OPTIMIZATION OF A STAGNATION POINT FLOW REACTOR DESIGN FOR METALORGANIC CHEMICAL-VAPOR-DEPOSITION BY FLOW VISUALIZATION

Various design parameters of a stagnation point flow reactor such as m ixing chamber, gas distributor and reactor shape are optimized by a te chnique of flow visualization. A dense smoke of TiO2 particles generat ed in the mixing cup with the help of unidirectional tangential jets o f TiCl4, H2O and helium is used to show the flow patterns. A sheet of laser (5 mW He-Ne) light formed with the help of a cylindrical lens is used to illuminate the trajectory of smoke particles. The flow patter ns are recorded photographically. Rapid and uniform mixing of a number of gas streams is achieved by tangential jets. A ''capillary plug'' a s an ideal gas distributor, incorporated in the inlet, removes the swi rl due to tangential jets completely and develops an axially uniform g as velocity profile across the inlet. Various reactor shapes such as c ylindrical, triangular, diffuser and modified diffuser (a diffuser wit h reduced height) are studied for their performance. The modified diff user with capillary plug as a gas distributor in the inlet is the only appropriate metalorganic chemical vapor deposition (MOCVD) reactor co nfiguration that can develop and sustain a smooth, laminar and vortex free flow at room temperature as well as at 773 K in absence of substr ate rotation and/or application of vacuum.