Performance of Horizontal Smooth Tube Absorber With and Without 2-Ethyl-Hexanol

Absorption of water vapor into aqueous lithium bromide is a fundamental step in absorption refrigeration. When the liquid film is laminar, the coupled heat and mass transfer process is controlled by mass transfer, resulting in low transfer coefficients. Significant augmentation of mass transfer, and hence of the coupled process, is achieved by introducing a trace amount (on the order of 100 ppm) of 2-ethyl-hexanol. The alcohol acts as a surfactant and drives Marangoni convection that effectively mixes the liquid providing a much higher effective mass diffusivity. The film flow in the presence of the alcohol is noticeably different with a complex, apparently unstructured appearance. The flow activity, which can be easily observed, has never been satisfactorily explained until the recent introduction of the Vapor Surfactant theory. This paper presents a series of experimental results of absorption in an actual chiller facility. The novel features of the work include measurement of the effect of inlet subcooling, discussion of the effect of droplets ejected from the tube bundle and an explanation of the importance of flux in the alcohol augmentation physics.