In this study the influence of cell tilting on flow dynamics and heat transport is explored experimentally within a rectangular cell (aspect ratios Γ x = 1 and Γ y = 0.25). The measurements are carried out over a wide range of tilt angles (0 β π/2 rad) at a constant Prandtl number (Pr 6.3) and Rayleigh number (Ra 4.42 × 10 9 ). The velocity measurements reveal that the large-scale circulation (LSC) is sensitive to the symmetry of the system. In the level case, the high-velocity band of the LSC concentrates at about a quarter of the cell width from the boundary. As the cell is slightly tilted (β 0.04 rad), the position of the high-velocity band quickly moves towards the boundary. With increasing β, the LSC changes gradually from oblique ellipse-like to square-like, and other more complicated patterns. Oscillations have been found in the temperature and velocity fields for almost all β, and are strongest at around β 0.48 rad. As β increases, the Reynolds number (Re) initially also increases, until it reaches its maximum at the transition angle β = 0.15 rad, after which it gradually decreases. The cell tilting causes a pronounced reduction of the Nusselt number (Nu). As β increases from 0 to 0.15, 1.05 and π/2 rad, the reduction of Nu is approximately 1.4 %, 5 % and 18 %, respectively. Over the ranges of 0 β 0.15 rad, 0.15 β 1.05 rad and 1.05 β π/2 rad, the decay slopes are 8.57 × 10 −2 , 3.27 × 10 −2 and 0.24 rad −1 , respectively.
The ocean bottom is the Earth's least explored region, and the bottom mixed layer (BML) is the pathway for communication between the ocean interior and the ocean floor. In this study, we used full‐depth conductivity‐temperature‐depth profiles archived by the World Ocean Circulation Experiment Program to obtain the first approximation of the global distribution of the oceanic BML thickness, HBML, by applying an integrated method (Huang, Cen, et al., 2018, https://doi.orag/10.1175/jtech-d-18-0016.1). We found that the median HBML values were 40, 42, and 64 m in the Atlantic, Indian, and Pacific Oceans, respectively, and 47 m globally. Statistically, the peak values for the median HBML were around 20°N or 20°S, and it had weak dependence on the buoyancy frequency, where a thin HBML corresponded to strong stratification. In addition, the median HBML became thicker with the ocean depth (D), according to HBML = 26.34 + 0.85e(D/1271.8).
In this study we examined the applicability of the threshold, curvature, maximum angle, and relative variance methods for identifying the oceanic bottom mixed layer (BML) thickness . Using full-depth temperature profiles along 17 WOCE sections covering the Atlantic, Indian, and Pacific Oceans, we found that the BML thicknesses determined based on the threshold, curvature, and maximum angle methods had wider 95% confidence intervals and much lower quality indexes compared with those based on the visual inspection (). The relative variance method appeared to perform better than the other methods because the 95% confidence interval and (0.60) values were closer to those determined based on the visual inspection, although differences were still present. We then proposed an integrated method by optimizing the possible values obtained from the four methods. The BML thicknesses determined using the integrated method were closest to those based on the visual inspection according to the higher (0.64) and more stations (71%) with . Compared with the results in previous studies, the integrated method determined the consistent BML thicknesses in most regions (e.g., the northern Atlantic), and it also effectively identified the BML thicknesses in some regions where the BML was considered to be not readily detectable (e.g., the Madeira Abyssal Plain).
Large eddy simulation model is used to simulate the fluid flow and heat transfer in an industrial Czochralski crystal growth system. The influence of Marangoni convection on the growth process is discussed. The simulation results agree well with experiment, which indicates that large eddy simulation is capable of capturing the temperature fluctuations in the melt. As the Marangoni number increases, the radial velocity along the free surface is strengthened, which makes the flow pattern shift from circumferential to spiral. At the same time, the surface tension reinforces the natural convection and forces the isotherms to curve downwards. It can also be seen from the simulation that a secondary vortex and the Ekman layer are generated. All these physical phenomena induced by Marangoni convection have great impacts on the shape of the growth interface and thus the quality of the crystal.
The nominal spatial distribution of diapycnal mixing in the South China Sea (SCS) is obtained with Thorpe-scale analysis from 2004 to 2020. The inferred dissipation rate ε and diapycnal diffusivity Kz between 100 and 1500 m indicated that the strongest mixing occurred in the Luzon Strait and Dongsha Plateau regions, with ε ~ 3.0 × 10-8 W/kg (εmax = 5.3 × 10-6 W/kg) and Kz ~ 3.5 × 10-4 m2/s (Kz max = 4.2 = 10-2 m2/s). The weakest mixing occurred in the thermocline of the central basin, with ε ~ 6.2 × 10-10 W/kg and Kz ~ 3.7 × 10-6 m2/s. The ε and Kz in the continental slope indicated that the mixing in the northern part [O(10-8) W/kg, O(10-4) m2/s] was comparatively stronger than that in the Xisha and Nansha regions [O(10-9) W/kg, O(10-5) m2/s]. The Kz in the continental slope region (200–2000 m) decayed at a closed rate from the ocean bottom to the main thermocline when the measured depth D was normalized by the ocean depth H as D/H, whether in the shallow or deep oceans. The diapycnal diffusivity was parameterized as Kz = 3.3 × 10−4 (1 + )−2 − 6.0 × 10−6 m2/s. The vertically integrated energy dissipation was nominally as 15.8 mW/m2 for all data and 25.6 mW/m2 for data at stations H < 2000 m. This was about one order higher than that in the open oceans (3.0–3.3 mW/m2), which confirmed the active mixing state in the SCS.
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