The results of a primarily experimental study of the transition from turbulent flow to laminar flow as a consequence of high heating rates are presented. Results are reported for hydrodynamically fully developed, low Mach number flows of air and helium through a vertical, circular tube. The electrically heated section was 100 diameters in length; entering Reynolds numbers ranged from 1700–40,000, and maximum wall-to-bulk temperature ratios reached 4.4. As a means of predicting the occurrence of a transition from turbulent flow to laminar flow, the experimental results are compared to the acceleration parameter suggested by Moretti and Kays and to a modified form of the parameter that is appropriate to a circular tube. It is suggested that the variable property turbulent flow correlations do not provide acceptable predictions of the Nusselt number and the friction factor if the value  
based on bulk properties, is exceeded for an initially turbulent flow situation. It is further suggested that Nusselt numbers and friction factors at locations down-stream from the point  
for bulk temperatures in degrees Rankine may be obtained from the laminar correlation equations even though the flow is initially turbulent.
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