Wettability measurement and criterion for a falling film absorber

The objectives of this paper are to develop a new method of wettability measurement and to study the effect of surface roughness on the wettability in a LiBr/H₂O falling film absorber. Three absorber tubes with micro-scale roughness are tested in a falling film absorber installed in a test rig. Inlet solution temperature (30 - 50°C), concentration (55-62 weight % of LiBr) and mass flow rate (0.74-2.71 kg/min) are considered as key parameters. A new method is proposed to estimate the wettability of a tube by measuring a minimum mass flow rate to wet the tube completely. Reynolds number is ranged from 30 to 120 by controlling the inlet mass flow rate. The wettability for the structured surfaces was higher than that for the bare tube. The wettability decreased linearly along the vertical location as low as 65 % for the bare tube and 75% for the micro-scale scratched tubes. The wettability increased with increasing the solution temperature and the solution mass flow rate. The effect of film Reynolds number on the wettability in the bare tubes was more significant than that in the micro-scale scratched tubes. The experimental results of wettability can be used in the design of absorbers with micro-scale roughness.