Heat and mass transfer in vertical tubular bubble absorbers for ammonia-water absorption refrigeration systems

doi:10.1016/0140-7007(84)90004-5

International Journal of Refrigeration

Volume 7, Issue 6, November 1984, Pages 348-357

https://doi.org/10.1016/0140-7007(84)90004-5 Get rights and content

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.

Résumé

On a mis au point un modèle en vue du calcul des transferts simultanés de chaleur et de masse dans des absorbeurs tubulaires verticaux de bulles à utiliser dans les réfrigérateurs à absorption ammoniac-eau. La forme de l'absorbeur est présentée Fig. 1 et le schéma de principe Fig. 2.

On a réalisé des expériences préliminaires en utilisant un absorbeur adiabatique, mais la plupart des expériences utilisaient une circulation annulaire de méthanol refroidi pour éliminer la chaleur de l'absorbeur. L'écoulement de gaz dans l'absorbeur passait de l'écoulement mousseux à l'écoulement diphasique intermédiaire et finalement à l'écoulement à bulles. Les tubes de l'absorbeur essayés avaient un alésage de 10.0, 15,3 et 20,5 mm et environ 1 m de long.

La chute de pression mesurée par unité de longueur est comparée par de diverses équations de prévision au tableau 1 et la fraction de vide est comparée tableau 2. Le coefficient global de transfert de chaleur est donné par l'équation (12) et le coefficient pelliculaire intérieur par léquation (16). Le coefficient de transfert de masse est corrélé par l'équation (20) l'effet de la hauteur du tube étant défini, pour le domaine expérimental donné, par l'équation (26).

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Heat and mass transfer performances of the bubble absorption process had been researched by some scholars. The researches were mainly focused on two kinds of structures, plate-type absorber [8–12] and tubular absorber [13–17], with NH3/H2O, NH3/LiNO3 or NH3/(LiNO3+H2O) as working fluids. Research results showed that the key parameters affecting heat and mass transfer performance of bubble absorption process were refrigerant vapor and absorption solution flow rates, absorption solution temperature and mass fraction, absorption pressure, cooling-water temperature and flow rate.
A comparing investigation between the simulated model and experimental verifications for the R124 (2-chloro-l,l,l,2,-tetrafluoroethane)-DMAC (N′, N′- dimethylacetamide) bubble absorption process in a vertical tubular absorber were performed. The objective of the investigation was to model the R124-DMAC bubble absorption process and to verify the model results with visual and non-visual experiments under similar operating conditions. The comparing results between the model and experiments were consistent well. The two-phase and single-phase convective heat transfer coefficient and two-phase mass transfer coefficient enhanced with increase of vapor and solution flow rates, and decreased with increase of solution inlet temperature, solution inlet mass fraction and nozzle orifice diameter. The two-phase mass transfer coefficient varied slightly with vapor flow rates rising. Finally, new correlations of the bubble absorption height, two-phase and single-phase convective heat transfer coefficients and two-phase mass transfer coefficient for R124-DMAC bubble absorption process in a vertical tubular bubble absorber were proposed. All of the correlation equations could predict about 90% of these parameters at a margin of error less than 15% under the operating conditions.
Vapour absorption enhancement using passive techniques for absorption cooling/heating technologies: A review
2018, Applied Energy
Citation Excerpt :
Interest on the investigation of the bubble absorption process for absorption systems has also been increasing in the last years. Researchers have focussed on the description and explanation of the phenomena that take place in the absorption and the way to improve it in an effort to contribute to the technological development of absorption systems for refrigeration or heating [84–101]. Documents reported in the open literature include sensitivity studies of the heat and mass transfer processes in bubble absorbers with different mixtures by analysing the effect of the absorption heat removal [85], internal tube diameter [85], solution flow [85–87,94,96,98,100,101], inlet solution temperature [84,86,88,96–98,100,101], solution concentration [85–87,92–98,100,101], solution side pressure [85–87,96], coolant flow [87,94,101], coolant temperature [87,94,101], inlet vapour temperature [88], inlet gas orifice size [90,91,98–101], inlet vapour flow [90,91,94–96,98,100,101].
The absorption cooling/heating system is an old technology that has been relegated by the more efficient mechanical vapour compression systems. However, if they were driven by residual heat or solar thermal energy, advanced absorption technologies for cooling or heating could supply current demand and have a much lesser impact on the environment. With the cost of electricity rising and the climate change more and more in evidence, it would be a positive move towards energy saving.
Since the absorber is recognized the key component of the absorption system due to the complex heat and mass transfer process that take place there, the improvement of the absorption process would mean reducing the absorber and desorber sizes to make them more compact, or reducing the system driving temperature for low grade temperature applications.
The objective of this paper is to identify, summarize, and review the experimental studies dealing with the enhancement of vapour absorption processes in absorbers by means of passive techniques i.e. advanced surface designs and the use of additives and nanofluids. This review also includes an exhaustive and detailed scrutiny on absorption processes in falling film, spray and bubble mode absorbers for different working fluids, evidencing the experimenting techniques, operating conditions, and latest advances in terms of heat and mass transfer enhancement in absorbers. Finally, the paper contains suggestions for future work to be carried out to obtain mass transfer enhancement in absorbers and absorption cooling/heating systems.
Development of bubble absorption refrigeration technology: A review
2018, Renewable and Sustainable Energy Reviews
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.).
Heat and mass transfer characteristics of R124-DMAC bubble absorption in a vertical tube absorber
2017, Experimental Thermal and Fluid Science
Citation Excerpt :
However, increases of solution temperature and mass fraction or cooling medium temperature had negative effects on the absorber performance. For the vertical tubular bubble absorber, the heat and mass transfer processes with ammonia-water as working pairs were also investigated by experiments and modeled analyses [25–29]. Generally, three kinds of flow patterns, churn, slug and bubble flow patterns would be formed in the absorber because the bubbles were constrained by tube wall.
Experimental investigation for a visual vertical tubular bubble absorber was done with R124 (2-chloro-l,l,l,2,-tetrafluoroethane)-DMAC (N′,N′- dimethylacetamide) as working fluid. The objective of this investigation was to obtain key parameters that affect on the heat and mass transfer performance of R124-DMAC bubble absorption, such as vapor and solution flow rates, solution inlet temperatures and mass fractions, and nozzle orifice diameters. The results showed that the overall heat and volumetric mass transfer coefficients increased with increase of vapor and solution flow rates, and decreased with increase of solution inlet temperatures and mass fractions, and the nozzle orifice diameter. Especially, solution inlet mass fractions and the nozzle orifice diameter significantly influenced on mass transfer performance, while solution inlet temperatures and vapor flow rates influenced greatly on the heat transfer performance. A correlation of Sherwood number for R124-DMAC mixture in a visual vertical tubular bubble absorber was provided by the method of multiple linear regressions. The error band from the present study was within ±15%.
A critical review of heat and mass transfer correlations for LiBr-H<inf>2</inf>O and NH<inf>3</inf>-H<inf>2</inf>O absorption refrigeration machines using falling liquid film technology
2017, Applied Thermal Engineering
This paper presents an extensive review of heat and mass transfer correlations in the framework of sorption machines operating based on the falling film technology, in which ammonia-water and lithium bromide-water are used as the working fluid pairs. Heat and mass transfer correlations are summarized as well as the application range and geometrical configuration. In order to compare the correlations found in the recent and classical literature, typical operation conditions for absorption refrigeration cycles have been adopted. Heat and mass transfer correlations have been evaluated for both working fluid pairs, mapping the possible heat and mass transfer values for refrigeration and air-conditioning applications. The study allowed comparing the two technologies using the same operational conditions. The ascertainment that the transfer correlations may behave differently has been showed. Finally, this work suggests that future researches about heat and mass transfer behavior should be to carry out for realistic operational condition of the absorption refrigeration cycles.
Experimental investigation for heat and mass transfer characteristics of R124-DMAC bubble absorption in a vertical tubular absorber
2017, International Journal of Heat and Mass Transfer
Experimental investigation for a copper vertical tubular bubble absorber was done with R124 (2-chloro-l,l,l,2,-tetrafluoroethane)-DMAC (N′,N′-dimethylacetamide) as working fluid. The objective of the investigation was to explore key parameters affecting heat and mass transfer characteristics of the bubble absorber and propose new correlations for heat and mass transfer coefficients respectively for the R124-DMAC bubble absorption. The parameters include vapor and solution flow rates, solution inlet temperatures and mass fractions, nozzle orifice diameters and cooling water inlet temperatures. The results showed that to reduce the solution, cooling water inlet temperature and nozzle orifice diameter or to increase vapor and solution flow rate could enhance the heat and mass transfer performance of the absorber. Finally, correlations of Nusselt number and Sherwood number for calculating heat and mass transfer coefficients were proposed, respectively. Both correlations could predict about 90% of the experimental values at a margin of error less than 20%.

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Heat and mass transfer in vertical tubular bubble absorbers for ammonia-water absorption refrigeration systemsTransfert de chaleur et de masse dans les absorbeurs tubulaires verticaux de bulles pour les systèmes frigorifiques à absorption ammoniac-eau

Abstract

Résumé

Chemical Engineering Science

Stofoverdracht door beweeglijke grensvlakken

Grundlagen der Einphasen- und Mehrphasenströmungen

What's new in absorption with chemical reaction?

Transactions of the Institution of Chemical Engineers

Stroming en warmteoverdracht

Physical and chemical mass transfer in horizontal cocurrent gas-liquid slug flow

Chemical Engineering Journal

Messungen zum Wärme- und Stoffübergang am Rieselfilm

Holdup and pressure drop with gas-liquid flow in a vertical pipe

AlChE J