(133i) Spontaneous Thermocapillary Interaction of Drops: the Effect of Surface Exothermic Reaction
AIChE Annual Meeting
2006
2006 Annual Meeting
Engineering Sciences and Fundamentals
Interfacial Flows I
Monday, November 13, 2006 - 5:15pm to 5:30pm
We have studied the spontaneous motion that may be induced when an exothermal surface reaction occurs on the interface of small drops suspended in an immiscible viscous fluid. The reactant that diffuses toward the interface in the ambient fluid reacts with a substance stored in the drops. The heat of reaction results in elevation of temperature on the drops' interfaces that, in turn, induces surface tension variation and Marangoni type flow. An interesting case appears when the reacting species are also surface active. In this case the thermocapillarity induced by the heat emitted by the exothermic reaction and the one induced by the local reduction of the concentration of the surface active substance, due to its depletion by the reaction, can be opposite effects counteracting each other. Naturally, a wide variety of motion patterns may arise depending on the drops' size ratio and separation, ratios of material properties and non-dimensional parameters such as Thiele modulus (or Damkohler number), heat production intensity, capillary and Peclet numbers etc. A sample of results for the concentration, temperature and flow fields are depicted including interesting cases of dynamic stationary states in which the thermocapillary induced flow proceeds while drops remain motionless.