A critical review of heat and mass transfer correlations for LiBr-H 2 O and NH 3 -H 2 O absorption refrigeration machines using falling liquid film technology

Narváez-Romo, Beethoven; Chhay, Marx; Aguilar, Elí Wilfredo Zavaleta; Simões-Moreira, José R.

doi:10.1016/j.applthermaleng.2017.05.092

Cited by 80 publications

(13 citation statements)

References 60 publications

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“…Experiments − reported an ammonia–water absorption process using a vertical tube-type falling-film absorber. The absorber consists of seven falling-film tubes with the diameter of φ20 × 2.5 mm, and a heat transfer area of 0.44 m 2 is formed.…”

Section: Results and Discussionmentioning

confidence: 99%

In Silico Modeling of a Novel Refrigeration Process of the Ammonia–Water Falling-Film Absorption

Wei

Zhang

et al. 2019

Ind. Eng. Chem. Res.

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Nowadays, the ammonia–water absorption refrigeration system (AARS) has attracted much attention due to its merits such as energy conservation and environment-friendliness. Meanwhile, growing studies have focused on the key equipment of ammonia–water absorber of AARS. Based on the thermodynamic and transfer property models that are specially determined in this study for the ammonia–water system, a calculational model of the ammonia–water falling-film absorber outside vertical tubes (AW-FFA-OVT) is established. The simulation of the ammonia absorption process is then carried out by the Fortran program in silico. The reliability of the physical models and the absorber model is verified by comparing with the experimental data from the literature. The mechanism of the proposed ammonia absorber is investigated by observing various key factors. The proposed model has already been successfully applied in the design and simulation of the key equipment in an actual AARS process.

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Section: Results and Discussionmentioning

confidence: 99%

In Silico Modeling of a Novel Refrigeration Process of the Ammonia–Water Falling-Film Absorption

Wei

Zhang

et al. 2019

Ind. Eng. Chem. Res.

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“…Economic and environmental factors are the main important reasons to initiate strong intention of improving efficiency of the thermal systems, which is mainly initiated by improving heat exchanger performance. Horizontal tube array type falling-film heat exchangers are actively utilized in process industries such as food industries [2], desalination [3,4], refrigeration [5,6], chemical, and petroleum refineries [7] and natural cooling methods [8]. The functional advantage of the gravity driven falling-film heat exchangers over the flooded heat exchangers makes them a better choice [9][10].…”

Section: Introductionmentioning

confidence: 99%

A 2-D numerical study of contact angle effect on transient falling-film flow over horizontal tubes

Kandukuri¹,

Deshmukh²,

Katiresan³

2022

Preprint

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The coverage of the liquid film over the horizontal tubes, particularly the wetting ratio, is important for heat transfer mechanism of gravity-driven evaporators and absorbers. A 2D, two-phase CFD model was developed to examine the falling-film hydrodynamics and transient flow mechanism for Reynolds numbers ranging from 100-500, contact angles spanning from 0°/30°/60°/90°, and inter tube spacing of 10 mm. The VOF method is used in this article to capture the gas-liquid interface. The findings showed that the complete spreading of the liquid film is difficult at low Reynolds numbers and high contact angles. The formation of dry regions on the tube wall as a result of insufficient liquid supply, liquid film breakage, and liquid film shrinkage. Furthermore, as the Reynolds number increases and contact angle decrease, the wetting ratio over the tube surface increases. It was worth noting that each contact angle must have a minimum Reynolds number in order to keep the surface completely wet. The research also found that for higher Reynolds numbers, the influence of contact angle on wettability of tube wall can be ignored. The liquid propagation time required to wet the tube surface increases as the contact angle value increases for the same Reynolds number. Fouling over the tubes can be aided by the formation of air voids near the lower stagnation zone.

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“…The majority of the heat and mass transfer takes place in the first three regions [9], thus the film distribution affects the heat and mass transfer mechanisms. In this study, a 2D CFD model for an aqueous LiBr solution falling over a horizontal tube was modeled, which is used in the refrigeration and multi-effect desalination industries [28][29][30][31].The LiBr concentration changes in an absorber and generator due to vapor absorption and evaporation. As the concentration varies, the thermophysical properties differ and alter the magnitude of forces and hence the film hydrodynamics.…”

Section: Introductionmentioning

confidence: 99%

CFD Analysis of Falling Film Hydrodynamics for a Lithium Bromide (LiBr) Solution over a Horizontal Tube

2020

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Falling film evaporators are used in applications where high heat transfer coefficients are required for low liquid load and temperature difference. One such application is the lithium bromide (LiBr)-based absorber and generator. The concentration of the aqueous LiBr solution changes within the absorber and generator because of evaporation and vapor absorption. This causes the thermophysical properties to differ and affects the film distribution, heat, and mass transfer mechanisms. For thermal performance improvement of LiBr-based falling film evaporators, in-depth analysis at the micro level is required for film distribution and hydrodynamics. In this work, a 2D numerical model was constructed using the commercial CFD software Ansys Fluent v18.0. The influence of the liquid load corresponding to droplet and jet mode, and the concentration, on film hydrodynamics was examined. It was found that the jet mode was more stable at a higher concentration of 0.65 with ±0.5% variation compared to lower concentrations. The recirculation was stronger at a low concentration of 0.45 and existed until the angular position (θ) = 10°, whereas at 0.65 concentration it diminished after θ = 5°. The improved heat transfer is expected at lower concentrations due to lower film thickness and thermal resistance, more recirculation, and a higher velocity field.

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A critical review of heat and mass transfer correlations for LiBr-H 2 O and NH 3 -H 2 O absorption refrigeration machines using falling liquid film technology

Abstract: h i g h l i g h t s A review of heat and mass transfer correlations based on falling film is showed. Heat and mass transfer correlations (Nu, Sh) are summarized. Non-dimensional (Nu, Sh) mapping for refrigeration and airconditioning are showed.

Cited by 80 publications

References 60 publications

In Silico Modeling of a Novel Refrigeration Process of the Ammonia–Water Falling-Film Absorption

In Silico Modeling of a Novel Refrigeration Process of the Ammonia–Water Falling-Film Absorption

A 2-D numerical study of contact angle effect on transient falling-film flow over horizontal tubes

CFD Analysis of Falling Film Hydrodynamics for a Lithium Bromide (LiBr) Solution over a Horizontal Tube

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