wetted surface has been established analytically. Experimental study of velocity profiles for turbulent liquid film flow in the entrance region is performed as well. Analysis of profiles allowed estimating the length of stabilization for turbulent film flow under different initial velocities.

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.

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