Mixed convection in a horizontal circular channel in high pressure conditions

The main aim of the research is to determine the range of mixed convection and setting the limits of its occurrence. The laboratory tests are conducted at the Technical University of Szczecin in the Department of Heat Transfer with the use of the horizontal circular heat exchanger. The measurements are made with the pressures from 0,1 to 10,0 [MPa] and different heating powers. In order to carry out the planned research and analyse its results, a criterion of mixed and free convection occurrence by Metals and Eckert [4] stating that the boundary between the free and mixed convection results from the comparison of convectional heat flux values resulting only from displacement forces (free convection) and the sum of displacement forces together with body forces (mixed convection) was applied. It was assumed that if the relative difference between the convectional heat flow occurring together with the existing combination of displacement forces, and body forces as well as the heat flux resulting from the influence on air molecules exceeded 10%, mixed convection took place. On the basis of such analysis it is possible to allot a boundary line between the area of occurrence of mixed and free convection (when the influence of the factor flow caused by body forces on the heat penetration is negligible).