Vibration Effects on the Average Heat Transfer Characteristics of the Natural Convection Field in a Square Enclosure.

2000

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In this paper the time-dependent characteristics of surface-averaged Nusselt number in a square enclosure with hot and cold side walls exposed to vertical vibrations were numerically examined. In the computation, the Prandtl number, the Rayleigh number, and the vibration Grashof number were held constant at 0.71, 10 4 , and 10 6 , respectively. The angular frequency of vibration was changed in the range between 10 and 7680. The results showed that the change in the characteristics of the surfaceaveraged Nusselt number proposed by Fu and Shieh corresponded to the change in the shape of reconstructed attractor and that these regions could also be characterized by the three indices defined in phase space: average location of trajectory, the largest Lyapunov exponent, and the correlation dimension. Moreover, the time scale with which the autocorrelated coefficient of the surface-averaged Nusselt number becomes 1/e was found to be a very important parameter for the time-and surface-averaged Nusselt number.

Section: Introductionmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 88%

“…The physical model and the coordinate system in the present study are the same as in a previous study [8], and are shown in Fig. 1.…”

Section: Numerical Methods and Definitionmentioning

confidence: 99%

Section: Numerical Methods and Definitionmentioning

confidence: 99%

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The structures of attractors reconstructed with time-evolution data of average heat transfer on thermal convection field in a vibrating square enclosure

2000

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“…These characteristics can be related to the hysteresis [7] and unstable [8] phenomena, and the geometrical characteristics constructed from the unsteady fluctuation of the fields were found to be very effective for the classification of thermal convection fields [7,9].…”

Section: Introductionmentioning

confidence: 99%

Quasi‐static and chaotic characteristics of the natural convection field between concentric vertical annuli

Gomi

2002

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In this study unsteady and chaotic characteristics of thermal convection fields between concentric annuli were experimentally examined, and they were compared with those reported in a vertical slot. The inner cylinder was heated by an embedded heater and the outer one was cooled by temperature-controlled cold water, and 84 wt% glycerol-water solution was used for the present test liquid. The main results are as follows: (1) The region where the characteristic frequency of temperature fluctuation is detected is located in the upper portion of the region where the secondary cells exist.(2) The time scale of the temperature change at which the autocorrelation coefficient becomes 1/e is relatively small in the secondary-cell region, and this corresponds to the result of the natural convection field in a vertical slot. (3) The significant chaotic characteristics of temperature fluctuation are observed in almost the same region where the characteristic frequency of temperature fluctuation is detected, and this also corresponds to the results on the vertical slot.

Internal gravity wave resonance of thermal convection fields in a square cavity with heat‐flux vibration

Matsumura

2006

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In this paper, the thermal convection field and its resonance phenomena in a square cavity with sinusoidal heat-flux vibration were numerically investigated. As the angular velocity ω is changed, the thermal convection field at Pr = 0.71, Ra = 10 6 is found to be classified into 5 regions. In particular, the field has the local maximum relative amplitude of midplane Nusselt's number at ω c = 350, which corresponds to the angular velocity of internal gravity wave ω r estimated by a theoretical equation proposed by Thorpe. This shows that the local enhancement is induced by internal gravity wave resonance. Such correspondence is observed for Ra ≥ 10 5 , Ra ≥ 10 6 for Pr = 0.71, 7.1, respectively. For these ranges of Ra we propose a correlation equation, a function of Pr and Gr only, to estimate the resonant angular velocity.