A STUDY OF HEAT TRANSFER IN VERTICAL CHANNELS FOR HIGH HEAT LOADS IN THE TRANSITION REGION
The presented experimental results illustrate the effect of fluid physical properties on forced convection in transitional laminar-turbulent flows and on forced - and free combined convection of coincident directions.
In forced pipe flows of gases, an increase of the critical Reynolds number was observed with an increase of the heat load. In mixed forced and free convection of coincident directions significant longitudinal temperature variations were found in the pipe wall. It was concluded, that the location of the first temperature maximum is here strongly dependent on Re and on the heat load. Heat transfer coefficients in such conditions are reduced to about 60% of the purely forced convection value. None of the available relations for local heat transfer can give reliable predictions, so far.