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Velocity measurements of a bench scale buoyant plume applying particle image velocimetry

Experimental investigation of the buoyant plume above an electrically heated block of copper.

2018 IHMTExperimental setup

This paper presents the experimental investigation of the buoyant plume above an electrically heated block of copper. The velocity field in a vertical plane along the plume axis is investigated via particle image velocimetry. Experiments with electrical power from 30 W to 96 W are carried out, which lead to heat source temperatures of 149 oC to 307 oC. The resulting flow is laminar for the lowest power setting and undergoes a transition to turbulent flow for higher heat inputs. With increasing heat input the point of transition from laminar to turbulent flow occurs at lower heights.

Time-averaged velocity fields are presented together with the according measurement uncertainty that results from the evaluation with particle image velocimetry. Based on these velocity fields a number of characteristic values for the plume is derived in different heights, e.g. maximum velocities, plume widths and flow integrals. In order to further evaluate the transition from laminar to turbulent flow the vertical velocity and the standard deviation of the horizontal velocity along the plume axis and as a function of the Grashof number are investigated. The transition occurs at Grashof numbers in the range 4 × 108 < Gr < 2 × 109, which is in accordance with previous findings. In addition to the velocity measurements, the temperature stratification inside the enclosure is measured to quantify the ambient conditions.

Figure 1Velocity profile of a time averaged PIV measurement

Figure 3Velocity profiles for different heating rates (30 W, 56 W, 78 W, 96 W)

Figure 2Velocity fluctuations