Advanced Topics in Mass Transfer 550 the surfactant under the action of solutocapillary forces was carried along the bubble surface toward the lower bubble boundary. Owing to fluid continuity, the arising flow accelerated the flux of the concentrated surfactant solution along the upper boundary of the channel towards the bubble surface, adding thereby intensity to the existing convective vortex. However, the originated vortex cell, entrapping more and more portions of highly concentrated surfactant solution, became increasingly light. Rising up it eventually cut off the arriving jet of surfactant from the top of the bubble. As a result, the vortex flow ceased abruptly and the bubble surface turned out to be surrounded by a thin layer of the surfactant solution having a uniform concentration. a) b) c) d) e) f) g) Fig. 12. Interferograms of concentration field evolution around the air bubble in rectangular layer with stratified isopropyl alcohol solution. t, sec: 0, 28.0, 28.1, 28.2, 29.2, 34.2, 34.3 Oscillatory Regimes of Solutocapillary Marangoni Convection 551 a) b) c) d) e) f) g) Fig. 13. Interferograms of concentration field evolution around the air bubble in rectangular layer with stratified ethyl alcohol solution. t, sec: 0, 0.2, 0.4, 0.8, 5.0, 10.0, 20.0 However, equalizing of the generated horizontal gradient of the surfactant concentration resulted in the development of a slow advective flow. This gravitational motion, by restoring the disturbed vertical stratification of the solution, again draws a concentrated surfactant solution to the upper bubble boundary. As soon as the flux of surfactant touched the bubble surface, the solutocapillary vortex recurred. The cycle repeated iteratively, with the difference that the oscillation period increased with time whereas the intensity of the vortex flow decreased due to a gradual decrease of the vertical concentration gradient. Marangoni convection ceased at the time when the concentration of the solution became almost uniform throughout the whole layer. Advanced Topics in Mass Transfer 552 A characteristic feature of this process is that during consecutive cycles the capillary flow was initiated at much less concentration differences at the bubble surface (thus, the onset of the second cycle happened at ΔC*~0.6%). At the same time, the average concentration of the surfactant at the bubble surface gradually increased, which might be one of the explanations for the essential decrease in the concentration difference at the bubble surface at the beginning of each consecutive cycle of the vortex convection motion. In order to verify this suggestion we investigated the dependence of the critical Marangoni numbers Mа*, defined by the maximum vertical concentration difference between the bubble poles at the moment of formation of the first vortex, on the surfactant concentration in the solution surrounding the bubble. To this purpose, the channel was initially filled not with pure water but with a homogeneous aqueous solutions of alcohols with different initial concentration С 0 . It was found that, as С 0 increases (and, respectively, as the surface tension at the bubble surface decreases) the values of Mа* decrease monotonically. Fig. 14 presents the critical Marangoni numbers at the beginning of different cycles of the vortex flow in solutions of ethanol and isopropanol (points 1 and 2) as functions of the crispation number Cr, characterizing the ratio of viscous and capillary forces. The crispation numbers, in turn, were calculated using the values of the surface tension corresponding to the average surfactant concentration at the air bubble surfaces at the moments of motion intensification. The diagram also presents the results of measurements of Mа* as a function of Cr, obtained from tests for solutions with different initial alcohol concentration (solid line drawn through points 3 for ethanol and 4 for isopropanol). It is seen that the values of Mа* obtained under various conditions are rather close and all curves are qualitatively coincide. Ma*, 10 6 0 20 40 510152025 Сr, 10 –6 Fig. 14. Critical Marangoni numbers as a function of crispation number In our experiments we also investigated the time dependence of the oscillation period of the convective flow near the bubble in solutions of ethanol, isopropanol and methanol. In all cases, the oscillation frequency of the flow near the bubble surface was first rather high (accordingly the period T was small ~ 5–10 sec). Then, the oscillation period increased 1 2 3 4 Oscillatory Regimes of Solutocapillary Marangoni Convection 553 monotonically with time, and after some time the oscillations suddenly came to an end. The experimental data obtained were compared with the results of numerical analysis (Birikh et al., 2006). The results of experiments and numerical calculations were found to be in good agreement with respect to the convective flow structure and the oscillation period. The period of the steady-state oscillations decreases with an increase of the Grashof number and depends weakly on the Marangoni number. This dimensionless relationship is represented in Fig. 15. The different points on the plot represent the results of experiments for various alcohol solutions (1 – ethanol at C 0 = 40%, 2 – ethanol at C 0 = 20%, 3 – isopropanol, 4 – methanol). The solid line corresponds to numerical calculations. Θ / τ 0 20 40 0369 Gr, 10 2 Fig. 15. Dimensionless oscillation period An analogous situation was observed on the chlorobenzene — aqueous isopropanol solution interface (Kostarev et al., 2008b). A chlorobenzene drop, immiscible in the water, was injected by means of a syringe into a channel cavity from one of its ends in such a way that completely bridged over the channel and formed lateral liquid/liquid boundary. A "tongue" of a concentrated (40%) isopropyl solution flowed along the upper channel boundary toward the drop surface, forming near it an area of nixture with vertical surfactant stratification. In contrast with the convection initiation around the gas bubble, a much more greater surfactant concentration gradient is needed to be created during the time between the moments when the alcohol reaches the droplet surface and before solutocapillary motion begins to develop, as is seen in the interferograms in Fig. 16. The difference of the solution concentration ΔC* between the upper and lower drop ends equalized to 4.1% against the value of 2.2% in case of gas bubble. The other distinction is that surfactant diffuses through the phase interface into chlorobenzene, thus creating a concentration gradient in the latter also. Initially, this process occurs rather uniformly along the droplet surface, so that a surfactant gradient at the surface itself is absent. Only later, an intense Marangoni convection develops in the solution (at Δt ~ 1 min after the contact between the surfactant tongue and the droplet surface. 1 2 3 4 Advanced Topics in Mass Transfer 554 a) b) c) d) e) f) g) Fig. 16. Interferograms of the concentration field in the experiment with a chlorobenzene droplet in a stratified aqueous isopropanol solution: t, sec: 0, 60, 61, 66, 70, 76, 77 6. Conclusion The performed experiments provided convincing evidence for the origination of intensive solutocapillary Marangoni convection in multiphase systems with inhomogeneous concentration of the soluble surfactant along the phase interface. The specific feature of these fluid flows was that they took place under conditions of weak surfactant diffusion (the values of the Schmidt number in experiments were about 10 3 ), and that the changes in the spatial concentration of the solution happened mainly due to convective mass transfer. The arising stresses and flows in some ways are similar to thermocapillary ones and are governed by similar relationships, for example, flow intensity is proportional to the surface tension gradient. On the other hand, the solutocapillary phenomena demonstrate some specific features, which are related both to fairly large values of the Marangoni numbers and Oscillatory Regimes of Solutocapillary Marangoni Convection 555 to a more complicated character of formation of the surface tension gradient. The mechanism of the transfer (absorption) of a surfactant at the phase interface is distinct from the mechanism maintaining the temperature at the interface. The interface has inertia, and a convective transfer of the surfactant is possible along it, accompanied by surface diffusion. The latter peculiarity is caused by slower (compared to heat transfer) diffusion of the fluid molecules with low surface tension onto the interface and adsorption of the surfactant at the inter-phase boundary. These specific features should be taken into account in constructing theoretical models of the boundary conditions at the interface allowing for the formation of a new, surface phase of the surfactant, controlling a transition of the soluble mixture component from one phase to another. The process of formation of such a surface phase includes two stages. First, the molecules of the surfactant reach the interface of the liquid system via diffusive transport, because the normal component of the convective velocity at the surface is zero due to impermeability of the boundary. This process is followed then by formation of the proper interface in itself, by means of adsorption and desorption. The experiments demonstrated that the solutocapillary convection displays well-defined non-stationary properties. The interaction between the buoyancy and the Marangoni convective flows is responsible for the onset of auto-oscillation regime of convective motion around the gas bubbles and insoluble drops in a vertically stratified surfactant solutions. The periodical outbursts of solutocapillary flow at the bubbles/drops interface intensify substantially the stirring of the solution and can be used for the control of this procedure. The clarification of the nature of the flows developing close to resting liquid and gaseous inclusions in inhomogeneous surfactant solutions and the discovery of a threshold for the excitation of solutocapillary motion allow explaining many aspects of mass exchange and material structure formation in a number of technological experiments in microgravity, and predicting the behavior of complex systems of liquids and multiphase media in thin channels and layers, and in cavities of complex geometry. The results obtained in the experiments can be used in designing systems of passive homogenization in liquids and in optimizing working regimes of the already operational technology lines in various branches of industry. A special role can be played by the Marangoni effects elaborated here in the design of microsystems for cooling and heat exchange with multi-component mixtures of liquids as a heat agent. 7. Acknowledgements The work was supported by Russian Foundation of Fundamental Research under project No 09-01-00484, joint project of SB, UB and F-EB of RAS (116/09-С-1-1005) and the program of the Department of Power Engineering, Mechanical Engineering, Mechanics and Control Processes of RAS No 09-Т-1-1005. 8. References Birikh, R.V.; Zuev, A.L.; Kostarev, K.G. & Rudakov, R.N. (2006). Convective self- oscillations near an air-bubble surface in a horizontal rectangular channel. Fluid Dynamics, Vol. 41, No. 4, pp. 514–520. Birikh, R.V.; Rudakov, R.N.; Kostarev, K.G. & Zuev, A.L. (2008). Oscillatory modes of solutocapillary Marangoni convection at a drop-liquid interface. Proceedings of 6 th Advanced Topics in Mass Transfer 556 EUROMECH Nonlinear Dynamics Conf., pp. 1–6., Saint Petersburg, Russia, 30 June – 4 July 2008. Bushueva, K.A.; Denisova, M.O.; Zuev, A.L. & Kostarev, K.G. (2008). Flow development at the surfaces of bubbles and droplets in gradient solutions of liquid surfactants. Colloid J., Vol. 70, No. 4., pp. 416-422. Gustafson, S.E.; Kjellander R.A.E. & Rolf A.E. (1968). An interferometer for direct recording of refractive index distributions. Z. Naturforch., Vol. 23a, No. 2, pp. 242–246. Kostarev, K.G.; Zuev, A.L. & Viviani, A. (2004). Oscillatory Marangoni convection around the air bubble in a vertical surfactant stratification. Comptes Rendus Mecanique, Vol. 332, No. 1, pp. 1–7. Kostarev, K.G.; Zuev, A.L. & Viviani, A. (2006). Thermal and concentrational Marangoni convection at liquid/air bubble interface. J. Applied Mechanics. Transactions ASME, Vol. 73, No. 1, pp. 66–71. Kostarev, K.G., Pisarevskaya, N. N., Viviani, A. & Zuev, A. L. (2007). Oscillatory Marangoni convection around bubbles and drops in heterogeneous solutions of surfactants. Int. J. Microgravity Science & Technology, Vol. 19, No. 2, pp. 12–17. Kostarev, K.G.; Zuev, A.L. & Viviani, A. (2008a). Experimental study of convective self- oscillations near the lateral surface of a bubble in a plane rectangular channel. Acta Astronautica, Vol. 62, No. 6-7, pp. 431–437. Kostarev, K.G.; Zuev, A.L. & Viviani, A. (2008b) Experimental studies of concentration convective surfactant mass transfer near a drop-liquid interface. Proceedings of 19 th Int. Symp. on Transport Phenomena, pp. 1-5, Reykjavik, Iceland, 17–21 August 2008. (In Electronic Conference Proceedings). Kostarev, K.G.; Zuev, A.L. & Viviani, A. (2009a). Experimental considerations of solutocapillary flow initiation on bubble/drop interface in the presence of a soluble surfactant. Int. J. Microgravity Science and Technology, Vol. 21, No. 1–2, pp. 59–65. Kostarev, K.G.; Zuev A.L. & Viviani A. (2009b). Convective stirring of a stratified surfactant solution by the oscillatory solutocapillary flow. Proceedings of 4 th Int. Conf. on Physics and Control, pp. 1-8, Catania, Italy, 1–4 September 2009. (In Online Conference Proceedings http://lib.physcon.ru/download /p1930.pdf). Marsters, G.F. & Advani, A.A. (1973). A tilted plate interferometer for heat transfer studies. Rev. Sci. Instrum., Vol. 44, No. 8, pp. 1015–1018. Vazquez, G.; Alvarez, E. & Navaza, J.M. (1995). Surface-tension of alcohol plus water from 20-degrees-C to 50-degrees-C. J. Chem. Eng. Data, Vol. 40, No. 3, pp. 611–614. Vazquez, G.; Alvarez, E.; Sanchez-Vilas. M.; Sanjurjo B. & Navaza J.M. (1997). Surface tension of organic acids + water binary mixtures from 20°C to 50°C. J. Chem. Eng. Data, Vol. 42, No. 5, pp. 957–960. Zuev, A.L. & Kostarev, K.G. (2006). Oscillation of a convective flow round the air bubble in a vertically stratified solution of a surfactant. J. Experimental and Theoretical Physics, Vol. 130, No. 2, pp. 363–370. Zuev, A. L.; Kostarev, K.G. & Viviani, A. (2008a). Peculiarities of the solutocapillary convection. Proceedings of 11 th Int. Conf. on Multiphase Flow in Industrial Plants, pp. 39–46, Palermo, Italy, 7–10 September 2008 Zuev, A.L. & Kostarev, K.G. (2008b). Certain peculiarities of the solutocapillary convection, Physics–Uspekhi, Vol. 51, No. 10, pp. 1027–1045. 24 Aerodynamics of Ceramic Regular Packing for Heat-Massexchenge Processes Alexandr Pushnov Department of Engineering, Moscow State University of Environmental Engineering, Staraya Basmannaya street 21 / 4, 105066 Moscow Russia 1. Introduction The chemical, petroleum and other industries in implementing the removal processes, distillation and purification of gases from the emissions are widely used structured, as well as structural attachment mesh configuration [1-2]. Both of these belong to the regular batch nozzles, forming a three-dimensional spatial multi-channel structure. Structured packing is usually implemented as a set of individual corrugated sheets assembled in packets (blocks). Themselves with sheets can be made of polymer, ceramic and other materials. Formed in this channel have a complex spatial configuration. The most common structured nozzle of this type in the industry are packing company Sulzer Chemtech (Switzerland). To clear the air of various pollutants also find application developed at the Vilnius Gediminas Technical University biological plants, the main element of which is a filter with bio-fill [3, 4]. As a sorbent in the biofilter used cheap and available material - pieces of fir bark of various fractions, eg, 35, 25 and 12,5 mm [4, 5]. Performance and prospects of biofilters for air cleaning from harmful impurities doubt. However, the use of apparatus thin layer pieces sorbent indicated linear sizes and fractions makes it difficult to organize an optimal homogeneous structure of the granular layer throughout the cross section of the apparatus described in [4]. At the same time of contact of microorganisms with pollution in different parts of the biofilter, it seems, can vary significantly. Unlike the bulk of irregular attachments regular structured [1] as the structural attachment [2] have a greater specific surface and at the same time have significantly lower hydraulic resistance. In addition, the structured packing sheet avoid contacting bypass flows due to inherent in bulk irregular layers (eg, rings and saddles Rashig Burley) phenomena wall anisotropy [6, 7, 16, 17]. However, the known sheet structured packing does not have the properties of isotropy. They are due to the peculiarities of its design will organize a system of parallel isolated from each other channels and therefore do not provide a satisfactory cross-mixing of contacting streams. This affects the effectiveness of a column of contact devices of chemical technology, as well as in power (cooling towers) processes. One possible way to improve a class of structured nozzles is to create three-dimensional isotropic structure on the basis of highly porous cellular materials (HPCM) [8], which in the European Community referred to the term "foam". Advanced Topics in Mass Transfer 558 Given the emergence of new highly porous cellular materials can offer the following tips for a new classification of heat and mass transfer processes (see Fig. 1). Recently, a number of publications devoted to studying the possibilities of using HPCM as industrial attachments for the implementation of the processes of heat and mass transfer in the chemical industry. So in [10] L. Padeste, A. Baiker, J.P. Gabathuler point to prospects of using ceramic foam packaging of cordierite as carriers for catalysts. In their experiments the authors of [10] based on the known method of determining the dwell time distribution of fluid flow in a layer of packing for writing marking substance (label). Moreover, for the greater persuasiveness of their results, the authors [10] conducted experiments for two cases: the sand layer of spheres of diameter 1, 2, 3 and 5 mm, as well as ceramic foam packaging. However, as shown by O. Levenspiel, J.C.R. Turner [11] using the principle of measuring the distribution of time spent using the tags must be complete confidence in the presence of a flat profile of velocity. Contrary to the authors of [10] with reference to the work of [12] for bulk layers of balls, this condition is just not satisfied. On the contrary, as follows from a series of special studies in the timing characteristics of devices with bulk layers of balls and other grains form in a wide range of Reynolds numbers in a layer have the balls characteristic velocity profile with an extreme surge near the walls of the apparatus of the greater looseness of packing of spheres in this area [6, 17]. Incidentally, this is also evidenced by the results of [12]. This circumstance gives rise to a certain degree of doubt and in other results [10] on ceramic foam packaging. Packing for the implementation of the processes of heat and mass Regular structured Highly cellular materials Irregular (bulk) Based china Fixed Ceramic-based On the basis of metals Fluidised Fig. 1. Classification of packing for the processes of heat and mass transfer Thus, the problem of studying the aerodynamics of packing on the basis of ceramic HPCM remains relevant. In another study [13] presented the results of experiments on samples of porous blocks of metallic foam. However, experimental data on the basic geometric characteristics of porous packing of ceramic materials technology HPCM in the literature is largely absent. Hydrodynamics of ceramic packing HPCM also is not yet sufficiently studied. [...]... bulk packing according to the Polevoy [28]; 2 - bulk packing according Vedernikov et al [29]; 3 - bulk packing according Kolev et al [30]; 4 - bulk packing "Inzhehim - 2000" according to the Laptev and Farahov [31]; 5 - regular packing according to [1, 29]; 6 - bulk packing according to [32]; 7 - bulk packing according to [33]; 8 - ceramic packing of HPCM according to [21]; 9 - ceramic packing of HPCM... considered as a method of weighing fragment packing of known 562 Advanced Topics in Mass Transfer volume Another widely known method - fill the porous packing water can in this case to make significant errors due to air bubbles remaining in the pore volume packing at filling it with water For a known specific weight of material value of porosity packing can be determined by the ratio: ε =1− γ pack... packing of the space pore HPCM is pentagondodecahedron, whose structure is shown in Fig 4 Fig 2 Photo samples from the packing HPCM 560 Advanced Topics in Mass Transfer Fig 3 Arch-labyrinthine structure of highly porous cellular material Fig 4 Structure pentagondodecahedron cell material from the packing HPCM, 1 - pore channel; 2 - wall 3 Geometric characteristics of layer packing 3.1 General The main... gas flow in the samples from HPCM Results of preliminary test experiments on the velocity field of airflow in the empty apparatus without attachment shown in Fig 14 572 Advanced Topics in Mass Transfer Fig 14 Profile of creasing longitudinal velocity of stream - V and degrees of turbulence - Tu in identical sections of empty experimental apparatus without sedimentation at the charge corresponding number... environment behind the block of sedimentation high porosity material at different numbers ReD: ● - ReD = 6 800; + - ReD = 156 00 Aerodynamics of Ceramic Regular Packing for Heat-Massexchenge Processes 573 As can be seen from the graph presented in Fig 15, the longitudinal component of velocity V in the aerodynamic wake behind the block of packing HPCM with increasing Reynolds numbers from 156 00 to 6800... shown promising ceramic materials for the manufacture of packing HPCM for a wide range of chemical technology processes, including those for hardware design methods for cleaning absorption of harmful gases to protect the ambient air 574 Advanced Topics in Mass Transfer It is shown that the profiles of longitudinal velocity and the degree of turbulence of the gas flow in the aerodynamic wake behind a block... samples of ceramic packing HPCM with other types of industrial attachments and dry granular materials is presented in Fig 11 in logarithmic coordinates in the form of dependence ΔР/Н = f(W0) From the Fig 11 graphs can be seen that the linear velocity of air flow W0 ≈ 0,5 m/s occurs characteristic kink curves, which indicates a change in flow regime of gas flow in a layer of packing From the Fig 11 experimental... Brasov Romania 1 Introduction Coupled heat and mass transfer by natural convection in a fluid-saturated porous medium is a dynamic domain of research, due to many important engineering and geophysical applications, see the books by (Nield & Bejan, 2006), (Ingham & Pop, 1998; 2002; 2005), (Pop & Ingham, 2001), (Ingham et al., 2004) where a comprehensive account of the available information in the field... 582 Advanced Topics in Mass Transfer θ ' ( 0; M ) = θ ' ( 0;0 ) 1+ M 2 , φ ' ( 0; M ) = φ ' ( 0;0 ) 1 + M2 (15) 1.1.2 Prescribed wall heat and mass fluxes At our best knowledge, in a single paper by (Lakshmi Narayana & Murthy, 2007), both Soret and Dufour effects have been considered in a free convection boundary layer along a vertical surface placed in porous medium, subject to wall heat and mass. .. characteristics, determining the structure and parameters of heat and mass transfer in a packed column apparatuses include: • • the proportion of free volume of the layer packing - ε (porosity), m3/m3; • • specific surface layer of regular or bulk packing in a unit volume - a, m2/m3 The magnitude of the porosity of the layer packing is numerically equal to the value of "live" section of the layer, determines the . the transfer (absorption) of a surfactant at the phase interface is distinct from the mechanism maintaining the temperature at the interface. The interface has inertia, and a convective transfer. thin channels and layers, and in cavities of complex geometry. The results obtained in the experiments can be used in designing systems of passive homogenization in liquids and in optimizing. Marangoni convection at a drop-liquid interface. Proceedings of 6 th Advanced Topics in Mass Transfer 556 EUROMECH Nonlinear Dynamics Conf., pp. 1–6., Saint Petersburg, Russia, 30 June – 4