ABSTRACT Experiments on natural convection in fluorocarbon liquid FC-72 from isothermal horizontal upward-facing disks of different diameters (12 to 40 mm) were performed in the range of Rayleigh number from 3106 to 2109. The heat transfer coefficient and the velocity field arising from the heated surfaces have been studied in laminar, transition and turbulent free convection. The flow field was obtained using the two velocity components Laser Doppler Velocimetry measuring technique. The main results consist in the description of the flow field on the diametrical plane at various heights above the heated surface for different temperature values. The mean velocity profiles and turbulence properties of flow were obtained by pointwise velocity measurements at different locations. Point velocity values at the edges of the thermal wake and flow visualizations have shown a vortex structure very similar to the ring vortex structure typical of an axisymmetric turbulent jet. Finally, experimental data seem to confirm that heat transfer coefficients increase as the heated surface size decreases below 20 mm diameters.
Velocity field measurements by LDV in free convection flow from horizontal heated disks
CHIARI, ANNA;GUGLIELMINI, GIOVANNI
1998-01-01
Abstract
ABSTRACT Experiments on natural convection in fluorocarbon liquid FC-72 from isothermal horizontal upward-facing disks of different diameters (12 to 40 mm) were performed in the range of Rayleigh number from 3106 to 2109. The heat transfer coefficient and the velocity field arising from the heated surfaces have been studied in laminar, transition and turbulent free convection. The flow field was obtained using the two velocity components Laser Doppler Velocimetry measuring technique. The main results consist in the description of the flow field on the diametrical plane at various heights above the heated surface for different temperature values. The mean velocity profiles and turbulence properties of flow were obtained by pointwise velocity measurements at different locations. Point velocity values at the edges of the thermal wake and flow visualizations have shown a vortex structure very similar to the ring vortex structure typical of an axisymmetric turbulent jet. Finally, experimental data seem to confirm that heat transfer coefficients increase as the heated surface size decreases below 20 mm diameters.
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