气固流化床内射流特性的研究

Numerical simulation of jetting characteristics in a gas-solid fluidized bed

采用Brandani等的数学模型模拟了中心射流宽度为0.01 m的二维气固流化床(高1.6 m、宽0.3 m)内鼓泡和射流的瞬态及时均流体动力学特性。一种典型的Geldart B颗粒--砂子(粒径为500 mm、密度为2660 kg/m3)作为研究的模拟物料。瞬态结果表明,床内射流产生和发展、射流崩塌后所形成气泡尺寸以及全床内的气体速度场和空隙率均存在明显的非对称性,但是由压力信号功率谱密度得到的时均压力特性则有较好的对称性。因此,对于商业化稳定运转的射流床,可以用半床模拟结果近似解释整床特性;然而,在考察射流床的瞬态特性时,半床模拟结果与整床结果存在明显偏差。

Jetting characteristics,i.e.,jet formation,jet development,bubble size,transient gas velocity field,transient voidage and spectral power density of pressure signals,have been investigated numerically in a gas-solid fluidized bed by using a new model proposed by Brandani and Zhang.Simulation is carried out for a two-dimensional fluidized bed of size 1.6 m ×0.3 m equipped with a jet of 0.01 m width in the central bottom of the bed.Sand belonging to Geldart B Group is selected as solid material,whose diameter and density are 500 mm and 2 660 kg/m3,respectively.Transient results show that there exist obviously axial-asymmetric behaviors for the jet above the nozzle,the bubble after the jet collapse as well as the gas velocity field and the voidage profile in the whole bed.The spectral power density of pressure signals,however,keeps almost equal at the axisymmetric positions in the jetting fluidized bed.The conclusions mentioned above imply that the simulated results in the half bed can represent the characteristics in the whole jetting fluidized bed for a stable operation in the commercial process.It is obviously different between the transient characteristics in the half bed and those in the whole bed.