无改性纳米颗粒喷射弥散机理及相关实验技术研究

Nano-particles, which physicochemical characteristics were not modified, laden gas flow is a common phenomenon in nature, and has been studied in the context of many engineering problems. The dynamic and biologic characteristics of the particle are significantly affected by its physical and chemical property. In the “wet” aerosolization methods, the physical and chemical characteristics of the dispersed-phase attained from the spray of liquid solution or suspension is apt to be modified. The existing “dry” aerosolization methods, which are usually used to the dispersion of micron-particles, fail to generate sub-micron and nano-paticle laden gas flow stably and consecutively. An effective method has been developed for the continuous aerosolization of dry powdered nanoparticles using a cost-effective vacuum generator. A commercial doser was used to supply nanoparticles continuously and precisely. A new device (called a pressure equilibrium unit) was designed to connect the doser and the vacuum generator to make sure both parts avoid suffering from pressure shock. This system is denoted as a continuous vacuum generator disperser (CVGD). Through experimental study and theory analysis, the following targets will be achieved: .① Powder disperser for the continuous aerosolizing of dry powdered nanoparticles and the method for nanoparticle multistage dispersing, in which the first fluidized aerosol would be compressed by a compressor, will be proposed. And the relationship between the characteristic distribution of dispersed-phase and the experimental parameter, e.g. primary particle size, dosing rate and Reynolds number related to the inlet pressure of the vacuum generator, will be discussed and modeled; .② The effect of the characteristic distribution in flow variables, such as shear stress and velocity field, on the particle size and mass distribution will be study. Furthermore, the mechanism of nanoparticle dispersion under aerodynamics singly in the vacuum generator will be revealed..③ Simultaneously concerning the aerodynamics and the particles-wall collision in the vacuum generator, the detailed dynamic evolution of the nanoparticles in the ejector would be tracked by solving the particle general dynamic equation (GDE) using Taylor-expansion moment method (TEMOM). Based on this, the correlative mechanism for the nanoparticles aerosolizing using CVGD will be analyzed combined with experimental results..Investigations above will not only improve the technology for the unmodified aerosoling of dry powdered nanoparticles and enhance our understanding on the fundamentals of the dispersion of the nano-agglomerates by CVGD, but also provide technology method and theoretical basis for practical applications.

无物理化学改性纳米颗粒两相流广泛存在于自然界和工程领域，颗粒的物理化学性质对其动力学与生物学特性有决定性的影响，然而通过雾化干燥等“湿式”方法获得的离散相会发生物理化学改性，以往纳米颗粒喷射弥散的“干式”方法无法连续稳定进行，其喷射弥散机理尚不清楚。本项目以压力平衡单元桥接精密定量给料器和气动真空发生器，实现无改性纳米颗粒的连续喷射弥散，并结合实验研究和数值模拟达到以下目标：.① 建立纳米颗粒连续喷射弥散系统及多级喷射弥散方法，给出颗粒相分布特性与雷诺数、初级粒子直径、给料速率等主要实验参数的关系；.② 确立喷射器内剪切应力分布等连续相分布特性与颗粒相特征谱之间的关系，探索纯空气动力下的颗粒弥散机制；.③ 给出颗粒-壁面碰撞与空气动力耦合作用下喷射器内的颗粒相弥散时空演化规律。. 通过本项目研究，完善颗粒喷射弥散方法，加深对该过程机理的认识，为实际应用提供技术与理论依据。

纳米颗粒两相流广泛存在于自然界和工业过程，纳米颗粒的粒径和团聚状态对其毒性、药物活性、催化活性等都有重要影响。通过雾化干燥等“湿式”方法获得的纳米颗粒会发生物理化学改性，而现有“干式”喷射弥散方法获得的纳米颗粒团聚程度较高且尚不能连续运行，严重削弱了其比表面积大的优势，进而影响其药物和催化活性。本项目结合实验和数值模拟深入研究了强剪切流场中干粉纳米颗粒的弥散机理，并发展了新型高效无改性纳米颗粒弥散技术，主要研究进展及其重要结果如下：.① 发展了纳米颗粒连续喷射弥散系统，实现了纳米颗粒的初级连续喷射弥散（纳米颗粒中径为（~100nm–200nm），发现随喷射器进口压力和纳米颗粒初始粒径的增加，弥散颗粒中径明显减小，而粉状纳米颗粒质量流率的增加会增大弥散颗粒粒径；.② 提出了基于自由衰减超音速射流的悬浮态纳米颗粒弥散方法，成功获得逼近初始粒径的弥散纳米颗粒；研究了悬浮态纳米颗粒在自由衰减超音速射流中的弥散特性和机理，并探讨了喷管的长度(L)和直径(D)对弥散纳米粒子粒径分布的影响；.③ 分析了扩散段扩散角α对其流动特性和纳米颗粒弥散的影响，建立了α与弥散纳米颗粒气溶胶粒径分布的关系；发现虽然剪切应力的最大值对干粉纳米颗粒的粒径分布无明显影响，而α增大后具有一定强度剪切应力的分布范围的随之增加，并在干粉纳米颗粒气溶胶化中发挥了关键作用。.④ 利用凡士林分别对喷射器内壁和自由衰减超音速射流圆喷管内壁进行“无反弹”壁面涂层处理，探讨纯空气动力剪切和颗粒-壁面碰撞的耦合弥散机制；明确了纯空气动力剪切在纳米颗粒弥散中的主导作用，而颗粒-壁面碰撞为次要弥散机制。.本项目研究成果有望为纳米药物和催化剂解聚提供有力的技术支持和理论参考，同时也为超音速流场中的纳米示踪粒子解聚和撒播提供了经济而有效的方法。