2019-08-012024-05-17https://scholars.lib.ntu.edu.tw/handle/123456789/684007摘要：許多化工產品常以粉粒體的形態呈現，而乾燥、混合、造粒、氣輸都是常見的粉體操作單元。具有內聚性(cohesive)細粉於操作時常因凡得瓦力、液橋力、靜電力等粒子間作用力而凝集，產生架橋、分散不良、輸送振盪等操作單元異常。但群體粉體間作用力尚無分析工具，且其受粒徑分布、粒子形狀、輸送介質等影響甚大，更導致粉子間作用力解析困難。 由於在氣固流體化床中，粉體可方便地表現其群體運動與作用力特性。本計畫應用流體化床中氣體與粉粒體作用力分析粒子間作用力的方法。初始流體化之拖曳力與粒子間作用力、重力與浮力的合力平衡；完全流體化之拖曳力與重力與浮力的合力平衡。此兩個狀態下的拖曳力差異(稱為過量壓力降pressure drop overshoot)可用於估算粒子間之作用力。過量壓力降若視為氣體破壞具內聚性粉體床所需的拉應力，則其與粒子間作用力Fc之關係可表示為： &#12310;pressure drop overshoot=σ&#12311;_t=((1-ε) F_c k)/(&#12310;d_p&#12311;^2 π) 其中k為一顆粒子與鄰接粒子的接觸數目(-)；ε為床孔隙度 (-)；dp為粒子粒徑 (m)。此方法理論可行，但ε的理論分析或量測、k的理論分析或量測、廣粒徑分布的問題、具內聚性粉體的難完全流體化現象等問題，仍待本研究釐清。 本三年期計畫，第一年以液橋力為主要之粒子間作用力，以不同黏度矽油與添加量加入單一粒徑玻璃珠，分析由本方法所得粒子間作用力與理論液橋力之差異，建立快速的粒子間作用力分析方法。第二年由堆積理論與液體滲透率實驗理論分析上述方程式的各參數。第三年則以振動流體化床將用於流體化具內聚性之難以流體化粉體，並用來分析各種顆粒之粒子間作用力。 <br> Abstract: Particulate products are frequently encountered in chemical industries. Particle drying, mixing granulation and pneumatic transportation are common operations for particle processing. Cohesive particles with strong interparticle forces, including mainly the van der Waals force, the liquid bridge force and the electrostatic force, are easily aggregated during processing. Aggregation of particles may cause bridging, poor dispersion, oscillating transportation and other problems. The interparticle forces must be evaluated in order to solve these problems. However, there are no easy tools for interparticle force analysis. Furthermore, the interparticle forces are influenced by the particle size and its distribution, the particle shape, the physical properties of the interstitial fluid and etc. In a gas-solid fluidized bed, the particles interact with fluidizing gas as an assembly. At fully fluidization, the particles are reported in discrete state. The gas drag force balances with the gravitational force and the buoyancy force. At incipient fluidization, the gas drag force balances with the gravitational force, the buoyancy force and the inter-particle forces. The difference of the gas drag forces between these two states, or the bed tensile stress σt, may be used to evaluate the interparticle forces. The pressure drop overshoot at incipient fluidization can be regarded as the bed tensile stress and relates to the interparticle force Fc as, &#12310;pressure drop overshoot=σ&#12311;_t=((1-ε) F_c k)/(&#12310;d_p&#12311;^2 π) where k is the coordination number; ε is the bed voidage and dp is the particle diameter. Although the method is promising, the theoretical predictions or measuring of k and ε, the particles with wide size distributions and the fluidization of cohesive particles remain challenging. In this three-year project, pressure drop overshoot at incipient fluidization will be used to evaluate the interparticle forces. In the first year, the liquid bridge force will be used as the model interparticle force. The system will be developed and the interparticle forces of the glass beads-silicone oil system will be determined. The results will be comprehensively compared with the classical liquid bridge force calculation. In the second year, the packing theory predictions and bed permeability tests will be carried out to accurately evaluate the k and ε values. In the third year, a vibrating fluidized bed will be used to fluidize the cohesive particles. This method will be used to evaluate the interparticle forces of particles of different sizes.內聚性流體化床過量壓力降粒子間作用力cohesivefluidized bedpressure drop overshootinginterparticle force