Showing papers in "Chemical Engineering in 1958"

Mixing Characteristics of Irrigated Packed Towers

Abstract: Mixing characteristics of flow reactors were studied, Using irrigated packed towers to make clear dynamic characteristics of reactors, flow mcchanisms of fluid and holding time of fluid in reactors, The method employed in our study was the residence time curve method, the commonest one employed in such a case.An equation for the residence time curve, with the boundary conditions suitable for these irri- gated packed towers, was analytically derived from the concepts of the mean velocity and the apparent diffusivity, as suggested and used by Dankoler3), Gilliland5), Danckwerts2), and Yagi11), in the course of studies of flow through tubular reactors, fluibized beds, and multistage agitated tanks.The results of the residence time curve equation thus obtained were compared with the data derived from the experiments with the irrigated packed towers whose total holdup had been measured. The region in the irrigated packed towers in which our investigations were centered, in connection with the mixing characteristics of the liquid holdup, was where the models of the mean velocity and the apparent diffusivity were reasonably applicable.Fig. 1, Table 1 and Table 2 show the apparatus and the dimensions of packings and towers used in these experiments. With this apparatus, the total holdup and the residence time curves, from which the values of M (Table 4) were determined by means of Eq. (7), were obtained under various conditions, either with or without gas flow.The conclusions derived from the experimental data illustrated in Figs. 2, 3, 4, 7, 8, 9 and 10 are as follows:1) Operating characteristics of liquid hold flowing in a packed tower are specifed by the mean flow velocity, u=L/θ=L/(Qt/F), and the dimensionless group, M=uL/2E, which represents the mixing characteristics of liquid flow.2) By Eqs. (12) and (15), the operating holdup without gas flow, Hop, and the apparent diffusivity, E, are respectively well correlated with the mean liquid velocity, u. A simplified method is proposed for estimating the static holdup, Hst, by the use of mean liquid velocity, u, instead of superficial liquid velocity; that is, by means of extraporating observed values of Ht relative to u=0; obtaining excellent results, as shown in Table 3. This is because Ht and u are linear correlation represented by a straight line, as illustrated in Fig. 3.3) The values of M in the case of irrigated packed towers, as listed in Table 4, are very high as compared with those in other types of flow reactors, indicating that the liquid flow in a packed tower closely resembles the piston flow, the more so, by increasing the length of the packed bed and the mean velocity of liquid and decreasing the diameter of packing.

Mass Transfer from Particles to Fluid in Packed Beds

Abstract: Mass transfer rates from solid particles to water in packed bed were measured for spherical and cylindrical β-naphthol particles.Data at low water velocities show that Sh tends to approach 2.0 with decrease of Rep, as shown in Fig. 2. The effect of Sc on Sh was examined and plotted as in Fig. 4. It was found that Sh-2 was proportional to Sc1/3.The present data and the previonsly published data of other investigators for spherical and cylind rical particles are shown in Fig. 5. The solid lines drawn in the figure correspond to the equations:(3)(4)The data for flakes11) and broken solids4), which are shown in fig. 6 for the experimental range of Rep>1, agree with the results obtained from Equations (3) and (4).

Motion of Water in a Hydraulic Cyclone

Abstract: Studies were made on the velocity distribution of water in a hydraulic cyclone, by taking photographs of the loci of polystyrene particies floating in the water, in various horizontal and vertical sections.For the measurements of the absolute velocity, two spot lights were obtained by means of a special stroboscope at certain definite time intervals. Based on these photographs we have calculated tangential, radial and vertical components of velocities in various positions. For the radial velocity calculation, we have taken into account possible errors due to the centrifugal force and the density difference, when ρp=1.03 and dp=70μ. The cyclone consisted of a cylindrical part, 79mm in inner diameter, 154mm in height, and 15° in angle of its conical part.With the tangential component (Figs. 5 and 6), two domains were found to be existing, represented by Eqs. (6) and (7), just like in case of a gas cyclone. The exponent of r in Eq. (7) increased up to a unity according as the position of the cyclone went downward. As for the radial velocity, remarkable fluctuations, unsymmetries and secondary flows were observed (Figs. 7, 8 and Table 3). On the average, however, as in Fig. 9, an inward velocity zone was found both near the wall and the central air column, between them existing an outward velocity zone. There were fluctuations in the vertical velocity. When all overflow happened (R=0), there was a downward flow near the wall and upward flow within, no maximum being observed. On the other hand, in case R=1, there was a downward flow near the air column, causing a maximum upward velocity, as a consequence. When R=1/6, the flow in the upper part resembled the flow in case R=0, while in the lower part, it resembled the flow in case R=1.The material balance of the water passing through the horizontal section was calculated, as well.

Mass Transfer between Drops of Organic Solvents and Water

Abstract: In the previous paper3), it was reported that the rate of mass transfer between drops of organic solvents and water was reduced by the addition of some substances. In the present work, a study on the rate of extraction from drops of organic solvents to drops in pure systems has been made paying special attention to these poisonous substances. For butylacetate, -IPE-and MIBK-water systems which are not liable to be contaminated easily, results agreed approximately with the published data (Table 2), but the observed Kd values were much larger than the published data for the benzene-water system (Table1). This discrepancy between the author's and the published data cannot be accounted for by any experimental errors. It seems likely that it is due to difference in purity of the benzenes, solutes and waters used and to the resultant contamination by trace quantities of poisonous substances.The observed Kd values were largest at the beginning of free rise, and they decreased when the height of rise increased due to the transfer of acetic acid or propionic acid whose distribution favors water.The observed Kd values for 24 systems (3 solutes and 8 solvents) were compared with the predicted Kd volues which were calculated by Eq. (3) for kd and ke (Fig. 8). The over-all mass transfer coefficients for non-contaminated systems can be approximately predicted by Eq. (3), but further studies with due attention to poisovous substances will have to be carried out to obtain more accurate correlations.

Mass Transfer to Single Spheres

Abstract: Studies were made on the rate of mass transfer to single spheres, with the aid of a diffusioncontrolled electrode reaction:Microelectrodes used as anode were platinum spheres having 1.66mm and 2.74mm diameters respectively, each with PVC-coated platinum wire of 0.6mm diameter. The reference electrode used as cathode was a thin platinum plate of 50×120mm. The experimental apparatus employed was as shown in Fig. 1. To obtain uniform distribution of liquid velocity over the entire column cross-section, glass beads of 5mm diameter were packed to a height of 30mm, topped with 10 sheets of Saran screen of about 12 meshes. Below the packing and 8mm above the spherical electrode, a Saran screen of about 150 meshes was placed.From the measurements of limiting current 6), 8) at various liquid flow rates, the mass transfer coefficients, kf, were calculated by the equation:kf=i/nFAc (7)The experimental results are shown in Table 1. It was found that neither the results thus obtained nor those by previous investigators3), 9), 10), 14), 16) showed good agreements with the Ranz-Marshall's eq. (2)14).Thereupon, assuming that the empirical equation might be presented as:Sh-2=kRepScq (8)the authors determined the values of the constants k, p and q (Figs. 3, 4 and 5), obtaining an equation:Sh=2.0+0.52Re0.54Sc0.35 (9)The value of the exponent of the Schmidt group, 0.35, agrees well with 0.348 obtained by Frossling3) from his experimental data.

Solubilities of Chlorine in Concentrated Sodium Chloride Solution

Abstract: A study was made of the effect of P, N, T and pH on the solubilities of chlorine in concentrated sodium chloride solution.The experimental range of P was from 0.1 to 1.0atm, N from 210 to 300g/L, T from 303 to 343°K (from 30 to 70°C), pH from 1 to 5. The results obtained of the solubilities which might be cosidered the sum of [Cl2(aq)], [Cl3-] and [HClO] were as follows:The effect of pH on [HClO] is given by Eq. (5). In the range of pH less than 3, where [HClO] is found to be approximately negligible, the relation between solubilities and P is explained by Henry's law, [Eq. (10), ] and the effect of N by Eq. (11). Hence, calculation of the solubilities of unhydrolyzed chlorine in th pH range given above are made by means of the following empirical equation:where P=0-1.0, N=200-300, and T=303-343.This value can also be obtained graphically by employing the nomograph of Fig. 10 which is prepared from the above equation.

Studies on Liquid Entrainment

Abstract: Bursting of gas bubbles was experimentally studied, using the liquids listed in Table 1. Large drops were caught on a slide coated with a mixture of vaseline and light mineral oil, and the diameters of the drops were measured through a microscope.The relation between the diameter of the gas bubble and the height which the drops entrained above the gas-liquid interface is shown in Figs. 3, 4 and 5, and the relation between the diameter of the gas bubble and the diameter of the drops is shown in Fig. 6. The velocity of the rising drops was calculated from Eq. (3).In the next stage, a general theoretical formula was derived for the case in which several drops were formed from a single bubble:where, N is the number of drops. Comparison of the theoretical values of the velocity of drops with the experimental data shown in Fig. 9 may verify the adequacy of the above equation, except for the case of liquids with high viscosity.A natural circulation type evaporator for radioactive liquid waste disposal was constructed, and overall decontamination factor was obtained. The factor ranged over 105 to 107 for vapor mass velocities of 200-3, 000 kg/mm2hr as shown in Fig. 12.

On the Characteristics of a Centriclone

Abstract: A centriclone is a dynamic combination of a conventional liquid cyclone and a centrifuge. To produce the required circular velocity, an internal impeller is employed instead of a tangential orifice inlet and feed pressure.In this study, the characteristics of a centriclone were investigated. First, we examined the velocity distribution inside the centriclone with a single hole Pitot tube. Then with the experimental arrangement as shown in Fig. 8, we studied the separating characteristics of the centriclone for Al (OH)3 slurry of 2-10 weight% conc.The results obtained were as follows:(1) As shown in Fig. 4, the tangential velocity in the zone of outer vortex is almost constant, and the inner vortex has a constant angular velocity like a rigid body. From the study of the velocity distribution, experimental equations such as Eqs. (3) and (4) have been obtained.(2) The turning point of flow from outer downward vortex to inner upward one is independent of the rate of feed, but it is influenced by flow ratio rf, and can be expressed as Eq. (2).(3 ) The effect of rotating speed of the impeller on concentration ratio rc under different conditions are shown in Figs. 11, 12, 14 and 15. In all cases, rc increases with the increase of N.(4) From the effect of the type of impellers on rc, the impeller with a small pumping capacity has been found best to serve the purpose, as shown in figs. 11 and 12, when the flow rate of feed is small, but as the feed rate increases, the impeller with a larger capacity becomes more useful.(5) When flow ratio rf is reduced, underflow of higher concentration is obtained as shown in Fig. 13.(6) Theoretical consideration of the size of the particles, all of which can be caught in heavy liquid, has led us to derive the follcwing equationwherex thus obtained is proved to be a close approximation to d50 determined experimentally.

How to estimate engineering properties to get viscosity for a gas mixture

Abstract: The various estimation methods with which mixture viscosities may be calculated from known purecomponent viscosities are given. Separate treatment for low- and high-pressures is given. (T.R.H.)

Some Physical Proerties of Methanol-Water Solutions at Various Temperatures up to the Boiling Point

Abstract: Specific gravity, viscosity and surface tension of methanol-water solutions at various temperatures were measured up to the boiling point and arep resented in Tables. The refractive index of the same solutions at 30°C is also given.In measuring specific gravity, the pycnometer method was used with due corrections for higher temperatures. Viscosity was measured using the Ostwald viscometer and the surface tension by the capillary rise method, both with due precautions necessary for higher temperatures. The refractive index was obtained using a dipping refractometer equipped with a sodium lamp and a thermostat.

Air-cooled heat exchangers

Abstract: The advantages of air as a coolant are generalized, and information useful for determining approximate surface, operating power, plan area, weight and prices for air-cooled heat exchanger applications is given. (T. R. H.)

Effects of AdditiVes on Extraction from Droplets in Liquid-Liquid Systems

Abstract: It was recently found by Carner4) (with nitrobenzene-water system) and Terjesen6-8) (withCCl4-water system) that an addition of a very small amount of surface active agents decreased the extraction of acetic acid from droplets of organic solvents.The authors carried out the experiment with 8 organic solvents to determine what surface active agents worked as poisonous substances for them. The results revealed that the range of poisonous substances for these organic solvents covered not only the surface active agents as shown by Carner and Terjesen but also other high molecular substances (cf. Tables 1 and 2). Moreover these poisonus substances were found to possess elective affinity, which was particularly obvious in polyethylenglycol (PEG mol wt.≅4000). Generally speaking, benzene, toluene, hexane, heptane and cyclohexane were easily contaminated with the poisonous substances, while butylacetate, isopropylether and methyl-isobutylketone were relatively not so.Photographs were taken by schlieren method, with the apparatus shown in Fig. 2, to make clear the mechanism of solute transfer. Fig. 7-I-a, II-a, III-a and IV-a show acetic acid transfer to pure water and Fig. 7-I-c, II-b, III-b and IV-b, to additives-containing water, In the latter group, but not in the former one, vortex ring motions were clearly observed behind the drops. Generally such a vortex ring was observed when the rigid sphere moved in a fluid at Re>25, so it was naturally supposed that the contaminated droplets were of stagnant sphere. Values of C2/C1 observed of the most contaminated drops of several solvents were compared with those calculated of rigid sphere by means of Ep. (3) as shown in Fig. 8 and Table 3. They showed good agreement in butylic acid (where m is small) transfer as well as acetic acid transfer, revealing that kc is very large in comparison with kd in the period of free rising.It was also found that the mechanism of transfer was effected even by the most purified solute, as well Fig. 7-V is a schlieren photograph of heat transfer from the pure benzene drop (none solute) to pure water, which is different from solute transfer shown in Fig. 7-I-a. Consequently we may safely conclude that the mass transfer from droplets in liquid-1iquid system where solute is contained is different, in mechanism, from the heat transfer from droplets in liquid-liquid system where no solute is contained, and that the method of Colburn and Welsh, in which, in order to obtain the data on individual coefficients, two pure liquids of limited solubility are contacted in the abscnce of a third solute, cannot be applied to the study of mass transfer from droplets.It is proposed that, in practice, when the contamination is unavoidable, PEG aqueous solution (0.2 -1%) should be added to water phase for the purpose of increasing the extraction rate, whichever side of the phases might be contaminated with poisonous substances.

Studies on Axial Turbulent Diffusion Coefficient in Water-Fluidized Beds

Abstract: The mixing characteristics of the fluid flowing through reactors are industrially important for the purpose of designing reactors and estimating the yield of the product. Recently several studies have been made on the mixing characteristics of the homogeneous and heterogeneous reactors. These mixing characteristics usually cover the field of turbulent diffusion whose coefficient is obtained on the assumption that the turbulent mass diffusion is superimposed on the convective flow with the uniform velocity.Studies on fluid mixing in the fluidized bed were made by Wilhelm et al for the liquid-solid system and by Gilliland et al for the gas-solid system. Wilhelm et al4) measured the turbulent diffusion coefficient by measuring the spreading of the methylene blue dye from a point source in water-fluidized bed of glass beads. Gilliland et al carried out the diffusion experiment on helium gas from a point source2), and employed the technique of the residence time curve3) for the fluidized bed of gas-solid system.The present authors have obtained the axial turbulent diffusion coefficients by measuring axial concentration gradients in the water-fluidized beds of β-naphthol cylindrical particles.When the concentration in the bed is very small as compared with the saturation concentration, the dissolution rate approximates to the zero-order reaction as expressed by Equation (1'). By using the boundary conditions at the inlet and outlet of the bed, that is by using Equations (2) and (3), Equation (4) can be derived from Equation (I').The experimental apparatus used for this work is shown in Figure 1. The inside diameter of the column is 52.1mm. City water is used as the fluid. The water, before entering the fluidized bed, passes through the calming section of fixed bed packed with glass beads. The water in the fluidized bed is slowly taken out by means of the injectors thrust along the tube wall at intervals of 5cm. The concentration of this water is measured by the spectrophotometer at the wave length of 2, 735 A and 2, 850 A.From the measured concentration gradients, the axial diffusion coefficient Ez is calculated with the help of Equation (4) at three points: η≡l/L=1/4, 1/2, 3/4.The results derived are presented in Table I, Figures 2 and 3. Figure 2 shows the relative axial Peclet number (Pe=Dpμ0/Ez) plotted against fractional void e, and the relative Pe vs. Rep is shown in Figure 3. From these figures we know that the turbulent diffusion coefficient Ez increases with the increase of fractional void and reaches the maximum value of about 70cmcm2/sec in this system.

On the Mechanism of Jet Pulverization

Abstract: Pneumatic pulverizers have come to be used widely in chemical industries for ultra fine pulverization, but it is very hard to analyze their characteristics quantitatively. We tried, by experiment, to analyze the mechanism of a jet pulverizer, which is expected to be one of the most efficient pneumatic finepulverizers.Thinking that in the mechanism of jet pulverization, suction of particles by jet was essential, we used a simple jet-suction pulverizer shown in Fig. (2-1), and found the relation between the suction of particles and the nozzle pressure relative to other factors, as given by Eq. (3·1). As to grinding, the relation between the rate of pulverization and the nozzle pressure was discovered as presented by Eq. (4·4), which is closely related to Eq. (3·1).Constant kj was defined to be grindability of pneumatic pulverization, which is completely independent of sizes of particles fed, and it was found that kj was closely related to the size distribution pattern of the pulverized material and that such characteristic of the material was clearly indicated by coefficient n, which represents the degree of surface grinding. When n=2.0, the mechanism of pulverization was defined as surface grinding, and when n=0, as bulk crushing (See Fig. 4-3). We believe that this analysis of mechanism will be widely applicable to the other sorts of grinding as well.Further, we experimented in impact jet pulverization by a couple of jets crossing each other (Fig. (7-1)) and obtained the results as shown in Fig. (7-2, 7-3). Another experiment led us to make clear the effects of secondary air on the suction of particles and on pulverization as shown in Fig. (6-2).

Studies on Through-flow Drying of Viscose Staple Fibers

Abstract: The mechanism of through-flow drying of viscose staple fiber was studied under various drying conditions and the experimental results were summarized as shown in Table 1. The experimental equipment employed was the same as illustrated in our previous report.1)Kinds of viscose staple fibers used are as follows:Crimp staple fiber, 1.5 denier×11/8" cutCrimp staple fiber, 2.0 denier×2" cutCrimp staple fiber, 5.0 denier×3" cutBright staple fiber, 1.5 denier×11/8" cutThe correlation of drying data, as expressed by a drying-time curve and a material-temperature curve, is illustrated in Fig. 1, and the effects of various factors on the drying rate are summarized in Figs. 2-5. Observcd pressure drops through beds of staple fibers are plotted in Fig. 6, which, again, are expressed by the follpwing equation:ΔP=30υg1.77 (1)where the depth of bed is 10cm.Mass transfer capacity coefficients calculated from the experimental data are plotted in Figs. 7 & 8, and are expressed as the functions of mass velocitv of air and size of thread.kGa=9.25G0.8D-0.27 (2)

The Mechanism of Freeze-drying

Abstract: In order to throw light on the mechanism of freeze-drying and to obtain fundamental design for that process, experiments with market milk were carried out from the standpoint of chemical engineering research.The experimental apparatus used are schematically shown in Fig. 1, and the results obtained are summarized as follows:(1) As illustrated in Fig. 2, the typical freeze-drying process can be divided into four stages, namely, i) the primary stage, ii) the steady stage characterized by constant drying rate, iii) the first stage, and iv) second stage, each characterized by decreasing drying rate.(2) As the process goes on, the frozen sample comes to be divided into two distinctive layers, i.e., the ice layer and the dried porous one, each having a temperature markedly different from that of the other, as shown in Fig. 6. (See also Fig. 12.)(3) There is a linear relationship between the drying rate and the heating rate, as shown in Fig. 8 and by Eq. (1). In this, the heat coming from the outsystem must be considered, as it causes the experimentally observed values of the drying rate to be greater than the theoretical ones, when the heat supply is small.(4) The drying rate per unit area is found to be constant, namely, to be independent of the area of the vessel, when the area is larger than a fixed value, 100cmcm2 or so. On the other hand, when it is smaller than 100cmcm2 or so, the drying rate is affected by the area of the vessel, as shown in Fig. 10.(5) In most cases, the heat coming through the side walls of the vessel has influence on the temperature distribution in the frozen sample, and the outer said of the sample is more rapidly dried than the inner side of the sample.Fig. 12 indicates the presumed profile of the sublimation surface, which is affected not only by the heat coming through the side walls, but by the cracks developed during the process, as well as by the thermocouples inserted in the sample.

Atomic-age metal extraction

Abstract: S>Processes for the separation of U, Zr, Hf, Co, Ni, Mn, Fe, V, and Ti from their ores are discussed from the standpoint of the chemistry and metallurgy involved. (W.L.H.)

Discharge Coefficient of a Nozzle in Centrifugal Field and Its Application to a Disc-type Centrifuge

Abstract: Theoretlcal and experimental studies on discharge coefficient of a small nozzle in centrifugal field were carried out, and its result was employed to determinc angular velocity of liquid which flows between discs of a disc-type centrifuge.The results obtained were summarized as follows:(1) The discharge coefficient based on the experimental results is calculated by:(2) The discharge coefficient in centrifugal field is identical with that in gavitational field concerning the same nozzle.(3) In the case of high Reynolds number above 3, 000, the discharge coefficient is considered to be nearly constant.(4) The average angular velocity of liquid which flows between discs through a nozzle with a known discharge coeffiiient is expressed by:(5) The angular velocity of liquid between discs is considered to be approximately equal to the angular velocity of a bowl, independently of the flow condition, number of revolution of the bowl and distance between the two adjacent discs.

Unsteady State Heat Transfer in Stationary Packed Beds

Abstract: Taking into consideration the temperature gradient within the solid particles, new solutions were given by way of differential equations describing unsteady state heat transfer in the stationary beds of granular solid particles, and these were compared with the results of the experiments performed at the Nu number, (Dph/λ)=0.2-2.0.The final differential equations obtained are as follows.Eq.(12):Eq.(25):These equations were solved numerically under the boundary condition shown in Eq. (13) and (26').The results are shown in Fig. 2, 3 and 4.These are easy in practical applications and agree satisfactorily with the experimental data as shown in Figs. 7 and 8.

How environment directs corrosion control

Abstract: A general discussion of the cause and inhibition of corrosion is presented. The considerations include the effect of Ph in relation to oxygen concentration, protective films, hydrogen overvoltage, and metal ion concenemperature effects, stream velocity effects, biological functions of inhibitors are discussed, pointing out that selection for a particular sysam is largely trial and error. Finally, the applications of cathodic proaction are described. (J.R.D.)

Nuclear power future

Abstract: An evaluation is made of the future of commercial nuclear power. The conclusion is that not before 1965 will nuclear electric power be competitive. (JSR.)

Influences of the Physical Properties of Powders upon the Mixing Degree and Mixing Speed of Several Types of Mixers

Abstract: In our previous papers, we reported on the optimum operating conditions of several types of mixers, [twin-shell (V-), double-cone (DC-), cubic (C-) and horizontal-cylinder (HC-) types] for one pair of dry powders, Na2CO3-polyvinyl chloride.In this paper, we make reports of our examination of the influences of the physical properties of powders upon the mixing degree and mixing speed of several types of mixers, as to several powders shown in Table 2 and several pairs of powders shown in Table 1.What were made clear by our experimental results are:1) With the same type and size of mixers, the optimum rotational speed of the mixer Nop(=Ns, σ) and the charged volume of the powder (Fb/V)op are constant for all pairs of powders having the same particle size distribution (as shown in Table 1).2) The influences of the physical properties of powders upon the mixing degree and mixing speed are described by the difference of characteristic constant CR (obtained by Equation 7 or Fig.3) of both powdersa) As ΔCR increased, the values of σs increased as shown in Fig. 7.b) As to the mixing degree, V- & C-type mixers are not suited to the mixing of the powders whose ΔCR is big, while HC- & DC-type mixers are recommendable for the mixing of the powders whose ΔCR is big.c) As to the mixing speed, a good mixing speed is expected of V- & C-type mixers for the mixing of the powders whose ΔCR is big, as shown in Fig. 7 and Table 3.

How oxidative corrosion occurs

Abstract: A review of the fundamental principles of electrochemistry is presented. The application of these principles to oxidative corrosion, including patterns of attack. are discussed. (J.R.D.)

Sodium-reduction route yields titanium

Abstract: A flowsheet for the commercial production of titanium sponge by the reduction of TiCl/sub 4/ with Na is given. (J.S.R.)