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Modelling of Coupled Heat and Mass Transfer in a Water-Cooled Falling-Film Absorber Working with an Aqueous Alkaline Nitrate Solution

Author

Listed:
  • María E. Álvarez

    (School of Chemical Engineering, Universidad Metropolitana, Av. Boyacá, Caracas-Miranda 1073, Venezuela)

  • Mahmoud Bourouis

    (Department of Mechanical Engineering, Universitat Rovira i Virgili, Av. Països Catalans No. 26, 43007 Tarragona, Spain)

Abstract

A theoretical model was developed to investigate a falling-film absorber on horizontal tubes with an aqueous alkaline nitrate solution as working fluid. The absorbent, composed of an aqueous solution of nitrates (Li, K, Na) in salt mass percentages of 53%, 28%, and 19% respectively, offers favourable thermal stability, corrosiveness, and heat and mass transfer conditions which can be appropriate for absorption cooling cycles driven by high-temperature heat sources. The mathematical model developed characterises the heat and mass transfer processes and the flow regime effect (droplet-formation, droplet-fall, and falling-film) on the falling-film absorber. The results show the importance of the falling-film and droplet-formation flow regimes in the absorption process. The solution temperature and concentration profiles inside the absorber were established together with their values at the exit. The results obtained by the theoretical model were well in agreement with the experimental data obtained by the authors in a previous study. Deviations in predicting the solution and cooling water temperatures at the absorber exit were around 1 °C and for the concentration of the solution leaving the absorber, around 0.49%. The mathematical model also predicts the absorption rate at 4.7 g·m −2 ·s −1 for the absorber design and operating conditions used in the present work. This value is 22% higher than the experimental value obtained by the authors in their previous experimental work. The deviation is attributed to approximations incorporated into the model, especially as regards surface wettability and calculation of the mass transfer coefficients for each flow regime.

Suggested Citation

  • María E. Álvarez & Mahmoud Bourouis, 2021. "Modelling of Coupled Heat and Mass Transfer in a Water-Cooled Falling-Film Absorber Working with an Aqueous Alkaline Nitrate Solution," Energies, MDPI, vol. 14(7), pages 1-23, March.
    • Handle: RePEc:gam:jeners:v:14:y:2021:i:7:p:1804-:d:523352
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    References listed on IDEAS

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    1. Álvarez, María E. & Bourouis, Mahmoud, 2018. "Experimental characterization of heat and mass transfer in a horizontal tube falling film absorber using aqueous (lithium, potassium, sodium) nitrate solution as a working pair," Energy, Elsevier, vol. 148(C), pages 876-887.
    2. Álvarez, María E. & Hernández, José A. & Bourouis, Mahmoud, 2016. "Modelling the performance parameters of a horizontal falling film absorber with aqueous (lithium, potassium, sodium) nitrate solution using artificial neural networks," Energy, Elsevier, vol. 102(C), pages 313-323.
    3. Amaris, Carlos & Vallès, Manel & Bourouis, Mahmoud, 2018. "Vapour absorption enhancement using passive techniques for absorption cooling/heating technologies: A review," Applied Energy, Elsevier, vol. 231(C), pages 826-853.
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    Cited by:

    1. Karolina Weremijewicz & Andrzej Gajewski, 2021. "Measurement Uncertainty Estimation for Laser Doppler Anemometer," Energies, MDPI, vol. 14(13), pages 1-11, June.
    2. Zhihua Wan & Ping Wang & Huanying Shen & Yanzhong Li, 2022. "Falling Film Flow and Heat Transfer of Cryogenic Liquid Oxygen on Different Structural Surfaces," Energies, MDPI, vol. 15(14), pages 1-18, July.

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