Abstract: A summary of the available literature on heat transfer to liquid—solid fluidized beds is presented. The influence of process parameters such as bed geometry, flow velocity, and fluid and particle properties on heat transfer is discussed. 36 correlations based on various models or empirical assumptions are presented. The predictions of the correlations are compared with a database comprising 2665 measured data for a variety of fluids and particles. A new empirical correlation is developed which predicts the measurements better than published correlations.

Abstract: The indirect heat transfer of steam-heated tube bundles in a moving bed has been examined in an experimental apparatus. Heat transfer in single tubes is typified by a characteristic flow of the bulk solids along the outer tube wall surface. A cuneiform rest zone is created at the upper tube wall (stagnation point), in which the particles remain for a long time. An ‘insulating’ effect is exhibited by the dammed bulk zone and is responsible for the poor heat transfer in this area. Near the sides of the lateral tubes heat transfer is good and icreases with increasing mass flux and bulk solids velocity. Bubbling occurs at the lower tube wall and the heat transfer again decreases due to the small number of wall-particle contacts. The experimentally confirmed ‘trace theory’ describes the temperature profile at the outlet of a moving bed heat exchanger, being characterized by very good cross-mixing of the bulk solids which allows the intergral heat transition to be calculated. A modelling approach to the heat transfer and bulk solids movement in the moving bed provides a physical model which describes the dependence of the heat transfer at a single tube on the flow profile between two neighbouring tubes. In order to determine the flow profile, the continuity equation is solved vectorially, allowing an analytical relationship of the velocity profile between two tubes to be obtained via the coaxiality of stress and deformation. To allow such a calculation, the heat-transfer model makes use of the residence and contact time behaviour resulting from the velocity profile, with the different components of heat transfer at a tube being determined from the friction properties of the specific bulk material. Calculation of the integral heat transfer in the moving bed may be achieved via heat transfer at a single tube. By using the theory of ‘extended contact time’, the total residence time of the bulk at the first tubes may be considered as a case history for the other tubes. The integral overall heat-transfer coefficients of moving bed heat exchangers thereby determined have been verified experimentally.

Abstract: Despite their drawbacks, chemical techniques are often the only means of determining volumetric gas—liquid mass-transfer coefficients kLa in gas—liquid and gas—liquid—solid reactors. Two techniques are considered here: the oxidation of sodium sulphite by oxygen in a viscous CMC solution and the oxidation of hydrazine catalysed by a copper ammonia complex. The latter technique is shown to be of use even when the liquid is not perfectly mixed. Furthermore, since hydrazine solutions exhibit coalescence, by adding sodium sulphate the coalescence behaviour of the liquid can be modified without affecting the kinetics of the reaction. In each case, the range of values of the mass-transfer coefficient kLa and the interfacial area allowing the use of this technique are given.

Abstract: Densities and thermodynamic equilibrium compositions of both the gas and the liquid phases were determined for binary mixtures of carbon dioxide and oleic acid, methyl myristate, and methyl palmitate, and for the ternary system carbon dioxide—methyl myristate—methyl palmitate at pressures up to 130 bar. Binary equilibria and densities were measured at 40°C, 50°C, and 60°C; the ternary system was studied at 40°C and 50°C. High-pressure densities were also recorded for all pure components. The apparatus used for the experiments consisted of a high-pressure view cell through which both phases were recirculated. Compositions were determined from samples taken with the help of six-way valves. Densities were measured with a vibrating sensor tube. Solubilities increase with pressure at a given temperature; however, the separation of a mixture of methyl myristate and methyl palmitate becomes less selective. All numerical values are given in full detail.

Abstract: The noble metal catalysed oxidation of CO by O2 has been studied on polycrystalline foils, ribbons and wires of Pt, Pd and Rh as well as on a variety of supported Pt catalysts. At temperatures from 180 to 600 °C, the partial pressure ratio was changed over the range 0.01 ⩽ pCO/pO2 ⩽ 50 at partial pressures varying over the range 10−6 ⩽ pi (mbar) ⩽ 40. In the total pressure region below 1 mbar, the results agree very well with model experiments conducted under ultra-high vacuum. The rate values measured at total pressures exceeding 1 mbar correspond to the highest activities ever observed on noble metal catalysts. Even at low temperatures and high gas velocities up to 14 m s−1, such values were mass transfer limited since the reaction was not inhibited by CO. Neither the structure nor the support influence the reaction in the case of supported Pt catalysts. The well-defined geometry of the experimental set up allowed an estimation of the appropriate mass-transfer coefficients and the calculation of the intrinsic reaction rate. The results clearly indicate that in the region where the reaction is first order with respect to the limiting component the intrinsic first-order rate constant has the same value as under high vacuum conditions within the precision of the approach. Thus the apparent gap between the rates of CO oxidation observed in model experiments and under ambient pressure must be attributed to the influence of mass-transfer limitations.

Abstract: For the collection of diesel soot particles, a two-stage collection system is employed consisting of a cyclone in combination with a preceding electrostatic agglomerator. By virtue of its design, the agglomerator is, in principle, a tubular electrostatic precipitator. The agglomeration mechanism is based on the fact that the electrically conductive soot particles accumulate at the collecting electrode of the agglomerator as flake-like structures. These are re-entrained when they exceed a certain size. The process of agglomeration can therefore be divided into three steps, i.e. particle transport, formation of agglomerates and emission. In order to assess the efficiency of the agglomerator, a measuring methodology has been developed which allows the determination of the size distribution of the soot particles over the range 17 nm to 40 μm. Investigations carried out in connection with this work show that the proportion of particles bound in agglomerates depends essentially upon the operating level of the engine. Depending on the various conditions employed, more than 90% of the particle mass may be bound in agglomerates whose sizes exceed 3 μm. With increasing engine load, the proportion of agglomerates decreases to ca. 40%. Varying the gas volume flow at a constant engine operating level demonstrates that such a dependency on load is not related to residence time, i.e. low efficiency does not arise from insufficient particle transport, but appears to be associated with one of the subsequent stages of the agglomeration process. Details of these processes have not been investigated so far. The total collection efficiency achieved via this system varies between 43% and 87% according to the various operating states of the engine. This significant difference can be explained in terms of the dependence of agglomeration and agglomerate collection upon engine load and speed.

Abstract: The kinetics of the esterification of mono-2-ethylhexyl phthalate in the presence of sulfuric acid as a catalyst has been investigated in an isothermal semibatch reactor. The reaction appears to be first order with respect to mono-2-ethylhexyl phthalate alone and the reaction rate does not depend on the concentration of 2-ethylhexanol. The kinetic parameters have been determined.

Abstract: A physical model for the flow in a vessel equipped with radial-flow impellers and baffles is presented. It is based on the fluid-dynamic interaction between impeller and baffle, i.e. basically the transport of angular momentum from the stirrer to the baffle. By employing some integral notions, it is possible to calculate power and discharge numbers in stirred vessels from the geometry of the impeller and baffles in the vessel.

Abstract: A leachate from a municipal landfill and an industrial wastewater from an emulsion-breaking unit have been treated by chemical wet oxidation using ozone and hydrogen peroxide as oxidants. The best results were obtained with UV radiation resulting in the formation of OH· radicals. If ozone is used, mass transfer will be the limiting step in the degradation reactions. The specific consumption of hydrogen peroxide is drastically reduced if pure oxygen or air is dispersed into the wastewater. Under optimum conditions, the COD of the leachate and of the industrial wastewater could be reduced by 90% in c. 3 and 5 h, respectively.

Abstract: Local gas holdups and bubble size distributions have been measured simultaneously in a standard-type bubble column equipped with a perforated plate as a gas disperser. High values in the time series of the local gas holdup which appear on a periodic basis could be detected and analyzed. The phenomenon of the bubble hose, defined as a zone of high bubble number density moving helically in a bubble column, has been recognized visually using photographs and by means of the recorded data. A formation mechanism for the bubble hose dependent on the gas disperser geometry capable of explaining the observed asymmetric liquid and gas flow pattern is suggested. The existence of a relationship between the bubble hose, the average bubble diameter and the superficial gas velocity has been demonstrated.

Abstract: In multicomponent batch distillation, several main cuts and slop cuts are collected into tanks. A general model (based on a superstructure) is proposed which allows the calculation of the proportion of each slop cut to be added to each initial load and to each new batch in order to optimise the global operation. The formulation of this problem leads to a non-linear programming (NLP) problem, where the set of decision variables are the proportions of each slop cut to be added to each batch and the reflux ratios. Two type of criteria and of reflux ratio policies as well as the number of batches and the number of trays, are explored. Results show the importance of the criterion choice, the little difference between an optimal constant reflux policy for a batch and a variable reflux policy, and the increase of the production rate (for problems without liquid holdup) with the number of trays.

Abstract: Validation of the gas-lift bubble column, a new laboratory device, has been achieved by studying the chemical absorption of carbon dioxide into carbonate/bicarbonate solutions. This reaction has been conducted over a range of temperatures extending from 293.2 K to 343.2 K, and using the hypochlorite ion as a catalyst, with corresponding NaClO molarities ranging from zero to 0.2 M. The Danckwerts model was used.The surface renewal rate s , the liquid-side mass-transfer coefficient k L and the rate constant K 2 wer determined. During the hydrodynamic study, the gas-liquid exchange area was evaluated by a photographic method.

Abstract: More than 40 years of research work in the domain of photochemical engineering has shown that quantitative modelling and solving of the radiant energy conservation equation coupled to the momentum, mass and heat balances are very difficult and therefore, even taking into account the most recent developments, of little impact on photochemical reactor design and process optimization. The kinetics of photochemical processes depend on light absorption, and the modelling of photochemical reactors and processes must take into account the spatial distribution of radiation emitted by a given light source (radiation field) and of the radiation absorbed. This task has proven to be extremely difficult, even under the most favourable experimental conditions (e.g. sensitized reactions) and simplest reactor geometries. On the other hand, emperical methods of reactor design and up-scaling do not necessarily lead to optimal results, and modelling by means of artificial neural networks holds the promise of solving problems so far beyond the scope of methods using the transport phenomena approach. In this work, neural networks have been applied to the modelling of a homogeneous liquid phase photochemical system: the photolysis of an aqueous uranyl oxalate solution. The algorithm used to adjust the weights in neural network application was back-propagation. The comparison between the calculated and experimental data show good agreement, even when simulation was performed outside the range of the learning set (extrapolated result).

Abstract: A basic parameter in two-phase gas—liquid flow is the size of the bubbles. From the point of view of calculating the interfacial area for mass transfer, the size of the bubbles is as important as the holdup. Many empirical expressions for bubble diameter have been proposed. The purpose of this paper is to see whether recent work on bubble diameter in developed flow in pipes can also be used for bubble columns. The new expression for bubble diameter, which is based on an analog with the structure of single-phase turbulent flows, is simpler to use and comparable in accuracy with the previous empirical expressions, in spite of not having any adjustable constants in it.

Abstract: The enzymatic cleavage of the amide bond of l -leucine-4-nitroanilide by the proteolytic enzyme Pronase E releases 4-nitroaniline. The production of this molecule can be observed by the increasing UV absorption of the solution. A decrease in the rate of hydrolysis reaction was obtained in the presence of different humic substances isolated from water, sediment and soil. This result indicates that humic substances influence enzyme activity by interacting with the applied enzyme. A mathematical relation between the concentration of humic substances and their inhibition effect was used to calculate an effective concentration for which 50% of the maximum effect was observed. The obtained concentration was defined as the EC 50 value. The EC 50 values of the investigated humic substances were in the range 153 mg l −1 to 6360 mg l −1 . The amounts of humic substances used in the experiment were higher than in most aquatic environments. However, in bog water or interstitial water of sediments and soils such large amounts of biologically and ecologically relevant natural organic matter can be expected.

Abstract: Interfacial tensions of the binary systems carbon dioxide-oleic acid, carbon dioxide-methyl myristate, and carbon dioxide-methyl palmitate were measured at 40 °C, 50 °C, and 60 °C and at pressures up to 175 bar. The surface tension of subcritical carbon dioxide and the interfacial tension of the ternary system carbon dioxide-methyl myristate-methyl palmitate at 40 °C and 50 °C and at pressures up to 71 bar were also determined. Experiments were performed by observing the rise in a glass capillary placed inside a high-pressure view cell. Interfacial tensions approach zero as the critical point of the system is attained. Higher temperatures at a given carbon dioxide concentration in the liquid phase reduce interfacial tension—the “temperature effect”. At constant pressure—except near the consolute point—interfacial tension remains nearly unchanged with rising temperature, as the “temperature effect” is being counterbalanced by the “surfactant effect” of decreasing carbon dioxide concentration. All systems studied are completely wetting. The occurrence of Marangoni instabilities is discussed. The numerical results are given in full detail.

Abstract: Experiments on heat transfer and pressure drop in a triangular-channel of a plastic heat exchanger are reported. The channel geometry was designed to cause the augmentation of near-wall mixing processes in air. Experiments were performed over a Reynolds number range of 400 to 4000. Enhancement of the heat-transfer coefficient on the gas side was used to compensate the overall heat-transfer coefficient for the low conductivity of the plastic. Within the same pumping power, the heat transfer augmentation in a specimen of heat exchanger with triangular channels was found to be on the same level as a specimen with pin-fin internal geometry and mirogrooved channels, but its construction was technologically simpler and remarkably cheaper.

Abstract: Mass transfer in pervaporation is usually regarded as limited by the solution-diffusion step inside the dense selective polymer layer. In the case of pervaporation for the extraction of volatile organic compounds through organophilic membranes, especially at low feed temperature (about 300 K), the influence of the downstream pressure cannot be neglected. A contribution to the study of the operating parameters on the vapour side in a pilot plant — from the membrane to the condenser — to the overall mass transfer is presented. A “convection-diffusion” model has been established to calculate the partial pressure gradients in the vapour phase up to the downstream face of the membrane. This equation has been combined with a relation for the mass transfer inside the membrane with a driving force expressed as a difference in fugacities. The partial permeate pressures and the pervaporate fluxes obtained first with a pure compound (water) and secondly with binary mixtures (water-ethanol) pervaporated through membranes of polydimethylsiloxane (PDMS) on a pilot plant scale are well predicted by the model. Moreover, on the permeate side, the effects of unavoidable non-condensable gases, of the condenser temperature and of the distance between the module and the condenser on the flux and on the selectivity have been established for different total permeate pressures (300–3000 Pa). At high pressure, the pervaporation selectivity towards ethanol exhibits a minimum value as a function of the permeate circuit design.

Abstract: Jet agglomeration has been used in the food industry for several years to produce agglomerates with favourable instant properties from fine powders. In a jet agglomeration plant, freely moving, wetted particles are made to collide with each other to form agglomerates. Agglomeration occurs if the relative kinetic energy of the particles can be dissipated by the viscous liquid layers on their surfaces. This size enlargement process can only be understood if the forces between the colliding particles, called dynamic adhesion forces, can be described. Following a description of the jet agglomeration process, an indirect approach to this problem is presented which uses an experimental set-up allowing determination of the adherence probability of spheres colliding with wetted surfaces.

Abstract: The velocity profiles and volume concentrations of free water and the solids matrix of flowing pastes can be mutually determined independently via flow experiments in an NMR tomograph. This supplies direct proof of the relative displacement of free water in flowing pastes. The two phases can be distinguished with the help of NMR by their different magnetic relaxation times ( T 2 ). It is possible to measure the wall-slip of the two phases and, hence, to differentiate between the shear and slip shares of the total volumetric flow. When the evaluation of the flow experiments is based on a material law, the accompanying material functions can then be derived for pastes or suspensions from the velocity and concentration distributions. For example, as in the case of the fully-developed steady-state pipe flow, without any additional assumptions or corrections as is normally necessary for capillary rheometry. Through the use of NMR, it is possible to correlate the rheological features of the material in question, its flow behaviour and its flow-induced structural changes.

Abstract: The gas-film controlled mass-transfer rate in a honeycomb packing, with stamped groove turbulizers (Turbo-Pack) which affect the region of the boundary layer, has been studied. An equation for determining the mass-transfer coefficient as a function of gas velocity and the geometrical dimensions of the packing has been derived. It is found that the effect of the height of packing blocks is far less than that forecast by Zhavoronkov's equation which was derived for packings with a much higher wall thickness. Comparison of experimental data relevant to the novel design with reference packings cited in the literature shows that as far as its low values of pressure drop per mass transfer unit are concerned the Turbo-Pack packing is superior to all other known packings.

Abstract: The well-known series solutions, developed in the early 19th century by Fourier (1822) in order to describe the transient process of heat conduction in a solid have since become standard tools of engineering science. Attempts have often been made to facilitate the practical use of that first mathematical theory of an irreversible process by the provision of charts and simpler approximate equations and thus avoid the cumbersome calculations involved in the series. Some of the more recent approaches to simplifying the application of Fourier's theory are briefly reviewed. Three degrees of approximation, essentially based on the same ideas have been developed by Hausen (1942) and Elgeti (1969), by Schlunder (1972), and by the authors of this paper in 1992. Our own improved version of the approximate equations provides higher accuracy, and the additional possibility to obtain centre and surface temperatures (concentrations), not merely volumetric average values as in the earlier versions.

Abstract: This paper deals with the analysis of the phenomenon of gas pressure drop across distributors with high free area ratio as used in multistage fluidized-bed vessels without standpipes. The phenomenon has been studied for selected types of plate distributors, viz. orifice distributors and slot distributors. On the basis of experimental studies, performed in the range φ = 0.1–0.4, information has been obtained about the character and magnitude of the effect of the fluidization conditions and the constructional features of the distributor upon the pressure drop in question. The similarity factors of the phenomenon have been analyzed for both distributor types. Equations describing the gas pressure drop through the distributor as a function of its constructional parameters have been derived and verified experimentally. It has been shown that one such equation [Eq. (18) in the text] when elaborated for orifice distributors with high free area ratio and taking the shape of the orifice's profile into account may be used for the calculation of the pressure drop through conventional distributors. Analogies between the analytical approach to various phenomena connected with the distribution of gas in fluidized-bed apparatus are presented.

Abstract: Particle-to-gas mass transfer in fluidized beds has been investigated by drying experiments. To avoid the introduction of additional unknowns into the problem, the particle-side kinetics are described by the method of normalization. The normalized single particle drying curve has been derived by separate, direct measurement. The Sherwood number can be obtained by comparison with a heterogeneous fluid bed model. This procedure is demonstrated by measurements with aluminium silicate particles. The resulting Sherwood number is significantly lower than the respective single particle value. Model discrimination reveals that this effect can hardly be explained by bypassing or axial dispersion. Discrimination of this kind would not have been possible on the basis of traditional measurements with sublimation of compact material or drying of surface-wet particles.

Abstract: Heat and mass transfer data are reported for the condensation of vapours of immiscible liquids. Condensation occurred on the outside of 0.0254 m diameter horizontal copper tube. Mixtures of organic vapours in steam have been studied, such mixtures being rich in steam and removed from the eutectic composition. The condensate flow pattern has been determined experimentally. In systems where the density ratio of the organic to water liquids is less than one, a standing-drop pattern is observed; when the ratio is greater than one, channeling flow is the main feature. For systems removed from the eutectic composition, diffusional resistance through the vapour phase adjacent to the vapour—liquid interface has a major effect on the transfer rates.

Abstract: An entrained flow process for hydrogen production by gasification (partial oxidation) of coarsely ground Chinese reed has been developed. One of the main characteristics of this process is the withdrawal of liquid slag from the reaction zone. The slag outlet is heated with two swirl burners in which fuel gas is burned with excess oxygen. The excess oxygen is heated up by the flames and subsequently used for the reed gasification. For gasifier design, the chemical and hydrodynamic behaviour of the reed has been investigated and a mathematical reactor model has been developed. The performance of the process has been demonstrated by gasification experiments on a semi-technical scale. These measurements show that Chinese reed can be gasified in an entrained flow reactor with a high degree of carbon conversion without grinding the feedstock to particle sizes below 100 μm as is necessary for coal gasification. Reed with particle sizes of a few millimeters can be gasified during short residence times in entrained flow reactors firstly because the volatile matter content of the reed is about twice that of coal and secondly the resulting char is extremely reactive.

Abstract: Various mechanical methods for dewatering the loatation concentrate of coking coal are discussed, including vacuum, pressure and centrifugal filtration of both the feed slurry and the slurry condensed by sedimentation, and also centrifugal filtration of the cakes obtained during vacuum filtration. It is demonstrated that the most efficient dewatering may be expected using centrifugal filtration of the cakes initially dewatered in vacuum filters. During large-scale laboratory researchers of centrifugal decantation, a considerably lower final moisture content of the product has been achieved than in vacuum or pressure filtration. Furthermore, it has been shown that the dewatering costs of the system are lower than in the case of vacuum filtration and subsequent drying. A secondary effect of the method presented is the reduction in pollution due to confinement of the drying centre.

Abstract: The small-scale mixing densely packed bulk material was modelled by Buggisch and Loffelmann in 1989, starting from a diffusion approach which had been developed previously. An equation could be deduced which the diffusion coefficient appears to be proportional to the shear rate. This model coception was confirmed through shearing experiments using a Couette apparatus. The model bulk consisted of vertically packed metal rods of various diameters, parts of which were marked by colours. The present paper investigates the influence of the particle size distribution upon the mixing process. It is to be expected that the distribution of the particle size has an influence upon the package structure of the bulk and hence, amongst other things, upon the shear rate, and, eventually, upon the intensity of the diffusion. It has been possible to confirm this prediction through shearing experiments with the model bulk in the Couette apparatus.

Abstract: In horizontal flow boiling conditions the heat transfer is affected by the saturation pressure, the composition of the mixture, the vapour fraction, the heat flux and the mass velocity. Furthermore, the heat transfer coefficients are different at different axial and circumferential positions on the heat transfer surface. In this work the calculation of averaged heat transfer coefficients is based on local (point) values. For the prediction of local heat transfer coefficients of pure substances a new correlation is proposed. Local heat transfer coefficients for two pure substances (SF 6 and CCl 2 F 2 ) and mixtures were measured for the condition of uniform wall temperature over the whole composition range and various values of the affecting parameters. In the nucleate flow boiling region a pronounced reduction of the local heat transfer coefficients occurs, which is dependent on the liquid composition, the heat flux and the saturation pressure. This reduction of nucleate flow boiling heat transfer coefficients of mixtures is predicted by the model of Schlunder. However, from the experimental results it can be concluded, that the reduction in vaporization heat transfer is smaller for high mass velocities. With a simple model for the evaluation of the wetting boundary circumferential averaged heat transfer coefficients can be computed.