scholarly journals The Effect of the Concentration Polarization and the Membrane Layer Mass Transport on the Membrane Separation

2017 ◽  
Vol 6 (1) ◽  
Author(s):  
Endre Nagy ◽  
Gábor Borbély
Keyword(s):  
Boundary Layer ◽  
Mass Transport ◽  
Concentration Polarization ◽  
Membrane Separation ◽  
Separation Efficiency ◽  
Enrichment Factors ◽  
Transport Parameters ◽  
Membrane Layer ◽  
Negative Effect ◽  
Concentration Polarization Layer

The negative effect of the concentration polarization layer on the membrane separation is well known. How the mass transport parameters of the membrane matrix, e.g. the solubility coefficient, membrane Peclet number, can affect the concentration profile of the boundary layer, and consequently, the separation efficiency is not investigated in detail yet. This paper gives the suitable mathematical expressions, in order to predict the well known parameters as polarization modulus, enrichment factors, etc., taking into account the transport parameters for both the concentration boundary and the membrane layers, and analyses the concentration distribution and the polarization modulus. It has been shown that the transport properties of the membrane layer have significant effect on the concentration profiles of the boundary layer and thus, on the polarization modulus, enrichment factors, etc., as well. Thus, the well known equations, e.g. the polarization modulus, enrichment factor given in the literature [see e.g. Equations (2) and (3)], could be considered as approaches.

scholarly journals 3D-printed electrodes with improved mass transport properties

2019 ◽  
Author(s):  
Matthias Wessling
Keyword(s):  
Boundary Layer ◽  
Mass Transport ◽  
Transport Properties ◽  
Concentration Polarization ◽  
Voltage Drop ◽  
Electrochemical Reactor ◽  
Limiting Current ◽  
Polarization Effects ◽  
Static Mixers ◽  
Conversion Rates

Today's electrochemical reactor design is a less developed discipline as compared to electrocatalytic synthesis. Although catalysts show increasing conversion rates, they are often operated without measures for the reduction of concentration polarization effects. As a result, a stagnant boundary layer forms at the electrode‐electrolyte interface. This stagnant boundary layer presents an additional voltage drop and reduces the energy efficiency. It is generally accepted that this phenomenon is caused by a combination of fast electrode reactions and slow diffusion of the reacting species. Our earlier work demonstrated the potential of non‐conducting static mixers to reduce concentration polarization effects. However, there are few studies on conductive static mixers applied as electrodes. In this study, we present a new concept of additive manufactured flow through electrode mixers. Our electrode geometry combines a high surface area with mixing properties, diminishing concentration polarization effects of transport‐limited reactions. Mass transport properties of these conductive static mixers are evaluated in an additive manufactured electrochemical reactor under controlled conditions by applying the limiting‐current method.

The Characteristic Analysis of Interrupted Flow Pulsation on Ultrafiltration System

2013 ◽  
Vol 479-480 ◽  
pp. 373-379
Author(s):  
Chyouhwu Huang ◽  
Hung Shyong Chen
Keyword(s):  
Concentration Polarization ◽  
Fruit Juice ◽  
Membrane Separation ◽  
Industrial Applications ◽  
Membrane Module ◽  
Characteristic Analysis ◽  
Oil Water ◽  
Concentration Polarization Layer ◽  
Interrupted Flow ◽  
Macromolecular Solution

Ultrafiltration (UF) process has been widely used in many industrial applications to separate or concentrate macromolecular solution such as the making of fruit juice, the separation of oil-water emulsions, the treatment effluents from the pulp and paper, and environmental protecting applications. However, this process exhibits a limiting flux behavior caused by concentration polarization and consequently reduces the life of the membrane module. Concentration polarization can be especially severe in macromolecular solutions due to low diffusivity in membrane separation. In this study, we introduce an interrupted pulsatile flow to improve the performance of the membrane and decrease the concentration polarization layer. This method involves pulsing the feed flow discontinuously. Our results show that this method can be applied to membrane module regardless of it geometry and materials. Also, when comparing with un-pulsatile module, this could further leader to the improvement of membrane life. Keywords: ultrafiltation, interrupted - pulsating flow, concentration polarization, limiting flux behavior

scholarly journals NUMERICAL INVESTIGATION OF THE OCCURRENCE OF A CONCENTRATION-POLARIZATION LAYER

2021 ◽  
Vol 18 (2) ◽  
pp. 56-59
Author(s):  
R.K. Manatbayev ◽  
Keyword(s):  
Boundary Layer ◽  
Particle Deposition ◽  
Concentration Polarization ◽  
Membrane Surface ◽  
Porous Wall ◽  
Numerical Approach ◽  
Co2 Gas ◽  
Mixture Concentration ◽  
Lower Permeability ◽  
Concentration Polarization Layer

This work describes the appearance of a concentration polarizing boundary layer on the membrane surface during the separation of the H2/CO2 gas mixture. Concentration polarization occurs when the rejection solution accumulates near the surface of the membrane, forming a boundary layer. The inclusion of concentration polarization effects in the processing of porous walls creates additional difficulties. The boundary layer formed by concentration polarization can be considered as a type of a second porous wall with a lower permeability than the membrane. The main difficulty in modeling this situation is to determine the appropriate boundary conditions for the concentration on the wall, since the concentrations on the wall will constantly change, and the wall geometry itself may change over time due to particle deposition. To account for this effect, a numerical approach was developed, which is discussed in this work

Experimental Studies Concerning the Semipermeable Membrane Separation Efficiency for 134Cs, 137Cs, 57Co, 58Co, 60Co, 54Mn in Liquid Radioactive Waste I. Treatment of secondary waste from POD decontamination procedure

2008 ◽  
Vol 59 (5) ◽  
Author(s):  
Mirela Dulama ◽  
Nicoleta Deneanu ◽  
Cristian Dulama ◽  
Margarit Pavelescu
Keyword(s):  
Membrane Separation ◽  
Separation Efficiency ◽  
Liquid Radioactive Waste ◽  
Experimental Studies ◽  
Experimental Tests ◽  
Suspended Solid ◽  
Process Efficiency ◽  
Active Charcoal ◽  
Precipitation Process ◽  
Pre Treatment

The paper presents the experimental tests concerning the treatment by membrane techniques of radioactive aqueous waste. Solutions, which have been treated by using the bench-scale installation, were radioactive simulated secondary wastes from the decontamination process with modified POD. Generally, an increasing of the retention is observed for most of the contaminants in the reverse osmosis experiments with pre-treatment steps. The main reason for taking a chemical treatment approach was to selectively remove soluble contaminants from the waste. In the optimization part of the precipitation step, several precipitation processes were compared. Based on this comparison, mixed [Fe(CN)6]4-/Al3+/Fe2+ was selected as a precipitation process applicable for precipitation of radionuclides and flocculation of suspended solid. Increased efficiencies for cesium radionuclides removal were obtained in natural zeolite adsorption pre-treatment stages and this was due to the fact that volcanic tuff used has a special affinity for this element. Usually, the addition of powdered active charcoal serves as an advanced purifying method used to remove organic compounds and residual radionuclides; thus by analyzing the experimental data (for POD wastes) one can observe a decreasing of about 50% for cobalt isotopes subsequently to the active charcoal adsorption.. The semipermeable membranes were used, which were prepared by the researchers from the Research Center for Macromolecular Materials and Membranes, Bucharest. The process efficiency was monitored by gamma spectrometry.

Separation of Biologically Active Compounds by Membrane Operations

2017 ◽  
Vol 23 (2) ◽  
pp. 218-230 ◽  
Author(s):  
Xiaoying Zhu ◽  
Renbi Bai
Keyword(s):  
Energy Consumption ◽  
Bioactive Compounds ◽  
Membrane Fouling ◽  
Membrane Separation ◽  
Separation Efficiency ◽  
High Energy ◽  
Separation Processes ◽  
Membrane Processes ◽  
Separation Technology ◽  
Pressure Driven

Background: Bioactive compounds from various natural sources have been attracting more and more attention, owing to their broad diversity of functionalities and availabilities. However, many of the bioactive compounds often exist at an extremely low concentration in a mixture so that massive harvesting is needed to obtain sufficient amounts for their practical usage. Thus, effective fractionation or separation technologies are essential for the screening and production of the bioactive compound products. The applicatons of conventional processes such as extraction, distillation and lyophilisation, etc. may be tedious, have high energy consumption or cause denature or degradation of the bioactive compounds. Membrane separation processes operate at ambient temperature, without the need for heating and therefore with less energy consumption. The “cold” separation technology also prevents the possible degradation of the bioactive compounds. The separation process is mainly physical and both fractions (permeate and retentate) of the membrane processes may be recovered. Thus, using membrane separation technology is a promising approach to concentrate and separate bioactive compounds. Methods: A comprehensive survey of membrane operations used for the separation of bioactive compounds is conducted. The available and established membrane separation processes are introduced and reviewed. Results: The most frequently used membrane processes are the pressure driven ones, including microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF). They are applied either individually as a single sieve or in combination as an integrated membrane array to meet the different requirements in the separation of bioactive compounds. Other new membrane processes with multiple functions have also been developed and employed for the separation or fractionation of bioactive compounds. The hybrid electrodialysis (ED)-UF membrane process, for example has been used to provide a solution for the separation of biomolecules with similar molecular weights but different surface electrical properties. In contrast, the affinity membrane technology is shown to have the advantages of increasing the separation efficiency at low operational pressures through selectively adsorbing bioactive compounds during the filtration process. Conclusion: Individual membranes or membrane arrays are effectively used to separate bioactive compounds or achieve multiple fractionation of them with different molecule weights or sizes. Pressure driven membrane processes are highly efficient and widely used. Membrane fouling, especially irreversible organic and biological fouling, is the inevitable problem. Multifunctional membranes and affinity membranes provide the possibility of effectively separating bioactive compounds that are similar in sizes but different in other physical and chemical properties. Surface modification methods are of great potential to increase membrane separation efficiency as well as reduce the problem of membrane fouling. Developing membranes and optimizing the operational parameters specifically for the applications of separation of various bioactive compounds should be taken as an important part of ongoing or future membrane research in this field.

scholarly journals Sub-seasonal Variability in the Boundary Layer Sources for Transport into the Tropopause Layer in the Asian Monsoon Region

2017 ◽  
Author(s):  
Bin Chen ◽  
Bärbel Vogel ◽  
Xiangde Xu ◽  
Shuai Yang
Keyword(s):  
Boundary Layer ◽  
Tibetan Plateau ◽  
Mass Transport ◽  
Seasonal Variability ◽  
The Tibetan Plateau ◽  
Southern Slope ◽  
Seasonal Behavior ◽  
Air Mass ◽  
Source Regions ◽  
Wide Range

Abstract. The Asian summer monsoon (ASM) is associated with an upper-level anticyclone and acts as a well-recognized conduit for troposphere-to-stratosphere transport. The Lagrangian dispersion and transport model FLEXPART forced by ERA-Interim data from 2001–2013 was used to perform climatological modeling of the summer season (May–July). This study examines the properties of the air mass transport from the atmospheric boundary layer (BL) to the tropopause layer (TL), with particular focus on the sub-seasonal variability in the tracer-independent BL sources and the potential controlling mechanisms. The results show that, climatologically, the three most impactful BL source regions are northern India, the Tibetan Plateau, and the southern slope of the Himalayas. These regions are consistent with the locations of sources identified in previous studies. However, upon closer inspection, the different source regions to the BL-to-TL air mass transport are not constant in location or shape and are strongly affected by sub-seasonal variability. The contributions from the Tibetan Plateau are most significant in early May but decrease slightly in mid-May to mid-June. In contrast, the contributions from India and the southern slope of the Himalayas increase dramatically, with peak values occurring in mid-July. Empirical Orthogonal Function (EOF) analysis provides further evidence that the BL sources in the ASM region vary across a wide range of spatiotemporal scales. The sub-seasonal behavior of these BL sources is closely related to the strength of persistent deep convection activity over the northern Bay of Bengal and its neighboring areas.

Fluid mechanics and mass transport in centrifugal membrane separation

2000 ◽  
Vol 176 (2) ◽  
pp. 277-289 ◽  
Author(s):  
J.G Pharoah ◽  
N Djilali ◽  
G.W Vickers
Keyword(s):  
Mass Transport ◽  
Fluid Mechanics ◽  
Membrane Separation
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