(699a) Understanding Drop-Drop Contacting Patterns in a Microchannel: A Reaction Engineering Perspective

Drops can be used as carriers of reactants and there could be transfer of mass between the drops when they come close to each other, allowing one to use this system as a micro-reactor system. In this paper, we use the simple models that were developed in a recent work (Danny and Rengaswamy, 2013) to explain the different forces on the drops inside a 2-D microchannel, in a multi-agent based simulation to study the performance of a diverging-converging microchannel as a drop-drop contactor. Our models are applicable to a wide range of 2-D geometries that are symmetric about the horizontal axis. A geometry similar to the one experimentally studied by (Jose and Cubaud 2011) is chosen to demonstrate the technique. In this system the initial spacing between the drops prior to entry into the microchannel affects the configuration of the drops inside the microchannel resulting in layers of drops. This motivates the investigation of the different patterns formed inside the microchannel as a function of the initial spacing between the drops prior to their entry into the channel. To study the efficiency of drop-drop contactor, the case where there are two different reactants in two different drops A and B is considered. One would simply expect an entry sequence of ABAB to get maximum contact between drop-A and drop-B. After a study of the patterns formed by drops inside the microchannel for a given entry sequences, it is found that ABAB is a favorable sequence only for a very small class of problems and the least preferred for the rest. A metric called the contact efficiency (CE) is defined which in some sense gives the number of drops A around B and vice versa, to quantify the efficiency of the pattern formed, to compare the effect of different input sequences.

Danny Raj M, Raghunathan Rengaswamy, 2013. Understanding emergent behavior in microfluidic systems. (Unpublished)

Jose BM, Cubaud T (2011) Droplet arrangement and coalescence in diverging/converging microchannels. Microfluidics and Nanofluidics 12:687–696.