An Experimental Study of Simultaneous Heat and Mass Transfer in Falling Film and Bubble Mode Absorbers

In this study we investigated the lithium chloride water vapor absorption process for falling film and bubble column absorbers under the same operating conditions. The results obtained were used to analyze the transfer process during the absorption of water vapor in an aqueous solution of LiCL. The performance of both absorbers was investigated for various solution flow rates and various gas flow rates. The results showed that bubble absorber is superior to the falling film mode for mass and heat transfer. Increasing the solution flow rates rarely affected the mass transfer but improved the heat transfer. As the gas flow rate increased, channels were formed in the film, which decreased the mass transfer in the falling film. But in the bubble column, increasing the gas flow rate influenced the boundary layer and therefore enhanced mass transfer. To evaluate the performance of mass and heat transfer, experimental results obtained were plotted as Nusselt and Sherwood numbers versus operating conditions for falling film and bubble modes, respectively, and the following empirical correlations were proposed: For falling film mode: N-u = 0.0137Re(sol)(0.5)Re(gas)(0.03) (Delta C/C-sol,C-i)(0.15) (Delta T/T-i)(0.3) Sh = 658.5Re(sol)(0.02)Re(gas)(0.96) (Delta C/C-sol,C-i)(0.064) For bubble mode: N-u = 3.13Re(sol)(0.26)Re(gas)(0.3) (Delta c/C-sol,C-i)(0.086) (Delta T/T-i)(0.068) sh = 43.57Re(sol)(0.04)Re(gas)(0.28) (Delta C/C-sol,C-i)(0.046)