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Journal ArticleDOI

A theoretical analysis of direct contact evaporation in spray columns

01 Nov 1983-International Communications in Heat and Mass Transfer (Pergamon)-Vol. 10, Iss: 6, pp 533-543

AbstractThis article deals with a theoretical analysis of direct contact latent heat transfer between two immiscible liquids in a counterflow spray column. The non-dimensional parameters governing the evaporation process are identified and a study of the effects of the variation of these parameters is made. The longitudinal dispersion in the continuous phase is taken into account in the analysis. The predicated column heights required for complete evaporation compare favourably with the available experimental data. The theoreatical model also predicts the temperatue profile of the dispersed phase along the column.

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Citations
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Journal ArticleDOI
Lihong Jiang1, Qunwu Huang1, Yiping Wang1, Yong Cui1, Hailing Fu1 
Abstract: Experimental study was conducted to investigate the effect of packing on performance of direct contact evaporative heat transfer for n-pentane and water operated in a bubble column with concurrent upward flow The optimal column height and volumetric heat transfer coefficient with and without Dixon rings were examined and compared under the conditions of different flow velocity ratios of n-pentane to water, temperature differences between water and n-pentane and distributor apertures It is found that packing enables optimal column height to decrease significantly Optimal column height considerably reduces maximally by 25% under temperature difference less than 8 °C and flow velocity ratio 0265 Volumetric heat transfer coefficient is 100–450 kW/(m3 °C) with packing while 40–150 kW/(m3 °C) without packing Especially when the flow velocity ratio is 0265 and 0192, volumetric heat transfer coefficient with packing is nearly twice as much as that in bubble column without packing at the temperature difference below 8 °C The effect of packing at temperature difference below 8 °C is more pronounced Besides, backmixing observed in the experiment was demonstrated, and its significant influence on evaporative heat transfer performance was also analyzed

8 citations

Journal ArticleDOI
Abstract: Reference [1] presented a simple model on direct contact heat transfer between two immiscible liquids in a countercurrent spray column and got the numerical solution with the variable step Runge-Kutta method. This paper obtains the analytical solution of this model, from which the exact relationships between target quantities and influence quantities are given. In this solution the explicit formulae for the column height required for complete evaporation and the temperature of continuous phase at the end of evaporation are given, which will be very useful for the initial design of spray columns in engineering. The two formulae have the following forms

6 citations

Journal ArticleDOI
Yanchao Jin1, Runzhi Hu1, Yiping Wang1, Yong Cui1, Yun Liu1, Qunwu Huang1 
Abstract: In the experiment, direct contact evaporation in both co-current and counter-current flow were compared with pentane as dispersed phase and water as continuous phase. Dixon rings were also added into the column to enhance heat transfer in those two different contact ways. Axial temperature distribution, optimal column height and volumetric heat transfer coefficient are important parameters to evaluate heat transfer performance. The influences coming from pentane flow rate, water flow rate and inlet water temperature have also been carefully studied. Compared with co-current flow, the optimal column height decreased 15–25% and but heat transfer coefficient increased in the same scale no matter with packing or not in the counter-current condition. The optimal column height was halved and heat transfer coefficient doubled with packing when other factors were the same. Both optimal height and heat transfer coefficient would decrease with the increasing inlet water temperature. Packing in the column was an effective approach to enhance heat transfer performance especially under the condition of low water temperature as well as high water flow rate.

5 citations


References
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Book ChapterDOI
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.

43 citations

Journal ArticleDOI
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.

43 citations

Journal ArticleDOI
Abstract: The initial drop size of volatile fluids evaporating within immiscible, nonvolatile liquids was experimentally related to the overall heat transfer coefficient in single and multiparticle systems. Coalescence and turbulence diminish the effects of the initial size, which are thus limited to the lower part of the exchanger where single-drop characteristics are maintained. Condensation data of single bubbles are in good agreement with the single-drop relationship.

39 citations

Journal ArticleDOI
Abstract: The present investigation deals with a theoretical analysis of direct contact sensible heat transfer between two immiscible liquids in a countercurrent spray column. The non-dimensional parameters governing the heat transfer process are identified and a study of the effects of the variation of these parameters is made. The predicted column heights and the temperature profiles of both the phases along the column compare favourably with the available experimental data.

7 citations