Transfer in Liquid Films

Brauer (B16), 1958 Same as previous citation, but application to mass transfer in liquid films comparison with previous experimental work. 

Extensive survey of flow and heat transfer in liquid films flowing outside tubes. Measurements of temperature and velocity profiles in films of various liquids are reported, and a heat transfer mechanism is proposed. 

Mass and Heat Transfer in Liquid Films, Tdbes, and Boundary Layers... 

Boyadjiev, Ch. and Beschkov, V., Mass Transfer in Liquid Film Flows, Publ. House Bulgar. Acad. Sci., Sofia, 1984. 

High-gravity field Spinning disc reactor Heat transfer from liquid film Mass transfer in liquid film Reaction time Equipment size Impurities level... 

Film Boiling and Heat Transfer in Liquid-Deficient Regions 274... 

FILM BOILING AND HEAT TRANSFER IN LIQUID-DEFICIENT REGIONS... 

LlM, S. T. Hydrodynamics and mass transfer processes associated with the absorption of oxygen in liquid films flowing across a rotating disc, Ph. D. thesis, (University of Newcastle upon Tyne, U.K., 1980). 

L denotes overall mass transfer coefficient in liquid film Im logarithmic mean... 

The overall coefficients of liquid-liquid mass transfer are important in the calculations for extraction equipment, and can be defined in the same way as the overall coefficients of gas-liquid mass transfer. In liquid-liquid mass transfer, one component dissolved in one liquid phase (phase 1) will diffuse into another liquid phase (phase 2). We can define the film coefficients /C i (nr h" ) and k (m h ) for phases 1 and 2, respectively, and whichever of the overall coefficients A (m h ), defined with respect to phase 1, or Al2 (mh ) based on phase 2, is convenient can be used. Relationships between the two film coefficients and two overall coefficients are analogous to those for gas-liquid mass transfer that is,... 

The third term of Equation 2.80 accounts for resistance to mass transfer in liquid phase. An obvious way of reducing this term is to reduce the liquid film thickness d. This causes a reduction in k and an increase in the term k1/(1 + k )2- However, using thinly coated column packings increases the probability of adsorption of solute molecules on the surface of support material, which might result in peaks tailing. 

A very early application of liquid film flow in the chemical industry is mentioned in a patent of 1836 (G5) hydrogen chloride gas produced in the Leblanc soda process was absorbed by water films flowing over packings. Much later the film coolers and evaporators used in the German beet sugar industry inspired the earliest detailed theoretical and experimental studies of flow and heat transfer in falling films (CIO, N6, N7). Chemical engineering interest in film flow has increased rapidly in recent years. 

Anderson el al. (A4), 1961 Theoretical and experimental study of heat transfer to liquid films in vertical long-tube evaporators. Theory based on use of universal velocity profile. 

Mass transfer in falling-film absorbers is strongly dependent on the gas velocity in the tubes, the liquid and gas distribution, and the tube surface conditions. The maximum capacity of falling-film absorbers is normally restricted either by flooding or by pressure drop. Another important limit in these absorbers is film breakup. If heat flux is excessive, dry areas may form at the tube wall and reduce mass transfer. 

At Reynolds numbers greater than about 30, it is observed that waves form at the liquid-vapor interface although the flow in liquid film remains laminar. I he flow in this case is said to be wavy laminar. The waves at the liquid-vapor interface tend to increase heat transfer. But the waves also complicate the analysis and make it very difficult to obtain analytical solutions. Therefore, we have to rely on experimental studies. The increase in heat transfer due to the wave effect is, on average, about 20 percent, but it can exceed 50 percent. The exact amount of enhancement depends on the Reynolds number. Rased on his experimental studies, Kutateladze (1963) recommended the following relation for the average heat transfer coefficient in wavy laminar condensate flow for p p, and 30 < Re < 1800,... 

Other known disadvantages of packed-bed reactors are low external and internal mass transfer rates. For trickle-bed reactors, a representative value for both and k/ig is 0.06 sec [18]. As was pointed out previously, the corresponding values for monolith reactors are higher due to the enhanced radial mass transfer in liquid slugs and to shorter diffusion length in both the liquid film and the solid catalyst. 

Because diffusion in the liquid phase is much slower than in the gas phase, the liquid film presents most of the resistance to mass transfer. Gas-liquid film theory defines the mass transfer rate (MTR) in terms of the liquid film, as follows... 

Nonisothermal flows through tubes and channels accompanied by dissipative heating of liquid are studied. Qualitative features of heat transfer in liquids with temperature-dependent viscosity are discussed. Some issues of film condensation are considered. 

The term /Ky can be considered an overall resistance to mass transfer, and the terms m//c, and l/ky are the resistances in the liquid and gas films. These films need not be stagnant layers of a certain thickness in order for the two-film theory to apply. Mass transfer in either film may be by diffusion through a laminar... 

S. Fukusako, T. Komoriga, and N. Seki, An Experimental Study of Transition and Film Boiling Heat Transfer in Liquid-Saturated Porous Bed, ASMEJ. Heat Transfer, (108) 117-124,1986. 

I. A. Mudawwar, T. A. Incropera, and F. P. Incropera, Boiling Heat Transfer and Critical Heat Flux in Liquid Films Falling on Vertically-Mounted Heat Sources, Int. J. Heat Mass Transfer (30) 2083-2095,1987. 

Acoustical vibration as a means of improving heat-transfer rates is under study by the Southwest Research Institute and results appeared in an OSW research and development report (30). Very briefly the results may be summarized as follows Acoustic vibration effected a marked improvement in liquid-film co-... 

In any catalytic system not only chemical reactions per se but mass and heat transfer effects should be considered. For example, mass and heat transfer effects are present inside the porous catalyst particles as well as at the surrounding fluid films. In addition, heat transfer from and to the catalytic reactor gives an essential contribution to the energy balance. The core of modelling a two-phase catalytic reactor is the catalyst particle, namely simultaneous reaction and diffusion in the pores of the particle should be accounted for. These effects are completely analogous to reaction-diffusion effects in liquid films appearing in gas-liquid systems. Thus, the formulae presented in the next section are valid for both catalytic reactions and gas-liquid processes. 

The presence of two liquid films leads to several combinations of regimes in the two films. In view of the importance of different regimes being operative in the two phases, we illustrate the approach by considering two combinations (1) fast reaction in one phase (reaction-diffusion in the film of this phase) and slow reaction in the other (reaction in the bulk of this phase with mass transfer in the film), and (2) fast reaction in both phases. The treatment can be readily extended to other combinations. 

Reactions requiring both a gaseous and a liquid reactant are usually performed in trickle-bed reactors in which the gas and liquid are pumped counter- or co-currently through a bed of catalyst particles [53, 54). Many of these systems encounter mass-transfer limitations as a result of intraparticle mass-transfer resistance, liquid-film resistance, liquid maldistribution and channelling. To overcome these problems, membrane reactors have been used for chemical reactions as well as biological conversions. 

Mass transfer in falling film has been considered mainly with the dependence of liquid-side mass transfer. Recent research activities are concentrated on the potential increase of mass transfer in the liquid film to enhance the reactor performance. For this purpose, different modifications of the surface structure of the reaction plates are proposed. 

Identical to gas-liquid Taylor flow, the mass transfer in liquid-liquid slug flow has two contributions film and slug caps. The specific interfacial area, ratio of surface area of the slug per unit its volume, can be written by neglecting the film thickness as... 

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