scispace - formally typeset
Search or ask a question

Showing papers in "Canadian Journal of Chemical Engineering in 1962"


Journal ArticleDOI
TL;DR: In this article, an approximate velocity profile and terminal velocities have been predicted for fluid spheres moving in viscous media under the influence of gravity, using a numerical method after Kawaguti.
Abstract: Approximate velocity profiles and terminal velocities have been predicted for fluid spheres moving in viscous media under the influence of gravity. The equations of motion were satisfied approximately using a numerical method after Kawaguti(1). Predicted terminal velocities are compared with literature data and with data measured by one of the authors(2). The agreement is reasonable for Reynolds numbers up to about 80. The effect of the asymmetry of the exterior flow upon the symmetry of the interior flow is discussed. Les auteurs predisent les profils de vitesse approximatifs et les vitesses terminales pour des spheres fluides qui se deplacent dans un milieu visqueux, sous l'influence de la gravite. On satisfait de facon approximative aux equations du mouvement en utilisant une methode numerique proposee par Kawaguti.1 On compare les vitesses terminales predites avec les donnees de la litterature et avec les valeurs mesurees par un des auteurs.2 L'accord est satisfaisant pour des nombres de Reynold allant jusqu'a 80. On discute l'effet de l'asymetrie de l'ecoulement exterieur sur la symetrie de l'ecoulement interieur.

82 citations


Journal ArticleDOI
TL;DR: A review and comparison of the various methods which have been proposed for the correlation of the pressure drop attending the flow of gas-liquid mixtures is made in this article, where the friction factor and other terms employed in the correlations are related mathematically.
Abstract: A review and comparison of the various methods which have been proposed for the correlation of the pressure drop attending the flow of gas-liquid mixtures is made. The friction factor and other terms employed in the correlations are related mathematically. The horizontal flow of air-water mixtures has been investigated in a 41 ft. length of cellulose acetate butyrate tubing of 1.026 in. i. d. The average system pressure was held constant at 36 p.s.i.a. maintaining a constant air density of 0.18 lb./cu. ft. Flow pattern, holdup and pressure drop data were obtained at air-water volume ratios from 0.1 to 200 (700 in some cases) for 10 superficial water velocities from 0.01 to 5.03 ft./sec. These data overlap and extend the range covered by previous investigators. The flow patterns observed at constant superficial water velocity with increasing air-water ratio were: bubble, plug, stratified, wave or ripple, slug and film. Bubble, plug and slug flow were encountered only at superficial water velocities above about 0.1 ft./sec. while stratified flow was encountered only at superficial water velocities below about 1 ft./sec. and superficial air velocities below about 5 ft./sec. The holdup ratio, a measure of the relative accumulation of the water in the flow section, increased with air velocity for all superficial water velocities reaching a maximum value of over 50. At constant superficial air velocity the holdup ratio increased rapidly with decrease in superficial water velocity. The pressure drop data were converted to a friction factor based upon the density and the superficial velocity of the water. The friction factors were correlated with the superficial Reynolds number for the water, and the air-water volume ratio. The data are compared in this form with previous data of Schneider, Thomsen, and Johnson and Abou-Sabe.

82 citations


Journal ArticleDOI
TL;DR: In this article, the Navier-Stokes equations were solved by a numerical procedure utilizing a digital computer, for the laminar stratified flow of two Newtonian liquids (oil and water) in a circular pipe, and liquid flow rates were obtained for the flow of five hypothetical oils ranging in viscosity from 4 to 1500 centipoises in the presence of water.
Abstract: The addition of water to crude oil pipelines appears to be an important method for decreasing the pressure gradient for a given oil throughput. Although the concentric oil-in-water flow pattern provides the greatest possible reduction, the general case, in which the liquids are stratified as a result of the oil and water having different densities, is also characterized by reductions in pressure gradient. To evaluate the magnitude of the pressure gradient reduction to be expected in stratified flow systems, the Navier-Stokes equations were solved by a numerical procedure utilizing a digital computer, for the laminar stratified flow of two Newtonian liquids — oil and water — in a circular pipe. Liquid flow rates were obtained for the flow of five hypothetical oils ranging in viscosity from 4 to 1500 centipoises in the presence of water, by computing the oil and water velocity profiles for a series of arbitrary oil-water interface positions. It was found that the maximum values for the pressure gradient reduction factor ranged from 1.12 to 1.31 for the five oils and occurred at water contents ranging from 12 to 93 per cent respectively. The computed reduction factors were considerably lower than experimental values and this appears to indicate that wave motion and mixing at the oil-water interface produces a further and very significant reduction in the pressure gradient. II semble que l'addition d'eau au petrole brut dans les oleoducs constitue un moyen important de diminuer le gradient de pression pour un debit donne de petrole. Měme si le mode d'ecoulement concentrique, huile dans l'eau, donne la plus grande reduction possible, on trouve egalement des gradients de pression reduits dans le cas general ou les liquides sont stratifies en raison de la difference de densite entre l'huile et l'eau. Dans le but de prevoir la reduction du gradient de pression dans les systemes a ecoulement stratifie les auteurs resolvent les equations de Navier-Stokes a partir de methodes numeriques, a l'aide d'un calculateur digital, pour l'ecoulement stratifie laminaire de deux liquides Newtoniens—huile et eau—dans un tuyau a section circulaire. Ils obtiennent les debits de liquide pour l'ecoulement, en presence d'eau, de cinq huiles hypothetiques dont les viscosites varient de 4 a 1,500 centipoises, apres avoir calcule les profils de vitesse pour l'huile et pour l'eau correspondant a un certain nombre de positions de l'interface huile-eau choisies arbitrairement. Les valeurs maxima du facteur de reduction du gradient de pression varient de 1.12 a 1.31 pour les cinq huiles et correspondent a des teneurs d'eau variant de 12 a 93 pour cent respectivement. Les facteurs de reduction calcules sont de beaucoup inferieurs aux valeurs experimentales. Ceci semble indiquer qu'un mouvement ondulatoire et une agitation a l'interface huile-eau provoquent une reduction additionnelle et tres importante du gradient de pression.

60 citations


Journal ArticleDOI
TL;DR: In this article, approximate local and overall Sherwood numbers were predicted theoretically for forced-convection transfer around solid and fluid spheres for Reynolds numbers up to 100 for the case of a thin concentration boundary layer.
Abstract: Approximate local and overall Sherwood numbers have been predicted theoretically for forced-convection transfer around solid and fluid spheres for Reynolds numbers up to 100. The diffusion equation was solved analytically for the case of a thin concentration boundary layer (NPo » 1). The predicted overall Sherwood numbers are in fair agreement with published semi-empirical correlations. On predit theoriquement les valeurs approximatives, locales et globales, des nombres de Sherwood pour le transfert par convection forcee autour de spheres solides et fluides, a des nombres de Reynold allant jusqu'a 100. Les auteurs resolvent analytiquement l'equation de diffusion dans le cas d'une couche limite mince (NPo » 1). Les valeurs globales predites pour les nombres de Sherwood se comparent assez bien a celles que donnent les expressions semi-empiriques deja publiees.

48 citations


Journal ArticleDOI
TL;DR: In this article, the velocity profiles for cocurrent laminar stratified flow of two immiscible Newtonian liquids in a circular pipe were determined in dimensionless form, for viscosity ratios of 1, 10, 100 and 1000, at eight positions of the horizontal liquid-liquid interface, which was incorporated into the relaxation procedure by a twodimensional finite difference method described by D. N. Allen.
Abstract: Complete numerical solutions were determined in dimensionless form, of the velocity profiles for cocurrent laminar stratified flow of two immiscible Newtonian liquids in a circular pipe, for viscosity ratios of 1, 10, 100 and 1000, at eight positions of the horizontal liquid-liquid interface, which was incorporated into the relaxation procedure by a twodimensional finite difference method described by D. N. de G. Allen. The velocity profiles were used to compute the theoretical hold-up ratios, pressure gradient reduction (or volumetric flow rate enhancement) factors and power reduction factors for the various viscosity ratios and interface positions; the maximum reduction factors for each viscosity ratio; and the input volume fractions of the two liquids corresponding to each of the above. The theoretical results for laminar flow were compared with experimental data in the literature, in particular those of Russell, Hodgson and Govier for the horizontal flow of a mineral oil and water (viscosity ratio = 20.1) in a circular pipe. Good agreement was obtained for both hold-up and pressure drop data when both water and oil were in laminar flow. As the water entered the transitional and turbulent regions, however, a deviation between the experimental and the computed results developed, the deviation increasing in the anticipated direction as the Reynolds number of the water increased. On a determine, sous forme non dimensionnelle, des solutions numeriques completes de profils de vitesse pour l'ecoulement laminaire, stratifie et concourant de deux liquides newtoniens immiscibles, dans un tuyau circulaire, en utilisant les rapports de viscosite de 1, 10, 100 et 1,000, pour huit positions differentes de l'interface horizontale liquide-liquide; on a tenu compte de la position de cette derniere en appliquant le processus de relaxation a la methode de difference finie a deux variables decrite par D. N. de G. Allen. A partir des profils de vitesse les auteurs ont calcule, pour les differents rapports de viscosite et les diverses positions de l'interface, le rapport theorique de retention, les facteurs de reduction des pertes de charge (ou d'accroissement du taux d'ecoulement volumetrique) et les facteurs de reduction de puissance; ils ont calcule de měme le facteur maximum de reduction pour chaque rapport de viscosite et egalement les fractions volumetriques respectives des deux liquides a l'entree dans chacun des cas cihaut mentionnes. Les resultats theoriques pour l'ecoulement laminaire se sont montres en parfait accord avec les donnees experimentales rapportees dans la litterature, tant pour la retention que pour les pertes de charge, quand l'ecoulement laminaire prevalait pour l'eau et l'huile. Cependant, a mesure que l'on passait par la periode de transition et par la zone de turbulence pour l'eau, on a constate une deviation entre les valeurs experimentales et les resultats obtenus par calcul; cette deviation croissait dans la direction anticipee a mesure que le nombre de Reynold pour l'eau augmentait.

43 citations


Journal ArticleDOI
TL;DR: In this article, the authors deal with some of the problems of choosing and fitting such models, called mixed models, to represent flow in real vessels, and the stimulus-response technique is a useful tool for this purpose, and matching response curves for model and real vessel then serves as the selection method.
Abstract: Models consisting of interconnected regions (dead-water, backmix, plug flow, etc.) with various modes of flow through and around these regions (bypass, recycle, cross flow) are used to represent real vessels in which flow deviates greatly from plug flow. This paper deals with some of the problems of choosing and fitting such models, called mixed models, to represent flow in real vessels. The stimulus-response technique is a useful tool for this purpose, and matching response curves for model and real vessel then serves as the selection method. Some of the simpler mixed models and their corresponding characteristic response curves are presented. On represente les contenants reels, ou le mode d'ecoulement differe appreciablement de l'ecoulement frontal, a l'aide de modeles formes de zones communicantes (zone morte, zone agitee, ecoulement frontal, etc.) et comportant differents modes d'ecoulement a travers et autour de ces regions (derivation, recirculation, ecoulement eroise). L'auteur considere, dans ce travail, quelques-uns des problemes associes au choix et a l'adaptation de tels modeles, ou modeles composes, pour representer l'ecoulement dans les contenants reels. La technique de la reponse a une demande quelconque constitue un outil utile dans ce cas et la methode de selection consiste a ajuster les courbes de reponse pour le modele et pour le contenant actuel. On presente quelques-uns des modeles composes les plus simples de měme que les courbes de reponse caracteristiques qui y correspondent.

36 citations


Journal ArticleDOI
TL;DR: In this article, velocity profiles and volumetric rates for axial, laminar flow of a Newtonian fluid in a circular pipe containing a fixed eccentric core were evaluated numerically using a digital computer.
Abstract: Velocity profiles and volumetric rates for the axial, laminar flow of a Newtonian fluid in a circular pipe containing a fixed eccentric core were evaluated numerically using a digital computer. The velocity profiles agree exceptionally well with those evaluated from an analytical expression derived by Heyda(2). The effect of displacing the inner surface from a concentric position is to increase the volumetric flow rate for a given pressure gradient, the maximum increase for a diameter ratio of 0.9 being 240% and for a diameter ratio of 0.1, 60%. The volumetric flow rates are presented graphically in terms of dimensionless ratios which enable the flow rate to be evaluated for any fluid, diameter ratio, relative displacement and pressure gradient. On a evaluee numeriquement, a l'aide d'une calculatrice digitale, les profils de vitesse et les taux d'ecoulement volumetrique pour l'ecoulement laminaire axial d'un fluide Newtonien dans un tuyau circulaire contenant un noyau excentrique fixe. Les profils de vitesse concordent exceptionnellement bien avec ceux que l'on a evaluees a partir de l'expression analytique suggeree par Heyda(2). En deplacant la surface interieure a partir de la position concentrique, on augmente le taux d'ecoulement volumetrique pour un gradient donne de pression, l'augmentation etant de 240% pour une rapport de diametre de 0.9, et de 60% pour un rapport de diametre de 0.1. On presente graphiquement les taux d'ecoulement volumetrique en fonction de rapports sans dimensions, ce qui permet d'evaluer le taux d'ecoulement pour tout fluide, rapport de diametre, deplacement relatif et gradient de pression.

33 citations


Journal ArticleDOI
TL;DR: In this paper, the area of the interface between the undecomposed sulphate and the oxide product was investigated, and it was shown that the rate of decomposition is proportional to the surface area of this interface.
Abstract: Kinetic studies were made of the thermal decompositions of ferric sulphate and aluminum sulphate. The reaction product gases were swept from the samples. Cylindrical pellets prepared from chemically pure anhydrous powders were used, and mathematical corrections were made to relate the reaction rate to the area of the interface between the undecomposed sulphate and the oxide product. The interface is the local of the reaction. The rate of the decomposition reaction is proportional to the area of this interface. Studies on ferric sulphate have shown that the rate of decomposition is also directly proportional to the difference between the equilibrium pressure of sulphur dioxide (or oxygen) over the sample and the partial pressure of sulphur dioxide (or oxygen) in the gas stream. The activation energies are 19.9 kcal. and 64.0 kcal. respectively for the ferric sulphate and aluminum sulphate decompositions. No oxysulphates were detected as intermediates in the transition from the normal sulphates to the oxides. On a etudie la cinetique de la decomposition thermique du sulphate ferrique et du sulphate d'aluminium. On a debarrasse les echantillons des produits gazeux de reaction. Les auteurs ont prepare pastilles cylindriques a partir de poudres anhydres chimiquement pures. Ils ont fait des corrections mathematiques pour relier la vitesse de reaction a l'aire interfaciale entre le sulphate non decompose et le produit oxyde. L'interface etant le site de la reaction, la vitesse de decomposition est proportionnelle a l'aire de l'interface. Les etudes sur le sulphate ferrique ont montre que la vitesse de decomposition est aussi directement proportionnelle a la difference entre la pression d'equilibre de l'anhydride sulphureux (ou de l'oxygene) au-dessus de l'echantillon et la pression partielle de l'anhydride sulphureux (ou de l'oxygene) dans le courant gazeux. Les energies d'activation pour la decomposition du sulphate ferrique et du sulphate d'aluminium sont de 19.1 kcal. et 64.0 kcal. respectivement. Les auteurs n'ont pas decele d'oxysulphates comme produits intermediaires lors du passage des sulphates normaux en oxydes.

32 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reviewed the theories for mass transfer to rigid or mobile interfaces and compared with selected experimental data. And they showed that the penetration theory holds exactly for many devices which expose liquid surfaces for a short and known contact time, and, judged by a 0.5 exponent for the diffusivity, probably holds for the liquid phase in absorbers and for both phases in bubble cap towers.
Abstract: The theories for mass transfer to rigid or mobile interfaces are reviewed and compared with selected experimental data. Except for transfer to particles in stagnant fluids, there is no case where the rate depends on the first power of the diffusivity, as implied by the film theory. The transfer coefficients for single rigid spheres, for particles in packed beds, and for the gas film in packed absorbers vary with about the 2/3 power of the diffusivity, as predicted by the boundary layer theory, which works fairly well for these cases because transfer to the wake region is relatively small. The penetration theory holds exactly for many devices which expose liquid surfaces for a short and known contact time, and, judged by a 0.5 exponent for the diffusivity, the penetration theory probably holds for the liquid phase in absorbers and for both phases in bubble-cap towers. Theory and data for transfer to mobile interfaces show the coefficients to vary with D0.5 to D3/5, the limiting solutions for high and low interface velocity corresponding to the penetration theory and the boundary layer theory. Mass transfer in turbulent fluids is an unsteady-state process, and the transfer coefficient varies with the 0.5-0.8 power of the diffusivity even with very high turbulence. L'auteur fait une revue des theories sur le transfert de masse aux interfaces rigides ou mobiles et les compare avec des resultats experimentaux selectionnes. Sauf pour le transfert aux particules dans les fluides stagnants, il ne se trouve aucun cas ou le taux varie proportionnellement a la diffusivite, comme l'implique la theorie des films. Les coefficients de transfert pour une sphere rigide, pour les particules d'un lit et pour le film gazeux dans une colonne garnie, varient suivant la diffusivite a la puissance 2/3, tel que le predit la theorie de la couche limite. Celle-ci s'applique assez bien dans ces cas parce que le transfert a la region du sillage est relativement faible. La theorie de la penetration tient exactement pour plusieurs dispositifs qui permettent l'exposition de surfaces liquides pendant un temps de contact court et connu. A en juger par la puissance 0.5 pour la diffusivite, la theorie de penetration est probablement applicable a la phase liquide dans les absorbeurs et aux deux phases dans les colonnes a plateaux. La theorie et les resultats pour le transfert aux interfaces mobiles montrent que les coefficients sont une fonction de la diffusivite allant de D1/2 a D2/3, ces solutions limites pour une vitesse d'interface elevee ou basse correspondant respectivement a la theorie de la penetration et a la theorie de la couche limite. Le transfert de masse dans les liquides ou il y a turbulence est un processus instable et le coefficient de transfert varie avec D0.5 a D0.6, měme quand la turbulence est tres grande.

30 citations


Journal ArticleDOI
TL;DR: The first commercial spouted bed driers have been installed in Canada and one has been used to dry three types of peas, lentils and flax as discussed by the authors, and the data obtained from this drier have been compared and correlated with previous drying studies in various laboratory spouted-bed driers.
Abstract: The first commercial spouted bed driers have been installed in Canada and one has been used to dry three types of peas, lentils and flax. The data obtained from this drier have been compared and correlated with previous drying studies in various laboratory spouted bed driers. An empirical relationship between solids temperature and other variables has been obtained: where TK and TA are respectively the particle and inlet air temperature, dgm the particle diameter, Do the column diameter, F the feed rate and Mf the feed moisture content. High drying capacity was achieved through the use of high air temperatures with the result that a two foot diameter spouted bed heater (plus cooler) dried almost two tons per hour of peas through 8.8% moisture range. No damage was evident in materials dried. Les premieres unites commerciales de sechage par technique “Spouted Bed” ont ete installees au Canada et l'une d'elles a ete utilisee pour le sechage de pois, de lentilles et de lin. Les valeurs obtenues de ce sechoir ont ete comparees avec des etudes anterieures sur sechoirs de laboratoire operant sur le měme principe. Une correlation empirique entre la temperature des solides et les autres variables a ete obtenue: ou TK et TA sont respectivement les temperatures des particules et de l'air a l'entree; dgm le diametre des particules; Do le diametre de la colonne; F le taux d'alimentation et Mt l'humidite dans l'alimentation. Une forte capacite de sechage a ete obtenue en utilisant des temperatures d'air elevees. II a ete possible de secher de 8.8% d'humidite pres de deux tonnes par heure de pois dans un sechoir ayant 2 pieds de diametre. Aucun dommage n'a ete observe sur le materiel ainsi seche.

21 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the transfer rate of water drops into cyclohexanol and from drops of cycloxide, isobutanol, and o-toluidine into water and verified the hypothesis that internal motion affects the external transfer rate.
Abstract: Rates of mass transfer from water drops into cyclohexanol and from drops of cyclohexanol, isobutanol, and o-toluidine into water were measured. These experimental data were augmented by published results, to cover, at drop Reynolds numbers less than 10, a Peelet number range of 0.01 to 5,000,000 for non-circulating spheres and 700 to 24,000,000 for circulating spheres. Transfer rates, expressed as Sherwood numbers, were in substantial agreement with those predicted from a theoretical model. The contribution of natural convection, inherent in the measurements, but omitted in the model, was approximately accounted for. Data for circulating spheres verified the hypothesis that internal motion affects the external transfer rate. This effect depends on the ratio of continuous to disperse phase viscosity of the system; a four to six-fold enhancement of mass transfer due to internal circulation was found for water drops falling in cyclohexanol. Les auteurs ont mesure les taux de transfert de masse a partir de gouttes d'eau dans le cyclohexanol et a partir de gouttes de cyclohexanol, d'isobutanol et de o-toluidine dans l'eau. On a ajoute aux resultats experimentaux en puisant a meme des resultats publies pour balayer, a des nombres de Reynold inferieurs a 10 pour les gouttes, un champ correspondant a un nombre de Peclet allant de 0.01 a 5,000,000 pour des spheres ne comportant pas de circulation, et de 700 a 24,000,000 pour des spheres avec circulation. Les taux de transfert, exprimes sous forme de nombres de Sherwood, s'accordent assez bien avec ceux que l'on a predits a partir d'un modele theorique. On a tenu compte, de facon approximative, de l'effet de convection naturelle inherent aux methodes de mesure mais omis dans le modele. Les resultats pour les spheres comportant une circulation interne verifient l'hypothese que cette circulation affecte le taux de transfert a l'exterieur. L'effet note depend du rapport de la viscosite de la phase continue a celle de la phase dispersee; on a trouve un accroissement, par un facteur allant de 4 a 6, du transfert de masse attribuable a la circulation interne pour des gouttes d'eau tombant dans le cyclohexanol.

Journal ArticleDOI
Chi Tien1
TL;DR: In this paper, the authors extended the classical Graetz-Nusselt Problem to the case of power-law non-Newtonian fluid flowing between parallel plates and gave expressions for the eigen value, eigen functions and its related expressions, average temperature and Nusselts modulus.
Abstract: The asymptotic solutions of the classical Graetz-Nusselt Problem is extended to the case of power-law non-Newtonian fluid flowing between parallel plates. Expressions are given for the eigen value, eigen functions and its related expressions, average temperature and Nusselt modulus. On etend la solution asymptotique du probleme classique de Graetz-Nusselt au cas d'un fluide non-Newtonien qui circule entre des plaques paralleles. On donne des expressions pour la valeur exacte, la fonction caracteristique et les expressions rattachees, la temperature moyenne et le module de Nusselt.

Journal ArticleDOI
TL;DR: In this paper, the Gilliland-Sherwood correlation was correlated empirically with the turbulent boundary layer mechanism of mass transfer between solids and liquids for agitated vessels, regardless of the actual geometry of the apparatus, in two main categories: the velocity term in the Re number defined as the velocity of the rotating device, i.e., impeller, cylinder or rotating annulus.
Abstract: Studies of mass transfer between solids and liquids for agitated vessels have been reviewed. Data from the literature correlated empirically by the Gilliland-Sherwood correlation, regardless of the actual geometry of the apparatus, in two main categories. The velocity term in the Re number was defined as the velocity of the rotating device, i.e., impeller, cylinder or rotating annulus. The characteristiclength term was taken as the impeller diameter in the cases of mass transfer from suspended pellets or flat surfaces, the gap-width in the case of rotating cylinders, and the hydraulic radius of the annulus in the case of rotating vessels. The empirical correlations were found to be in general agreement with the turbulent boundary layer mechanism of mass transfer. Les etudes relatives au transfert de masse entre solides et liquides dans des recipients sous agitation ont ete examinees. Les valeurs obtenues dans la bibliographie, comparees a l'aide de l'equation de Gilliland-Sherwood, sont exprimees en deux categories principales, quelle que soit la geometrie du recipient. Le terme “vitesse” dans le nombre de Reynolds est defini par la vitesse de l'impulseur, cylindre ou anneau rotatif. Le terme “diametre” a ete pris comme etant le diametre de l'impulseur, dans les cas de transfert de masse depuis les granules en suspension ou les surfaces planes, la largeur de l'espacement dans le cas de cylindres en rotation et le rayon hydraulique de l'anneau dans le cas de recipients en rotation. Les correlations empiriques sont en accord general avec le mecanisme de transfert de masse en couche limite turbulente.

Journal ArticleDOI
TL;DR: In this paper, a procedure was developed for systematically studying the effect of the three variables: bubble volume, formation frequency, and seal height on the mass transfer coefficient for carbon dioxide bubbles rising in water.
Abstract: Continuous phase mass transfer coefficients have been measured for carbon dioxide bubbles rising in water. A procedure was developed for systematically studying the effect of the three variables: bubble volume, formation frequency, and seal height. The mass transfer coefficient was independent of bubble volume, increased 35% with a ten-fold increase in frequency and varied only 8% over a 30 cm. range in seal height. The data, extrapolated to zero frequency, agreed well with the single bubble study of Hammerton and Garner. The Higbie equation predicted results very close to those obtained here but was not too successful in explaining the effect of bubble size or frequency. The average mass transfer coefficient is about four times that for a solid particle as reported by Akselrud; this enhancement is attributed to internal circulation. Surface absorption rates were determined as a function of bubble frequency. New data has also been presented on the factors which control frequency, velocity of rise, and bubble shape. A partial correlation was developed relating bubble frequency to chamber volume. Les auteurs ont mesure les coefficients de transfert de masse en phase continue pour des bulles ascen-dantes de bioxyde de carbone dans l'eau. Ils ont elabore une methode d'etude systematique de l'effet des trois variables: volume des bulles, frequence de formation et hauteur du liquide. Le coefficient de transfert de masse a ete trouve independent du volume des bulles; il s'accroit de 35% quand la frequence decuple et varie de 8% seulement pour une fluctuation de 30 cm. dans la hauteur du liquide. Par extrapolation des resultats a la frequence zero, on a verifie leur accord avec ceux de Hammerton et Garner pour une seule bulle. L'equation de Higbie predit des valeurs tres voisines de celles que l'on a obtenues ici mais ne parvient pas a tenir compte des effets de la grosseur des bulles et de la frequence. Le coefficient moyen de transfert de masse est environ quatre fois superieur a celui que rapporte Akselrud pour une particule solide; cette augmentation est attributuee a la circulation interne. On a determine les taux d'absorption a la surface en fonction de la frequence des bulles. On presente egalement des donnees sur les facteurs qui contrǒlent la frequence, la vitesse d'ascension et la forme des bulles. On a etabli une correlation partielle reliant la frequence des bulles au volume de la chambre.

Journal ArticleDOI
TL;DR: In this article, the authors describe a method for producing compact spherical agglomerates from a liquid suspension of solids following a method outlined by Farnand, Smith, and Puddington.
Abstract: A description is given of a practical technique for producing compact spherical agglomerates from a liquid suspension of solids following a method outlined by Farnand, Smith, and Puddington. This method involves the addition of an immiscible liquid which preferentially wets the solids and forms liquid bonds between colliding particles. Using a rotatingdrum agglomerator, pellets ranging in size from 0.020 to 0.75 in. diameter were produced from an aqueous suspension of finely-divided graphite. The effects of operating variables such as drum load, speed of rotation, suspension and bridging liquid concentrations are described, followed by a discussion of the mechanism of particle growth. Selective agglomeration is also described. Une technique experimentale pour la production d'agglomerats compacts et spheriques a partir d'une suspension liquide de solide, selon la methode proposee par Farnand, Smith & Puddington, est decrite. L'addition du liquide immiscible mouille preferentiellement les solides et forme un lien liquide entre les particules entrant en collision. Utilisant un agglomerateur a tambour rotatif, des pastilles variant de 0.020 a 0.75” diametre ont ete produites a partir d'une suspension aqueuse de graphite pulverise. L'effet des variables telles que: charge, vitesse de rotation, concentration des liquides selectifs, est decrit. Une discussion relative au mecanisme de croisance de particules et une description de l'agglomeration selective sont donnees.

Journal ArticleDOI
TL;DR: In this paper, the authors deal with the calculation of the evaporative load distribution in a spray of droplets suspended in an absorbing gas medium contained in a cylindrical column after a temperature profile for the gas has been assumed.
Abstract: This paper deals with the calculation of the evaporative load distribution in a spray of droplets suspended in an absorbing gas medium contained in a cylindrical column after a temperature profile for the gas has been assumed. Preliminary experimental data obtained for water sprays in an 8-in. i.d. by 10-ft. high pilot-plant atomized suspension reactor at wall temperatures up to 800°C. are used to illustrate the method of calculation. The calculated results emphasize the importance of the physical characteristics of the spray, such as initial drop-size and distribution, drop velocities and spray angle. They also indicate that the dynamics of such spray systems, as well as their heat and mass transfer aspects, require further elaboration. Ce travail se rapporte au calcul de la distribution de la charge d'evaporation dans un jet de gouttelettes suspendues dans un milieu gazeux absorbant, a l'interieur d'une colonne cylindrique, quand on a suppose une certain distribution de temperature dans le milieu gazeux. On illustre le methode de calcul au moyen des resultats experimentaux preliminaires obtenus dans un reacteur pour suspension pulveriee ayant comme dimensions un diametre interieur de huit pouces et une hauteur de dix pieds, pour des temperatures de la paroi allant jusqu'a 800°C. Les resultats obtenus par calcul font ressentir l'importance des caracteristiques physiques du jet, comme la distribution et la grosseur initiales des gouttelettes, leur vitesse et l'angle du jet. Ils indiquent egalement la necessite d'etudier davantage la dynamique de tels jets pulverises, de měme que les aspects ayant trait aux transferts de chaleur et de masse.

Journal ArticleDOI
TL;DR: The modified Rayleigh equation as discussed by the authors is a non-linear differential equation governing the growth of bubbles during cavitation, and it has been programmed on an analog computer, and the effects on the initial conditions and the physical properties of the system, such as density, viscosity and surface tension, have been made the subject of a detailed parameter study.
Abstract: The modified Rayleigh equation is a non-linear differential equation governing the growth of bubbles during cavitation. It has been programmed on an analog computer, and the effects on the growth of bubbles of the initial conditions and the physical properties of the system, such as density, viscosity and surface tension, have been made the subject of a detailed parameter study. The observations that the initial growth may be delayed and that the rate of bubble growth may pass through a minimum have been explained by an energy balance. A first order perturbation method has been applied to the case where the effect of viscosity is small. L'equation modifiee de Rayleigh est une equation differentielle non lineaire qui regit la croissance des bulles au cours de la cavitation. Les auteurs en ont deduit, au moyen d'un calculateur analogique, l'influence des conditions initiales et des proprietes physiques du systeme sur la croissance des bulles. Ils ont ainsi fait une etude detaillee de differents parametres, dont la densite, la viscosite et la tension superficielle. On explique au moyen d'un bilan d'energe le retard observe dans la croissance initiale des bulles et le fait que le taux de croissance des bulles peut passer par un minimum. On a applique une methode de perturbation du premier ordre dans le cas ou l'effet de la viscosite est faible.

Journal ArticleDOI
TL;DR: In this article, it was shown that the unit operation of size reduction can be considered to be the result of many individual comminution events and that the distribution modulus of a comminuted solid is a property of the material, independent of whether the material has been ground separately or as part of a mixture.
Abstract: This investigation has shown that the unit operation of size reduction can be considered to be the result of many individual comminution events and that the distribution modulus of a comminuted solid is a property of the material, independent of whether the material has been ground separately or as part of a mixture. Investigation of the comminution of quartz and limestone in a rod mill has shown that the energy-size reduction relationships which have been developed for the comminution of homogeneous materials can be used to analyze the comminution of mixtures. Size reduction of mixtures in rod mills has been found to be complex because energy is consumed preferentially by the harder material. Methods are presented to predict the distribution modulus, size modulus, and energy consumption for the size reduction of mixtures. Ce travail montre que l'on peut considerer l'operation fondamentale du broyage comme le resultat de plusieurs etapes individuelles de comminution et que le module de distribution d'un solide broye est une propriete de cette substance, que cette derniere ait ete broyee separement ou faisant partie d'un melange. Les resultats de travaux sur la comminution de quartz et de pierre a chaux dans un broyeur a barres montrent que l'on peut etudier la comminution de melanges a partir des relations etablies pour la comminution de materiaux homogenes, ou l'energie est exprimee en fonction du degre de reduction. On trouve que l'etude du broyage de melanges dans les broyeurs a barres est plutǒt complexe parce que l'absorption d'energie se fait de preference par les corps plus durs. On presente des methodes qui permettent de predire le module de distribution, le module de grosseur et l'energie consommee pour le broyage de melanges.

Journal ArticleDOI
TL;DR: In this article, general analytical and graphical conditions for the optimality of the MT combination are given and it is shown that, save for autocatalytic reactions, the combination is only optimal for sufficiently exothermic reactions.
Abstract: Some fairly general considerations arising out of the work of Cholette and Blanchet on combined stirred tank and tubular reactors are here presented. General analytical and graphical conditions for the optimality of the MT combination are given and it is shown that, save for autocatalytic reactions, the combination is only optimal for sufficiently exothermic reactions. The proportions of the optimal combined reactor can be readily calculated and it is shown that the stirred tank design is always stable. A circumstance under which the TM combination is optimal is also suggested but it is thought to be of rare occurrence. L'auteur presente des considerations tres generales qui ont ete suggerees par le travail de Cholette et Blanchet sur les combinaisons de reacteurs bien agite et tubulaire. Il donne les conditions generales, analytiques et graphiques, qui ont trait a l'optimalite de la combinaison MT et montre que sauf pour les reactions autocatalytiques la combinaison est optimale uniquement dans le cas de reactions suffisamment exothermiques. L'auteur indique que l'on peut calculer facilement les proportions de la combinaison optimale de reacteurs et montre que le reacteur bien agite est toujours stable. Il suggere un cas ou la combinaison TM est optimale mais croit que ce soit un cas d'exception.

Journal ArticleDOI
TL;DR: In this article, a method is presented for estimating the values of axial thermal conductivities at high flow rates from the existing data on radial thermal conductivity, and the necessity for considering packed bed axial conduction in design work can be determined from these results.
Abstract: Radial thermal conductivities in packed beds have been extensively studied and correlated, but there is little published work on axial conductivities. The data on axial conductivities that is available is limited to low flow rates because of measurement difficulties at high flow rates. In this paper, a method is presented for estimating the values of axial thermal conductivities at high flow rates from the existing data on radial thermal conductivities. The necessity for considering packed bed axial conduction in design work can be determined from these results. Les conductivities thermiques radiales dans les lits de particules ont deja fait l'objet d'etudes poussees, mais on trouve peu de resultats publies au sujet des conductivites axiales. Les donnees disponibles sur les conductivites axiales se limitent aux taux d'ecoulement peu eleves en raison des difficultes de mesure aux taux plus eleves. On presente dans ce travail une methode d'evaluation des conductivites thermiques axiales aux taux eleves a partir des conductivites thermiques radiales. On conclut de ces resultats a la necessite de considerer, dans l'elaboration de projets, la conduction axiale dans les lits de particules.

Journal ArticleDOI
TL;DR: In this paper, two quasi-analytical methods are given for the approximate solution of the nonlinear differential equation governing the effect of longitudinal dispersion on the concentration profile in an isothermal flow reactor with reaction orders other than zero or first.
Abstract: Two quasi-analytical methods are given for the approximate solution of the nonlinear differential equation governing the effect of longitudinal dispersion on the concentration profile in an isothermal flow reactor with reaction orders other than zero or first. The first method converts the nonlinear differential equation and its boundary conditions into a nonlinear integral equation which is solved by iteration, while the second method generates approximate solutions by considering axial dispersion as a perturbation on the reaction kinetics. By using the perturbation method a dimensionless group has been generated that is characteristic of the interaction between axial diffusion and reaction kinetics. It is also demonstrated that an axial dispersion coefficient characteristic of Taylor diffusion can be applied in the presence of a reaction of any order and that the effect of depletion of concentration by chemical reaction is to aid in the reduction of radial concentration gradients. Deux methodes quasi-analytiques sont donnees pour la solution approchee de l'equation differentielle non-lineaire relative a la dispersion longitudinale du profil des concentrations pour les reactions autres que celles du premier degre dans un reacteur a ecoulement isothermique. La premiere methode consiste dans la conversion de l'equation differentielle non-lineaire et de ses conditions limites en une equation integrate non-lineaire qui est resolue par iteration. La seconde methode consiste a creer des solutions approximatives en considerant la dispersion axiale comme perturbation de la cinetique de la reaction. En utilisant cette methode de perturbation un groupe sans dimensions, caracteristique de l'interaction entre la diffusion axiale et la cinetique de la reaction, a ete genere. II est aussi demontre qu'un coefficient de dispersion axiale, caracteeristique de la diffusion Taylor, peut-ětre applique en presence d'une reaction de tout degre et que l'effet d'amoindrir la concentration par reaction chimique est d'attenuer les gradients de concentration radiale.

Journal ArticleDOI
TL;DR: In this paper, a study was made of the kinetics of the vapor phase hydration of acetylene over a zinc phosphate-phosphoric acid-activated carbon catalyst, and a tentative mechanism was suggested which is consistent with this equation.
Abstract: A study has been made of the kinetics of the vapor-phase hydration of acetylene over a zinc phosphate-phosphoric acid-activated carbon catalyst. Rates of acetylene hydration were measured in a fixed bed flow reactor operated at low conversions. The majority of the data was obtained at 350°C. The amounts of acetylene hydrated were determined by analyzing the products for acetaldehyde, crotonaldehyde and acetic acid. The catalyst activity diminished with increasing process time. The reaction rate data obtained at low conversions of acetylene were correlated by an empirical equation and a tentative mechanism suggested which is consistent with this equation. The data obtained in the low conversion (differential) reactor have been compared to the data obtained using a fixed bed flow reactor operated at high conversions, using the integrated form of the rate equation. Une etude de la cinetique d'hydratation en phase vapeur de l'acetylene en presence d'un catalyseur de charbon active - phosphate de zinc - acide phosphorique a ete entreprise. Les taux d'hydratation de l'acetylene ont ete mesures dans un reacteur a lit fixe opere a faible rendement. La majorite des valeurs ont ete obtenues a 350°C. Les quantites d'acetylene hydratee ont ete determinees par l'analyse des acetaldehyde, crotonaldehyde et acide acetique dans les produits de la reaction. L'activite du catalyseur diminue avec une augmentation du temps de reaction. Une correlation empirique des taux de reaction obtenus est presentee et un mecanisme est suggere. Les resultats obtenus dans le reacteur a faible conversion sont compares a ceux obtenus dans un reacteur similaire opere a forte conversion.

Journal ArticleDOI
TL;DR: In this article, a procedure for computing the minimum reflux rate for multicomponent distillation systems is presented, which is applicable to both distributed and non-distributed systems.
Abstract: A procedure for computing the minimum reflux rate for multicomponent distillation systems. The equations developed apply to both distributed and non-distributed systems. The suggested method of solution is by iteration, beginning with the assumption the system will be distributed. Complete heat and material balances are carried out in the course of each plate calculation. The calculated minimum reflux rates are compared with those of other techniques. On decrit une methode de calcul du taux minimum de reflux pour la distillation fractionnee des melanges complexes. Les equations presentees sont d'ordre general et s'appliquent a tous les systemes, que leurs composants soient ou non partages entre le distillat et le residu, quoique la methode iterative de solution suggeree presuppose un tel partage. Les calculs relatifs a chacun des plateaux comportent des bilans complets de chaleur et de matiere. On compare les taux minima de reflux obtenus par calcul avec ceux que l'on obtient au moyen d'autres techniques.

Journal ArticleDOI
TL;DR: The hydraulic characteristics of a 12 in. diameter sieve plate have been studied and data are presented for plate pressure drop, clear liquid head on the plate and foam height, measured over a range of gas and liquid phase rates and outlet weir heights as mentioned in this paper.
Abstract: The hydraulic characteristics of a 12 in. diameter sieve plate have been studied and data are presented for plate pressure drop, clear liquid head on the plate and foam height, measured over a range of gas and liquid phase rates and outlet weir heights. The mass transfer performance of the plate, as expressed in terms of an equivalent number of transfer units, was measured for conditions of both gas and liquid film control over a similar range of operating variables. The number of transfer units are shown to be directly related to the appropriate phase contact time on the plate. The equations developed by A.I.Ch.E., to correct for back mixing effects on the plate efficiency, have been found to under-estimate the degree of mixing on the plate used, and hence predict lower liquid efficiencies than might be expected from a comparison with literature values. Les caracteristiques hydrauliques d'un plateau perfore de 12” diametre ont ete etudiees et les valeurs pour la perte de charge du plateau, la těte hydrostatique du liquide et la hauteur de mousse sont presentees. Les mesures ont ete etablies pour divers taux de gaz et de liquide et diverses hauteurs du deversoir de sortie. Le rendement du plateau au point de vue transfert de masse, exprime en nombre equivalent d'unites de transfert, a ete mesure pour les films contrǒlants soit liquide soit gaz pour toute la gamme des variables d'operation etudiee. Le nombre d'unites de transfert a ete demontre comme etant proportionnel au temps de contact approprie des phases sur le plateau. Selon les resultats obtenus les equations developpees par l'A.I.Ch.E. pour corriger les effets de postagitation sur l'efficacite du plateau sous-estiment le degre d'agitation sur le plateau utilise et predisent done un rendement liquide moindre que ceux obtenus par comparaison des valeurs dans la bibliographie.

Journal ArticleDOI
TL;DR: A pyrometer based on this principle was designed and constructed for measuring temperatures both in the infra-red (500-900 C) and the visible (800-1200 C) ranges as mentioned in this paper.
Abstract: The measurement of particle temperature in gas-solids suspensions by conventional pyrometric methods is complicated by a lack of knowledge of the particle emissivity and the absorption strength of the cloud. Further difficulties may be caused by background re-radiation, variations in geometrical factors and - if the particles are undergoing chemical reaction - rapid changes in the particle temperature. These difficulties can be eliminated if the radiant energies emitted by the particles at two different wavelengths (close in value) are measured simultaneously. A pyrometer based on this principle was designed and constructed for measuring temperatures both in the infra-red (500–900 C.) and the visible (800–1200°C.) ranges. The radiation from the particles was passed through suitable pairs of monochromatic filters inserted in diametrical opposition into a metal disk rotating at speeds up to 8,000 r.p.m. The two alternating beams were focused on the cathode of a photoelectric cell, and the resulting voltages measured by means of a cathode-ray oscilloscope. The instrument was used successfully in an investigation of the rate of reduction of small iron oxide particles in the presence of hydrogen at temperatures ranging from 500 to 1100°C. La mesure de la temperature des particules dans les suspensions gaz-solides, par les methodes pyrometriques conventionnelles, est compliquee en raison du manque de connaissances sur l'emissivitee des particules et sur le pouvoir d'absorption du nuage. D'autres difficultes peuvent provenir du re-rayonnement de l'arriere-plan, de variations dans les facteurs geometriques-si les particules sont soumises a une reaction chimique - et de changements rapides de temperature des particules. On peut eliminer ces difficultes en mesurant stimultanement les energies rayonnantes emises par les particules a deux longueurs d'onde differentes, mais rapporchees. Les auteurs ont elabore et construit un pyrometre base sur ce principe pour les mesures de temperature a la fois dans l'infra-rouge (500–900 C) et aux longueurs d'onde visibles (800–1200 C). La radiation en provenance des particules passait par des paires de filtres monochromatiques appropries, places en opposition diametrale dans un disque de metal tournant a des vitesses allant jusqu'a 8000 r.p.m. On dirigeait les deux faisceaux alternes sur la cathode d'une cellule photo-electrique et on mesurait les voltages resultants au moyen d'un oscilloscope a rayons cathodiques. L'instrument s'est comporte de facon satisfaisante au cours d'une etude sur le taux de reduction de petites particules d'oxyde de fer en presence d'hydrogene a des temperatures allant de 500 a 1100 C.


Journal ArticleDOI
TL;DR: In this article, the authors derived the partial coefficients of heat and mass transfer in air from and to a drying fluidized mass of silica gel, by an inspection of the relation between the two coefficients.
Abstract: The determination of the partial coefficients of heat and mass transfer in air from and to a drying fluidized mass of silica gel is given. The analogy between the two methods of transport in the bed has been studied by an inspection of the relation between the two coefficients. A correlation of these coefficients with the void fraction, the superficial velocity, the particle size and the tube diameter of the bed has been derived. This correlation has been transformed into a correlation of dimensionless groups. On determine les coefficients partiels de transfert de chaleur et de transfert de masse entre l'air et une masse fluidifiee de gel de silice, pour des echanges dans les deux sens. Les auteurs etudient l'analogie entre les modes de transfert dans le lit par inspection de la relation entre les deux coefficients. On a deduit une correlation entre ces coefficients et la porosite, la vitesse superficielle, les dimensions des particules et le diametre du tube. On a transforme cette correlation et une expression a groupes sans dimensions.

Journal ArticleDOI
TL;DR: In this paper, a square-root analogue of the Margules equation, χG = Σckx1(k-2)/2, is proposed, which satisfactorily accounts for the rapid increase in χ as the mole fraction of alcohol becomes small.
Abstract: The excess free energy of mixing (ΔGE) has been used to show that the Margules and van Laar equations are reciprocally related. Thus if the Margules equation is written as χG = ΔGE/x1x2 = Σakx1k, then the van Laar equation can be written as χG−1 = Σbkx1k. It is known from previous work that the Margules equation does not adequately represent the thermodynamic properties of solutions of alcohols in non-polar solvents over the whole range of composition, and it is pointed out that the van Laar equation cannot be used if the excess function changes sign. In such cases the use of a square-root analogue of the Margules equation, χG = Σckx1(k-2)/2, is proposed. This equation satisfactorily accounts for the rapid increase in χ as the mole fraction of alcohol becomes small and is empirically useful. However, it has theoretical disadvantages; it cannot be used to determine by extrapolation the value of the partial molar excess thermodynamic property for component 1 in an infinitely dilute solution; furthermore, it predicts a violation of the second law in the case of free energy of mixing for solutions dilute in component 1, but the region of violation lies outside the experimental range for x1 as low as 0.01.

Journal ArticleDOI
TL;DR: In this paper, the authors show no simple relation between the various sulphite oxidation rates and the transfer coefficient for oxygen from air to fermentation media, and show no relation simple entre the differents taux d'oxydation des sulfites and le coefficient de transfert pour l'oxygene, de l'air au milieu de fermentation.
Abstract: Sulphite oxidation rates using several metal ions as catalyst in four types of contacting equipment have been measured over a considerable range of agitation levels. The data show no simple relation between the various sulphite oxidation rates and the transfer coefficient for oxygen from air to fermentation media. On a mesure les taux d'oxydation de sulfites a des niveaux d'agitation tres varies, en utilisant plusieurs ions metalliques comme catalyseurs, dans quatre types de contacteurs. Les resultats ne permettent pas d'etablir une relation simple entre les differents taux d'oxydation des sulfites et le coefficient de transfert pour l'oxygene, de l'air au milieu de fermentation.

Journal ArticleDOI
TL;DR: In this article, a study was undertaken to confirm and extend available information on the inflammable limits of ammonia in air or oxygen-nitrogen mixtures, and particularly the effects of water vapor on these limits.
Abstract: A study was undertaken to confirm and extend available information on the inflammable limits of ammonia in air or oxygen-nitrogen mixtures, and particularly the effects of water vapor on these limits. Such information should prove helpful in the prevention of explosion in equipment handling these gas mixtures, for example in the autoclaves for leaching of nickel sulphide concentrate under pressure, with ammonia and compressed air. Flame-quenching technique was used for determinations at atmospheric pressure, and the dynamic bomb method at ten atmospheres. At atmospheric pressure, the inflammable limits of ammonia in dry air were found to be 17.2 and 30.2% ammonia, but these limits were found to narrow as the water vapor is increased, until at 10.8% H2O and 20.8% NH3 no flame could survive. With a dry oxygen-ammonia mixture, the lower limit was found to be 15.2% ammonia. At ten atmospheres, the explosive limits of ammonia in dry air were found to be 16.9 and 28%, and these limits were narrowed with addition of water vapor until, above 9% water, no explosion occurred. Une etude a ete entreprise pour confirmer et accroǐtre les resultats existants sur les limites d'inflammabilite de I'ammoniac dans l'air ou de melanges oxygene - azote et plus particulierement des effets de la vapeur d'eau sur ces limites. Ces renseignements seront d'utilite pour la prevention d'explosions dans l'equipement utilisant ces gaz, tel les autoclaves pour la lixiviation sous pression de concentres de sulfure de nickel avec I'ammoniac et l'air comprime. La methode par extinction de la flamme a ete utilisee a pression atmospherique et la methode dynamique, a 10 atmospheres. A pression atmospherique les limites d'inflammabilite dans l'air ont ete trouvees comme etant 17.2 et 30.2% ammoniac; ces limites diminuent avec une augmentation de la quantite de vapeur d'eau et a 10.8% H2O et 20.8% NH3 aucune flamme ne subsiste. La limite inferieure est de 15.2% ammoniac avec le melange sec oxygene - ammoniac. A 10 atmospheres les limites explosives de l'ammoniac dans l'air sec sont de 16.9 et 28% et ces limites ont ete reduites par l'addition de vapeur d'eau; au-dessus de 9% d'eau aucune explosion n'a lieu.