Stagnation flow buoyancy

Not all reactor designs and operating conditions lead to the stagnation-flow similarity regimes illustrated in Fig. 6.1. Buoyancy-induced flow, owing to large temperature gra-... 

The flow configuration is oriented upward so that the buoyancy effect on the stagnation-flow field is diminished. This configuration provides a stagnation-flow field with a radially uniform velocity profile at the inlet. Gas fines are also heated to prevent the condensation of liquids. The gases are exhausted through an annular pipe and burned in a Bunsen burner which is also housed in the reactor. 

Vertical CVD Reactors. Models of vertical reactors fall into two broad groups. In the first group, the flow field is assumed to be described by the one-dimensional similarity solution to one of the classical axisymmetric flows rotating-disk flow, impinging-jet flow, or stagnation point flow (222). A detailed chemical mechanism is included in the model. In the second category, the finite dimension of the susceptor and the presence of the reactor walls are included in a detailed treatment of axisymmetric flow phenomena, including inertia- and buoyancy-driven recirculations, whereas the chemical mechanism is simplified to a few surface and gas-phase reactions. 

A reactor with vertically-upward flowing core coolant, unconstrained by internal flow channels within the core, has relatively stable hydraulics. Employing a vertical core ensures a potential to initiate and continue buoyancy-driven natural circulation. An upward normal core coolant flow direction avoids any concern of momentary core flow stagnation during transition from forced-convection to natural-circulation core cooling. A safety margin penalty is incurred with upward... 

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