Research On New Annular Gap Nozzles For Supercritical Fluid Precipitation

Compared with the traditional preparation method of ultrafine powder,supercritical fluid precipitation technology has been concerned by researchers.with advantages of high purity,controllable particle size,no solvent residue and so on,In this paper,the methods,process flow and equipments of supercritical fluid preparation of ultrafine powder are reviewed,and the shortcomings of the present technology were summarized.A new type of annular gap nozzle(abbreviated as AGN),which propagates along the radial direction,have short size chain with high precision and can be adjusted on-line was proposed on the basis of the existing AGN of supercritical fluid preparation of ultrafine powder.The new AGN structure was divided into preparation section and adjusting section according to its function.Class A annular gap was formed by the core cone of the nozzle core and the inner throat of the cone end sleeve while calss B annular gap was formed by the outer throat of the cone end sleeve and the inner cone surface of the next cone end sleeve.According to the specific supercritical fluid preparation method,the internal mixing nozzle,the outer mixing nozzle and the inner and outer mixing nozzle with different channel number can be obtained.In addition,according to the newAGN,a new supercritical fluid preparation of ultrafine powder process was designed to save energy consumption in the process of supercritical fluid formation by energy saving combined heat exchanger with regenerative device.The FLUENT software was used to simulate the jet flow field of the new AGN basic structure.The jet flow field was divided into annular jet zone,vortex zone,entrainment zone and confluence zone,and three indexes for judging the flow field of the nozzle were obtained.According to these three indexes,the orthogonal simulation jet flow field of different structural parameters of the nozzle was evaluated,and the optimal level of each parameter and optimal combination of basic structure parameters were obtained.The structure of the nozzle core was optimized on the basis of the optimum level of the basic structure of the new AGN.The simulation results of the second half cone angle γ1 of the extension nozzle cone and the half conical angle γ2 of the inner nozzle core in the studied range showed that the flow field in the annular jet region and the vortex zone has been obviously improved.the nozzle core is optimized to the extension and innner structure.In additition,the bore-hole interceptor is installed to intercept large particles and optimize.entrainment zone.The results obtained can be helpful to the further development and research of supercritical fluid precipitation technology.