Vertical-tube aqueous LiBr falling film absorption using advanced surfaces

A heat and mass transfer test stand was fabricated and used to investigate nonisothermal falling film absorption of water vapor into a solution of aqueous lithium bromide. The absorber was made of borosilicate glass for visual inspection of the falling film. Experiments were conducted on internally cooled tubes of about 0.019 m outside diameter and of 1.53 m length. Testing evaluated a single absorber tube's performance at varying operating conditions, namely different cooling-water flow rates, solution flow rates, pressures, temperatures, and concentrations. Advanced surfaces were identified that enhanced absorber load and the mass of absorbed vapor. A pin-fin tube with 6.4-mm pitch absorbed about 225% more mass than did a smooth tube. A grooved tube was the second best performer with 175% enhancement over the smooth tube. Increasing the cooling water flow rate to 1.893×10^-4 m³/s caused about a 300% increase in the mass absorbed for the grooved tube compared with the smooth tube. Results showed that the pin-fin tube with 6.4-mm pitch and the grooved tubes may enhance absorption to levels comparable to chemical enhancement in horizontal smooth tube absorbers. Absorber load, the transport coefficients, and pertinent absorption data are presented as functions of dimensionless numbers. These experimental data will prove useful in formulating analytical tools to predict vertical-tube absorber performance.