TED-AJ03-341 HEAT TRANSFER IN A ROTATING CYLINDRICAL CELL WITH AND WITHOUT GAS EVOLUTION

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概要

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• The effect of gas evolution on heat transfer in a rotating cylindrical cell is investigated experimentally. The top wall of the cell is heated and the bottom wall is cooled. The cell is rotated about its axis. Convection is generated in the cell mainly by buoyancy due to centrifugal force. Hydrogen bubbles are generated by water electrolysis from the cold bottom wall. The flow field without gas generation is investigated by numerical simulation. The numerical scheme is based on the SIMPLEC algorithm. The flow is assumed to be steady, axisymmetric, and laminar. A modified Boussinesq approximation is employed. First, the flow field without gas evolution is investigated based on the numerical simulation and scale analysis. In the present experiment, the flow structure is in the so-called Ekman suction regime, in which the thermal boundary layer is thicker than the Ekman layer. The main quantity of interest is thicker than the Ekman layer. The main quantity of interest is the heat transfer rate between the hot and cold walls or the Nusselt number (Nu). The numerically predicted Nu is compared with the experiment data. As shown in Figure A-1,the experimental data generally agree well with the computational result. One important feature of the flow in the Ekman suction regime is that the radial flow is suppressed by the Coriolis force associated with the azimuthal flow, and as a result, the heat transfer is also reduced. The heat transfer rate is computed with and without the azimuthal flow. Without the azimuthal flow, the radial velocity and Nu increase substantially. Experimentally, the azimuthal flow can be reduced by placing partitions in the container. The result shows that Nu increases by a few factors but not as much as in the case with completely zero azimuthal flow. With gas evolution, the experiment shows the bubble size is between 40 and 100 microns in the stationary cell. With the rotating cell, the bubble size reduces to 20-30 microns. When the cell is rotated, the bubble moves toward the center and also moves up to the top of the cell, resulting in a spiraling motion. The bubble region shrinks as the rotation speed increases. It is observed that the bubble region is not affected significantly by heat transfer. From the experiment, it is found that the temperature field and the heat transfer rate become oscillatory. The oscillation phenomenon seems to be related to the azimutal velocity field in the core region. The azimuthal velocity is generated mainly by the radial velocity in the Ekman layers, which then induces the azimuthal velocity in the core region by the viscous diffusion. In the meantime, it is difficult to balance the Coriolis force and the centrifugal buoyancy in the core region. Without rotation, gas was introduced from the bottom of the cell. The overall heat transfer rate increased by about 30%. With rotation, a large part of the top wall is no longer covered by the bubbles, so the top wall temperature is not affected by the bubble as in the stationary case. While the cold wall temperature rises due to the bubble agitation. It is found that the bubble evolution affects the oscillation phenomenon strongly.[figure]

著者

• Kamotani Yasuhiro

  Department Of Mechanical And Aerospace Engineering Case Western Reserve University

• BOONPONGMANEE THAVEESAK

  Department of Mechanical and Aerospace Engineering Case Western Reserve University

関連論文

• TED-AJ03-341 HEAT TRANSFER IN A ROTATING CYLINDRICAL CELL WITH AND WITHOUT GAS EVOLUTION
• Effect of Free Surface Heat Transfer on Onset of Oscillatory Thermocapillary Flow of High Prandtl Number Fluid
• Oscillatory Thermocapillary Flow(Abstract from International Seminar on Manufacturing of Advanced Materials)

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