(306d) Application of Weber Number-Based Regime Map for Scaling and Control of Pharmaceutical Coating Sprays

A Weber-number based regime map for describing the patternation of twin-fluid pharmaceutical coating sprays is proposed.  The map was developed according to the dynamics of the spray evolution at the point where the two shaping air flows meet (the ‘junction’ point)—depending on the spray drop size, drop velocity, shaping air velocity, and surface tension at the junction point, the shaping air can either redistribute the drops, cause additional (secondary) drop breakup, or pinch the spray.  A Gaussian spray results when the spray evolution process is driven mainly by drop redistribution; a homogeneous pattern is observed when there exists balance between the redistribution and secondary breakup effects; a dumbbell-shaped spray results when the pinching effect dominates spray evolution.  The We-based regime map was constructed by plotting the junction point We against a dimensionless spray parameter calculated from the product of two flow ratios: the shaping-to-atomizing air flow rates ratio and the liquid supply rate-to-maximum nozzle liquid flow rate capacity ratio.  Experimental results show a linear relationship between the junction point We and this dimensionless spray parameter.  More importantly, different regions of the We-dimensionless spray parameter plot correspond to the three different spray patternations.  Several scale-up scenarios we have explored demonstrate the We-based regime map reliability in achieving homogenous spray patterns.  These examples also support the We-based regime map applicability in providing quantitative solutions for the design and optimization of sprays for pharmaceutical coating applications.