Numerical Research On Drop Formation Of Rotating Prilling Sprayer

Rotating prilling sprayer, which due to centrifugal forces the molten jets emergefrom rotating drum and break up into droplets, is the key equipment to produce thesolid urea particles. The droplets cool and solidify forming pellets. Basing onproducing the controlled release urea project, the paper tries to find out the regular ofprimary drop formation and break-up length through the simulation analysis aboutdrop formation in rotating prilling sprayer. And the effect on primary drop formationand break-up length was examined. Then, a new rotating prilling sprayer wasdesigned according to new demand.Based on the principle of drop formation in rotating prilling sprayer, physicalmodel was simplified to two-dimensional and reasonable assumptions were made.Experiment in Simon Gramlich et al (2012) was simulated using VOF model inAnsys fluent, with favourable agreement. Mesh independent was examined in widerphysical property. Compared with changes in primary drop diameter and break-uplength, the optimal grid size was select as0.11mm×0.11mm considering calculationtime.Through18orthogonal experiments, the effects on drop formation in rotatingprilling sprayer were examined. The order of each factor influencing on primary dropdiameter was as follows: orifice diameter>surface tension>density>dynamicviscosity>jet velocity>can radius>can rotation rate. The order of each factorinfluencing on break-up length was as follows: orifice diameter>can radius>dynamicviscosity>jet velocity>can rotation rate>density>surface tension.Analyzed the break-up process in orthogonal experiments, two break-up modeswere obtained. When liquid jet broke into droplets, the pressure amplitude in liquidjet was reached maximum and the velocity amplitude in surface of liquid jet wasreached minimum. And amplitude reached maximum when break-up length wasshorter. When liquid jets have same break-up mode, the distribution of amplitude was same. Anasyzled the vector of velocity field during drop formation, vortex wasobtained in reverse of rotating liquid jet, which was mainly reason of wave on theliquid jet surface. The vortex moved along liquid jet track. And it departed from jetwhen liquid jet broke.Dynamic viscosity and density had a great effect on the primary drop diameterwhen orifice diameter was2mm. The primary drop diameter increased when dynamicviscosity increased and when dynamic viscosity was more than0.03Pa s primary dropdiameter decreased. Break-up length increased with viscosity increasing and break-uplength with orifice diameter2mm is longer than length with orifice diameter1mm.Primary drop diameter decreased with density increasing and diameter was1.50mmwhen density was more than1100kg/m3. Break-up length increased when densityincreased and it decreased when density was more than1200kg/m3. Surface tensionand jet velocity and can rotation rate have a little effect on primary drop size.Break-up length linearly increased with increasing of orifice diameter and jet velocity,which was contrary with increasing of can radius and can rotation rate.Based on requirement of product slow-release urea,2mm orifice diameter with200mm can radius was examined. In original condition, primary drop was1.84mm,which was bigger than the drop in slow-release urea condition. Only change theorifice diameter, when it is3.1mm, we got1.81mm primary drop which was meet theproduct requirement. Changing the can rotation rate or can radius, we can’t get thequalified drop.