Study of the influence of surfactants and surface treatments on the minimum wetting rate of falling films of aqueous LiBr and Carrol solutions

The wettability is one of the critical properties of the falling film type absorber, limiting the wetting area in the absorber, hence the total mass transfer performance. To achieve low values of wetting rate in the absorber is an interesting feature to decrease the pumping power and, therefore, the size of the solution pumps. However, studies about the relationship between surface tension, contact angle, and minimum wetting rate are limited. In this work, working pairs LiBr - H2O and Carrol - H2O (Carrol contains LiBr and EG - Ethylene glycol - with a mass ratio at 4.5:1) with additives 2 - EH (2 - Ethyl - 1 - hexanol) and PCM (1 - Phenylethanol) are studied focusing on the surface tension and minimum wetting rate. The surface tension of the two solutions is measured at various temperatures and concentrations employing the Du Rouy method. The experimental results demonstrate the surface tension of both solutions and the effect of liquid/gaseous surfactants on the surface tension is similar. Also, the minimum wetting rate (MWR) is measured in an annular falling film experimental set-up employing the dewetting method using different materials tubes and fluids. The experimental results of MWR test agree with theoretical predictions and empirical correlations with a discrepancy of less than 10%. When the tube is coated with a hydrophilic surface, a contact angle at 30 degrees is achieved, and the minimum mass flow of water to achieve complete wettability on the coated SS tube is reduced from 0.096 to 0.025 kg center dot m(-1)center dot s(-1).

Automated summary

Wettability is a critical property of falling film type absorbers. This study focuses on the relationship between surface tension and minimum wetting rate, as well as the influence of different working fluids on surface tension and minimum wetting rate.