scholarly journals Numerical Analysis of Laminar Convective Condensation with the Presence of Noncondensable Gas Flowing Downward in a Vertical Channel

2019 ◽  
Vol 2019 ◽  
pp. 1-15
Author(s):  
Mustapha Ait Hssain ◽  
Youness El Hammami ◽  
Rachid Mir ◽  
Sara Armou ◽  
Kaoutar Zine-Dine
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Relative Humidity ◽  
Liquid Film ◽  
Vertical Channel ◽  
Dimensionless Temperature ◽  
Condensation Process ◽  
Inlet Temperature ◽  
Mixture Flow ◽  
Noncondensable Gas

The purpose of this paper is to study and perform a numerical analysis of the simultaneous processes of mass and heat transfer during the condensation process of a steam in the existence of noncondensable gas (NCG) inside a descending vertical channel. In this study, the flow of the vapor-air mixture is laminar and the saturation conditions are prevailing at the inlet of the channel. The coupled control equations for liquid film, interfacial conditions, and mixture flow are solved together using the approach of finite volume. Detailed and valuable results are presented both in the liquid condensate film and in the mixing regions. These detailed results contain the dimensionless velocity and dimensionless temperature profiles in both phases, the dimensionless mass fraction of vapor, the axial variation of the dimensionless thickness of the film liquid δ⁎, and the accumulated condensate rate Mr as well the local Nusselt number Nuy. The relative humidity at the inlet varies from 60% to 100% and the inlet temperature from 40°C to 80°C. The results confirm that a decrease in the mass concentration of NCG by the increasing the inlet relative humidity has a direct influence on the liquid film layer, the local number of Nusselt, and the variation of condensation rate accumulated through the channel. The results also designate that an increase of the inlet relative humidity and the inlet temperature ameliorates the condensation process. The comparison made for the coefficient of heat transfer due to condensation process and the condensate liquid film thickness with the literature results is in good concordance which gives more credibility to our calculation model.

Numerical Investigation of Condensation Heat Transfer Characteristics of R134A in Rectangular Minichannel

2019 ◽  
Author(s):  
Di Lv ◽  
Wei Li ◽  
Jingzhi Zhang
Keyword(s):  
Heat Transfer ◽  
Pressure Gradient ◽  
Liquid Film ◽  
Mass Flow ◽  
Mass Flux ◽  
Condensation Heat Transfer ◽  
Condensation Process ◽  
Vapor Quality ◽  
Vof Model ◽  
Friction Pressure

Abstract This study numerically investigated the condensation heat transfer and flow characteristics of refrigerants R134a in rectangular minichannels. Three-dimensional simulations were carried out at different mass flux values, vapor qualities and gravity conditions through using the VOF model, the turbulence model and the phase transition model. The effects of various parameters on the surface heat transfer coefficient and the friction pressure gradient is clarified. The condensation process is found to be enhanced due to the increase of vapor quality and mass flow, while the friction pressure gradient decreases with the decrease of vapor quality and mass flow. According to the data obtained from the simulation, the liquid film tends to accumulate along the corner of the cross section in retangular minichannel. And the thickness of liquid film increased with the decrease of mass flux and vapor quality.

Experimental Study of Electrohydrodynamic Induction Pumping of a Dielectric Micro Liquid Film in External Horizontal Condensation Process

2003 ◽  
Vol 125 (6) ◽  
pp. 1096-1105 ◽  
Author(s):  
K. Brand ◽  
J. Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Flux ◽  
Liquid Film ◽  
Phase Change ◽  
Electric Conductivity ◽  
Traveling Wave ◽  
Condensation Process ◽  
Liquid Motion ◽  
Fundamental Understanding

Electrohydrodynamic (EHD) induction pumping is based on charges induced in a dielectric liquid and delayed at a gradient or discontinuity of the electric conductivity. A traveling electric wave (AC) attracts or repels these induced charges, leading to liquid motion. EHD induction pumping of a dielectric micro condensation film, in an external horizontal configuration, is investigated experimentally. The pumping and its effect on heat transfer are explored by varying the voltage and frequency of the electric traveling wave, as well as the condensation heat flux. This study provides a fundamental understanding of induction pumping of micro liquid film and illustrates its potential for managing the flow and enhancing the heat transfer in the presence of phase change.

Comparative Analysis of Heat Transfer Characteristics for CO2 and Conventional Refrigerants

2011 ◽  
Vol 130-134 ◽  
pp. 1306-1309
Author(s):  
Jun Lan Yang ◽  
Yi Tai Ma ◽  
Min Xia Li
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Heat Transfer Performance ◽  
Quantitative Comparison ◽  
Condensation Heat Transfer ◽  
Condensation Process ◽  
Transfer Performance ◽  
Comparison Study ◽  
Cooling Process ◽  
Thermo Physical Properties

s: The obvious characteristics of transcritical CO2 cycle are that the heat rejection process takes place in the supercritical region (about 8-12Mpa). The heat transfer features of CO2 under supercritical pressure are different from those of the conventional refrigerants. And the heat transfer performances comparison study for supercritical CO2 fluid and the conventional refrigerants are carried out by means of thermo-physical properties analog analysis and experimental results quantitative comparison. The special properties variation of supercritical CO2 fluid makes its heat transfer performance different from the conventional fluids. From the view of properties analysis and quantitative comparison, the heat transfer performance of supercritical CO2 is equivalent to the condensation heat transfer of conventional refrigerants. Although the condensation coefficient is very large since there is phase change and latent heat variation in the condensation process, there is liquid film thermal resistance. While in the supercritical CO2 cooling process, there is no liquid film in existence and the thickness of the boundary layer is very thin. The heat transfer temperature difference is very large, so the heat transfer performance in the supercritical CO2 cooling process is equivalent to that of the condensation heat transfer.

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.

scholarly journals Air-side performance of a micro-channel heat exchanger in wet surface conditions

2017 ◽  
Vol 21 (1 Part A) ◽  
pp. 375-385 ◽  
Author(s):  
Raviwat Srisomba ◽  
Lazarus Asirvatham ◽  
Omid Mahian ◽  
Ahmet Dalkılıç ◽  
Mohamed Awad ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Relative Humidity ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Micro Channel ◽  
Surface Conditions ◽  
Air Inlet ◽  
Wet Surface

The effects of operating conditions on the air-side heat transfer, and pressure drop of a micro-channel heat exchanger under wet surface conditions were studied experimentally. The test section was an aluminum micro-channel heat exchanger, consisting of a multi-louvered fin and multi-port mini-channels. Experiments were conducted to study the effects of inlet relative humidity, air frontal velocity, air inlet temperature, and refrigerant temperature on air-side performance. The experimental data were analyzed using the mean enthalpy difference method. The test run was performed at relative air humidities ranging between 45% and 80%; air inlet temperature ranges of 27, 30, and 33?C; refrigerant-saturated temperatures ranging from 18 to 22?C; and Reynolds numbers between 128 and 166. The results show that the inlet relative humidity, air inlet temperature, and the refrigerant temperature had significant effects on heat transfer performance and air-side pressure drop. The heat transfer coefficient and pressure drop for the micro-channel heat exchanger under wet surface conditions are proposed in terms of the Colburn j factor and Fanning f factor.

Prediction and Comparison of Shell Condensers With Straight or Helical Channels for Underwater Vehicles

2019 ◽  
Vol 11 (5) ◽  
Author(s):  
Peiyu Chen ◽  
Gongnan Xie ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Underwater Vehicles ◽  
Condensation Process ◽  
Inlet Temperature ◽  
Mass Rate ◽  
R Ratio ◽  
Universal Prediction ◽  
Inlet Conditions ◽  
Degree Of Condensation ◽  
Helical Channels

The shell condenser is one of the key components of underwater vehicles. To study its thermal performance and to design a more efficient structure, a computational model is generated to simulate condensation inside straight and helical channels. The model combines empirical correlations and a MATLAB-based iterative algorithm. The vapor quality is used as a sign of the degree of condensation. Three calculation models are compared, and the optimal model is verified by a comparison of simulated results and available experimental data. Several cases are designed to reveal the effects of various inlet conditions and the diameter-over-radius (Dh/R) ratio. The results show that the inlet temperature and mass rate significantly affect the flow and heat transfer in the condensation process, the heat transfer capabilities of the helical channels are much better than that of the straight channel, and both the heat transfer coefficient and total pressure drop increase with the decrease of Dh/R. This study may provide a useful reference for performance prediction and structural design of shell condensers used for underwater vehicles and may provide a relatively universal prediction model for condensation in channels.

Experimental Study of Electrohydrodynamic Induction Pumping of a Dielectric Micro Liquid Film in External Horizontal Condensation Process

2002 ◽  
Author(s):  
K. Brand ◽  
J. Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Flux ◽  
Liquid Film ◽  
Phase Change ◽  
Traveling Wave ◽  
Change Process ◽  
Change Processes ◽  
Condensation Process ◽  
Flow Management

Electrohydrodynamic induction pumping of a dielectric micro condensation film is experimentally investigated in an external horizontal configuration. The pumping and its effect on heat transfer are explored by varying the voltage and frequency of the electric traveling wave, as well as the condensation heat flux. The induced pumping impacts the phase change process, but it provides first and foremost a tool for effective flow management. This is of significant importance in phase-change processes.

Sign in / Sign up

Export Citation Format

Share Document