Enhancement of Vapor Absorption into a Solution Using the Marangoni Effect

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It is highly important to develop a new technology for heat and mass transfer enhancement in the process of refrigerant vapor absorption in order to realize the advanced absorption heat pump. In most commercial machine, absorption enhancement has been done by adding a small amount of various kinds of surfactants, thereby reducing the surface tension of the absorption solution drastically and generating Marangoni convection near the solution surface at the time of refrigerant vapor absorption.This paper clarifies the effect of the surfactant on absorption enhancement by measuring the unsteady temperature distribution in the vapor absorption process by adding a small amounts of octanol and decanol into the aqueous solution of LiBr with 50 mass% contained in a test cell and by conducting a visualization experiment using holographic interferometry. It was found, on the basis of the solution surface observation using a microscope and the measurement of the surface tension, that octanol and decanol in a state higher than their solubilities distributed in the dropwise states on the solution surface were the initial cause of violent Marangoni convection. The model of the mechanism generating this Marangoni convection was presented also a guide dealing with the development of a highly efficient absorber to be used for heat pumps was provided.Furthermore, the effort was made to visualize the Marangoni convective behavior during the steam absorption into a dynamic falling thin film flow of the aqueous solution of LiBr with the addition of small amount of Octanol. An interferometric measuring technique was introduced to visualize the displacement of the film flow in the dynamic stage by using double pulsed luby laser. For the comparison of the interference fringe configurations obtained with and without the aurfactant (Octanol), it was cleary shown the occurrence of the Marangoni convection in case with Octanol. these basic study enables us to design high-performance absorber.