Interchange of fluid mechanics and mass exchange in droplets

Streicher, Robert; Schügerl, K.

doi:10.1016/0009-2509(77)80191-7

Cited by 18 publications

(2 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1 or Eq. 2 (Johnson and Hamielec, 1960;Skelland and Wellek, 1964;Hughes and Gilliland, 1955;Whitman et al, 1926;Streicher and Schiigerl, 1977;Garner and Lane, 1959;BoyeChristensen and Terjesen, 1959). These high mass transfer rates are generally attributed to oscillations and/or turbulence produced during drop formation or as a result of drop motion through the continuous medium.…”

Section: March 1986mentioning

confidence: 91%

Effects of surfactants on mass transfer during spray drying

Frey

King

1986

AIChE Journal

View full text Add to dashboard Cite

A study was conducted to investigate the effects of added surfactants on mass transfer during spray drying. Measurements were made of retention of volatile components and amount of water evaporation at various points near the atomizer inside a spray dryer of pilot plant scale. Experimental data indicate that surfactants can have a substantial effect on transport processes when certain types of liquid solutions are spray dried. Experimental results are interpreted in terms of transport mechanisms and are compared with relevant previous studies on nonspray systems. D. D. Frey C. J. King Department of Chemical EngineeringUniversity of California Berkeley, CA 94720 SCOPESpray drying is widely used for dehydration of liquid foods such as coffee and tea extracts, milk concentrates, and purees. Because of the economic importance of these products, and because of numerous other industrial applications of spray drying, there is growing interest in a better understanding of the mechanisms of mass transfer during spray drying. This knowledge should aid optimization of these processes for minimum cost, for better retention of volatile aroma components, and/or for improving other product quality factors.In spite of the large number of fundamental mass transfer studies to be described below, most previous work dealing with added surfactants has been on idealized systems and does not take into account the following complexities which are characteristic of industrial spray drying: Haven. CT 06520.3. Turbulence and oscillations in drops caused by 4. Effects of drying on the internal motions of drops 5. Formation of a surface crust or a selective-diffusion barrier Notwithstanding the relatively small amount of past work in this area, it is important to understand the effects of surfactants upon spray drying. Many or all liquid foods contain natural surfactants. In situations such as foam-spray drying, it may be necessary to add surfactants to the liquid feed to obtain the desired processing effect. Finally, addition of surfactants may be a convenient means to affect and control mass-transfer rates during spray drying or in other types of spray contacting.For these reasons, an experimental and theoretical investigation was undertaken of the spray drying of surfactant-containing aqueous sucrose and coffee solutions, with acetates as model aroma components. The principal aims of this investigation were to determine the effects of various surfactants on the retentions of highly volatile aromalike components and on the rate of water evaporation in regions close to the nozzle. An aerodynamic model of spray behavior was used to interpret the experimental results. CONCLUSIONS AND SIGNIFICANCEThis study indicates that surfactants can have a large effect on volatiles retention during spray drying. The primary effect of a surfactant appears to be on droplet hydrodynamics and particularly on oscillations, turbulence, and internal circulation in drops. In solutions of high solids content where volatiles losses from drops are small, surfactant...

show abstract

Section: March 1986mentioning

confidence: 91%

Effects of surfactants on mass transfer during spray drying

Frey

King

1986

AIChE Journal

View full text Add to dashboard Cite

show abstract

“…In Eqs (8) and (9), dimensionless groups appear to represent the mass transfer enhancement in the dimensionless conversion rates. We will call these the reactivity enhancement factors, RE, defined as: …”

Section: Boundary Diagrams For Fast Reactionsmentioning

confidence: 99%

Thermally safe operation of a semibatch reactor for liquid‐liquid reactions–fast reactions

Steensma

Westerterp

1991

Chem Eng & Technol

View full text Add to dashboard Cite

Accumulation of the reactant supplied to a cooled semibatch reactor (SBR) will occur if the mass transfer rate across the interface is insufficient to keep pace with the supply rate. Then, due to a low starting temperature or supercooling, the reaction temperature does not rise fast enough to the desired value. This accumulation may eventually lead to a temperature runaway. We investigated the possibility of such an event for reactions of the type "chemically enhanced mass transfer" or "fast" and found that only low distribution coefficients, i.e. or lower, can lead to accumulation. At higher distribution coefficients, the mass transfer rate across the interface of a well-mixed dispersion is generally sufficient to prevent accumulation. A thermal runaway in the fast regime exerts a moderate effect, because the effective activation energy is halved. Calculations for the "instantaneous" reaction regime, regarded as a special case of fast reactions, show that there is no runaway possible.

show abstract