Experimental investigation of heat and mass transfer in a LiBr-H2O solution falling film absorber on horizontal tubes: Comprehensive effects of tube types and surfactants

Abstract

This paper studied the effects of various surface geometries and surfactants on the LiBr-H2O solution falling film absorption, and the heat and mass transfer during the absorption process. Three different tubes (plain tube, floral tube and floral finned tube) were tested for the LiBr-H2O solution with two different surfactants (2-Ethyl-1-hexanol and 1-Octanol). The results indicate that the heat and mass transfer coefficients of each tube gradually decrease with solution falling down the tube bundle. It is also showed that the effect of surfactant on heat and mass transfer is obviously greater than that of tube surface geometry. Furthermore, with 2-Ethyl-1-hexanol as the surfactant, the heat and mass transfer can be improved by 400% and 350%, respectively. The results of comparative study show that the heat and mass transfer performance of floral tubes with 2-Ethyl-1-hexanol is more stable and reliable than others. Keywords: w water copper copper film falling film absorbed absorbed v vapor Greeks β mass transfer coefficient (g/(m 2 ⋅s)) ρ density (kg/m 3 ) solution mass fraction (wt%) logarithmic mean mass fraction difference (%) ′ equilibrium mass fraction of LiBr-H2O solution (%) Γ spray density (kg/(m⋅s)) λ thermal conductivity (W/(m⋅K))

Numerical analysis of different mass transfer models for falling film absorbers

“…Here, the diffusion flux of LiBr was evaluated using Fick's first law (Eq. ( 11)): (11) Most of the studies considered the commonly used vapour pressure equilibrium to calculate properties at equilibrium conditions at the interface. According to Yuan and Herold [46], when the interface reaches equilibrium, the chemical potential of the water in the solution ( ) is equal to the chemical potential of the vapour ( ) at equilibrium conditions.…”

“…Also, dry patches were observed in both studies of vertical plates of Kim and Infante Ferreira [7,8]. To improve the wettability, some studies included surfactants in the working mixture, primarily to decrease the surface tension and increase the wettability [9][10][11]. However, the results showed up to 400% improvement on the heat transfer coefficient.…”

Effect of using an ionic liquid as additive in water/LiBr mixture in a horizontal falling film absorber

“…In absorption chillers, the absorber holds utmost importance, influencing the performance, cost, and size of these machines significantly. The prevalent design in these machines involves a horizontal tube falling film, facilitating simultaneous heat and mass transfer [6]. Good wettability of horizontal tubes is important for absorption process which can be challenging in this configuration.…”