Computational Transport And Its Application To Mass Transfer And Reaction Processes In Packed-Beds

The first part of this dissertation is the summary of some basic knowledge about computational fluid dynamics (CFD), computational heat transfer (CHT) and computational mass transfer (CMT), and their related turbulent theory and turbulent models are briefly reviewed. The application of CFD, CHT and CMT to the chemical engineering unit operations, such as predicting the fluid flow, temperature profile and concentration profile in packed columns or fixed-bed, are also summarized.The second part is the detailed derivation of the basic differential equations of the proposed computational transport, including the conservation equation of the general transport variableΦ, its Reynolds averaged equation together with its closure two equations and their modeled equations. From the generalized transport equation, the precise governing conservation equations of continuity, momentum transfer, heat transfer, mass transfer, as well as their auxiliary equations of turbulent kinetic energy k and its dissipation rateε, temperature variance t 2and its dissipation rateεt, concentration variance c 2 and its dissipation rateεc can be obtained, which formulates the system of equation for the transport computation. The definition and physical meaning of the turbulent kinetic viscosityμ, turbulent heat transfer diffusivityαtand turbulent mass transfer diffusivity Dt which are introduced by the Boussinesq hypothesis are analyzed and compared. Furthermore, the inlet and outlet boundary conditions of k,ε, t 2,εt, c 2,εc differential equations are also discussed and suggested.The third part is the application of the computational transport model to various chemical processes, including (1) the modeling of liquid flow in the randomly packed column of 0.5m and 1.0m I.D. in predicting the velocity profile and its evolution; (2) the modeling of chemical absorption processes in the randomly packed columns of 0.1m I.D. and 1.9m I.D. respectively for removing CO2 from gas mixtures by the alkaline solutions in predicting the profiles of CO2 concentrations in gas phase, the alkali concentrations (carbonation ratio of the alkali aqueous solutions) and the temperature in liquid phase; (3) the modeling of distillation process in randomly packed column of 1.22m I.D. in predicting the profiles of component concentration and the height equivalent of theoretical plate (HETP) as function of gas phase F-factor; (4) the modeling of the wall-cooled fixed bed catalytic reactor of 0.041m I.D for the gas phase synthesis process of vinyl acetate from acetic acid and acetylene in predicting the profiles of conversion and the temperature along the reactor axial and radial directions. All foregoing predictions were compared with the experimental measurements taken from literatures, and good agreements were found. The predicted profiles of turbulent kinetic viscosity, turbulent heat transfer diffusivity and turbulent mass transfer diffusivity calculated by using the k-ε, t 2-εt, c 2-εc two equations models respectively along the radial and axial directions in randomly packed columns displayed some similarity, which is in agreement with the reported literatures. However, they were not totally identical, which demonstrates that the turbulent momentum, heat and mass transports are not completely analogous, and they have their own characteristics.The fourth part is the description of the experimental work of the extractive distillation processes for separating the mixture of benzene and thiophene using N-methyl-2-pyrrolidone (NMP) as the extractant under the different operating conditions in a randomly packed column and the process simulation in predicting the benzene concentrations in gas phase and liquid phase by the proposed computational transport model. The prediction is confirmed by the experimental measurements.Finally, several aspects concerning the prospect and further investigation of computational transport are suggested.