| Budget Amount *help |
¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 2000: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1999: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
Three-dimensional, time-dependent numerical simulation has been performed on natural convection of low Prandtl number (Pr) fluids such as liquid metals. Calculations are carried out for rectangular enclosures with differentially heated sidewalls and adiabatic walls of aspect ratios (Ar) 2 and 4, and width ratios (Wr) ranging 0.5 to 4.2. The results are as follows.
1. In cases (Ar, Wr)=(2, 1), (2, 2) and (4, 1), the critical Grashof number (Gr^c) at which the onset of oscillation occurs largely depends on Pr.
2. The flow structure is characterized by cellular pattern and longitudinal vortices (rolls). As Wr is increased, Gr_c decreases except in a short range of Wr. An abrupt change in Gr_c occurs there. This is attributed to transition in the cellular pattern, or to variation in the arrangement of rolls.
3. In cases Pr=0 and 0.015, the convective structures at Gr_c are unicellular in general.
4. In the case Pr=0.025, however, oscillatory two-cell patterns are observed in the range Wr【less than or equal】1 for Ar=2, or Wr【less than or equal】1.4 for Ar=4. The flow structures are unicellular for other range of Wr.
5. The oscillatory convection has significant effect on heat transfer rate. For Ar=4, oscillations make an about 10 percent difference among the average Nusselt numbers.
The experiments conducted using Gallium for Arz2, 4, and Wr=0.5-4 show following results.
1. Reproducible oscillations occur. The critical Grashof numbers determined from temperature oscillations show qualitative agreement with numerical ones.
2. In both aspect ratios, Gr_c decrease as Wr is increased. Some hystereses exist among Gr_c.
3. The period of oscillation varies from about 10 seconds to one minute. The period shows a jump around a particular Wr. For Ar=4, experimental data are in good agreement with simulation results.
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