Vertical cylindrical enclosures are used in the crystal growth industry as crystal growth reactors. Gallium nitride crystals are grown in ammonothermal growth reactors that requires temperatures in the range of 600-1000 K (620-1340 degrees F) and pressures in the range of 1000-6000 bar (14,504-87,022 psi). The process conditions make any experimental measurements difficult, in particular, flow pattern visualization and velocity measurements. A geometrically similar transparent reactor and similar fluid dynamic conditions for crystal growth were used in the process of experimental observation and measurement of the flow. Boundary and fluid temperatures along with velocity vectors were recorded. The flow proved to be oscillating in nature with steady and uniform time-averaged patterns. Fluid temperatures showed a higher standard deviation in the mixing region suggesting that the fluctuations are stronger at this location. Flow patterns and fluid temperatures indicated that the heat transfer between the two sections is driven by conduction and advection. (C) 2019 Elsevier Ltd. All rights reserved.