Flow structure and heat transfer in a horizontal converging channel heated from below

A detailed experimental study is carried out to investigate the flow structure and heat transfer in a converging horizontal channel with localized heating on the bottom surface. This configuration arises in typical chemical vapor deposition (CVD) systems and the impact of the transport mechanisms on the deposition process is of particular interest. Experimental observations of various flow circumstances indicate the appearance of longitudinal and transverse roll structures. These flow structures have direct implications with respect to CVD processing where deposition rates and film quality are critically dependent on reactive species and byproduct transport onto the deposition surface. Different flow regimes are observed for typical operating conditions, and their existence is described using regime maps. Regime boundaries are correlated in terms of important parameters that describe the flow rate, heating rate, and tilt angle. A regime transition from longitudinal rolls to transverse rolls occurs at around Gr/Re2=6000, while the critical Rayleigh number is found to be dependent on the flow. Heat transfer correlations are also derived and it is seen that the heating rate is the dominant effect on the susceptor temperature, while the effects of flow rate and tilt angle are small. The implication of heat transfer results on mass transfer are discussed for horizontal CVD reactors. The flow structure and heat transfer phenomena observed in this study yield valuable insight into the basic buoyancy and forced-flow-induced transport in horizontal channels as well as guidelines for the modeling and design of CVD systems.