Heat transfer and time-dependent flow of an impinging jet on a heated substrate mounted vertically downward or vertically upward

Abstract

Heat transfer and time-dependent flow of an impinging jet on a heated substrate mounted vertically downward ($+g$) or vertically upward ($-g$) have been studied for various hole diameters of inlet d_H and gas flow rate Q_H2 in order to investigate suitable conditions for chemical vapor deposition (CVD). For the $+g$ condition, vortices due to forced convection and natural convection at steady state, except for particular experimental conditions, were almost always observed in the neighborhood of the impinging jet flow. On the other hand, for the $-g$ condition, there was no vortex and no “flow separation phenomena” (Shekhar et al., 2014) and the fluid flow was at steady state. The Nu distribution was evaluated by the Richardson number, Ri. The average Nu increased slightly with + Ri for $+g$ while the average Nu decreased with −Ri for $-g$. In these experimental conditions, there was a suitable condition for CVD for -240 < Ri < -160 whereby the deviation of the Nusselt number along the radial position on the heated substrate was less than 0.2. Time-dependent flow with a time period of 2.7 s was observed due to the collision of fresh hydrogen flow and buoyant upward flow on a heated disc at 0.05 < S_H/S_C (open area ratio of the hole to the cylindrical flow channel) < 0.1 and Ri < 100 for $+g$.