Showing papers in "Canadian Journal of Chemical Engineering in 1969"

Structural properties of packed beds — A review

Abstract: Some structural properties of packed bed systems on both the local and overall scales which are available in the literature and of interest in chemical engineering applications are discussed. Regular and random packings of uniformly sized spheres are initially analyzed as a basis for the later examination of the more general case of random packed beds containing particles of various sizes and shapes, with or without restraining surfaces. On discute, sur une echelle locale et globale, certaines proprietes structurales deg systemes a base de lits garnis qu'on mentionne dans des ecrits et qui sont interessantes a cause de leurs applications en genie chimique. On analyse d'abord des garnitures regulieres et irregulieres de spheres aux dimensions uniformes, et ce comme base d'un examen ulterieur du cas des lits qui sont garnis irregulierement, continnent des particules de dimensions et formes diverses et possedent des surfaces restreintes on non.

Studies on cocurrent gas‐liquid flow in helically coiled tubes. I. Flow patterns, pressure drop and holdup

Abstract: The effects of tube diameter, coil diameter, helix angle and liquid viscosity on flow patterns, pressure drop and holdup for cocurrent gas-liquid flow in helically coiled tubes have been investigated. Nine coils of varying coil diameter and helix angle have been used with liquids of three different viscosities and air at varying pressures. The effect of tube diameter on pressure drop and holdup was determined by using tubes of diameters up to 2-in. Flow patterns were adequately predicted for all the systems by Baker's plot. Small helix angles were found to have no effect on pressure drop or holdup in coiled tubes. Both pressure drop and holdup could be adequately correlated using the Lockhart-Martinelli approach with modified correlating parameters. On a etudie les effets des diametres des tubes et de l'enroulement, de l'angle de l'helice et de la viscosite du liquide sur l'allure de l'ecoulement, la chute de pression et la retenue liquide, dans le cas d'un ecoulement parallele de gaz et liquids dans des tubes pourvus d'un enroulement helicoidal. On a utilise neuf enroulements possedant differents diametres et angles d'helice ainsi que des liquides de trois viscosites distinctes et de l'air a diverses pressions. On a determine l'effet du diametre du tube sur la chute de pression et la retenue liquide au moyen de tubes de deux pouces de diametre. On a pu predire exactement l'allure de l'ecoulement pour tous les systemes au moyen de la courbe de Baker. On a constate que les petits angles d'helice n'exercaient aucun effet sur la chute de pression ou la retenue liquide dans des tubes pourvus d'enroulement. On a pu etablir une correlation satisfaisante entre la chute de pression et la retenue liquide, en utilisant la methode de Lockhart et Martinelli avec modification des parametres de correlation.

Prediction of thermodynamic properties of polar mixtures by a group solution model

Abstract: A modified group solution model for liquid mixtures is presented. The model differs from previous models in that the Bronsted-Koefoed congruence principle is used to describe the effect of molecular size. The model has been tested for mixtures involving paraffin hydrocarbons, alcohols and water at low pressures. Such systems involve binary mixtures of the groups methylene and hydroxyl, and are reasonably represented by the model. Data presented enable the approximate equilibrium properties of such solutions at low pressures to be predicted at 40°C and 90°C. Interpolation and reasonable extrapolation from these temperatures should be satisfactory. On presente un modele de solution pour groupes modifies dans le cas de melanges liquides. Le modele differe des precedents en ce qu'on utilise le principe de congruence de Bronsted-Koefoed pour decrire l'effet des dimensions des molecules. On a soumis le modele a des essais executes sur des melanges d'hydrocarbures paraffines, d'alcool et d'eau a des basses pressions. Des systemes de ce genre comprennent des melanges binaires des groupes methylenique et hydroxyle et le modele les represente assez bien. Les resultats qu'on presente permettent de predire approximativement les proprietes des dites solutions soumises a des basses pressions a 40°C et 90°C. L'interpolation et l'extrapolation a partir de ces temperatures devraient s'averer satisfaisantes.

Bubble drag and mass transfer in non‐newtonian fluids: Creeping flow with power‐law fluids

Abstract: The drag and mass-transfer characteristics of a gas bubble moving in power-law non-Newtonian fluids are examined analytically in terms of the rheological properties of the system. An approximate solution for the case of creeping flow around circulating bubbles shows that the mass-transfer coefficient is enhanced for pseudoplastics and depressed for dilatants compared to the situation for Newtonian fluids. Some preliminary experimental results in support of the analysis are presented. On examine analytiquement, d'apres les proprietes rheologiques du systeme, les proprietes de friction et de transfert de masse d'une bulle de gaz qui se deplace dans des fluides non-newtoniens et soumis a la loi d'energie. Une solution approximative, dans le cas du mouvement ascendant autour de bulles en mouvement, indique une augmentation du coefficient de transfert de masse pour leg pseudo-plastiques et une diminution de celui-ci pour les produits expansibles, en comparaison de ce qui se passe pour les liquides newtoniens. On presente certains resultats d'experiences qui confirment l'analyse precitee.

On the use of the imperfect tracer pulse method for determination of hold-up and axial mixing†

Abstract: The imperfect pulse method is a powerful technique for experimental analysis of chemical engineering flow systems. The authors have employed this method in studies of holdup and mixing in gas-liquid fluidized beds. In the present paper are discussed two problems connected with reduction of the experimental data obtained in such studies. Tailing is a phenomenon that may seriously affect the accuracy of mixing coefficients determined by the imperfect pulse method. Accurate methods of data reduction, based upon analysis of moments, have been developed, and their applicability is demonstrated by analysis of experimental data. Interphase transfer of tracer material is of particular importance in investigations of gas phase mixing in a gas-liquid system where absorption of tracer gas into the liquid phase normally takes place. A semiempirical method is described for correction of the experimental data in such cases. La methode de pulsation irreguliere est tres utile pour l'analyse experimentale des systemes d'ecoulement en genie chimique. Les auteurs ont utilise le dit procede en rapport avec la retenue et le melange dans des lits fluidises ou entrant en jeu un gaz et un liquide. On discute dans le present travail deux problemes, lesquels ont trait a la simplification des resultats experimentaux qu'on a obtenus dans des etudes de ce genre. La retenue (tailing) est un phenomene qui peut affecter serieusement la precision des coefficients de melanges determines par la methode de pulsation irreguliere. On a mis au point des methodes precises de simplification de donnees, lesquelles sont basees sur l'analyse des moments, et l'on demontre leurs possibilites d'application par l'analyse des resultats experimentaux. Le transfert d'un traceur d'une phase a l'autre est particulierement importante dans l'etude du melange en phase gazeuse dans un systeme a base de gaz et de liquide, ou il se produit normalement absorption du gaz traceur dans le liquide. On decrit une methode semi-empirique pour corriger les resultats experimentaux dans de tela cas.

The growth and dissolution of potassium sulphate crystals in a fluidized bed crystallizer

Abstract: The nucleation, growth and dissolution characteristics of potassium sulphate have been studied in a laboratory scale fluidized bed crystallizer under carefully controlled conditions of temperature, supersaturation and solution velocity Aqueous solutions of potassium sulphate can withstand high degrees of supercooling (∼ 13°C) even when agitated, but this is reduced to about 5°C when the crystalline phase is present Nevertheless, this is still a high level of supercooling for an aqueous salt solution The importance of measuring nucleation data for crystallizer design purposes under the appropriate conditions is clearly demonstrated The ‘order’ of the nucleation process, m, defined by Rn = KnΔcm is about 9 The growth process, defined by Rg = KgΔcn is second-order (n = 2) with an activation energy of 43 kcal/mole, and the dissolution process, Rd = KdΔcp, in first-order (p = 1) with an activation energy of 34 kcal/mole The growth step is therefore considered to be diffusion controlled, and this is confirmed by the observation that the growth rate of potassium sulphate in a fluidized bed is dependent on the size of the crystals

Simulation and Optimization of an Existing Ethylbenzene Dehydrogenation Reactor.

Abstract: The dehydrogenation of ethylbenzene to styrene in an ideal, adiabatic reactor has been modelled using side reactions in addition to the main one The differential equations describing the process were integrated on an IBM 7040 digital computer A profit function ($ gained/hour) was chosen and for various combinations of process variables, which were subject to constraints, the single bed reactor was optimized by the method of Rosenbrock(1,2) Studies of a proposed two-bed reactor were also carried out Catalyst deactivation during the reaction was not considered because of a lack of data The results showed that the existing reactor could be operated more efficiently if the present plant constraints were removed Two beds in series gave still better results

The kinetics and mechanism of the hydration of magnesium oxide in a batch reactor

Abstract: The kinetics of the reaction between water and MgO powders has been investigated at 9°, 18°, 28° and 38°C in a stirred batch reactor. Six commercial samples of MgO prepared from Mg(OH)2 plus two of unknown origin, with specific surface areas of 12 to 80 mg/g, were studied. After correcting for particle size distribution, the rate of reaction was found to be directly proportional to the surface area contained in a shell at the surface of the particles. The activation energy is 14.1 ± 0.2 kcal/g-mole indicating chemical reaction as the rate controlling process. A reaction mechanism has been proposed./

Recent experience with the spherical agglomeration process

Abstract: : The process of removing particles from liquid suspension by selective wetting and agglomeration with a second immiscible liquid has many possible applications. Depending upon the amount of the second liquid used and the type of agitation to which the suspension is subjected, the particles to be separated are settled as flocs, as dense pellets or may simply be transferred to a continuous phase of the second liquid. This paper first describes the types of mixing equipment which have been used to carry out the process in its various forms and goes on to discuss a number of specific applications. These include the upgrading of coking coals by selective agglomeration, the pelletization of soluble salts, the formation of highly spherical bodies from various materials and the benefication of ores. (Author)

Mass transfer from a single rising bubble

Abstract: The absorption rates of carbon dioxide, ethylene, and butene from single rising bubble of equivalent diameter 04–20 cm in water have been measured using an apparatus in which the bubble volume change with time of rise can be measured The apparatus uses techniques previously reported but also is suitable for studies of mass transfer without and with chemical reaction at higher pressures (up to 4 atmospheres) The results have been compared with theoretical equations for rate of gas solution at the frontal surface of the bubble based upon potential flow theory and Higbie theory The data are assessed together with those of others to show that they can be correlated well by This equation is valid for bubbles of equivalent diameter 06 < d < 40 cm and within the range 500 < NRe < 20,000 On a mesure les vitesses d'absorption de l'anhydride carbonique, de l'ethylene et du butene a partir d'une simple bulle de diametre equivalent a 04–20 centimetres qui s'elevait dans l'eau; on a utilise a cette fin un appareil ou l'on pouvait mesurer le changement de volume de la bulle avec le temps d'elevation et qui permettait, tout en utilisant des methodes deja connueg, d'etudier le transfert de masse avec ou sans reaction chimique a des pressions plus elevees (allant jusqu'a 4 atmospheres) On a compare les resultats obtenus avec ceux des equations theoriques utilisees pour mesurer la vitesse d'une solution d'un gaz a la surface frontale d'une bulle en se basant sur les theories de l'ecoulement potentiel et de Higbie On a evalue les resultats en meme temps que ceux que d'autres ont obtenus pour demontrer qu'on peut les decrire et etablir une correlation entre eux au moyen de l'equation NSk=113 Npe(de/045+02de)1/2 laquelle est valide pour des bulles de diametres equivalents a 06 < d, < 40 centimetres et dans l'echelle correspondante a 500 < NRe < 20,000

The optimal control of polymerisation reactors

Abstract: Two separate but related problems are treated in this paper: (i) the optimal control policy for continuous stirred tank polymerization reactors; (ii) the optimal control program for batch polymerization reactors. The first problem concerns determining the temperature and initiator control policy which brings the reactor to the desired steady state while minimizing some objective functional (e.g. start-up time, cost of control action, etc.). The second problem is concerned with finding the best temperature and initiator program so that the product from the batch reactor has the best possible molecular weight distribution. Both free radical polymerization and linear condensation polymerization examples are considered with molecular weight distribution moments being used to characterize the polymer. Kinetic parameters typical of styrene are used for the free radical case, and realistic parameters are chosen for the condensation examples. The techniques used can be immediately carried over to other polymerization systems, and hopefully generalizations about the character of the optimal policies for such new systems can be made by considering the policies found for the systems studied. The results of the study demonstrate some of the potential gains possible through supervisory computer control of polymerization reactors. On traite dans ce travail deux problemes separes, mais apparentes, a savoir (1) la meilleure methode de reglage pour les reacteurs a polymerisation pourvus d'un reservoir soumis a une agitation continue et (2) le meilleur systeme de controle dans le cas des reacteurs a polymerisation du genre discontinu. Le premier probleme comprend l'etablissement d'une methode de reglace pour la temperature et l'amorce qui permet au reacteur de parvenir a un regime permanent, tout en minimisant certaines fonctions objectives (telles que temps de mise en route, le cout du reglage, etc.). Le second probleme a trait a la mise au point du meilleur systeme de temperature et d'amorce pour que le produit provenant du reacteur a action discontinue possede la meilleure distribution possible de poids moleculaire. On etudie des cas de polymerisation a base de radicaux libres et de condensation lineaire, en utilisant les moments de distribution du poids moleculaire pour caracteriser le polyinere. On a choisi les parametres cinetiques et typiques du styrene dans le cas des radicaux libres et des parametres realistes pour la condensation. On peut appliquer les methodes utilisees a d'autres systemes de polymerisation et esperer pouvoir faire des generalisations sur la nature des meilleurs methodes pour ces systemes en se basant sur celles qu'on a trouvees dans le cas des systemes etudies. Les resultats de l'etude precitee indiquent certains gains qu'on peut realiser par telecommande, au moyen de calculateurs, des reacteurs a polymerisation.

Dissolution mass transfer in a turbine agitated baffled vessel

Abstract: Mass transfer coefficients were measured for the dissolution of crystalline electrolytes suspended in a baffled vessel by means of disc turbines. A 3-fold range of density differences, a 5-fold range of diffusivities and a 50-fold range of particle size were covered and the effect of impeller speed, size and clearance from the base was studied. The increase in coefficent with speed is both a function of the clearance and solid density and size and is difficult to quantify. However, in the most economic configuration of small clearance and large impeller, this is not of great importance since the coefficient increases but slowly with speed and the minimum suspended coefficient can be calculated. This is done by means of a slip velocity theory which has been extended to include larger particles, which allows for the effect of concentration dependent physical properties and which is based on the impeller speed at which particle suspension occurs. On a mesure les coefficients de transfert de masse en rapport avec la dissolution d'electrolytes crystalling suspendus dans un recipient a chicanes ay moyen de turbines a disques. Les sujets de l'etude ont compris des differences de densite, des diffusivites et des dimensions granulo-metriques dans une echelle respective de valeurs allant an triple, au quintuple et au cinquantuple; on a aussi etudie les effets de la vitesse, des dimensions et de l'espace libre au-dessus de la base dans la cas de la roue a aubes. L'accroissement dans la valeur du coefficient avec la vitesse est fonction de l'espace libre, de la densite solide et des dimensions et il est difficile de l'evaluer quantitativement; ce fait, toutefois, n'est pas bien important dans le cas de la configuration la plus economique qui comporte un faible espace libre et une grosse roue a aubes, vu qu'alors le coefficient n'augmente que lentement avec la vitesse et qu'on peut calculer le coefficient minimum dans la suspension. Le dit calcul se fait en utilisant la theorie de velocite coulissante qui inclue par extension les plus grosses particules, tient compte des proprietes physiques qui dependent de la concentration et est basee sur la vitesse de la roue a aubes a laquelle la suspension des particules se fait.

Electric field phenomena in fluidized and fixed beds

Abstract: Stabilization of a bed of dielectric particles against fluidization by an electric field (≥ 103 volts/cm) is described. Glass bead and silica gel particle beds have been observed to behave as packed beds with flow rates (and pressure drops) of the fluidizing gas up to 15 times the normal incipient fluidization rate. The pressure drop at the breakup of this fixed bed was dependent on the second power of voltage, the particular bed material, and geometry of the system. Under suitable conditions 100% bed expansion without diffusive particle motion or bubble formation was obtained using silica gel particles. Comparison with iron particle bed-magnetic field effects are presented. Surface polarization charge effects are the simplest explanation of the phenomena. Several of the possible applications are suggested, such as precipitation enhancement in an aerosol filter or as a new tool for investigating aggregative fluidization.

A survey of recent soviet research on the drying of solids

Abstract: The importance of internal moisture migration in the drying of solids and the various approaches to the study of this phenomenon are outlined briefly. The extensive Soviet work in this field, particularly by Lykov's school, is reviewed, and the advantages, disadvantages and practical applications of this approach are discussed. Some of the more interesting practical Soviet studies of drying plant and processes are also mentioned briefly. On expose brievement l'importance de la migration de l'humidite interne dans le sechage des solides ainsi que les diverges voies d'acces a l'etude de ce phenomene. On passe en revue le travail intensif qu'ont fait les Russes dans ce domaine (particulierement les, disciples de Lykov) et discute les avantages, inconvenients et applications pratiques de leur methode d'etude. On souligne aussi quelques-unes des etudes leg plus interessantes el pratiques que les Russes ont faites en ce qui a trait aux usines et procedes de sechage.

Longitudinal gas dispersion in transitional and turbulent flow through a straight tube

Abstract: Longitudinal dispersion data are reported for a straight tube (internal dia. 1¼′ (2.77 cm)). Three binary gas systems were examined over the regime 3 × 102 < Re < 104 with special emphasis on the transition from laminar to turbulent flow. Effect of Schmidt number is studied in detail over the transition regime, and practical variation with Sc for the lower turbulent regime is compared with the predicted effect based on existing theories of turbulence. In the laminar regime results are reported which diverge from Taylor's theory at Re lower than the normally accepted value for the onset of turbulence. On rapporte les resultats obtenus pour une dispersion longitudinale dans un tube droit (dont le diametre interne est de 1¼′ ou de 2.77 centimetres). On a etudie trois systemes binaires de gaz dans le regime 3 × 102 < Re < 104, en insistant particulierement sur le passage de l'ecoulement laminaire au turbulent. On a etudie en detail l'effet du nombre de Schmidt sur le regime de transition et compare la variation pratique avec Sc, que presentait le regime turbulent inferieur, avec l'effet qu'on avait predit en se basant sur les theories actuelles sur la turbulence. Dans le systeme laminaire, les resultats qu'on a rapportes se sont ecartes de la theorie de Taylor pour une valeur de Re plus faible que cello qu'on accepte normalement pour le debut de la turbulence.

On liquid‐liquid mass transfer inside drops in a turbulent flow field

Abstract: Mass transfer in liquid-liquid dispersions in a turbulent flow field has been investigated for the particular case where the overall process rate is governed by the diffusional resistance in the dispersed phase. Experiments with the system water-iodine-carbon tetrachloride have shown that the transfer mechanism in this case is similar to that for single drops at high Reynolds numbers. The results obtained show that the so-called correlation factor R depends strongly on the turbulence of the system. This relationship can be expressed as R ˜ R2, which is valid for the mass transfer rate both in turbulent liquid-liquid dispersions and for some cases of solute diffusion in single oscillating drops. On a etudie le transfert de masse, a l'interieur de dispersions d'un liquide dans un liquide, dans un champ d'ecoulement turbulent, en considerant le cas particulier ou la vitesse globale du procede est regie par la resistance a la diffusion dans la phase dispersee. Les experiences executees avec le systeme eau-iode-tetrachlorure de carbone ont demontre que le mecanisme de transfert dans ce cas est semblable a celui qu'on rencontre avec de simples gouttes lorsque les nombres de Reynolds sont eleves. Les resultats obtenus indiquent que le soi-disant facteur de correlation R depend fortement de la turbulence du systeme. On peut exprimer la dite relation avec l'expression R ∼ Re2, laquelle est valide pour la vitesse de transfert de masse dans une dispersion turbulente d'un liquide dans un liquide et dans certains cas de diffusion du solute dans des gouttes simples qui oscillent.

Designing experiments for precise estimation of all or some of the constants in a mechanistic model

Abstract: An important experimental problem in chemical engineering is to collect data in order to estimate constants such as rate constants and activation energies which are needed, for example, in equipment and plant design. For a given amount of experimental effort, the engineer wants these constants to be estimated as precisely as possible. In this paper, we discuss statistical design procedures that might be used to accomplish this goal. Available procedures are reviewed for estimating precisely all the constants in a mechanistically based mathematical model. In addition, a new procedure is illustrated for precisely estimating only some of the constants which may be of more interest than the others. Un important probleme experimental, dans le domaine du genie chimique, est de recueillir des donnees pour estimer les constantes (comme celles qui ont trait a la vitesse et aux energies d'activation) qui sont necessaires, par exemple, lors de la conception de l'outillage et de l'usine. Pour un certain degre de travail experimental, l'ingenieur desire determiner ces constantes avec autant de precision que possible; on traite, dans le present travail, des procedes de calcul statistique qu'on peut utiliser pour atteindre ce but. On examine les procedes disponibles pour determiner avec precision toutes les constantes dans un modele mathematique du genre mecanistique On illustre egalement un nouveau procede pour estimer avec precision quelques constantes seulement qui peuvent presenter un interet parti-culier.

Axial dispersion coefficients in packed beds at low reynolds numbers

Abstract: Peclet numbers describing axial dispersion in gas flow through packed beds of spheres were obtained using a two measurement point, pulse technique in a test section four inches inside diameter and 5.14 feet high. Three packing sizes were investigated, corresponding to tube to particle diameter ratios of 6.4, 17, and 66 In the experiments the contribution of the velocity profile to axial spreading was reduced by using thermal conductivity detectors which responded to dispersion only in the central part of the bed cross-section. In this region of a packed bed the velocity profile is relatively flat. The results point to a particle diameter effect which is more pronounced than has been previously reported. This is in accord with the diffusive mechanism of axial dispersion in a packed bed provided dispersion caused by the velocity profile does not affect the measured pulse response. In the absence of velocity profile effects, the spreading of residence times in void cells is caused primarily by the shedding of the decelerated boundary layers on the downstream side of the particles. At low velocities however, molecular diffusion predominates. Implicit in this discussion is the hypothesis that the uniformity of shape and size of packing particles has an important bearing on the manner in which the Peclet number approaches its limiting value as the gas velocity is increased. On a obtenu les nombres de Peclet qui decrivent la dispersion axiale qui se fait dans un ecoulement gazeux a travers des lits garnis de speres, en utilisant une methode de pulsation comportant deux mesures dans une zone d'essai de 4′ de diametre interieur par 5.14′ de hauteur. On a etudie trois dimensions de garniture, lesquelles corres-pondaient a des rapports de 6.4, 17 et 66 entre le diametre du tube et celui des particules. On a diminue, dans les experiences, la contribution du profil de velocite a l'extension axiale en employant des detecteurs de conductivite thermique qui ne repondaient qu'a la dispersion au centre de la section transversale du lit; dans cette region d'un lit garni, le profil de velocite est relativement plat. Les resultats obtenus indiquent que le diametre des particules exerce une action qui est plus prononcee qu'on ne l'avait rapportee, ce qui concorde avec le mecanisme de diffusion d'une dispersion axiale dans un lit garni, pourvu que la dispersion causee par le profil de velocite n'affecte pas la reponse des pulsations mesurees. En l'absence des effets du profil de velocite, l'extension des temps de sejour dans les cellules poreuses est due surtout a la chute des couches-limites dont l'allure est ralentie sur le cote en aval des particules; toutefois, a de faibles velocites, la diffusion moleculaire predomine. Il y a dans cette discussion une hypothese implicite que l'uniformite de la forme et des dimensions des particules de garniture exerce une influence importante sur la maniere avec Iaqulle le nombre de Peclet s'approche de sa valeur-limite lorsque la velocite du gaz augmente.

Exact solution for diffusion to flow down an incline

Abstract: The concentration of solute in a film flowing down an inclined plane has been obtained by solving the complete diffusion equation, including the diffusion effect in the direction of flow. The formulation leads to the necessity of solving non-orthogonal characteristic value problem, treatment of which is, however, quite straightforward. Though the motivation for the study was the diffusion of oxygen to plasma or blood films, solutions are presented for the complete range of fluid properties, due to the great significance of this mode of flow for wider application in chemical engineering. On a determine la concentration d'un solute dans une pellicule qui descend sur un plan incline en resolvant l'equation complete de diffusion, y compris l'effet de diffusion dans la direction de l'ecoulement. La formulation exige la solution du probleme d'obtention d'une valeur caracteristique dans une forme non-orthogonale, ce qui n'est pas complique. Bien que le but du travail ait ete la diffusion de l'oxygene dans des pellicules de plasma ou de sang, on presente des solutions pour toute la gamma des proprietes fluides, a cause de la grande importance qu'a ce genre d'ecoulement pour d'autres applications dans le domaine du genie chimique.

A lumped parameter approximation to a general model for catalytic reactors

Abstract: Consideration ig given to the solution of the highly exothermic fixed bed catalytic reactor problem taking into account heat and mass transfer resistances inside the catalyst pellets and across the external fluid film, as well as radial temperature and concentration gradients in the fluid phase. Even on large digital computers, the computation time is excessively long if the sets of differential equations are solved simultaneously. By considering the intra-particle equations in detail, it is shown that they may be reduced to a lumped parameter form which permits rapid evaluation of an effectiveness factor. The functional dependence of this effectiveness factor is determined primarily by the external film resistance. While still retaining the characteristics of the general problem, the lumped parameter approximation may be solved in a substantially shorter time, thus permitting its use in optimization and control studies.

The vapor-phase oxidation of benzene over a vanadium oxide catalyst

Abstract: : The kinetics of the reaction of benzene with oxygen over a vanadium oxide/potassium sulphate-promoted catalyst have been studied in a differential flow reactor. Rates of oxidation of benezene to maleic anhydride, p-benzoquinone and carbon dioxide were measured at temperatures from 350 to 400C. The rate data were correlated by the steady state adsorption model and, by comparison with previous published results, it was concluded that this model provides a valuable means of correlating and interpreting catalytic oxidation rate data. Earlier data for benzene oxidation on the same catalyst were critically evaluated and a possible source of error was suggested. (Author)

Heat transfer between an axisymmetric jet and a plate held normal to the flow

Abstract: Heat transfer between a submerged jet of water and a flat surface held normal to the flow was studied experimentally over a wide range of plate to nozzle diameter ratios (8 ⩽ D/d < 58). The average heat transfer coefficients were found to be independent of nozzle to plate distance (γ) in the region studied, (γ/d < 7). An equation was developed by separating the target area into the impingement and the wall jet regions. The data were correlated by For nozzle Reynolds numbers 2,000 to 40,000; D/d ⩾ 8 and γ/d < 7. On a etudie experimentalement, pour une vaste echelle de rapports entre le diametre d'un plateau et celui de l'injecteur (8 ⩽ D/d < 58), le transfert de la chaleur d'un jet d'eau submerge a une surface plate qu'on maintient perpendiculaire a l'ecoulement. On a trouve que les coefficients moyens de transmission de la chaleur ne dependaient pas de la distance (γ) entre l'injecteur et le plateau dans la region (γ/d < 7). On a mis au point une equation, en separant la region etudiee en zone d'impact et en zone entourant le jet, et tabli la correlation suivante entre les resultats dans le cas de nombres de Reynolds variant entre 2,000 et 40,000 pour l'injecteur et D/d ⩾ 8 et γ/d < 7.

The strength of agglomerates bound by salt bridges

Abstract: The correlation between the drying behavior and the tensile strength of agglomerates bound by salt bridges in the dry state was investigated. The pellets examined had been prepared by compacting limestone powders, which were premoistened with a salt solution, in a manually operated die press. The percentage liquid saturation of the moist agglomerate, the concentration of the salt solution and the drying temperature were altered. The influence of the surface incrustation on the drying process could be examined by measuring the temperatures within the cylindrical pellet at different radial positions during drying and by determining the drying rate curves. The tensile strength of the dried pellets, which was usually measured after removing the salt crust, depends on the quantity and the local distribution of the crystallized salt, and the strength of the salt bridges. The latter depends on the crystal structure which is influenced by the drying rate. On a etudie la relation entre le comportement au sechage et la resistance a la traction d'agglomerats lies par des ponts de sel a l'etat sec. On a prepare les granules etudies en comprimant des poudres calcaires qu'on avait prealablement impregnees d'une solution de sel dans une decoupeuse mue a la main. On a modifie le pourcentage de la saturation liquide de l'agglomerat impregne, la concentration de la solution saline et la temperature de sechage. On a pu examiner l'influence de l'incrustation de la surface sur le procede de sechage en mesurant les temperatures dans le granule cylindrique a differentes positions radiales, durant le sechage, et en etablissant des courbes de vitesse de sechage. On a trouve que la resistance a la traction des granules seches (qu'on mesurait d'ordinaire apres avoir enleve la croute de sel) dependait de la quantite et de la repartition locale du sel crystallise ainsi que de la resistance des points de sel; cest ponts dependent de la structure des cristaux, laquelle est influencee par la vitesse de sechage.

Generalized polynomial programming

Abstract: Conventional design procedures use physical reasoning to construct equations describing the system. To find the optimal design for some specified performance criterion, it is desirable to change these equations into inequalities so that generalized polynominal programming, a highly nonlinear optimization technique, can be used. For illustration, a chemical reactor system optimal design problem with 11 variables and 8 constraints is formulated as an equality constrained optimization problem, then transformed into an inequality constrained generalized polynominal program and finally solved on the computer. On utilise un raisonnement physique, dang les procedes ordinaires de conception d'un systeme pour etablir des equations qui le decrivent. Pour trouver la meilleure conception en rapport avec certains criteres specifiques de rendement, il est desirable de changer les dites equations en inegalites, de maniere a pouvoir utiliser une programmation generalisee et a nombres multiples, laquelle est une technique d'optimisation non-lineaire. Pour fin d'illustration, on a formule un probleme de conception optimale pour un systeme de reacteur chimique comportant 11 variables et 8 constantes; il s'agissait d'abord d'un probleme d'optimisation a limites egales, puis d'un programme generalise a nombres multiples et a limites inegales, dont on a trouve la solution au moyen d'un ordinateur.

Freezing of hydraulic systems

Abstract: A theoretical technique is developed for predicting the conditions under which a hydraulic system freezes shut. The investigation considers laminar liquid flow through a tube between two reservoirs. Freezing is assumed to occur within a portion of the tube having a uniform wall temperature lower than the liquid freezing temperature. Analytical results indicate the minimum allowable pressure drop which must be maintained across the system to prevent it from freezing shut. The theoretical predictions are then compared with experimental results. On a mis au point une methode theorique pour predire les conditions responsables du blocage d'un systeme hydrau-lique par congelation. On considere un ecoulement liquide et laminaire dans un tube entre deux reservoirs. On suppose que la congelation doit se produire dans une partie du tube ou la temperature de la paroi est uniforme et moindre que la temperature de congelation du liquide. Les resultats de l'analyse indiquent quelle est la diminution minimum et adminissible de pression qu'il faut maintenir dans tout le systeme pour l'empěcher de se bloquer par congelation. On compare ensuite les predictions theoriques avec les resultats experimentaux.

Liquid‐liquid‐vapor equilibria in the nitrogen‐methane‐ethane system

Abstract: Liquid-liquid-vapor equilibrium compositions were measured for the nitrogen-ethane binary and the nitrogen-methane-ethane ternary systems from –255° to –219.8°F and at pressures up to 591 psia. A forced-recirculation apparatus was employed for the determinations. Experimental results were interpreted and correlated. Optimum operating temperature for nitrogen separation has been suggested. On a determine les compositions d'equilibre entre liquide et melange de liquide et vapeur dans le cas du systeme binaire azote-ethane et du systeme ternaire azotemethane-ethane a des temperatures variant entre –255° et –219.8°F et des pressions absolues s'elevant jusqu'a 591 livres au pouce carre. On a utilise un appareil a re-circulation forcee pour les dites determinations. On a interprete les resultats experimentaux et etabli une correlation entre eux. On a propose une temperature optimale d'operation pour la separation de l'azote.

The activity of commercial water gas shift catalysts

Abstract: Published kinetic data for commercial water gas shift catalysts are interpreted in terms of pore diffusional effects. The Arrhenius plots of apparent activity show the curvature typical of the transition from reaction to pore diffusion control and the apparent activities of different catalyst pellets vary quite widely. Effective diffusivity data are used to calculate intrinsic rate constants from the apparent activity data and it is found that the intrinsic activities of the catalysts considered are all similar. Furthermore the intrinsic activities, calculated in this way, give linear Arrhenius plots and activation energies which are in good agreement with values obtained experimentally using small catalyst particles (22–27 K. Cals). The effect of pressure on apparent catalyst activity is also discussed and it is shown that this effect may be accounted for satisfactorily by pore diffusional effects and it is not necessary to assume a change in the intrinsic rate equation at least at pressures below 20 atms. On interprete, en fonction des effets de diffusion par les pores, les resultats cinetiques qui ont paru relativement aux catalyseurs employes dans la fabrication commerciale du gas a l'eau. Les traces d'Arrhenius pour l'activite apparente montrent que la courbure typique du passage de la reaction au controle de la diffusion par les pores, et les activites apparentes de differents catalyseurs en pastilles varient beaucoup. On a utilise les resultats de la diffusivite effective pour calculer les constantes de vitesse intrinseque a partir des donnees de l'activite apparente et l'on a trouve que les activites intrinseques des catalyseurs employes etaient toutes semblables. En outre, les activites intrinseques calculees de cette maniere produisent des traces d'Arrhenius lineaires et des energies d'activation qui concordent bien avec les valeurs obtenues experimentalement en utilisant des petites particules de catalyseur (22–27 kilocalories). On discute egalement l'effet de la pression sur l'activite apparente des catalyseurs et l'on demontre qu'on peut l'expliquer d'une maniere satisfaisante par les effets de diffusion par les pores et qu'il n'est pas necessaire de supposer qu'il y a changement dans l'equation de vitesse intrinseque, au moins lorsque la pression est inferieur a 20 atmospheres.

Theoretical patterns of selectivity in aging catalysts with special reference to the catalytic cracking of petroleum

Abstract: The catalyst decay theory of Wojciechowski(1) is applied to a simplified theoretical mechanism of catalytic gas oil cracking. The resulting patterns of selectivity are presented and general conclusions drawn. It is shown that selectivity in gas oil cracking is bounded by optimum and minimum performance envelopes which confine the range of possible product distributions. On applique la theorie de degradation des catalyseurs de Wojciechowski(1) a un mecanisme theorique et simplifie de craquage catalytique de gaz-huile. On presente les diagrammes de selectivite resultants et tire des conclusions generales. On demontre que la selectivite dans le craquage de gaz-huile est limitee par des enveloppes de rendement optimal et minimal qui restreignent l'etendue des distribution possibles des produits.

Kinetics of the ammoxidation of propylene over a bismuth‐molybdate catalyst

Abstract: Integral conversion data for the ammoxidation of propylene were obtained using a flow reactor and 10.0 gms. of a bismuth-molybdate catalyst. Analysis by gas chromatography for carbon-containing compounds in the product gases showed the presence of unreacted propylene, acrolein, acrylonitrile, carbon dioxide and small amounts of acetonitrile. The data obtained at 390°C were correlated on the basis of a simplified scheme of first-order reactions with acrolein as an intermediate. The results from experiments at higher temperatures and with reduced amounts of oxygen in the feed indicated that both the activity and selectivity of the catalyst were affected by the oxygen content of the catalyst. On a obtenu des donnees de transformation integrale dans le cas de l'animoxydation du propylene, en utilisant un reacteur a debit et 10.0 grammes d'un catalyseur a base de molybdate de bismuth. L'analyse par chromatographic en phase gazeuse des composes contenant du carbone qui etaient presents dans les gaz du produit a revele la presence de propylene inaltere, d'acroleine, d'acrylonitrile, d'auhydride carbonique et d'une faible quantite d'acrylonitrile. On a etabli une correlation entre les resultats obtenus a 390°C en se basant sur un systeme simplifie de reactions de premier ordre avec l'acroleine comme produit intermediaire. Les resultats provenant des experiences a des temperatures plus elevees et avec des quantites moindres d'oxygene dans le systeme d'alimentation ont indique que l'activite et l'action selective du catalyseur etaient affectees par la teneur en oxygene de ce dernier.

Free convection boundary-layer flow over horizontal plates and discs

Abstract: Free convection flows near horizontal surfaces are discussed for those cases in which a similarity solution can be obtained. Particular cases considered are those of asymptotically large and vanishingly small Prandtl numbers. The solution for the relevant velocity, temperature and pressure functions has to be carried-out numerically. For the particular cases when the Prandtl number is either sufficiently large, or sufficiently small, this integration would yield general functions, no longer dependent on the Prandtl number. Numerical data are included. L'article donne des solutions des equations fondamentales de l'ecoulement et de la transmission de chaleur par convection libre au dessus d'une surface chauffee, plane et horizontale, ceci pour les cas qui admettent des transformations de similitude. Les vitesses, les pressions et les temperatures sont obtenues par integrations numeriques. En particulier, les cas asymptotiques de nombre de Prandtl tres eleve d'une part, et d'une tres faible de ce parametre d'autre ont ete examines en detail.