The flow of non-Newtonian slurries through fixed and fluidised beds

Measurements have been taken of the flow rate, pressure drop and bed height characteristics when non-Newtonian slurries flow through fixed and fluidised beds of uniformly sized spherical particles.In the case of fixed beds, the pressure drop-flow rate data has been interpreted using the capillary model of a porous medium together with rheological data for the slurries obtained from a tubular viscometer. The resulting friction factor-Reynolds number relationship is

This correlation was used to satisfactorily predict the minimum fluidisation velocity for a given solid/liquid system by equating the pressure drop to the net weight per unit area of particles in the bed. However, the correlation was not adequate for the prediction of bed expansion in the fluidised state. For systems which have a Reynolds number at minimum fluidisation, Re′_mf′ less than 40 an effect of particle diameter to bed diameter was observed. For systems having Re′_mf >40 the velocity, υ, and voidage, ?, were related to their values at minimum fluidisation by

It is therefore clear that, in the fluidised state, the capillary model does not present an adequate basis for the prediction of bed expansion.     

A quantitative analysis of the mixing of two segregating powders of different density in a gas-fluidised bed

The mixing/segregation behaviour of binary mixtures of powders differing in density has been studied experimentally. The mixing index M can be related to the fluidising velocity U by means of the logistic equation:

where

U_TO in the gas velocity at which M = 0.5, and U_F is the lower of the two minimum fluidisation velocities. U_TO, the take-over velocity, is related to the size, density, shape and proportion of the two powders and the bed aspect ratio. A complex empirical equation including all these factors has been obtained.If there is no density difference between the powders, the logistic equation can still be used provided U_TO is evaluated experimentally.     

Prediction of bubble size in a gas fluidised bed

It is shown that existing data on bubble size (when this is not restricted by the vessel dimensions) can be described by

where (U — U_mf) is the excess gas flow, h is the height above the distributor and h₀, a measure of the initial bubble size, characterises the distributor. h₀ is effectively zero for a porous plate but may be more than a meter for large tuyeres.     

Heat transfer from immersed surfaces in liquid fluidised beds

Heat transfer data were obtained using a small electrically-heated simulated plate immersed in a liquid—fluidised bed. For steel balls and for spherical and cylindrical particles of glass fluidised by dimethyl phthalate, two correlations valid over the voidage range 0.40–0.85 were obtained; one was based on the Reynolds number (Re₀), involving the particle diameter and its terminal falling velocity, and the other on a modified Reynolds number (Re_m) incorporating the interstitial velocity and the volume: surface ratio of the voids.

and

In the above eqns, St is the Stanton number, J_h the Colburn heat transfer factor and e the voidage. K is a constant depending on the properties of the solid particles.     

Studies on frequency and magnitude of fluctuations of pressure drop in gas—solid fluidized beds

The characteristic frequency f and magnitude of maximum pressure drop fluctuations δ in gas—solid fluidised beds have been experimentally determined using a computerised data processing system. Correlation of the above parameters to solid properties and flow conditions by linear regression analysis results in the following empirical equations (c.g.s. units):

A simple equation relating δ to the bubble diameter is also proposed:

The correlations are valid for the group B solids of Geldart's classification.     

The nature of the flow just above the perforated plate distributor of a gas-fluidised bed, as imaged using magnetic resonance

Flow patterns within a 3D bed of oil-containing seeds fluidised by nitrogen have been observed for the first time using magnetic resonance imaging (MRI). Attention was focused on the lower region of the bed, just above the multi-orifice distributor: the orifices were 1.0 or 1.5 mm in diameter with square or triangular layouts, of pitch 7-10 mm. Two sizes of seeds were used: 1.2 and 0.50 mm. Each MRI image was a time-average over and measured the local concentration of seeds. Values of U/U_mf were in the range 0.0-3.6, where U is the superficial gas velocity and U=U_mf at incipient fluidisation. The images revealed:

(1)

There was a substantial ‘jet’ above each orifice in the distributor, remarkably these ‘jets’ were found even when U?U_mf. The length of a ‘jet’ increased with U/U_mf. Because of the time-averaged nature of the measurements, a ‘jet’ could be: (a) a permanent void, (b) a stream of bubbles, or (c) a ‘jet’ followed by bubbles.

(2)

When U/U_mf<1.0, the particles surrounding each ‘jet’ were in motion. This was apparent, particularly as U/U_mf approached 1.0, even though the bed was not fully fluidised at all points.

(3)

When U/U_mf>1.0, the upper parts of the ‘jets’ merged with each other forming a central dilute core. For the first time, a time-averaged velocity map over a horizontal plane was obtained; it demonstrated that the central core was rising upwards and that the surrounding material was descending.

(4)

Between each pair of ‘jets’, there was a small region of motionless particles sitting on the upper surface of the distributor, forming a fixed dead zone. A criterion for the maximum pitch of the orifices, to minimise the volume of this dead zone between pairs of ‘jets’, has been derived.

Simple correlations between dimensionless groups summarise the measurements well, giving the length and half angle of a ‘jet’ in terms of the gas velocity and other variables. These correlations are consistent with published results and include a dependence on the pitch of the orifices, which was found to be important.     

Mass transfer in fluidised bed electrochemical reactors

Electrochemical mass transfer experiments involving the cathodic deposition of copper from aqueous solutions containing H₂SO₄ have been performed for two distinct cases. (a) Determination of mass transfer rates at a plane wall electrode in the presence of a fluidized bed of inert particles (glass beads). In this work bed height, bed size and fluidization conditions have been varied and a correlating equation:

is suggested as applying over the range

Comparison is made with mass transfer data of several other authors, revealing considerable variance. (b) Determination of mass transfer rates between electrolyte and particles within an active bed of fluidized conducting copper particles. Analysis of the data yields a correlating equation:

in the range

This compares very well with another source for electrolytic fluidized bed mass transfer, but is somewhat lower than other equations for particle to fluid non-electrolytic mass transfer.     

Lösungsthermodynamik von FeCl2 und NiCl2 in mischschmelzen aus zwei alkalichloriden oder alkali- und erdalkalichlorid

The excess chemical potential (μ^E) and the partial heat of solution of FeCl₂ and NiCl₂ in molten mixtures of chlorides were determined at 820 and 920°C for diluted solutions by emf-measurements with Galvanic cells of the type

An average cationic potential

is defined and used to fix a common ionic radius and distanceparameter

for the mixed solvent. There exist correlations of the type

and the corresponding constants are tabulated.     

Entrainment of air into liquids by a high speed continuous solid surface

The paper reports a wide range of experimental data on air entrainment velocities and apparent dynamic contact angles, were a continuous surface entersThe main dimensional correlation took the form:

for variables in the range:

However, due to the limited range of fluid densities used (0.785-1.26 * 10³kg.m³), a simpler correlation for air entrainment velocity was found

for the case of the entrainment of air by a plunging solid surface where 0.2 <(ηs/η9u)>< 3.2m.sec^-1 was found to be the corresponding rThe critical capillary number Ca_c was found to lie in the range 0.2 <Ca_c< 1.26 which agrees very well with a recent study due to GuThe investigation also showed that anomalous behaviour could occur with charged surfaces or surfaces with significant roughness. Surfactant type was al     

Effect of gamma radiation on the chlorine overvoltage at a titanium anode provided with an active film of RuO2 and TiO2

High-dose gamma irradiation of electrodes provided with an active film consisting of 5 mol. % RuO₂ and 95 mol. % TiO₂ may produce electrodes whose chlorine overvoltage at 60°C in a solution containing 300 g NaCl per dm³ conforms to the relation

for

A ⁶⁰Co source and doses about 4.9.10⁵ C kg^?1 (1.9 GR) were used. The gamma radiation has a positive effect of short duration in that it decreases the chlorine overvoltage, especially at higher cds. In the course of time the chlorine overvoltage of irradiated electrodes will increase beyond the values obtained with untreated electrodes.     

Theory of spectroelectrochemistry under galvanostatic conditions—II. Irreversible and quasi-reversible simple charge transfer reactions

This paper deals with a new mathematical formulation of methods for spectroelectrochemical examination of irreversible

and quasi-reversible

simple charge transfer reactions on planar electrodes under conditions of semi-infinite linear diffusion making use of electrolysis under galvanostatic conditions. It is a continuation of previous theoretical considerations published in Part I of this series. The principal equations relating to electrode potential and transition absorbances of the spectrally monitored species O or R are derived. A possibility of determining the parameters of electrode process from measurements by transmission or reflection spectroscopy methods is presented.     

Metal catalysed oxidative coupling of mercaptan-containing poly(dimethyl siloxanes)

The oxidative coupling of mercaptan-containing poly(dimethyl siloxane) polymers:

catalysed by different metals has been studied. In the presence of excess oxygen, the kinetics obey the law, $\text{d(SH)}\text{d}\text{t}\text{= ?k(}\text{SH}\text{)}{}^{\mathrm{n}}$, where n = 0 or 2 dependent upon temperature and the specific metal. The rate constant, k, is independent of x and y in the range studied but is a function of the metal. An activation energy of 18.4 ± 0.6 kcal/mol was found. It is postulated that the following sequence of reactions occurs:

Depending upon the metal and temperature, desorption (step 3) or reaction (step 2) may be the ratelimiting step. Steps (3) and (4) may occur simultaneously. Metals for which no oxidation/reduction couple exists show little catalytic effect even though a strongly bonded interfacial layer is formed. The interfacial layer which formed rapidly was studied via reflection spectroscopy and protective ability. It is strongly bonded, of low critical surface energy and consists primarily of:

However, it is enriched in sulphur over the bulk polymer.     

Ionic mass transfer by free convection with simultaneous heat transfer

Rates of electrochemical mass transfer by free convection under the influence of simultaneous thermal free convection have been measured for upward facing horizontal disc electrodes. The electrode reaction was the cathodic deposition of copper from cupric sulphate solutions containing H₂SO₄ as swamping electrolyte. Results have been correlated by the equations.

and

where GR_m is a combined Grashof number for concentration and thermal buoyancy effects.

.Mass transfer has also been measured for the novel situation of nucleate boiling at the electrode surface and diffusion layer thicknesses as small as 1·7 × 10^?3mm have been obtained.     

The heat transfer coefficient between a particle and a bed (packed or fluidised) of much larger particles

The heat transfer coefficient has been measured for a heated phosphor-bronze sphere (diam. 2.0, 3.0 or 5.56 mm) added to a bed of larger particles, through which air at room temperature was passed. The bronze heat transfer sphere was attached to a very thin, flexible thermocouple and was heated in a flame to before being immersed in the bed. The cooling of the bronze sphere enabled the heat transfer coefficient, h, to be measured for a variety of U/U_mf, as well as diameters of both the particles in the bed and the heat transfer sphere. It was found that before the onset of fluidisation, h rose with U, but h reached a constant value for U?U_mf. These measurements indicate that in this situation (of a relatively small particle in a bed of larger particles) all the heat transfer is between the hot bronze sphere and the gas flowing over it. Consequently, a Nusselt number, based on the thermal conductivity of the gas, is easy to define and for U?U_mf (i.e. a packed bed), Nu is given by

     

The effect of bed materials on the solid/bubble motion in a fluidised bed

Gas fluidisation provides good mixing and contact of the gas and particle phases as well as good heat transfer. These attractive features are achieved by the high degree of bubble-induced particle circulation within the bed. Bubble and particle motion vary with bed materials and operating conditions, as investigated in the present study, by the use of the non-intrusive positron emission particle tracking (PEPT) technique. The selected materials were spherical polyethylene and glass particles.The data obtained by the PEPT technique are used to determine the particle velocities and circulation pattern. Bubble rise velocities and associated sizes can be inferred from the particle velocity data, since particles travel upwards mostly in the bubble wake. The results indicate that the flow structure and gas/solid motion within the fluidised beds were significantly different, even at the same value of the excess gas velocity, U-U_mf. The solid circulation pattern within the beds differ: if for glass beads, a typical UCDW-pattern existed (upwards in the centre of the bed, downwards near the wall), the pattern in the polyethylene bed is more complex combining a small zone of UWDC movement near the distributor and a typical UCDW-pattern higher up the bed. Transformed data demonstrate that at the same value of excess gas velocity, U-U_mf, the air bubbles in the polyethylene fluidised bed were smaller and rose more slowly than in the fluidised bed of glass beads, thus yielding a longer bubble residence time and improved gas/solid contact. For polyethylene beads, the size and rise velocity of air bubbles did not increase monotonically with vertical position in the bed as would be predicted by known empirical correlations, which however provide a fair fit for the glass beads data. Bubble sizes and solid circulation patterns are important parameters in the design of a fluidised bed reactor, and vary with the bed material used.     

Polarographic study of the system containing cadmium(II) and cobalt(II) and TTHA reagent

Polarographic study of the substitution reaction between cadmium(II) complex with Triethylenetetramine-N, N, N′, N″, N?, N?-hexaacetic acid (TTHA = H₆L) and cobalt(II) ion is described. According to the amperometric titration curves and polarograms, the existence of mixed binuclear complex and a new wave (Wave P appears above pH 4.5, ?0.8～?0.9 V. vs sce) involved in the reactions between two different metal ion (Cd(II) and Co(II) and TTHA was presented. The mixed complex [CdLCo]^2? then decomposed forming slowly the complex CdHL^3? and Co²⁺, as expressed by the reactions

and binuclear complexes were formed according to the reactions.

The logarithmic formation constant, K^Cd_CdLCo was calculated to be 8.10 using (1) and the known values of log K^H_CoHL = 8.12, log α_Cd(OAc) = 0.46 and log K′_CdLCo = 4.32 at pH 4.80.

The calculated value verified the proposal of mixed binuclear complex formation is low compared to log K^Cd_CdLNi = 9.2. The mixed complexes of TTHA reagents are stable species compared with binuclear type of EDTA complexes which exist only as reaction intermediates.The electrode reaction of wave P is proposed.

The species: CoL^4? obtained has a strong adsorption on the dropping mercury electrode.     

Interplay between nitronates and nitriles accomplished in a PtIV-mediated reaction

Reaction between the coordinated propanenitriles in trans-[PtCl₄(EtCN)₂] and the cyclic nitronate

(1) gives the N-acylated iminocomplex

(2) which is unstable in wet solvents and undergoes hydrolysis to furnish

(3). The formulation of 2 and 3 was supported by satisfactory C, H, and N elemental analyses, agreeable HRESI⁺-MS, IR, ¹H NMR spectroscopies, and single-crystal X-ray diffraction (for trans-3).     

Mechanism of electrodeposition of copper from cupric pyrophosphate solutions

Cathodic polarization curves were measured for copper in cupric pyrophosphate solutions of different concentrations and temperatures. A rotating disc electrode was used to eliminate concentration polarization. For all solutions, two potential regions are distinguishable in the polarization curve; one is less negative than a critical potential E_b around ?0.75 V vs sce (Region I) and the other more negative than E_b (Region II). A weak adsorption of pyrophosphate ions and hence some inhibition of the electrodeposition of copper is expected for Region I but there is no adsorption in Region II. The exchange current density i_o for the copper deposition was obtained by extrapolating the Tafel relation observed in Region II to the rest potential corresponding to the equilibrium potential. The following reaction mechanisms are proposed to explain the dependence of i_o on the concentration of Cu(P₂O₇)^6?₂ and P₂O^4?₇ ions.

Apparent activation energies are estimated to be about 11 kcal/mol in both cases.     

1H- and 13C-n.m.r. studies on naphtha and light distillate saturate hydrocarbon fractions obtained from in-situ shale oil

Shale oil, obtained from an in-situ oil shale experiment, from the Green River formation in Southwestern Wyoming was thermally fractionated into naphtha, light distillate, heavy distillate and residue fractions. The naphtha and light distillate fractions were further separated into saturates, olefins and aromatic subfractions. ¹H- and ¹³C-n.m.r. spectra and mass spectral data were obtained for the saturated hydrocarbons of the naphtha and light distillate fractions. Resonances in the n.m.r. spectra were assigned to normal alkanes and to methyl- and dimethyl-branched alkanes. The composition as determined by n.m.r. of the naphtha saturates was found to be ≈82% straight-chain alkanes with an average carbon-chain-length of ≈C₁₁ and ≈18% branched/cyclo-alkanes. The composition of the light distillate saturates was found to be ≈ 69% straight-chain alkanes with an average carbon-chain-length of ≈C₁₅and ≈31% branched/cyclo-alkanes. The dimethyl-branched alkanes in both saturate fractions were proposed to have the molecular substructure of saturated isoprenoids. In the naphtha saturates the isoprenoid substructure

is evident. However, in the light distillate saturates, both isoprenoid substructures,

and

, are evident. ¹³C spin-lattice re-laxation times also were determined for the dominant resonances observed in the spectra of the naphtha and light distillate saturates. Relaxation times for the molecular species in the naphtha saturate fraction were observed to be longer than those observed for the light distillate saturate fraction. It was found that the ratio of the overall average relaxation times for the naphtha and light distillate saturate fractions corresponded to the inverse ratio of the average molecular weights of each fraction as determined from average alkane carbon-chain-length determination. Intermolecular (segmental) motion of the carbon chain of the straight-chain alkanes in both saturate fractions is also evident from the relaxation time measurements.     

Interphase mass transfer during drop or bubble formation

In derivation of all previous unsteady-state equations for prediction of mass transfer during formation of drops, it has been explicitly assumed that (i) the boundary layer around the drop is planar and, (ii) the concentration within the drop is reasonably constant. In the present work, it is shown that both these assumptions may be discarded by using the following expression for fractional approach to equilibrium, E, as a function of diffusivity, D, distribution coefficient, H, drop diameter, d, and formation time, t,:

where

However, the error introduced through assumption (ii) alone may be eliminated by using the equation:

where E_c is the fractional approach to equilibrium obtained by assuming constant concentration within the drop. These alongwith other existing equations are used to reevaluate the experimental data reported in the literature.