Direct contact heat transfer with change of phase: Spray-column studies of a three-phase heat exchanger (original) (raw)

Abstract

Transfer characteristics are presented for a perforated plate-spray column in which a volatile dispersed phase evaporates while rising in the continuous, counterflowing, immiscible phase. Optimal column heights, volumetric transfer coefficients, holdup, and foam heights are reported as functions of flow rate and temperature approach for a pentane-water system, A comparison with related studies is presented. Recently multiphase exchangers where latent heat rather than sensible heat is transferred between immiscible fluids have been effectively used in water desalination by direct contact freezing. Some of the technical and economical aspects of utilizing these multiphase exchangers were reported by Umano (1), Wiegandt (2, 3) , and others (4). Experimental direct freezing pilot plants (5) are presently in the process of accumulating valuable technical know-how. Unlike the multiphase exchangers, where both the dispersed and the continuous fluids undergo change of phase, three-phase exchangers may be used for heat transfer at various temperature levels. The latter obviously depends on the choice of the transfer fluid. Stagewise operation of three-phase exchangers in a closed evaporation and condensation cycle was recently proposed by Harriott and Wiegandt (6) for simultaneous cooling and heating of sea water and desalined water streams in countercurrent flow. Some experimental data of condensation of methylene chloride in water flowing concurrently in a two-stage packed bed and a single-stage sieve-plate column were reported (6). Limited data were also reported on cocurrent flow evaporation of methylene chloride or pentane in water in a 2-in. diameter column. Wilke et al. (7) studied evaporation of water from sea water flowing concurrently in direct contact with hot Aroclor in an horizontal 3-in. pipe and steam condensation in direct contact with Aroclor in packed columns. Studies of condensation of steam in Aroclor in a simulated cocurrent spray cohmn were also reported (8). Despite increasing interest in technical information on direct contact heat transfer with change of phase, very little is known regarding the basic mechanism and heat transfer characteristics associated with evaporation of dispersions in immiscible liquids. Studies of single-drop evaporation in immiscible liquid media were recently reported by Sideman et al. (9, 10). These, however, may not be directly extended to population of drops, where the onset of nucleation is not simultaneous (and should be dependent on the vapor holdup and degree of turbu

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