Effect of viscosity difference in static stratified fluids on the convective flux of double-diffusion
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摘要: 为研究双扩散对流过程中流体黏性对通量的影响，设计梯度浓度的双扩散试验，黏度随着浓度的增大而增大。在设计有中间挡板的试验水箱中注入根据糖盐组分质量分数精确配制的溶液，以控制盐指密度稳定比在1.073；扩散型密度稳定比在0.93。移开挡板后，水箱会内形成静止状态的糖盐双层系统。为了更精确地评估双扩散现象并最小化误差，试验设置了三种时间段的双扩散试验，分别为300 s、600 s和
1800 s。试验发现：短时间内通量会受黏度影响而显著减小，但随着时间的增长，这些影响被继发的扩散通量所掩盖。盐指型和扩散型双扩散的糖通量与黏度之间均存在非线性关系，在扩散型双扩散中通量比γ*与黏度比之间拟合得出两者呈幂律关系；而盐指型通量比 γ 与黏度比之间的变化则相对复杂，需要更精细化研究。Abstract: To investigate the impact of fluid viscosity on flux during double-diffusive convection, a gradient-concentration double-diffusion experiment was designed, where viscosity increases with concentration. Precisely formulated sugar-salt solutions based on mass fraction were injected into a test tank equipped with an intermediate baffle, controlling the salt-fingering density stability ratio at 1.073 and the diffusion-dominated density stability ratio at 0.93. After removing the baffle, a stationary sugar-salt two-layer system formed within the tank. To accurately evaluate double-diffusive phenomena and minimize experimental errors, three time intervals were established for the double-diffusion tests: 300 s, 600 s, and1800 s. The experimental results revealed that short-term flux is significantly reduced under the influence of viscosity. However, this effect becomes masked by subsequent diffusive fluxes as time progresses. Both salt-fingering and diffusion-dominated double-diffusion exhibit nonlinear relationships between sugar flux and viscosity. In diffusion-dominated double-diffusion, a power-law correlation was established between the flux ratio γ* and viscosity ratio. Nonetheless, the discrepancy between γ and the viscosity ratios of salt finger fluxes is relatively intricate and necessitates a more exhaustive analysis.-
Key words:
- double diffusion convection /
- density stability ratio /
- flux ratio /
- viscosity
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图 1 实验室中的盐指(a)和扩散(b)型双扩散图
Fig. 1 Laboratory experiment on salt finger (chart a) and diffusion convection (chart b)
图 2 盐指型双扩散不同时间下的糖和盐通量与粘度变化趋势
Fig. 2 Trends in sugar (chart a) and salt (chart b) fluxes versus viscosity at different times for salt finger
图 3 扩散型双扩散不同时间下的糖盐通量与粘度趋势
Fig. 3 Trends in salt (chart a) and sugar (chart b) fluxes versus viscosity at different times for diffusion convection
图 4 扩散型双扩散的通量比与黏度比（糖/盐）趋势图
Fig. 4 Trends in flux ratio versus viscosity ratio (sugar/salt) for diffusion convection
图 5 盐指型双扩散的通量比与黏度比(盐/糖)趋势图
Fig. 5 Trends in flux ratio versus viscosity ratio (sugar/salt) for salt finger
表 1 盐指(a)中的拟合结果
Tab. 1 Fitting results in salt finger (chart a)
组数 A1 A2 t1 t2 R² y0 300 s 2.42 3.5 0.64 0.64 0.9 0.381 600 s 6 12 0.311 0.311 0.658 0.328 1800 s−0.168 0.021 / / 0.729 0.468 
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表 2 扩散型双扩散的拟合结果
Tab. 2 Fitting results in diffusion convention
时长 a b R² 300 s 0.57 0.28 0.53 600 s 0.57 0.29 0.78 1800 s0.57 0.32 0.91
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