The paper deals with the development of convective flows in a complex system of thin liquid layers occurring under the effect of thermal load. To study this process a mathematical model which is ...based on the decomposition of complex problem into unitary elements (modules) with some set of rules allowing their linkage with each other was constructed. Each module represents a monotypic local model. The fluid flow and heat transfer in each of these modules are described by the Navier-Stokes and thermal conductivity equations. The boundary conditions required to solve these systems of equations are represented explicitly and written in the form of conservation laws. The numerical analysis of effect of thermal load on the characteristics of the liquid layers movement depending on the Marangoni number is carried out. It is shown that physical and thermophysical properties of liquid layers play the decisive role. It is exactly they control the convective flows in layers and determine the position and shape of interfaces. The results of model problem solutions are presented.
The problem of thermocapillary convection under the conditions of weak evaporation in a plane confined volume is studied. The mathematical model to investigate the processes of heat- and mass ...transfer and phase transition parameters in a bilayer system subjected to local heating is suggested. A two-sided model based on the Boussinesq approximation of the Navier–Stokes equations is formulated in the “stream function–vorticity” terms. It includes governing equations and boundary conditions on the interface which are the consequences of the conservation laws and conditions on the outer boundaries of a cuvette. Special attention is given to the study of the effects of evaporation at the thermocapillary interface. The conditions of the heat and mass balance at the deformable interface with respect to the diffusive-type evaporation are assumed to be fulfilled. The temperature relations on the solid walls of a cell take into account the presence of thermal elements of finite size. The Dufour and Soret effects are considered in the interface conditions and in the governing equations describing the fluid motion in a gas-vapor mixture. A numerical algorithm is developed to calculate the basic characteristics of the liquid–gas system and interface location at any time. The results of the numerical study of the interface evolution and non-stationary flows in a cavity being under normal gravity conditions are presented. The possibility of intensifying the evaporation due to the arrangement of additional thermal elements is discussed. The proposed approach allows one to reliably feature the basic characteristics of convective regimes, to evaluate amplitude of the interface deformations and to forecast parameters of vapor content in a gas phase.
In this paper, we compare the Marangoni effect and the effect of the Prandtl number variation on features of the liquid film rupture under the action of a thermal load and show a principal difference ...between these two effects. Results of computational analysis allow us to make the following conclusions. When affecting on the free surface of the plane liquid film by thermal beam, in order to obtain the initial holes of the same size in films with various thermal physical properties, one should apply a thermal load of a certain well-defined type, more specifically, concentrated thermal load, which provides the predetermined temperature at least on one of the film boundaries. In this case the size of the holes will depend only on the width of a thermal beam applied to the film free surface. Paper presents the solutions of the model problems.
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•Novel composite PSf/PTMSP hollow fiber membranes are fabricated.•Ethylene/ethane separation in membrane contactor with aqueous AgNO3 is studied.•Highest ethylene overall permeance ...(83 GPU) at ethylene recovery of 44% is achieved.•Ethylene overall permeance decreases only by 24% during six months of MC operation.•Membrane and liquid phase resistances are significant and comparable.
The novel highly permeable composite membranes with a thin selective layer made of poly(1-trimethylsilyl-1-propyne) (PTMSP) on polysulfone hollow fiber support were proposed for application in gas-liquid membrane contactor for ethylene/ethane separation. The effects of AgNO3 concentration in aqueous absorbent and its velocity on the ethylene mass transfer coefficient were evaluated. High ethylene permeance (83 GPU) at ethylene recovery of 44% was achieved. Six months of membrane contactor operation revealed only 24% drop in the overall mass transfer coefficient. The contributions of membrane and liquid phase to the overall mass transfer resistance were estimated. The contributions were found to be comparable values.
In the framework of the complete formulation of the conjugate problem, the liquid–gas flow structure arising upon local heating using thermal sources is investigated numerically. The two-layer system ...is confined by solid impermeable walls. The Navier–Stokes equations in the Boussinesq approximation in the ‘streamfunction–vorticity’ variables are used to describe the media motion. The dynamic conditions at the interface are formulated in terms of the tangential and normal velocities, while the temperature conditions at the external boundaries of the system take into account the presence of local heaters. The influence of the number of heaters and heating modes on the dynamics and character of the appearing convective regimes is analysed. The steady and commutated heating modes for one and two heaters arranged at the lower boundary are investigated. The heating initiates convective and thermocapillary mechanisms causing the fluid motion. Transient regimes with the successive formation of two-vortex, quadruple-vortex and two-vortex flows are observed before the stabilization of the system in the uniform heating mode. A stable thermocapillary deflection appears at the interface above the heater. The commutated mode of heating entails oscillations of the interface with a change in the deflection form and the formation of travelling vortices in the fluids. The impact of particular mechanisms on the flow patterns is analysed. The paper presents typical distributions of the velocity and temperature fields in the system and the position of the interface for the considered cases.
A novel phase inversion technique for preparation of high flux polyphenylsulfone (PPSU) ultrafiltration membranes employing the systems which feature upper critical solution temperature (UCST), gel ...point and lower critical solution temperature (LCST) is proposed. These systems include PPSU, polyethylene glycol (PEG) with molecular weight in the range of 6 ÷ 40 × 103 g mol−1 and N-methyl-2-pyrrolidone (NMP) as a solvent. According to the triangular phase diagrams obtained, the polymer solutions consisting of 20 wt% PPSU – 15 wt% PEG (Mw = 6 ÷ 40 × 103 g mol−1) – NMP are revealed to be two-phase systems at T > 100 °C and gels at T < 38–40 °C. The developed technique involves PPSU solution processing at the temperature region between LCST and UCST (gel point). Meanwhile, the coagulation bath temperature has to be between UCST (gel point) and LCST. The effect of PEG molecular weight, casting solution composition and coagulation bath temperature on membrane structure, performance and hydrophilic-hydrophobic balance of the membrane selective layer was studied. Applying the proposed technique flat-sheet membranes with pure water flux of 486 L m−2 h−1 bar−1 and human serum albumin rejection of 90% were prepared which is the best performance for PPSU ultrafiltration membranes reported up-to-date. It was found that introduction of PEG (Mw = 6 ÷ 40 × 103g mol−1) into the casting solution results in the efficient membrane hydrophilization, which is confirmed by FTIR spectroscopy of the membrane selective layer.
Preparation of PPSU membranes applying the systems with LCST and UCST Display omitted
•Novel technique for preparation of high flux PPSU UF membranes was developed.•PPSU-PEG-NMP systems feature critical solution temperatures and gel point.•Combination of NIPS and TIPS yields the formation of extra high flux UF membranes.•PEG molecular weight affects the structure and performance of PPSU membranes.•Membrane hydrophilicity is influenced by PEG MW and coagulation bath temperature.
Phase diagrams of the polyphenylsulfone (PPSU)
–
polyethylene glycol (PEG)
–
N-methyl-2-pyrrolidone (NMP) system have been plotted as a function of PEG molecular weight. For 15 wt % PPSU solutions ...containing 15 wt % of PEG with molecular weight of 6000
–
40 000 g mol
–1
, the occurrence of an upper critical solution temperature (UCST, solution
–
gel transfer (gel point)) and a lower critical solution temperature (LCST) was found. According to the phase diagrams analysis, a method for the preparation of high flux PPSU membranes using the systems with UCST and LCST in an experimentally attainable temperature range has been proposed. The method involves casting solution processing at a temperature of the existence of a one-phase homogeneous solution (UCST < T < LCST), and the use of a coagulation bath at a temperature between UCST (gel point) and LCST. Membranes prepared from 15 wt % PPSU solutions with the addition of PEG-20000 were found to have the highest pure water flux (500–1000 L m
–2
h
–1
at 0.1 MPa), and a human serum albumin rejection of ca. 90%.
The kinetics of oxidation of allyl alcohol to glycidol in the presence of extruded titanium silicalite was investigated. Based on the experimental data obtained, a kinetic model of the process was ...developed and the activation energies of the target and side reactions, the rate constants and the adsorption equilibrium were determined. Testing of the process of allyl alcohol epoxidation was carried out and the adequacy of the proposed kinetic model was evaluated at the bench laboratory installation of continuous action.
Graphic Abstract
Transcriptomic and proteomic analysis were performed on 72 h biofilms of the acneic strain Cutibacterium acnes and planktonic cultures in the presence of epinephrine. Epinephrine predominantly ...downregulated genes associated with various transporter proteins. No correlation was found between proteomic and transcriptomic profiles. In control samples, the expression of 51 proteins differed between planktonic cultures and biofilms. Addition of 5 nM epinephrine reduced this number, and in the presence of 5 µM epinephrine, the difference in proteomic profiles between planktonic cultures and biofilms disappeared. According to the proteomic profiling, epinephrine itself was more effective in the case of C. acnes biofilms and potentially affected the tricarboxylic acid cycle (as well as alpha-ketoglutarate decarboxylase Kgd), biotin synthesis, cell division, and transport of different compounds in C. acnes cells. These findings are consistent with recent research on Micrococcus luteus , suggesting that the effects of epinephrine on actinobacteria may be universal.
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