Visual and Numerical Study for Dropwise Condensation Heat Transfer Mechanism of Steam-Air Mixture Vapor

2014 ◽  
Author(s):  
Xuehu Ma ◽  
Wen Rongfu ◽  
Zhong Lan ◽  
Xingdong Zhou
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Gas Phase ◽  
Heat And Mass Transfer ◽  
Diffusion Layer ◽  
Numerical Study ◽  
Mass Diffusion ◽  
Transfer Mechanism ◽  
Condensation Heat Transfer ◽  
Dropwise Condensation

Non-condensable gas (NCG) is well known for degrading condensation heat transfer due to the accumulation of NCG near the gas-liquid interface. It has been found that a small amount of NCG results in a significant reduction of heat transfer performance. In the present work, dropwise condensation heat and mass transfer mechanism of steam-air mixture were studied on a vertical plate experimentally and theoretically. Considering the dynamic interaction of condensate and gas-vapor diffusion layer, the study focused on the interfacial effect on heat and mass transfer of condensation in the presence of NCG. Comparison of growth rates of new nucleated droplets in different regions showed the enhancement of mass transfer by the gas phase perturbation. Taking advantage of visualization, the influences of droplet curvature, departure movement and transversal suction effect on mass transfer in the interfacial mass diffusion layer were investigated. The numerical simulation subsequently revealed the mixing characteristic of steam and air in the mass diffusion layer which was corroborated by the visual results inspected by PIV technology. Due to the relative motion of condensed droplet and steam-air mixture vapor, eddy flow occurred in the gas phase resulting in a perpendicular velocity of the bulk vapor to the condensing surface and a perpendicular velocity of the accumulated NCG to the vapor bulk which enhanced the heat and mass transfer in dropwise condensation. The study provides an insight into the disturbance of the diffusion boundary layer by droplet departure movement, as well as the need to design specific surface to promote the droplet departure movement and achieve enhanced heat and mass transfer during dropwise condensation in the presence of NCG.

Numerical Study on Heat and Mass Transfer of Plate Falling Film Absorber with Wire-Meshed Fins

2012 ◽  
Vol 204-208 ◽  
pp. 4305-4314
Author(s):  
Jing Jing Zhang ◽  
Dan Dan Zhao ◽  
Lu Chun Wan ◽  
Bao Huai Zhang ◽  
Ya Ping Chen
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat And Mass Transfer ◽  
Absorption Rate ◽  
Numerical Study ◽  
Mass Transfer Process ◽  
Falling Film ◽  
Better Than

A mathematical model of heat and mass transfer process in plate falling film absorber with wire-meshed fins was developed. The model could predict temperature and concentration distribution as well as the solution side heat transfer coefficient and the absorption rate. The results verify that heat and mass transfer performance of the plate falling film absorber with wire-meshed fins is better than the past absorber. Compared with the plate falling film absorber without fins, heat transfer coefficient of the absorber in this article increases 1.06 times and the absorption rate increases 2.32 times.

A Study of Enhanced Heat and Mass Transfer From Variable Height Fin Array Undergoing Natural Convection

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Debayan Dasgupta ◽  
Kankan Kishore Pathak ◽  
Asis Giri
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Natural Convection ◽  
Heat And Mass Transfer ◽  
Latent Heat ◽  
Numerical Study ◽  
Boussinesq Approximation ◽  
Heat Transfer Analysis ◽  
Simpler Algorithm ◽  
Fin Spacing

Abstract A numerical study is performed on simultaneous heat and mass transfer from a shrouded vertical nonisothermal variable height fin array, representing dehumidification process under natural convection. Fluid properties are treated as uniform, and the fluid is assigned to comply with Boussinesq approximation to include the effect of density variation with temperature and concentration. Semi-implicit method for the pressure linked equations revised (SIMPLER) algorithm is adopted to resolve pressure and velocity coupling. A detailed parametric investigation of fin spacing, variable fin height, and fin tip to shroud clearance for a range of thermal and mass Grashof number is undertaken. Results indicate that in case of smaller fin spacing, involving fin length of 0.3 m, coefficients of sensible and latent heat transfer increase with the decreasing variable height (H1*) of fin and become maximum at H1*=0.5, for all thermal and mass Grashof numbers considered presently. Further, total heat transfer analysis on a particular base length due to sensible heat shows a maximum of 24.4% enhancement, whereas same due to the latent heat shows a maximum of 25.8% enhancement, depending on the values of clearance. Induced velocities also increase with the decreasing variable height of fin (H1*), which influences the heat and mass transport. The output parameters of this analysis, like induced velocities and overall Nusselt numbers due to the sensible and latent heat, are correlated with the governing parameters. The correlation coefficients are found to be in a range from 0.97 to 0.99.

A Semi-Empirical Model for Condensation Heat Transfer Coefficient of Mixed Ethanol-Water Vapors

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Yang Li ◽  
JunJie Yan ◽  
JinShi Wang ◽  
GuoXiang Wang
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Empirical Model ◽  
Condensation Heat Transfer ◽  
Dropwise Condensation ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Transfer Characteristics ◽  
Semi Empirical

A semi-empirical model describing the heat transfer characteristics of the pseudo-dropwise condensation of binary vapor on a cooled vertical tube has been formulated. By ignoring the thin film always present on the condensation surface and the intensification of mass transfer caused by the Marangoni effect, the heat transfer characteristics of pseudo-dropwise condensation are tentatively formulated. The model involved an analysis of the diffusion process in the vapor boundary layer along with the heat transfer process through the condensate drops. This model was applied to the condensation of the saturated binary vapor of ethanol and water, and was examined using experimental data at vapor pressure values of 101.33 kPa (provided by Utaka and Wang, 2004, “Characteristic Curves and the Promotion Effect of Ethanol Addition on Steam Condensation Heat Transfer,” Int. J. Heat Mass Transfer, 47, pp. 4507–4516), 84.52 kPa and 47.36 kPa. Calculations using the model show a similar trend to the experimental measurements. With the change of the vapor-to-surface temperature difference, the heat transfer coefficients revealed nonlinear characteristics, with the peak values under all ethanol mass fractions of binary vapor. The heat transfer coefficients increased with decreasing ethanol mass fraction.

Characteristics of combined heat and mass transfer on mixed convection flow of Sisko fluid model: A numerical study

2020 ◽  
Vol 34 (24) ◽  
pp. 2050255
Author(s):  
Aamir hamid ◽  
Abdul Hafeez ◽  
Masood Khan
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Fluid Flow ◽  
Differential Equations ◽  
Mixed Convection ◽  
Heat And Mass Transfer ◽  
Numerical Study ◽  
Convection Flow ◽  
Sisko Fluid ◽  
The Impact

In this paper, the combined heat and mass transfer of mixed convection, non-similar Sisko fluid flow in the presence of a magnetic field is studied. The combined effects of thermal radiation and heat generation/absorption are examined for Sisko fluid flow via local non-similar method. For the radiative heat transfer, Rosseland approximation model is used. The governing partial differential equations of the present problem are transformed into a system of nonlinear ordinary differential equations by employing the Sparrow–Quack–Boerner local non-similarity method (LNM). The obtained equations are then numerically investigated by utilizing the bvp4c function in MATLAB. The impact of different supervising parameters on the velocity, temperature, skin friction and rate of heat transfer is performed graphically. It is observed that the velocity is more for a higher rate of the buoyancy force parameter while it is less for opposing buoyancy fluid. The thermal boundary layer thickness for the shear thickening fluids is smaller than the shear thinning fluids.

scholarly journals Heat-Mass Transfer of Nanofluid in Lid-Driven Enclosure under three Convective Modes

2019 ◽  
Vol 38 ◽  
pp. 73-83
Author(s):  
MS Rahman ◽  
R Nasrin ◽  
MI Hoque
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Temperature Difference ◽  
Richardson Number ◽  
Numerical Study ◽  
Mass Transfer Rate ◽  
Square Enclosure ◽  
Coupled Equations ◽  
Wide Range

Heat is a form of energy which transfers between bodies which are kept under thermal interactions. When a temperature difference occurs between two bodies or a body with its surroundings, heat transfer occurs. Heat transfer occurs in three modes. Three modes of heat transfer are conduction, convection and radiation. Convection is a very important phenomenon in heat transfer applications and it occurs due to two different gradients, such as, temperature and concentration. This paper reports a numerical study on forced-mixed-natural convections within a lid-driven square enclosure, filled with a mixture of water and 2% concentrated Cu nanoparticles. It is assumed that the temperature difference driving the convection comes from the side moving walls, when both horizontal walls are kept insulated. In order to solve general coupled equations, a code based on the Galerkin's finite element method is used. To make clear the effect of using nanofluid on heat and mass transfers inside the enclosure, a wide range of the Richardson number, taken from 0.1 to 10 is studied. A fair degree of precision can be found between the present and previously published works. The phenomenon is analyzed through streamlines, isotherm and iso-concentration plots, with special attention to the Nusselt number and Sherwood number. The larger heat and mass transfer rates can be achieved with nanofluid than the base fluid for all conditions at Richardson number, Ri = 0.1 to 10. It has been found that the heat and mass transfer rate increase approximately 6% for water with the increase of Ri = 0.1 to 10, whereas these increase about 34% for nanofluid. GANIT J. Bangladesh Math. Soc.Vol. 38 (2018) 73-83

Numerical Analysis of the Sugarcane Bagasse Drying by Cyclone

2018 ◽  
Vol 20 ◽  
pp. 106-123
Author(s):  
J.A. Ribeiro de Souza ◽  
Severino Rodrigues de Farias Neto ◽  
E. Santana de Lima ◽  
A.G. Barbosa de Lima ◽  
H. Monteiro Lopes
Keyword(s):  
Mass Transfer ◽  
Gas Phase ◽  
Heat And Mass Transfer ◽  
Sugarcane Bagasse ◽  
Numerical Study ◽  
Flow Direction ◽  
Tangential Velocity ◽  
Reynolds Stress Model ◽  
Lagrangian Model ◽  
Lumped Model

Drying is a simultaneous process of heat and mass transfer and dimensional changes. In recent years, cyclones have been used as a modern drying technology. In this sense, this research proposes a numerical study to describe drying of sugarcane bagasse, using the cyclone as dryer. Herein, it was adopted the Eulerian-Lagrangian model in steady state. The Reynolds stress model was considered to describe turbulence of the gas phase, while a transient lumped model was used to describe heat and mass transfer on the particulate phase (sugarcane bagasse). Particles were considered with irregular shape, composed of a binary mixture (solid part and water). The solution of the proposed model was obtained using the commercial software Ansys CFX 12. Results of the moisture content, temperature, dimension variation, and paths of particles, as well as velocity, pressure, and temperature distributions of the gas phase inside the cyclone are presented and analyzed. It has been found that the obtained components for axial and tangential velocity inside the cyclone are in good agreement with experimental data available in the literature, and that the drying kinetics, heating, dimensional variations, and residence time of particles are affected by the velocity of the gas phase, velocity of the particles, and the flow direction of gas and particles at the entrance of the feed duct.

The Condensation Heat Transfer Characteristics of Zeotropic Hydrocarbon Mixtures in a Helical Pipe

2020 ◽  
Author(s):  
Shulei Li ◽  
Rui Zhu ◽  
Gongnan Xie ◽  
Yiqiang Jiang ◽  
Weihua Cai
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Saturation Pressure ◽  
Condensation Heat Transfer ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Transfer Resistance ◽  
Hydrocarbon Mixtures ◽  
Heat Transfer Coefficients

Abstract In order to explore tube-side heat transfer characteristics in the spiral wound heat exchange (SWHE) used in liquid natural gas (LNG) plants, the study on zeotropic hydrocarbon mixtures condensation heat transfer in a helical pipe is proposed. Firstly, based on two-fluid model and thermal phase change model, a numerical method coupling with empirical correlations is established to predict condensation heat transfer for zeotropic mixtures, in which the mixed effects are taken into account. Meanwhile, the rationality of the above methods is verified based on existing experimental results. Then, the effects of refrigerant components and operating parameters on flow patterns, heat transfer coefficients and heat and mass transfer resistance are discussed as the ranges of mass flux, saturation pressure and vapor quality are 200–800 kg/(m2·s), 2–4MPa and 0.15–0.90, respectively. It can be found that the predicted results coincide with the experimental ones, with deviations within ±15%. For different zeotropic hydrocarbon mixtures, as the vapor quality increases, the stratified flow, half-annular flow and annular flow appears in turn. The condensation heat transfer coefficients are always smaller than film heat transfer coefficients owing to the existence of heat and mass transfer resistance in vapor core. Besides, both film and condensation heat transfer coefficients increase with the increase of vapor quality and mass flux, while decrease with the rise in saturation pressure. Further, heat and mass transfer resistances increase as the vapor quality and saturation pressure increase and the mass flux decreases. In addition, compared to methane/ethane/propane/nitrogen (65/25/5/5, mole%) mixture, the averaged heat transfer performance for methane/ethane (90/10, mole%) mixture improves by 19.55%, whereas, the average heat and mass transfer resistance decreases by 53.51%. This study is helpful for understanding the zeotropic mixtures condensation in tubes and gives some suggestions for the choice of refrigerant components used in LNG SWHE, to design more effective SWHE.

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