Xiaogang Yang

CFD Modelling of Cadmium Telluride (CdTe) Thin Film Coating with Inline AP-MOCVD

A CFD numerical model has been established to study the growth of cadmium telluride (CdTe) on substrate using metalorganic chemical vapour deposition technique in atmospheric pressure (AP-MOCVD) and hydrodynamics in an inline MOCVD reactor. The numerical simulations have been conducted using the CFD code – ANSYS Fluent. Dimethylcadmium (DMCd) and diisopropyltelluride (DIPTe) have been employed as precursors while H2 is acting as the carrier gas. In order to assess the effect of various conditions on CdTe film growth and uniformity, heat transfer and mass transport behaviours of the chemical species in the reactor have been fully investigated. In addition, material utilization and fluid dynamics in the reactor are also discussed.

Numerical simulations of fluid dynamics and mixing in a large shallow bubble column: effects of the sparging pipe allocations for multiple-pipe gas distributors

Numerical simulations of gas-liquid flow in a bubble column of 800 mm in diameter using two-fluid model and multi-size-group (MUSIG) model were conducted to investigate the effect of allocation of sparging pipes in gas distributors on hydrodynamic flow, gas hold-up, mixing characteristics, turbulence and bubble size. In the simulation, six different arrangements were assessed, which four-sparging pipes are mounted to a gas distributor with the allocation ring to bubble column ratios (d/DT) being 0.3, 0.37, 0.4, 0.5, 0.6 and 0.7, respectively. The simulation results have clearly demonstrated that the allocation of sparging pipes to the gas distributor has an important impact on gas hold-up and mixing characteristics. It was found from the simulations that the mixing time and overall gas hold-up increase initially with the increase of d/DT but decrease with further increase of d/DT. As a result, it was revealed that the optimum value of d/DT is around 0.4 for the highest overall gas hold-up and is confirmed by the experiment. It was also indicated from the simulation that d/DT of 0.5 yields the maximum mixing time.

Micro-bubble dispersion in a two-dimensional mixing layer

Dispersion of microbubbles (db < 100 ?m) in a turbulent mixing layer was investigated numerically using a Discrete Vortex Modelling (DVM) while two-way interaction between the dilute dispersed cloud of microbubbles and free-shear layer was taken into consideration. The emphasis of this study is to examine the instantaneous dispersion features of microbubbles entrained by large-scale vortex structures embedded in the free-shear layer, and the effect of interphase momentum coupling on the evolution of the large-scale vortex structures due to the presence of the microbubbles. It was found that the laterally local void fraction profiles achieve similarity conditions downstream of the mixing layer. The simulation revealed that the growth rate of the lateral void fractions is similar to those of the velocity thickness but the lateral void fractions spread greater than the velocity thickness. The correlations between the local void fractions and local vorticity indicated that there is not prominent enhancement of the local void fraction in the centre of the large-scale vortices. In the numerical modelling, two important parameters, drag and lift coefficients in the equation of motion, were also assessed.