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La désorption de gaz à partir de solutions sursaturées est un phénomène qui intervient très fréquemment dans les industries chimique, biochimique et alimentaire : détente de solutions saturées, fermentations, réactions entre composants liquides conduisant à des produits volatiles et peu solubles, électrolyses, réactions parasites lors d'électro-synthèse. La désorption peut avoir lieu de manière diffusionnelle (c'est-à-dire sans formation de bulles), ou de manière nucléée. Si le premier type a été étudié par plusieurs auteurs, le second n'a fait l'objet que de quelques rares travaux soit purement empiriques et non généralisables, soit théoriques et difficilement applicables. Les auteurs présentent l'état des connaissances dans ce domaine et indiquent quelques voies de recherche d'intérêt.

The effect of a periodic liquid feed on the effective radial heat conductivity, Λr, in a trickle bed was investigated. The mean Λrunder periodic operation was found to be well estimated by time‐weighed averaging of steady state values. The actual effect of periodic operation can therefore be predicted by the shape of the Λr, uL— curve in steady state operation. The effect of periodic operation is attenuated with decreasing gas flow rates and with decreasing liquid flow rate amplitudes in a bed of spherical particles. Practically no effect was observed with cylindrical particles.

The applicability of velocimetry techniques based on the Doppler effect — such as laser and ultrasound Doppler velocimetry — for investigating local hydrodynamics in bubble columns and airlift reactors have been extended to non‐coalescing media. Their limitations are highlighted, especially as a function of gas sparger and reactor type. The ultrasound technique was shown to be able to measure either bubble or liquid velocity. Differences in local hydrodynamics due to coalescence behaviour were used to support the analysis. Data validation was carried out both by mass balance and by comparison with other techniques, such as electrochemical probes, Pavlov tubes and optical probes.

The dynamic surface renewal model of Maucci et al. (2001) is applied to transient mass transfer problems and extended to transient heat transfer measurements in pulsating, two‐phase flows. The model is also used to simulate mass transfer for square‐wave liquid velocity pulses in a liquid‐solid column. Experiments and simulation show that, when flow reversal occurs, the average mass transfer for a pulsating flow can be significantly higher than for steady state flow at the same bulk flow rate. This increase depends mainly on the relative pulse magnitude. The influence of pulse frequency and symmetry is second‐order. Apparent differences between various published studies are resolved.

A state‐of‐the‐art correlation for the prediction of frictional gas‐liquid pressure drop in cocurrent upflow fixed bed reactors was derived based on a wide hydrodynamic data bank of flooded packed‐bed reactors. The data bank, which contains more than 3400 measurements, was constructed using information collected from 22 sources over the past 40 years. The correlation, which relied upon combination of dimensional analysis and artificial feed‐forward neural networks, was expressed as a two‐phase friction factor function of the five most pertinent dimensionless groups (ReLG, Mo, St, FrL, XL). The prediction and generalization capabilities of the proposed correlation and the limits of existing literature correlations and models were demonstrated by systematic statistical tests over the constructed data bank.

The influence of pressure on gas-liquid interfacial area in cocurrent trickle flow fixed bed reactors is investigated. Interfacial areas have been determined from diethanolamine carbamation of aqueous more or less viscous solutions of ethylene glycol for pressure up to 3.1 MPa in a 0.395m-height and 23mm-ID column packed with hydrophilized polypropylene extrudates, porous carbon cylinders or glass beads. At gas superficial velocities less than 0.02m/s, interfacial areas are found to be pressure-independent, allowing for an acceptable estimation at atmospheric pressure. However, above this limit, even if the flow regime is still trickling, gas-liquid interfacial area increases with pressure for constant gas and liquid velocities. These findings are tentatively explained by the influence of gas inertia on break-up of bubbles trapped in the liquid films trickling over the particles.

Gas desorption from supersaturated solutions is a phenomenon which occurs very frequently in the chemical, biochemical and food industries expansion of saturated solutions, fermentations, reactions between liquid elements resulting in volatile and slightly soluble products, electrolyses and parasitic reactions during electrosynthesis. Desorption may occur diffusionally (i.e. without bubbles forming) or nucleated. If the first type has been examined by several authors, the second has only been rarely considered, either purely in an empirical way and which cannot be generalized, or in a theoretically and difficult to apply manner. The authors are submitting what they know of this field and indicate several channels of fruitful research.La d?sorption de gaz ? partir de solutions sursatur?es est un ph?nom?ne qui intervient tr?s fr?quemment dans les industries chimique, biochimique et alimentaire : d?tente de solutions satur?es, fermentations, r?actions entre composants liquides conduisant ? des produits volatiles et peu solubles, ?lectrolyses, r?actions parasites lors d'?lectro-synth?se. La d?sorption peut avoir lieu de mani?re diffusionnelle (c'est-?-dire sans formation de bulles), ou de mani?re nucl??e. Si le premier type a ?t? ?tudi? par plusieurs auteurs, le second n'a fait l'objet que de quelques rares travaux soit purement empiriques et non g?n?ralisables, soit th?oriques et difficilement applicables. Les auteurs pr?sentent l'?tat des connaissances dans ce domaine et indiquent quelques voies de recherche d'int?r?t.

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