Concentration boundary layer under general steady-flow conditions

1990 ◽  
Vol 55 (10) ◽  
pp. 2404-2416 ◽  
Author(s):  
Ondřej Wein
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Velocity Field ◽  
Transfer Coefficient ◽  
Solid Surface ◽  
Active Surface ◽  
Flow Conditions ◽  
Liquid Stream ◽  
Concentration Boundary ◽  
Overall Mass Transfer Coefficient

An explicit formula is given for the overall mass-transfer coefficient between a steady liquid stream and a small active part of a solid surface in the stream. This is a generalization of the well-known Lighthill formula to the form applicable for any velocity field and any shape of the active surface. Its use is demonstrated for the circular electrodiffusion probes under various kinematic conditions.

Modeling Vapor Transport in a Hollow Fiber Membrane Humidifier Using ε-NTU Approach

2020 ◽  
Author(s):  
Hoang Nghia Vu ◽  
Xuan Linh Nguyen ◽  
Sangseok Yu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Fuel Cell ◽  
Relative Humidity ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Water Content ◽  
Vapor Transport ◽  
Overall Mass Transfer Coefficient ◽  
Mass Exchanger

Abstract In a fuel cell vehicle, the water content of the gas supply within certain ranges plays a key role in improving the performance of a proton exchange membrane. The lower limit of water content in the air supply is to avoid the problem of drying-out, while the upper prevents flooding. Water management can be accomplished by a membrane humidifier which allows water vapor to permeate the mixture from the side having the higher water concentration, moving to the other side of the membrane. In this study, the variation in water content collected at the outlet of a membrane humidifier is investigated with a one-dimensional mass exchanger model and various operating variables. The vapor concentration of outlet flows is affected by operating temperature and relative humidity of the membrane humidifier. Relative humidity of the dry side at the point of outlet flow, to be supplied to the fuel cell module, is the key characteristic. The analogy of the effectiveness-NTU approach for heat transfer is used to analyze the characteristics of the mass exchanger. Mass flux through the membranes is estimated with an overall mass transfer coefficient which represents vapor transport characteristics moving through the membrane module. This coefficient has a similar role to the overall heat transfer coefficient in heat exchanger analysis. This parametric study is conducted to understand the effects of different variables. The Effectiveness-NTU methodology of mass transfer uses the overall mass transfer coefficient and the mass transfer rate, as evaluated experimentally. Simulink software is then employed to deliver outcomes of the model for different operating conditions.

scholarly journals Overall Mass Transfer Coefficient of CO2 Absorption in a Diameter-varying Spray Tower

2017 ◽  
Vol 114 ◽  
pp. 1665-1670 ◽  
Author(s):  
Xiaomei Wu ◽  
Min He ◽  
Yunsong Yu ◽  
Zhen Qin ◽  
Zaoxiao Zhang
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Co2 Absorption ◽  
Spray Tower ◽  
Overall Mass Transfer Coefficient

Flow and Mass Transfer in Bends Under Flow-Accelerated Corrosion Wall Thinning Conditions

2009 ◽  
Author(s):  
John M. Pietralik ◽  
Chris S. Schefski
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Flow Conditions ◽  
Ferrous Ions ◽  
Local Flow ◽  
Accelerated Corrosion ◽  
Flow Effects ◽  
Flow Accelerated Corrosion

The three groups of parameters that affect flow-accelerated corrosion (FAC) are flow conditions, water chemistry, and materials. Nuclear power plant (NPP) data and laboratory tests confirm that under alkaline water chemistry there is a close relationship between local flow conditions and FAC rates in piping components. The knowledge of local flow effects can be useful for developing targeted inspection plans for piping components, predicting the location of the highest FAC rate for a given piping component, and determining what piping components should be replaced. A similar evaluation applies also to FAC in heat transfer equipment such as heat exchangers and steam generators. The objective of this paper is to examine the role of flow and mass transfer in bends under FAC conditions. Bends experience increased FAC rates compared to straight pipes, and are the most common components in piping systems. When the flow effects are dominant, the FAC rate is proportional to the mass flux of ferrous ions, which, in turn, is proportional to the mass transfer coefficient in the flowing water. The mass transfer coefficient describes the intensity of the transport of corrosion products (ferrous ions) from the oxide-water interface into the bulk water. Therefore, this parameter can be used for predicting the local distribution of the FAC rate. The current paper presents plant and laboratory evidence of the relationship between local mass transfer conditions and the FAC rate in bends. It shows correlations for mass transfer coefficients in bends and reviews the most important flow parameters affecting the mass transfer coefficient. The role of bend geometry and, in particular, the short and long radii, surface roughness, wall shear stress, and local turbulence is discussed. Computational fluid dynamics calculations and plant artefact measurements for short-radius and long radius bends are presented. The effect of the close proximity of two bends on FAC rate is also examined based on CANDU™ NPP inspection data and compared with literature data.

scholarly journals Selection of Mixed Amines in the CO2 Capture Process

2021 ◽  
Vol 7 (1) ◽  
pp. 25
Author(s):  
Pao-Chi Chen ◽  
Hsun-Huang Cho ◽  
Jyun-Hong Jhuang ◽  
Cheng-Hao Ku
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Co2 Capture ◽  
Absorption Rate ◽  
Absorption Efficiency ◽  
Optimum Conditions ◽  
Capture Process ◽  
Overall Mass Transfer Coefficient ◽  
Selection Of

In order to select the best mixed amines in the CO2 capture process, the absorption of CO2 in mixed amines was explored at the required concentrations by using monoethanolamine (MEA) as a basic solvent, mixed with diisopropanolamine (DIPA), triethanolamine (TEA), 2-amino-2-methyl-1-propanol (AMP), and piperazine (PZ). Here, a bubble column was used as the scrubber, and a continuous operation was adopted. The Taguchi method was used for the experimental design. The conditional factors included the type of mixed amine (A), the ratio of the mixed amines (B), the liquid feed flow (C), the gas-flow rate (D), and the concentration of mixed amines (E). There were four levels, respectively, and a total of 16 experiments. The absorption efficiency (EF), absorption rate (RA), overall mass transfer coefficient (KGa), and scrubbing factor (ϕ) were used as indicators and were determined in a steady-state by the mass balance and two-film models. According to the Taguchi analysis, the importance of the parameters and the optimum conditions were obtained. In terms of the absorption efficiency (EF), the absorption rate (absorption factor) (RA/ϕ), and the overall mass transfer coefficient (KGa), the order of importance is D > E > A > B > C, D > E > C > B > A, and D > E > C > A > B, respectively, and the optimum conditions are A1B4C4D3E3, A1B3C4D4E2, A4B2C3D4E4, and A1B1C1D4E1. The optimum condition validation results showed that the optimal values of EF, RA, and KGa are 100%, 30.69 × 10−4 mol/s·L, 1.540 l/s, and 0.269, respectively. With regard to the selection of mixed amine, it was found that the mixed amine (MEA + AMP) performed the best in the CO2 capture process.

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