This study focuses on the performance of a falling-film plate generator involved in ammonia-water absorption machines. The generator comprises an array of parallel vertical grooved plates between which the heat transfer fluid and the ammonia-water desorbing solution circulate alternately. The solution forms falling films along the plates. The vapor generated by desorption flows downward in the center of the channel. A mathematical model is developed to analyze the performance of the generator in co-current and counter-current heating modes. The model is validated using results from the literature. Ammonia mass fraction in the outlet vapor, the mass effectiveness of the generator, and the energy per unit mass of ammonia generated at the exit of an ideal rectifier connected to the generator are used to compare the effects of different parameters such as the heating mode, the length and the number of plates, as well as the temperature and the flow rate of the heat transfer fluid. A reflection on the design and the conditions of use of the generator combining compactness and energy performance concludes the study.

falling film generator, plate heat exchanger, ammonia-water absorption chiller, generator numerical model.

Received: May 30, 2021; Accepted: July 8, 2021; Published: Janaury 31, 2022

How to cite this article: Ankita Gaur, Benoit Stutz, Shyam and François Boudéhenn, Modeling of an ammonia-water falling-film generator, JP Journal of Heat and Mass Transfer 25 (2022), 27-60. DOI: 10.17654/0973576322002

This Open Access Article is Licensed under Creative Commons Attribution 4.0 International License 

References:

[1] D. Azbel, Fundamentals of Heat Transfer for Process Engineering, Noyes Publications, Park Ridge, NJ, 1984, pp. 382.
[2] T. H. Chilton and A. P. Colburn, Mass transfer (absorption) coefficients, Ind. Eng. Chem. 26(11) (1934), 1183-1187.
[3] M. Conde, Thermophysical properties of ammonia-water mixtures for the industrial design of absorption refrigeration equipment, M. Conde Engineering (2006), 1-47.
[4] W. Cullen, Of the Cold Produced by Evaporating Fluids and of Some Other Means of Producing Cold, Essays and Observations Physical and Literary Read before a Society in Edinburg and Published by Them, II. (1756), 145-156.
[5] M. Determan and S. Garimella, Ammonia-water desorption heat and mass transfer in microchannel devices, Int. J. Refrigeration 34 (2011), 1197-1208.
[6] J. Fernandez-Seara, F. Uhia and J. Sieres, Analysis of an air cooled ammonia water vertical tubular absorber, Int. J. Thermal Sciences 46 (2007), 93-103.
[7] S. Garimella, Method and Means for Miniaturization of Binary-fluid Heat and Mass Exchangers, United States Patent 7,066, 241 B2 (2004).
[8] S. Garimella, Miniaturized heat and mass transfer technology for absorption heat pumps, Int. Sorption Heat Pump Conference, Munich, Germany, 1999.
[9] N. Goel and D. Y. Goswami, Analysis of a counter-current vapor flow absorber, Int. J. Heat and Mass Transfer 48 (2005), 1283-1292.
[10] K. E. Herold and M. Pande, Counterflow vapor-liquid exchange processes using ammonia/water, Int. Absorption Heat Pump Conference, Montreal, Quebec, Canada, 1996, pp. 481-488.
[11] S. Kakac, R. K. Shah and W. Aung, Handbook of Single-phase Convective Heat Transfer, New York., Wiley ed., 1987.
[12] Y. T. Kang, A. Akisawa and T. Kashiwagi, Experimental correlation of combined heat and mass transfer for Nh3-H20 falling film absorption, Int. J. Refrigeration 22 (1999), 250-262.
[13] T. Khir, A. Ben Brahim and R. K. Jassim, Boiling by forced convection of water-ammonia mixtures in a vertical tube, Canadian J. Chemical Engineering 83(3) (2005), 466-476.
[14] B. Kim, Heat and mass transfer in a falling film absorber of ammonia-water absorption systems, Heat Transfer Eng. 19(3) (1998), 53-63.
[15] Y. Lu, F. Stehmann, S. Yuan and S. Scholl, Falling film on a vertical flat plate - Influence of liquid distribution and fluid properties on wetting behavior, Applied Thermal Engineering 123 (2017), 1386-1395.
[16] B. Michel, N. Le Pierrès and B. Stutz, Performances of grooved plates falling film absorber, Energy 138 (2017), 103-117.
[17] L. Mendes, M. Collares and F. Ziegler, A rich solution spray as a refining method in a small capacity, single effect, solar assisted absorption machine with the pair Nh3/H2o: experimental results, Energy Conversion and Management 48(11) (2007), 2996-3000.
[18] H. Perez-Blanco, A model of an ammonia-water falling film absorber, ASHRAE Trans. 94(1) (1988), 467-483.
[19] F. Taboas, M. Valles, M. Bourouis and A. Coronas, Flow boiling heat transfer of ammonia/water mixture in a plate heat exchanger, Int. J. Refrigeration 33 (2010), 695-705.
[20] D. Triché, S. Bonnot, M. Perier-Muzet, F. Boudéhenn, H. Demasles and N. Caney, Experimental and numerical study of a falling film absorber in an ammonia-water absorption chiller, Int. J. of Heat and Mass Transfer 111 (2017), 374-385.
[21] P. Van Carey, Liquid vapor phase change phenomena: an introduction to the thermophysics of vaporization and condensation processes in heat transfer equipment, 2nd ed., CRC Press, 2018, pp. 600.
[22] W. Nusselt, Die oberflachen kondensation das wasserdampfes, VDI-Zeitschrift 54 (1910), 1154-1158.
[23] F. Xu and Y. Goswami, Thermodynamic properties of ammonia-water mixtures for power-cycle applications, Energy 24(6) (1999), 525-536.
[24] W. Yangda, R. Chengqin, X. Li and Y. Yang, Analysis of heat and mass transfer characteristics in vertical plat channels with falling film evaporation under uniform heat flux/uniform wall temperature boundary conditions, Int. J Heat and Mass transfer 108 (2017), 1279-1284.
[25] S. M. Yih and K. Y. Chen, Gas absorption into wavy and turbulent falling liquid films in a wetted-wall column, Chem. Eng. Commun. 17 (1982), 123-136.