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Journal ArticleDOI

Experiments on a bubble absorber

01 Oct 1999-International Communications in Heat and Mass Transfer (Pergamon)-Vol. 26, Iss: 7, pp 975-984

AbstractExperiments are carried out on a bubble absorber, operating as part of a vapour absorption refrigeration system working with HCFC22-DMF to obtain heat and mass transfer and pressure drop data. The results are evaluated to obtain the dependence of absorption process on different parameters. Experimental data are compared with the numerical correlation relating Sherwood number, Reynolds number, Schmidt number and length to diameter ratio developed earlier by the authors. Also the experimental pressure drop is compared with the pressure drop obtained from other well known classical correlations and the numerical model.

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Citations
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Journal ArticleDOI
Ki Bong Lee1, Byung Hee Chun1, Jae Cheol Lee1, Chan Ho Lee1, Sung Hyun Kim1 
Abstract: An experimental analysis of ammonia–water absorption was performed in a plate-type absorber. The flow of water and ammonia gas was performed in the bubble mode. The experiments were made to examine the effects of solution flow rate and gas flow rate on the performance of the absorber. It was found that the increase of solution flow rate rarely affected the mass transfer, but improved the heat transfer. As the gas flow rate increased, slugging occurred in the bubble mode and influenced the thermal boundary layer. Finally, the results were converted into dimensionless numbers to elucidate physical phenomena and plotted as Sherwood number versus Reynolds number for mass transfer performance and Nusselt number versus Reynolds number for heat transfer performance.

43 citations

Journal ArticleDOI
Mahdi Ramezani1, Bo Kong1, Xi Gao1, Michael G. Olsen1, R. Dennis Vigil1 
Abstract: Experimental measurements of the volumetric liquid mass transfer and bubble size distribution in a vertically oriented semi-batch gas–liquid Taylor–Couette vortex reactor with radius ratio η = ri/ro = 075 and aspect ratio Γ = h/(ro − ri) = 40 were performed, and the results are presented for axial and azimuthal Reynolds number ranges of Rea = 119–143 and ReΘ = 0–35 × 104, respectively Based on these data, power-law correlations are presented for the dimensionless Sauter mean diameter, bubble size distribution, bubble ellipticity, and volumetric mass transfer coefficient in terms of relevant parameters including the axial and azimuthal Reynolds numbers The interaction between wall-driven Taylor vortices and the axial passage of buoyancy-driven gas bubbles leads to significantly different dependencies of the mass transfer coefficient on important operating parameters such as inner cylinder angular velocity and axial superficial gas velocity than has been observed in horizontally oriented gas–liquid Taylor vortex reactors In general, the volumetric mass transfer coefficients in vertical Taylor vortex reactors have a weaker dependence upon both the axial and azimuthal Reynolds numbers and are smaller in magnitude than those observed in horizontal Taylor vortex reactors or in stirred tank reactors These findings can be explained by differences in the size and spatial distribution of gas bubbles in the vertically oriented reactor in comparison with the other systems

43 citations

Journal ArticleDOI
Abstract: An absorber is a major component in the absorption refrigeration systems, and its performance greatly affects the overall system performance. In this study, both the numerical and experimental analyses in the absorption process of a bubble mode absorber were performed. Gas was injected into the bottom of the absorber at a constant solution flow rate. The region of gas absorption was estimated by both numerical and experimental analyses. A higher gas flow rate increases the region of gas absorption. As the temperature and concentration of the input solution decrease, the region of gas absorption decreases. In addition, the absorption performance of the countercurrent flow was superior to that of cocurrent. Mathematical modeling equations were derived from the material balance for the gas and liquid phases based on neglecting the heat and mass transfer of water from liquid to gas phase. A comparison of the model simulation and experimental results shows similar values. This means that this numerical model can be applied for design of a bubble mode absorber.

34 citations

Journal ArticleDOI
Abstract: This study reviews the developments of bubble absorption refrigeration technologies. Firstly, the principles of the bubble absorption refrigeration systems as well as bubble absorbers were introduced; And then bubble behavior characteristics during the absorption process were observed and expressed graphically; Thirdly, available bubble absorbers were investigated, modeled and compared; In addition, current and potential refrigerant-absorbent pairs in the bubble absorption refrigeration systems were analyzed, and about fifty fluids were involved totally. What’s more, methods of enhancing bubble absorption performance were researched, and also the influence mechanisms of these physical and chemical methods were explained; Finally, the development of bubble absorption refrigeration technologies were discussed from the aspects of driving energies, performance enhancement and application extension. The tendency of bubble absorption refrigeration technologies is expected to be high efficiency, miniaturization, and intellectualization. The expressed contents in this paper are expected to be useful for readers in the fields of absorption refrigeration technologies and the medium-low grade heat utilization technologies, especially for the equipment operating in the unsteady conditions (e.g. swing, bump, jolt, scram, etc.).

25 citations

Journal ArticleDOI
Abstract: A phenomenological theory of heat and mass transfer is applied to model the absorption of the R134a gas bubble in liquid R134a–dimethyl formamide (DMF) solution. Required properties of R134a–DMF liquid solution namely liquid density, surface tension, diffusion coefficient, thermal conductivity, specific heat, etc., have been calculated using experimental correlations. Results have been obtained by modeling on a computer using MATLAB. The bubble dynamics during bubble growth are studied using this model. Liquid concentration, temperature, heat and mass transfer rates, local heat and mass transfer coefficients are estimated at the bubble interface. Absorption rate, coupled heat transfer rate, average heat and mass transfer coefficients over the entire bubble life span are also calculated. This model results are validated using experimental results of ammonia–water solution. The maximum bubble radius determined from this study is compared with available experimental correlations and it is found that agreement is good. Heat and mass transfer rates obtained from this model are compared with the literature experimental results. The results are in good agreement with the predictions of the model.

23 citations


Cites background from "Experiments on a bubble absorber"

  • ...[7] have also carried out experimental studies on a vertical tubular bubble absorber working with R22–DMF....

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References
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Journal ArticleDOI
Abstract: The various factors contributing to the motion of the bubbles in two-phase flow are analysed. A theory is presented which shows that the velocity of the bubbles consists of a component equal to the superficial liquid velocity, a component equal to the superficial gas velocity and component due to buoyancy. A simple experiment in support of the theory (involving direct measurement of the buoyancy component of velocity by suddenly stopping the flow of gas and timing the rise of the swarm of bubbles) is described. The energy losses associated with two-phase gas-liquid flow are discussed at some length, and it is shown that in bubble flow “the energy loss due to slip” is closely related to the buoyancy component of bubble velocity.

249 citations

Journal ArticleDOI
Abstract: Vertical upward concurrent air-liquid flow was investigated under isothermal conditions in a test section of 1-in. schedule 40 pipe. Pressure drop was measured with a mercury manometer connected to two pressure taps 20 ft. apart in the section. Liquid was trapped between two quick shutoff valves activated by two solenoid valves. The liquid was druined from the section to provide the holdup data. Six liquids were used to determine the effect of density, viscosity, and surface tension. The experimental holdup, and two-phase pressure drop data were not in agreement with Lockhart-Martinelli type of correlation for horizontal flow. A statistical correlation for holdup was developed to include fluid physical properties, total mass velocity, and the air-liquid ratio entering the pipe. Similarly a pressure drop correlation was developed which expressed the two-phase pressure drop as a function of the slip velocity, liquid physical properties, and total mass velocity. This correlation showed an average percentage error of less than 15% between the observed and the calculated total pressure drop.

70 citations

Journal ArticleDOI
Abstract: A model is developed for calculation of simultaneous heat and mass transfer processes in vertical bubble absorbers as used for ammonia-water absorption refrigeration systems. Some preliminary experiments have been performed in an absorber without heat removal. The results from these experiments are compared with the literature and give a first indication about the methods for prediction of the absorption process. Experiments have also been performed with simultaneous heat removal. The internal diameters of the absorbers tested were 10.0, 15.3, and 20.5 mm. The mass transfer coefficients resulting from these experiments are correlated by a modified Sherwood relation. An interative procedure is presented which allows design of vertical tubular bubble absorbers for ammonia-water absorption refrigeration systems.

43 citations

Book ChapterDOI
Abstract: Publisher Summary Two-phase gas–liquid glow is encountered in an increasing number of important situations, and a clear understanding of the rates of transfer of momentum, heat, and material are required for logical and careful design and operation of a very wide variety of chemical engineering equipment and processes. In the production and transport of crude petroleum and petroleum products, two-phase flow is finding increasing use. Two-phase flow systems may be classified initially by composition, as containing a single component, or two or more components with any one component present in both phases or only essentially in one or the other phase. Varieties of flow patterns include bubble flow, plug flow, stratified flow, wavy flow, snug flow, annular flow, mist or spray flow. The problem of two-phase-flow classification is complicated by the inevitable differences because of individual interpretations of visual observations and also by differences in terminology. This chapter investigates a number of definite flow patterns. In the case of single-component two-phase flow—such as in vaporizing water—physical equilibrium is commonly assumed and seems to yield reasonable results, even though it might seem that supersaturation could occur. The rate of mass transfer among phases, therefore, is not a limiting process for single component flow.

43 citations

Journal ArticleDOI
Abstract: A model of the absorption process in a vertical tubular bubble absorber working with R22-DMF, R22-DMA, R22-DMETEG, R22-DMEDEG and R22-NMP is developed using finite element method employing Galerkin's technique. The objective of this paper is to study the influence of the liquid and gas properties on the volumetric mass transfer coefficient. Analysis have also been done using ammonia-water as working fluid, the results obtained are compared with those in the literature and the agreement is found to be good. A correlation for mass transfer coefficient is proposed as a function of Reynolds number, Schmidt number and length to diameter ratio. The correlation can be used either in estimating the mass transfer rates or in fixing up any of the major design parameters namely length required for complete absorption and diameter.

28 citations