Drop formation is widely encountered in nature and industry through processes such as dripping, emulsification, and microencapsulation. Industrially, many applications incorporate a co-flowing fluid to better control drop formation as the flow rate of the outer fluid can be used to control the breakup of the inner fluid into drops of specific sizes. In this thesis, experimental results of studying drop formation in co-flowing fluids, both Newtonian and non-Newtonian, with and without surfactants are presented. The effect of flow rate ratio on the primary and satellite drop volumes and remnant drop lengths was investigated. Smaller primary drops were formed when the flow of the outer bulk phase was increased due to increased shear stresses. As the viscosity of the drop phase is increased, the rate of neck thinning slows down. Both Newtonian and non-Newtonian drops were observed to typically break at the primary neck. Non-Newtonian drop breakup behavior was found to be less predictable than Newtonian fluids, especially in relation to satellite drops. The number and sizes of satellite drops formed for non-Newtonian fluids varied greatly compared to Newtonian fluids. The addition of surfactants changed the neck behavior for both Newtonian and non-Newtonian fluids. Surfactants accumulate at the neck region and cause Marangoni stresses to arise that slows down the rate of neck thinning. Surfactants lower primary and satellite drop sizes as the average interfacial tension of the drop interface reduces. However, their influence on how many satellites are formed depends on the fluid system it is added to. In some instances, surfactants were found to suppress the number of satellite drops formed, in other instances, the addition of surfactants increased the number of satellites formed.
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