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Book ChapterDOI

Direct Contact Heat Transfer Between Immiscible Liquids

01 Jan 1966-Advances in Chemical Engineering (Academic Press)-Vol. 6, pp 207-286
TL;DR: In this paper, heat transfer to drops moving in a constant-temperature field and continuously varying temperature field is discussed, and three models are taken into account: rigid drop, completely mixed drop, and drop with internal circulation.
Abstract: Publisher Summary The basic characteristics of heat transfer between dispersed and continuous media are of both scientific and practical interest. The advantages of direct-contact heat transfer over the conventional processes using metallic transfer surfaces have lately stimulated research on its utilization for water desalination projects. Despite intensive efforts toward better understanding of transfer phenomena between drops and continuous media, accurate prediction of the transfer coefficients for a given system can as yet only be hoped for. Nevertheless, accumulated experience may provide an indication of the transfer mechanism to be encountered and the relevant coefficients may be estimated accordingly. This chapter discusses heat transfer to drops moving in a constant-temperature field and continuously varying temperature field. Heat is transferred to drops and bubbles with simultaneous phase change. While discussing about constant-temperature field, three models are taken into account: rigid drop, completely mixed drop, and drop with internal circulation. Work on direct-contact heat exchangers was stimulated earlier by the quest for economic water-desalination units. Multiphase exchange, where latent heat is transferred among the immiscible fluids, has been effectively used in direct-contact freezing units in which a dispersed volatile fluid evaporates in the saline water with simultaneous freezing of part of the water.
Citations
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14 Mar 1960
TL;DR: In this article, the mathematical derivation of solutions for longitudinal dispersion in chemical-process equipment is extended to the case of cocurrent flow and the extent of completion of the process, in dimensionless form, is given as an analytical function of rates of dispersion.
Abstract: The mathematical derivation of solutions for longitudinal dispersion in chemical-process equipment is extended to the case of cocurrent flow. The extent of completion of the process, in dimensionless form, is given as an analytical function of rates of dispersion in the two phases, over-all heat- or mass- transfer coefficient, partition coefficient, rates of fluid flow, and fractional height in the equipment. Numerical results for a large number of typical conditions are given in tubular form. (auth)

121 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) to measure the velocity and temperature of steam injected centrally at the bottom of a vertical rectangular water vessel.

74 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the literature regarding gas-liquid direct contact evaporators is presented, addressing classic and potential applications, bubble regimes, gas holdup and bubble size distributions, as well as mathematical models proposed for simulating the unit.
Abstract: Gas-liquid direct-contact evaporators are characterized by the bubbling of a superheated gas through the solution to be concentrated. In other words, they are nonisothermal bubble columns. Despite their simplicity of construction, these units exhibit rather complex hydrodynamics and, similar to what occurs to isothermal bubble columns, the design of such units still poses a problem. The present paper reviews the literature regarding this kind of equipment, addressing both experimental studies and modeling efforts. The covered issues include classic and potential applications, bubbling regimes, gas holdup and bubble size distributions, as well as mathematical models proposed for simulating the unit. Additionally, pertinent literature on isothermal bubble columns is also discussed. Recommendations are made for future research.

57 citations

Book ChapterDOI
TL;DR: Direct contact condensation (DCC) as mentioned in this paper is used in many chemical process industries, usually for quenching and partial or total condensation, particularly when corrosive vapors are involved.
Abstract: Publisher Summary This chapter introduces the direct contact condensation (DCC) in the design of equipment such as contact condensers, cooling towers, contact feed water heaters and deaerators. The DCC studies are usually related to single-component, two-phase (steam-water) systems, either pure or including traces of noncondensables (air). The advantages of direct contact condensation over the conventional processes using metallic transfer surfaces are due to the relative simplicity of design, less corrosion and scaling problems, lower maintenance costs, higher specific transfer areas, and higher transfer rates. Direct contact condensation can be accomplished by utilizing various contacting devices that include: cross-flow sieve tray columns, concurrent pipe contactors, spray columns, baffle-tray columns, and packed bed columns. All are designed to increase the vapor–liquid contact area. Direct contact condensation is utilized in various chemical process industries, usually for quenching and partial or total condensation, particularly when corrosive vapors are involved. The chapter discusses the large-scale applications of DCC of current interest that includes: emergency core cooling systems, water desalination systems, and geothermal energy recovery processes. The chapter concludes that condensation on a solid surface is limited in practice only by the extent of the surface and the rate of cooling the surface, DCC is inherently limited by the balance between the latent heat of condensation and the sensible heat that the liquid can absorb until saturation.

54 citations

01 Jan 1976
TL;DR: In this article, a survey of heat and mass transfer around droplets in spray dryers and the diffusional transport inside them is given, which includes variable diffusion coefficients in the drying liquid and swelling or shrinking of droplets.
Abstract: A survey is given of heat and mass transfer around droplets in spray dryers and the diffusional transport inside them. A calculational model is developed which includes variable diffusion coefficients in the drying liquid and swelling or shrinking of droplets. Calculations for droplets containing soluble solids show how the drying histories of droplets are influenced by three extreme patterns of air circulation and spray dispersion, and by droplet inflation. The influence of these factors on the properties of spray-dried liquid foods are discussed. Furthermore diffusion equations for binary systems are surveyed and diffusion coefficients for super-saturated aqueous maltose solutions are reported.

50 citations


Cites background from "Direct Contact Heat Transfer Betwee..."

  • ...Many surveys on correlations between the Nusselt and Sherwood numbers on the one hand and the Reynolds, Prandtl, Schmidt, and Peclet numbers on the other hand are available (Acrivos & Taylor, 1962; Sideman & Shabtai, 1964; Pritchard & Biswas, 1967; Rowe et al., 1965; Sideman, 1966)....

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References
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Journal Article

2,679 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe measurements of the shape and rate of rise of air bubbles varying in volume from 1·5 to 200 cm. 3 when they rise through nitrobenzene or water.
Abstract: Part I describes measurements of the shape and rate of rise of air bubbles varying in volume from 1·5 to 200 cm. 3 when they rise through nitrobenzene or water. Measurements of photographs of bubbles formed in nitrobenzene show that the greater part of the upper surface is always spherical. A theoretical discussion, based on the assumption that the pressure over the front of the bubble is the same as that in ideal hydrodynamic flow round a sphere, shows that the velocity of rise, U , should be related to the radius of curvature, R , in the region of the vertex, by the equation U = 2/3√( gR ); the agreement between this relationship and the experimental results is excellent. For geometrically similar bubbles of such large diameter that the drag coefficient would be independent of Reynolds’s number, it would be expected that U would be proportional to the sixth root of the volume, V ; measurements of eighty-eight bubbles show considerable scatter in the values of U/V 1/6 , although there is no systematic variation in the value of this ratio with the volume. Part II. Though the characteristics of a large bubble are associated with the observed fact that the hydrodynamic pressure on the front of a spherical cap moving through a fluid is nearly the same as that on a complete sphere, the mechanics of a rising bubble cannot be completely understood till the observed pressure distribution on a spherical cap is understood. Failing this, the case of a large bubble running up a circular tube filled with water and emptying at the bottom is capable of being analyzed completely because the bubble is not then followed by a wake. An approxim ate calculation shows that the velocity U of rise is U = 0·46 √( ga ), where a is the radius of the tube. Experiments with a tube 7·9 cm. diameter gave values of U from 29·1 to 30·6 cm./sec., corresponding with values of U /√( ga ) from 0·466 to 0·490.

999 citations

Journal ArticleDOI
TL;DR: In this article, it has been demonstrated that small bubbles in pure liquids can be held stationary or driven downwards by means of a sufficiently strong negative temperature gradient in the vertical direction, due to the stresses resulting from the thermal variation of surface tension at the bubble surface.
Abstract: It has been observed experimentally that small bubbles in pure liquids can be held stationary or driven downwards by means of a sufficiently strong negative temperature gradient in the vertical direction. This effect is demonstrated to be due to the stresses resulting from the thermal variation of surface tension at the bubble surface. The flow field within and around the bubble is derived, and an expression for the magnitude of the temperature gradient required to hold the bubble stationary is obtained. This expression is verified experimentally.

894 citations