Acta Chim. Slov. 2002, 49,

Transcription

1 Acta Chim. Slov. 00, 49, IMPACT OF STRUCTURED PACKIN ON BUBBE COUMN MASS TRANSFER CHARASTERISTICS. PART. ANAYSIS OF AS-IQUID MASS TRANSFER MEASUREMENTS Ana akota, Melita Jazbec, Janez evec Faclty of Chemistry and Chemical Technology, University of jbljana, Aškerčeva 5, SI-1000 jbljana, Slovenia Received Abstract The impact of the Slzer SMV 16 packing elements on mass transfer characteristics in a packed was stdied. The gas phase (oxygen) and the liqid phase (tap water) passed the device in a concrrent pflow mode. The measrements of physical absorption of the oxygen into the liqid were taken in both hydrodynamic regimes, partly in the homogeneos and partly in the heterogeneos. Also, the experiments were dobled in an empty for comparison. In the calclation of the volmetric gas-liqid mass transfer coefficients, k a, axial dispersion model (ADM) and plg flow model (PFM) were tested. It is systematically shown, that ADM gives far more reliable interpretation of the recorded data than PFM. For both modifications of the the gas velocity affects the mass transfer coefficients the most. Higher vales of k a were fond in the packed bed, and the impact of internals increases progressively with the gas velocity. For an empty the correlation of Akita and Joshida 5 gives the coefficients close to ors within 18.5%. Introdction The design and scale-p procedre of bbble s is still not a straightforward procedre. Simple in constrction bbble s show a very complex flid dynamic behavior. Ths the estimation of the design parameters has mainly empirical base. Depending on the natre of processes the bbble s are modified in varios ways. 1 However, as an absorber device the bbble mst provide an efficient contact between the flowing phases, which reslts in high interfacial area and high mass transfer coefficient. Nowadays strctred packing is sed to increase efficiency by splitting the flow into sbflows and then recombining them again. And this is why the performance characteristics of these packings are somewhat sperior to those of the classical random packings. Bbble s with or withot internals are primarily meant for the gas-liqid absorption processes accompanied with a slow reaction. In this case the volmetric mass transfer coefficient, k a, defines the mass transfer between the flowing phases reasonably well. Ths there is no need to split this parameter into the liqid side mass A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

2 588 Acta Chim. Slov. 00, 49, transfer coefficient, k, and the specific interfacial area, a. However this is not the case for fast and instaneos reactions. Experimental determination of this combined parameter, k a, is a straightforward procedre. Most experimental stdies are performed in the absence of chemical reaction. Pre physical transport of a gas component from the gas phase into the flowing liqid is evalated at the inlet and otlet of the. The volmetric gas-liqid mass transfer coefficient evalation then strongly depends on the selected flow model. Mainly based on the geometry of, the following flow patterns are imposed: for a large diameter or a small ratio of length to diameter, complete mixing of the liqid phase seemed to be an adeqate approximation of the actal flow pattern in the. Under stationary condition the volmetric mass transfer coefficient is then calclated as k a c 0 =. (1) c c c This model is restricted to s whose diameters are either larger than 0.3 m or their length do not exceed three times the diameter. On the other hand, the mass balance, that is based on the ideal plg flow model (PFM), with no backmixing in the liqid phase, is only applicable to tall and narrow s. The mass balance on the gas component transferred into the liqid reslts to the following expression k a c = ln c c c 0. () PFM offers the highest possible driving force for the mass transfer between the phases and conseqently, the calclated vales of k a are the lowest. Nevertheless, a certain degree of the backmixing in the liqid phase always exists, the gas phase passes the in the form of bbbles, which are responsible for nonideal flow of the liqid in the, as already explained in Part 1. 3 It seems that the one dimensional axial dispersion model (ADM) is more appropriate choice in the analysis of mass transfer measrements. The differential mass balance of the gas component in the liqid phase can be written A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

3 Acta Chim. Slov. 00, 49, Pe d c dz dc dz + St(c c ) = 0. (3) The axial dispersion coefficient, E, which can be taken as a measre of backmixing phenomenon in liqid, is expressed throgh the modified Peclet nmber Pe =, (4) E (1 ε ) and the volmetric gas-liqid mass transfer coefficient, k a, is fond in the Stanton nmber,st, defined as St = k `a. (5) With the Dankwerts bondary conditions 1 dc c = c for z=o (6) 0 Pe dz and dc = 0 for z=1 (7) dz the analytical soltion of Eq.(3) yields the following concentration profile along the axis ( z) A exp(r z) + A exp(r z) + c c. (8) = 1 1 The coefficients A 1 and A in the above eqation are defined as A A r =, (9) ( r ) 1 A exp r1 r1 = Pe r ( c c ) ( Pe + ) exp( r r ) r1 and the roots, r 1,and r, are 0 ; (10) r 1, 1 ± 1 + 4St Pe =. (11) Pe The satration concentration of the gas component in the liqid, c, is given by the Henry s law and is taken as a constant along the. This assmption fails in the A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

4 590 Acta Chim. Slov. 00, 49, case of tall s. When the axial dispersion model is involved in mass transfer analysis, the vales of the gas hold-p and the liqid dispersion coefficient mst be known either throgh the experimental measrements or predicted by the reliable correlations. The volmetric gas-liqid mass transfer coefficient experimental stdies Nmeros experimental stdies of the mass transfer phenomena in bbble s confirmed that for a certain system of flid phases and for a certain type of gas distribtor, the gas velocity has the major impact on the mass transfer coefficient. Even the well known Kastanek s expression for k a evalation k ( + C) a =, (1) + C 13 0 which was derived on the bases of the Higbie s mass transfer theory and the Kolmogoroff s isotropic trblence 1, can be redced to a simple form k a = b. (13) n Both parameters b and n are empirical constants. The liqid phase physical properties and the type of gas distribtors strongly affect the vale of b, whereas the exponent n is rather insensitive to both of them over a wide range of sperficial gas velocity. Decker et al. 4 confirmed this experimentally. They fond n to be in the range of 0.78 to 0.8, and b was affected by both, the gas distribtor and the liqid properties. In their analysis of the measred O concentration profiles, ADM was applied. Akita and Joshida 5 assmed the total dispersion in the liqid and the plg flow behavior of the gas phase. The reslt of their extensive mass transfer stdy yields the following dimensionless correlation ka D ν gd ρ gd 1.1 = 0.6 ε. (14) The D D σ ν athors fond that the gas hold-p is proportional to the gas velocity on the exponent of 0.64, therefore Eq. (14) can be frther simplified, ths ka D. (15) Even thogh an assmption of complete backmixing gives the highest vales of the volmetric mass transfer coefficients, Akita and Joshida s correlation 5 was fond to cover the data of other investigators evalated with ADM sprisingly well. As explained A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

5 Acta Chim. Slov. 00, 49, by Deckwer and coworkers, in a large diameter the concentration at the gas inlet jmps de to the liqid backmixing, which brings the operation closer to the well mixed system. The se of PFM in the evalation of k a sally reslts in the coefficient dependency on the liqid velocity as well. 6,7 Deckwer et al. criticized this conclsion and they have proved that the se of an inadeqate flow model lead to erroneos conclsions. Shah and coworkers 8 derived a simple correlation for k a in a bbble with air-water system k a = , (16) 0.8 where the gas velocity is given in cms -1. Nmeros investigators stdied gas-liqid mass transfer in s with different internals. 9,10,11 Althogh the affirmative role of motionless static mixers has been emphasized, yet no nified correlation for the evalation of k a is proposed till now. The approach for packed s is similar to that for empty bbble s. For certain types of internals the fnctional dependence of k a mainly relies on the gas sperficial velocity (Eq. 13), whereas the two parameters, b and n, in Eq. (13) mst be determined by experiments. Wang and Fan 9 measred the absorption of pre oxygen into water in empty bbble and in packed with Koch motionless mixers. The oxygen inlet and otlet concentrations in the liqid phase were recorded, and the k a vales were calclated according to Eq. (). They proposed the following correlation k a a. (17) β γ = 1 For empty the inflence of the liqid velocity was insignificant ( β = ), bt for packed s β ranged from to 0.611, depending on the mixers arrangement within the. The exponent γ was in the first case and a little lower in the later case (from to 0.63). The experimental part of this work incldes extensive measrements of the physical absorption of oxygen from the gas phase into the liqid phase nder different operating conditions. The aim of this work was, however, first to look for a model which is able to A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

6 59 Acta Chim. Slov. 00, 49, give a reliable interpretation of the recorded gas-liqid mass transfer data and second, to determine the impact of the liqid and gas velocities on the volmetric gas-liqid mass transfer coefficient in both types of s, packed and nonpacked. We also made some comparison with the existing correlations for the evalation of k a valid for empty s. Experimental The details of the apparats and packing material are all given in Part 1. 3 The Plexiglas had a high length to diameter ratio (13.5). The operated in the cocrrent pflow mode, tap water and oxygen were employed as the flowing phases. The was packed with motionless mixing elements (Slzer SMV 16). The sperficial velocity of the liqid varied from 0.31 cms -1 to 5.41 cms -1 and the gas velocity was in the range of 0.91 cms -1 to 9.0 cms -1. Ths, both hydrodynamic regimes, the homogeneos and heterogeneos, were partly covered in this experimental stdy. The perforated plate with 43 holes, each of 1. mm in diameter, served as the gas distribtor. The volmetric gas-liqid mass transfer coefficient - measring techniqe For the evalation of mass transfer characteristics the measrement of oxygen concentration profiles in the liqid phase were taken nder stationary conditions. At given operating conditions the liqid samples were conseqently withdrawn from the at for different axial positions (36.6 cm, 74.4 cm, 11.1 cm and cm above the gas inlet) and then lead into a sample cell, in which the concentration of the absorbed oxygen was determined by a polarographic electrode (OXI 196; WTW). The experiments were performed in empty and packed. The packing configration of the internals is shown in Figre 3 in Part 1. 3 The liqid may become satrated with the gas at some operating conditions, what is a severe drawback of this method. Indeed, we were confronted with this problem at low liqid flow rates (0. and 1 m 3 h -1 ) and high gas throghpts (5 m 3 h -1 ). This limited or range of operating conditions. Only those experiments were considered for mass transfer characterization, A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

7 Acta Chim. Slov. 00, 49, in which the measred liqid oxygen concentration did not exceed 95% of the satration concentration. For the evalation of the volmetric mass transfer coefficients the se of PFM (Eq. ) and ADM (Eq. 3 to 11) seemed to be a reasonable choice regarding the geometry. For both the models bottom-to-point calclations were performed. The experimental vales of the integral gas hold-ps and the axial dispersion coefficients were available at the same experimental conditions (Part 1 3 ) so we were able to extract the k a data from ADM based on a single measred liqid concentration as well. as hold-p Reslts and discssion as hold-p plays an important role in the performance of bbble. Actally it represents the integral vale of all volme of bbbles throghot the. Therefore the gas-liqid interfacial area and conseqently the gas-liqid mass transfer rates are proportional to the gas hold-ps. The gas hold-p depends on the diameter, physical properties of the system and the type of gas distribtor, bt mainly on the velocity of the gas phase. Introdction of a packing is expected to change the hydrodynamic behavior of the. The measrements of the experimental gas hold-ps for both modifications of the were already performed in Part 1 3.The data are most evidently shown in the fnction of the liqid sperficial velocity (Figre 1). The role of the gas velocity as a decisive factor for ε is clear: higher gas velocities enlarge the gas hold-p vales. An increase in the liqid velocity slightly decrease ε for both modifications of the, what becomes more evident at higher gas velocities. The negative impact of the liqid velocity on gas hold-p is in agreement with the work of Mostiri and his coworkers 1 and with Hill s finding 14. The reason for a sdden increase in ε at the liqid velocity of 5.41 cms -1 is not clear. High vale of the gas hold-p at =3.61 cms -1 in packed bed at the highest gas velocity is rather de to an experimental error. The presence of internals becomes significant only at higher gas velocities ( 4cms 1 ) and their effect is A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

8 ε 594 Acta Chim. Slov. 00, 49, evalated and represented in Figre. At higher gas velocities the static mixers enlarged the holdp even p to 50%. It is interesting to note, that a slight redction in gas hold (cms -1) , packed non-pak. (%) (cms -1) Figre 1. as hold-p as a fnction of liqid sperficial velocity for both modifications of the. ps was observed in packed according to those in an empty one at lower gas velocities. This is in agreement with the observation of Mostiri and his research grop. 1 The sperficial gas velocity is the most crcial factor for ε. In order to evalate this effect, we ignored the minor inflence of the liqid velocity and represented the experimental data in a form of simple power-law fnctions ε = (1.81 cms -1 < < 9.0 cms -1 ) (18) 0.44 valid for empty and ε = , (0.91 cms -1 < < 9.0 cms -1 ) (19) 0.81 which holds for packed with SMV static mixers. In this way the mean relative errors are relatively high (e y is 1.5% in the first case and 1% in the latter). Both relationships are shown in Figre. The high exponent (0.81) over the gas velocity in the case of packed indicates, that the homogeneos regime is prolonged in the presence of internals. A weaker dependence of the gas hold-p on gas velocity in empty A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

9 ε Acta Chim. Slov. 00, 49, shows that the transition from the homogeneos to heterogeneos hydrodynamic regime occrred. According to the flow chart 1, the homogeneos regime prevails p to the gas velocity of 3 cms -1, and the heterogeneos regime develops approximately at =5 cms -1. In the presence of internals Spicka et al. 13 experimentally proved, that the homogeneod regime is extended, even p to =9cms -1. (%) (cms -1 ) packed non-pack. 10 Eqation (18) Eqation (19) (cms -1 ) Figre. as hold-p as a fnction of gas sperficial velocity for both modifications of the. For more detailed characterization of the hydrodynamic behavior of bbble the slip velocity (or the relative velocity between the phases) is an extremely helpfl parameter. For cocrrent flow the following eqation holds v S =. (0) ε 1 ε Up to the gas velocity of 4 cms -1 this vale is roghly abot 0 cms -1 (Figre 3). At low gas velocities the internals promote the rising of gas bbbles throgh the channels and the slip velocity is higher than in empty. Then at higher vales of the slip velocity in empty increased sharply, even p to 40 cms -1, de to the formation of larger bbbles in the heterogeneos regime. In the packed the presence of the motionless mixing elements prevents the bbble coalescence, therefore the bbbles are A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

10 596 Acta Chim. Slov. 00, 49, smaller and their rising velocities are low. This is reflected in lower slip velocities in comparison with the reslts obtained in an empty. As one may conclde from Fig.3, at higher liqid velocity even the decreasing vales of v S with the gas sperficial velocity,, was observed. Mostiri et al. 1 assmed that the packing also hinder the bbble rising. v s (cms -1 ) (cms -1 ) packed non-pack (cms -1 ) Figre 3. Slip velocity as a fnction of gas sperficial velocity for both modifications of the. Volmetric gas-liqid mass transfer coefficient The measred liqid oxygen concentrations were between 7% and 95% of the satration concentration. The data recorded along the for two sets of operating conditions are shown in Figre 4. As expected, at any operating conditions the concentration of oxygen increases along the for both modifications. In packed were always higher than those in empty one except near the bottom of the. At the first measring point (that is 36.5 cm above the gas inlet) the concentrations in empty were always higher than those in the packed. This confirms the fact, that the concentration jmp near the gas inlet is rather de to the considerable backmixing of the liqid in the than to an increase of mass transfer rate. Deckwer 1, did criticize a wrong interpretation of this phenomenon, which appears A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

11 Acta Chim. Slov. 00, 49, in pblished works 6,7. As it was already conclded in Part 1 3, the presence of the Slzer motionless mixers diminishes the backmixing in. Correspondingly the liqid axial dispersion coefficients in packed are therefore lower than those in empty for abot 0% to 50% c (mgl -1) 30 non- pack. packed non-pack. packed =1.81 cms -1 =1.81 cms -1 =3.61 cms -1 =5.41 cms z Figre 4. Oxygen liqid concentration as a fnction of dimensionless height for both modifications of the at different operating conditions. It is obvios, however, that sing either PFM or ADM wold lead to different k a vales. When ADM was applied the Peclet liqid nmbers (Pe ) were calclated from the experimental vales of gas hold-ps and the liqid axial dispersion coefficients (Part 1 3 ); they varied from 0.06 to 10. The Stanton nmbers, fond from fitting the measred point concentrations, took the vales lower than 9 in 90% of calclation. In endeavors to asses the k a along the, which are shown in Figres 5 and 6, the coefficients are based on the concentration measrements from Figre 4. As expected, the PFM evalation always yielded lower vales of the coefficients than the ADM evalation, and the difference increased with gas velocity. Both models gave higher vales of the coefficients in packed according to those in empty one, except for the first measring point. This phenomenon is already discssed in the previos section. A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

12 598 Acta Chim. Slov. 00, 49, k a (s -1) =1.81 cms -1 =1.81 cms -1 PFM evalation, non- pack. ADM evalation, non-pack. PFM evalation, packed ADM evalation, packed z Figre 5. Volmetric gas-liqid mass transfer coefficient as a fnction of dimensionless height for both modifications of the (homogeneos regime) k a (s -1) PFM evalation, non- pack. 0.0 =3.61 cms -1 =5.41 cms -1 ADM evalation, non-pack. PFM evalation, packed ADM evalation, packed z Figre 6. Volmetric gas-liqid mass transfer coefficient as a fnction of dimensionless height for both modifications of the. A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

13 Acta Chim. Slov. 00, 49, At low gas velocity ( 1 = 1.81cms ) a slight decrease in the volmetric gas-liqid mass transfer coefficients, based on PFM, was observed along the (Figre 5), for packed and nonpacked. For both cases the se of ADM gave nearly constant k a vales. At this operating condition the homogeneos regime exists in the. When the gas velocity was increased to 5.41 cms -1, both models reslted in decreasing k a with the axis, either packed or nonpacked. Based on a phenomenological model of the bbble break-p and coalescence, a simlation model of Shimiz and his coworker 15 also predicts the decrease in k a along the at higher gas flow rates. According to their simlations, increased nmbers of larger bbbles at the top of are responsible for decrease in k a. In order to validate both of the models, (PFM and ADM), only those volmetric gasliqid mass transfer coefficients were involved, which were estimated by means of the the liqid oxygen concentrations measred on the last (i.e. forth) position. In Figre 7 the reslts of k a based on PFM, are shown as a fnction of the liqid sperficial velocity. For the empty the coefficients were lower than 0.08 cms -1, and for the packed lied in the range of cms -1 to 0.11 cms -1. Ths, coefficients in packed 0.0 k a (s -1 ) (cms -1) , packed non-pak (cms -1) Figre 7. Volmetric gas-liqid mass transfer coefficients based on PFM as a fnction of liqid sperficial velocity for both modifications of the. A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

14 600 Acta Chim. Slov. 00, 49, are always higher than those in empty, the difference increases when the gas velocity increases. The PFM evalation actally exhibits the positive impact of the liqid velocity on k a, which becomes more evident at higher gas flow rates. For instance at 1 = 9.0cms, a three-times higher liqid velocity almost dobles the coefficients in empty, and cases for abot 50% higher k a in the presence of internals.according to the previos reslts on the axial dispersion coefficients, gas holdps and slip velocities, sch a strong dependance of k a on can not be jstified; this conclsion is eqaly valid for packed and nonpacked. Thogh in the packed the axial dispersion coefficients were fond to increase with the liqid sperficial velocity (Part 1, 3 ), this wold not reslt in sch an enlargement of k a. The k a vales evalated with the help of ADM are depicted in Figre 8, as a 0.0 k a (s -1 ) (cms -1) , packed non-pak (cms -1) Figre 8. Volmetric gas-liqid mass transfer coefficients based on ADM as a fnction of liqid sperficial velocity for both modifications of the. fnction of the liqid sperficial velocity. The coefficients fond in packed are higher than those in empty one. The coefficients are only slightly affected by the liqid flow rate, actally they show the same trend as the gas hold-ps on Figre 1. We conclded that for an empty bbble as well as for a packed, the se of ADM is far more realistic for the analysis of mass transfer measrements than PFM. A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

15 Acta Chim. Slov. 00, 49, This is also in agreement with Deckwer 1,. The se of PFM does not only lead to the wrong conclsion abot the impact of liqid velocity, it also nderestimates the coefficients significantly; at lower liqid flow velocities for nearly 100%. As was already shown, the gas velocity affects the mass transfer coefficients most. The dependence of k a on the gas sperficial velocity is shown in Figre 9, for packed and nonpacked. The coefficients are based on the ADM evalation. The data can be reasonably well correlated with the following power-law relation, valid for empty k a = , (1) 0.70 and for packed k a = () 0.86 The gas velocity in the above eqations is in cms -1. The mean relative error (e y ) for Eqation 0 is 1.3%, and for Eqation 1 slightly higher, that is 17.1%. The presence of internals reslts in higher exponent on, de to the extended range of the homogeneos regime (cms -1 ) packed Eqation (1) Eqation () k a (s -1 ) non-pack Shah et al. (198) Akita and Joshida (1973) (cms -1 ) Figre 9. Volmetric gas-liqid mass transfer coefficients based on ADM as a fnction of sperficial velocity for both modifications of the. A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

16 60 Acta Chim. Slov. 00, 49, It is interesting to note, that in both correlation (Eq. 0 and Eq. 1) the constants are eqal, i.e Higher vales of k a were fond in the packed bed, and the impact of internals was fond to increase progressively with the gas sperficial velocity. For empty bbble s the correlation of Shah et al. 8 (Eq. 16) gives mch lower vales for k a compared to or experimental data (e y =31%). The coefficients predicted from the correlation of Akita and Joshida 5 are close to ors. This is not srprising since we have sed or own experimental gas hold-ps (Part 1, 3 ) in their correlation (Eq. 14); and the mean relative error was 18.5%. Conclsion In the analysis of gas-liqid mass transfer measrements the se of ADM gives the volmetric gas-liqid mass transfer coefficients, which are more consistent with the complex hydrodynamic behavior of the than those evalated from PFM. In both modification of the, packed and nonpacked, the vales of k a increase with the gas sperficial velocity, while the effect of the liqid velocity is negligible. At the same operating conditions the coefficients in packed are higher than those in an empty, and this difference increases with the gas sperficial velocity. At lower gas velocities the se of ADM gives nearly constant vales of k a along the axis, while at higher gas flow rates the coefficients decrease with the height, either in packed or nonpacked. Acknowledgements This work was spported by the Slovenian Ministry of Edcation, Science and Sport throgh grant PO Nomenclatre A 1 defined with Eq. 9, / A defined with Eq. 10, / a specific srface area of internals, m m -3 a 1 constant in Eq. 17 b constant in Eq. 13 C constant in Eq. 1 c liqid oxygen concentration, mgl -1 D diameter, m D diffsivity, m s -1 A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

17 Acta Chim. Slov. 00, 49, E dispersion coefficient, m s -1 e y () () mean relative error, () 100 N y MES i y PRED i = i =, % 1 N y MES i k mass transfer coefficient in the liqid phase, ms -1 k a volmetric gas-liqid mass transfer coefficient, s -1 g acceleration de to gravity, ms - length, m N nmber of experimental data n exponent over sperficial gas velocity (Eq. 13) Pe modified Peclet nmber in the liqid phase, E ( 1 ε ) r 1, defined with Eq. 11 St Stanton nmber, k a, / sperficial velocity, ms -1 v S slip velocity, ms -1 z dimensionless length of a, / sperficial velocity, ms -1 reek letters β exponent over the liqid sperficial velocity in Eq. 17 ε phase hold-p, / γ exponent over the gas phase sperficial velocity in Eq. 17 ν viscosity of the phase, kgm -1 s -1 ρ density of the phase, kgm -3 σ srface tension, kgs - Sbscripts gas phase liqid phase MES measred vale o entrance of the PRED predicted vale * in eqilibrim References and Notes 1. Deckwer, W. D. Bbble Colmn Reactors; J. Wiley & Sons td., Chicester (B), Deckwer, W. D.; Ngyen-Tien, K.; Kelkar, B..; Shah, Y. T. AIChE Jornal 1983, 9, akota, A.; Jazbec, M.; evec, J. Acta Chim. Slov. 001, 48, Deckwer, W. D.; Brckhart, R.; Zoll,. Chem. Eng. Sci. 1974, 9, Akita, K.; Yoshida, F. Ind. Eng. Chem. Proc. Des. Dev. 1973, 1, Alvarez-Cenca, M.; Baker, C.. J.; Bergogno, M. A. Chem. Eng. Sci. 1980, 35, Alvarez-Cenca, M.; Nerenberg, M. A. AIChE Jornal 1981, 7, Shah, Y. T.; Kelkar, B..; odbole, S. P.; Deckwer, W. D. AIChE Jornal 198, 8, Wang, K. W.; Fan,. T. Chem. Eng. Sci. 1978, 33, Hofmann, H. Chem. Ing. Tech. 198, 54, A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer

18 604 Acta Chim. Slov. 00, 49, Sawant, S. B.; Pangarkar, V..; Joshi, J. B. Chem. Eng. J. 1979, 18, Mostiri, S.; Hebrad,.; Rostan, M. Chem. Eng. Process. 00, 41, Spicka, P.; Martins, A. A; Dias, M. M.; opes, J. C. B. Chem. Eng. Sci. 1999, 54, Hills, J. H. Chem. Eng. J. 1976, Shimiz, K.; Takada, S.; Minekawa, K.; Kawase, Y. Chem. Eng. J. 001, 78, 1 8. Povzetek Prikazani so rezltati eksperimentalne štdije vpliva strktriranega polnila (Slzer SMV 16) na volmetrični koeficient snovnega transporta plin-kapljevina v kolonah z mehrčki. Za primerjavo so bili vsi posksi izvedeni še v koloni brez polnila. Pri analizi eksperimentalnih merjenj se je aksialno disperzno model (ADM) pokazal, da daje realnejšo sliko dogajanja v koloni kot model čepastega toka (PFM). Na osnovi ADM izračnanih koeficientov je razvidno, da je k a odvisen od hitrosti plinaste faze, medtem ko lahko vpliv hitrosti tekočine zanemarimo, in to v obeh tipih kolon. Prisotnost polnilnih elementov poveča koeficiente snovnega transporta, njihov vpliv je izrazitejši pri višjih hitrostih plina. Z porabo ADM izračnane točkovne vrednosti koeficientov so pri nižjih hitrosti plina konstantne vzdolž kolone, medtem ko pri visokoh plimskih hitrosti le-ti z višino kolone padajo. A. akota, M. Jazbec, J. evec: Impact of strctred packing on bbble mass transfer