科研之友
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摘要
We report high-precision measurements of the Nusselt number Nu as a function of the Rayleigh number Ra in water-filled rectangular Rayleigh-Benard convection cells. The horizontal length L and width W of the cells are 50.0 and 15.0 cm, respectively, and the heights H = 49.9, 25.0, 12.5, 6.9, 3.5, and 2.4 cm, corresponding to the aspect ratios (Gamma(x) equivalent to L/H; Gamma(y) equivalent to W/H). (1, 0.3), (2, 0.6), (4, 1.2), (7.3, 2.2), (14.3, 4.3), and (20.8, 6.3). The measurements were carried out over the Rayleigh number range 6 x 10(5) less than or similar to Ra less than or similar to 10(11) and the Prandtl number range 5.2 less than or similar to Pr less than or similar to 7. Our results show that for rectangular geometry turbulent heat transport is independent of the cells' aspect ratios and hence is insensitive to the nature and structures of the large-scale mean flows of the system. This is slightly different from the observations in cylindrical cells where Nu is found to be in general a decreasing function of Gamma, at least for Gamma = 1 and larger. Such a difference is probably a manifestation of the finite plate conductivity effect. Corrections for the influence of the finite conductivity of the top and bottom plates are made to obtain the estimates of Nu(infinity) for plates with perfect conductivity. The local scaling exponents beta(l) of Nu(infinity) similar to Ra-beta l are calculated and found to increase from 0.243 at Ra similar or equal to 9 x 10(5) to 0.327 at Ra similar or equal to 4 x 10(10).
- 出版日期2012-11-10
- 单位上海大学
