Miniature spray nozzles are interesting to several applications from micro-thrusters to lithographic patterning.We investigate geometric scaling effects of pressure swirl atomizers,both theoretically and experimentally.The objective of the study is to determine the range of length scales when performance-both in terms of drop size and flow rates-deviate from accepted correlations.The experimental study considers atomizers spanning an order of magnitude in dimensional scale(1x,3x,5x and 10x).These atomizers were all kinematically similar and are fabricated by using micro electro mechanical systems(MEMS)technology as well as rapid prototyping technology(RPT).The geometrical parameters such as ratio of exit orifice length to diameter,ratio of swirl chamber diameter to exit orifice diameter,ratio of inlet slot width to height are maintained same for all the trails.Each atomizer is operated at varying flow conditions with water as the working fluid.Spray characteristic parameters such as sheet thickness,breakup length,and spray cone angle are captured by high speed imaging.Sauter mean diameter(SMD)as well as joint drop size and velocity distributions are two of the key characteristics measured experimentally using Phase Doppler Interferometry(PDI)technique.The performance of a small scale atomizer to a large scale atomizer is compared over a wide range of operating condition of the atomizer.This study unravels the following three conclusions.(i)A length scale at which conventional correlations governing spray performance fail,is identified.(ii)An optimum range of scale factors are identified to yield good atomization,with miniaturized spray nozzles.(iii)It is observed that the air core structure of microsprays is markedly different for microsprays from that in macrosprays.