Absorption of water vapor into LiBr solutions with 2-ethyl-1-hexanol
- Arizona State Univ., Tempe, AZ (United States)
Absorption of water vapor into a liquid falling film of 50 to 63% lithium-bromide solution is a part of a typical absorption refrigeration cycle. The heat- and mass-transfer rate of the absorption step is often an important factor in the economic design. Significant enhancements in the heat- and mass-transfer rate can be obtained by adding small amounts of surface active agents such as 2-ethyl-hexanol. However, when both mass transfer and surface active agents are present, the surface tension gradients due to concentration differences can lead to instability. In spite of this general understanding of the mechanism, in the system with aqueous lithium bromide and 2-ethyl-1-hexanol the exact role of surface tension gradients due to temperature, concentration of solute, and concentration of surfactant are not well documented. A linear stability analysis for a jet (which is equivalent to a stagnant pool) under adiabatic conditions was presented by Ji et al. (1993). Based on this theoretical study, the critical Marangoni number (Ma) for the onset of the instability should be of the order 10{sup 8}. Using the values of surface tension gradients from Kim et al. (1994), the mass-transfer enhancement in falling films of 50--60% lithium-bromide with 2-ethyl-1-hexanol should be evident at surfactant concentrations above approximately 5 ppm. Experiments to verify the onset hypothesis and the effect of other variables on the mass-transfer coefficient are the major objectives of this work.
- OSTI ID:
- 218618
- Journal Information:
- AIChE Journal, Vol. 42, Issue 3; Other Information: PBD: Mar 1996
- Country of Publication:
- United States
- Language:
- English
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