Combined heat and mass transfer under different inlet subcooling modes during NH3-H2O falling film absorption process

Yong Tae Kang, Y. Fujita, T. Kashiwagi

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1 Citation (Scopus)

Abstract

Experiments were conducted for ammonia-water falling film absorption in a plate heat exchanger with offset strip fins. The objectives of this paper were to analyze combined heat and mass transfer during the ammonia-water absorption process under different inlet subcooling modes, and to obtain heat transfer coefficients (Nusselt number). This paper examined the effects of the inlet subcooling modes, the inlet concentration difference, liquid Reynolds number, and vapor Reynolds number on the heat transfer performance. Inlet liquid concentrations were set at 0, 5, 10, and 15 percent in mass of ammonia, while inlet vapor concentration ranged from 64.7 to 83.6 percent. Experiments were conducted in three ways according to the inlet subcooling conditions, i.e., Case A (Tv>Tl), Case B (TV∼Tl), and Case C (Tv<Tl). In Case A, there was a rectification process at the top of the test section by the inlet subcooling effect. Water desorption was confirmed in the experiments, which resulted in a lower absorption performance. The heat transfer coefficient increased as the inlet subcooling increased in all cases. The effect of inlet subcooling on heat transfer performance was more significant in Case A than in Cases B and C. The inlet subcooling had more significant effect on the heat transfer performance than the inlet concentration difference. Nusselt number increased as liquid and vapor Reynolds numbers increased. The vapor velocity should be maximized to increase absorption performance in cocurrent ammonia-water absorption process. The parametric analysis provides fundamental understandings of the ammonia-water absorption process, and thus gives a guideline for heat exchanger compactness in ammonia-water absorption systems.

Original languageEnglish
Pages (from-to)242-249
Number of pages8
JournalJournal of Energy Resources Technology, Transactions of the ASME
Volume123
Issue number3
Publication statusPublished - 2001 Sep 1
Externally publishedYes

Fingerprint

Ammonia
heat transfer
mass transfer
Mass transfer
Water absorption
Heat transfer
ammonia
Vapors
Reynolds number
Nusselt number
Heat transfer coefficients
Heat exchangers
Liquids
water
liquid
Water
Experiments
experiment
Desorption
desorption

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Fuel Technology
  • Renewable Energy, Sustainability and the Environment

Cite this

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abstract = "Experiments were conducted for ammonia-water falling film absorption in a plate heat exchanger with offset strip fins. The objectives of this paper were to analyze combined heat and mass transfer during the ammonia-water absorption process under different inlet subcooling modes, and to obtain heat transfer coefficients (Nusselt number). This paper examined the effects of the inlet subcooling modes, the inlet concentration difference, liquid Reynolds number, and vapor Reynolds number on the heat transfer performance. Inlet liquid concentrations were set at 0, 5, 10, and 15 percent in mass of ammonia, while inlet vapor concentration ranged from 64.7 to 83.6 percent. Experiments were conducted in three ways according to the inlet subcooling conditions, i.e., Case A (Tv>Tl), Case B (TV∼Tl), and Case C (Tv<Tl). In Case A, there was a rectification process at the top of the test section by the inlet subcooling effect. Water desorption was confirmed in the experiments, which resulted in a lower absorption performance. The heat transfer coefficient increased as the inlet subcooling increased in all cases. The effect of inlet subcooling on heat transfer performance was more significant in Case A than in Cases B and C. The inlet subcooling had more significant effect on the heat transfer performance than the inlet concentration difference. Nusselt number increased as liquid and vapor Reynolds numbers increased. The vapor velocity should be maximized to increase absorption performance in cocurrent ammonia-water absorption process. The parametric analysis provides fundamental understandings of the ammonia-water absorption process, and thus gives a guideline for heat exchanger compactness in ammonia-water absorption systems.",
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