A test of the Tate equation to predict bubble size at an orifice in the presence of frother

Air bubbles of uniform size (ca. 1 mm diameter) were generated at a submerged orifice (glass capillary) under controlled frequency (down to ca. 0.06 s^− 1) in aqueous solutions of frother (Dowfroth 250). The bubbles were sized with an imaging technique. One objective was to establish whether the Tate equation (static balance between buoyancy and capillary forces) could be used as a standard sizing calibration method. Another aim was to verify whether with decreasing surface tension (due to increasing frother concentration) the anticipated decrease in bubble size agreed with the equation prediction. An effect of frother was detected compatible with the role of surface tension but divided into two concentration regions, seemingly the result of a gradual change in bubble shape and wetting: > 6 ppm the bubble holds a spherical shape and the capillary appeared to be completely wetted while at ≤ 6 ppm a degree of non-wetting and bubble distortion (neck formation just prior to detachment) were apparent, supported by qualitative observations. In addition, at > 6 ppm the Tate value was only approached by decreasing the bubble frequency but not attained. Plausible causes for the failure to reach the predicted size are discussed.     

实验室合成石盐包裹体的均一温度以及古气候意义

石盐是表生环境下形成蒸发岩系的主要矿物,在形成过程中捕获大量的原生包裹体。通过低温冷冻测温技术,可以得到石盐中原生包裹体的一系列均一温度,如何正确理解这些数据是应用石盐原生包裹体恢复古气候的关键。石盐沉积可以发生在气水界面以及水体底部,其均一温度记录了卤水结晶的温度。Lowenstein et al. (1998) 曾经用水浴法在恒定水温下合成了人工合成石盐,进行原生包裹体的均一温度研究,然而如何用水温来恢复古气温是古环境解释的关键。本次实验通过40℃下(气温,烘箱中蒸发)人工合成石盐,在岩相学观察基础上,对形成于气水界面漏斗晶中的包裹体和在底水沉积人字晶中的包裹体的均一温度进行低温冷冻测温法测定。测温过程中石盐包裹体可以得到一系列均一温度(10.6~39.9℃),而只有最大均一温度才能反映卤水结晶时的温度,两种类型的包裹体也显示了相似的最大均一温度。因此在浅水环境下,两种包裹体都可以用来反映古气温。     

Variations in rates of nucleation and growth of biotite porphyroblasts

Differences in rates of nucleation and diffusion‐limited growth for biotite porphyroblasts in adjacent centimetre‐scale layers of a garnet‐biotite schist from the Picuris Mountains of New Mexico are revealed by variations in crystal size and abundance between two layers with strong compositional similarity. Relationships between fabrics recorded by inclusion patterns in biotite and garnet porphyroblasts are interpreted to reflect garnet growth following biotite growth, without substantial alteration of the biotite sizes. Sizes and locations of biotite crystals, obtained via high‐resolution X‐ray computed tomography, document that of the two adjacent layers, one has a larger mean crystal volume (9.5 × 10^?4v. 2.4 × 10^?4 cm³), fewer biotite crystals per unit volume (232 v. 576 crystals cm^?3), and a higher volume fraction of biotite (23%v. 14%). The two layers have similar mineral assemblages and mineral chemistry. Both layers show evidence for diffusional control of nucleation and growth. Pseudosection analysis suggests that the large‐biotite layer began to crystallize biotite at a temperature ～67 °C greater than the small‐biotite layer. Diffusion rates differed between layers, because of their different temperature ranges of crystallization, but this effect can be quantified. The bulk compositional difference between the layers, manifested in different modal amounts of biotite, has an effect on the biotite sizes that is also quantifiable and insufficient to account for the difference in biotite size. After these other possible causes of variation in crystal sizes have been eliminated, variability in nucleation and diffusion rates remain as the dominant factors responsible for the difference in porphyroblastic textures. Numerical simulations suggest that relative to the small‐biotite layer, the large‐biotite layer experienced elevated diffusion rates because of the higher crystallization temperature, as well as increased nucleation rates in order to achieve the observed size and number density of crystals. The simulations can replicate the observed textures only by invoking unreasonably large values for the thermal dependence of nucleation rates (activation energies), strongly suggesting that the observed textural differences arise from variations between layers in the abundance and energetics of potential nucleation sites.     

Fluid Inclusions in Surface‐temperature Halite: Sample Preparation and Application

Paleo-temperature and paleo-environment can be interpreted from measuring homogenization temperatures of fluid inclusions within halite. In order to conduct such measurements, vapor bubbles within low-temperature fluid inclusion often need to be created through cooling process by using cooling stage or freezer. Proper cooling is critical for interpreting measured temperature data. We tested two common cooling methods, using heating/freezing stage and freezer, for studying fluid inclusions in halite precipitated in laboratory at conrtolled temperature of 25℃. While using the heating/freezing stage, halite samples were kept at-18℃ for 40–50 min; whereas for freezer, samples were stored at-18℃ for 1, 10, 20 and 40 days, respectively. By comparing the homogenization temperatures of the two cooling processes, we explored the detailed experimental processes and developed an optimal cooling nucleation procedure for homogenization temperature analyses of fluid inclusions within surface-temperature halite. The results show that the maximum homogenization temperatures from both methods approximate the actual brine temperature of 25℃. However, extended refrigeration time has noticeable influence on the results. The refrigeration time of the experiment can be shortened to meet requirements.     

Reduction of bend scour with an air-bubble screen-morphology and flow patterns

The interplay between streamwise flow,curvature-induced secondary flow,sediment transport and bed morphology leads to the formation of a typical bar-pool bed morphology in open-channel bends.The associated scour at the outer bank and deposition at the inner bank may endanger the outer bank’s stability or reduce the navigable width of the channel.Previous preliminary laboratory experiments in a sharply curved flume with a fixed horizontal bed have shown that a bubble screen located near the outer bank can generate an additional secondary flow located between the outer bank and the curvature-induced secondary flow and with a sense of rotation opposite to the latter.This bubble-induced secondary flow redistributes velocities and bed shear stresses.The reported study investigates the implications of a bubble screen on the flow and the morphology in configurations with mobile bed.Velocity measurements show that the bubble-induced secondary flow shifts the curvature-induced secondary flow in inwards direction and reduces its strength.The bubble screen considerably reduces morphological gradients.Maximum bend scour is reduced by about 50%and occurs further away from the outer bank where it does not endanger the bank stability anymore.The location of maximum scour coincides with the junction of the curvature-induced and bubble-induced secondary flows.At this same location,the maximum streamwise velocities and maximum vertical velocities impinging on the bed also occur,which indicates their importance with respect to the formation of bend scour.The bubble screen also substantially reduced deposition at the inner bank.These preliminary experiments show the potential of a bubble screen to influence and modify the bed morphology.     

CFD-based modelling of bubble-particle collision efficiency with mobile bubble surface in a turbulent environment

Flotation modelling to date has concentrated either on macroscale processes or on ideal microscale processes — there has been no attempt to integrate detailed models at different scales. In this paper, bubble-particle collision efficiency with mobile bubble surfaces in a turbulent flow is investigated from a multiscale modelling viewpoint and a general methodology for modelling is present. Comparisons are carried out to illustrate the method. Turbulence effects on bubble-particle collision efficiency are systematically studied using a 3D k–ε turbulence model.     

花岗岩变形破坏的阶段性模型--应力速度及预存微裂纹密度对断层形成过程的影响

依据对具有较高微裂纹密度的筑波花岗岩和极低微裂纹密度的花岗斑岩 2种极端的岩石标本、在等应力速率的快速加载 (约 6MPa/min)和蠕变加载 (轴向应力保持在约 95 %破坏强度 ) 2个极端的加载条件下的实验结果 ,讨论了预存微裂纹密度与加载速度对多晶质结晶岩变形破坏过程的影响。实验中利用高速多通道声发射波形数字记录系统 (每秒可记录多达 5 0 0 0个声发射事件的 32通道波形 ) ,获得了岩石标本破坏前微破裂活动的详细时空分布数据。声发射的发生率、震级 -频度关系中的b值及震源的空间分布揭示出岩石变形破坏过程中微破裂活动具有 3个典型阶段 :初期阶段、第 2阶段和成核阶段。尤其是在成核阶段 ,还观测到发生率和b值有大幅度前兆性起伏。一般而言 ,在相同加载条件下预存微破裂密度越高 ,或对同一岩石加载速度越慢 ,对应的断层成核过程就越长 ,因此最终破坏的可预报性也越高。为了进一步探讨微破裂活动的阶段性特征及其物理本质 ,还利用亚临界破裂扩展模型对声发射数据进行了理论分析     

作物霜冻与低温强度及冰核菌密度的关系

应用辐射型霜箱进行控制试验，研究玉米霜冻害程度与低温强度和冰核菌密度的关系。结果表明逻辑斯蒂克(logistic)方程只有在没有冰核菌或冰核菌密度很小的条件下才能描述霜冻与温度的关系，而理查兹(Richards)方程能够在各种冰核菌密度下很好地描述三者的关系。进而讨论了这种关系在确定霜冻指标，制作霜冻预报，选用防霜方法等方面的应用。     

云中可溶性物质对冰核化影响的实验研究

用冷台冻滴和２ｍ３云室试验相结合的方法，研究了云中可溶性物质对冰核化的影响。实验结果表明，一般云中观测到的可溶性盐类气溶胶（如ＮａＣｌ、（ＮＨ４）２ＳＯ４等）在温度高于－１８℃时不易成为冰核。而高浓度的可溶性铵盐（如（ＮＨ４）２ＳＯ４，ＮＨＣｌ等）则能显著提高ＡｇＩ的成冰温度。（ＮＨ４）２ＳＯ４能使ＡｇＩ成冰晶数在－１０℃提高２个量级，－６℃提高约１个量级。该结果对人工催化技术有一定指导意义。     

气溶胶核化清除的化学效应──Ⅱ：动力学参数对云滴化学非均匀性的影响

运用已建立的气溶胶核化清除的物理化学模式，研究了云的动力学因子（如：气块上升速度、夹卷作用）对云滴化学非均匀性的影响。计算结果表明：较强烈的云发展（较大的气块上升速度）可加强由于气溶胶核化和云滴凝结增长造成的云滴化学的非均匀程度。夹卷作用抑制了云的发展，因而减弱了这种非均匀程度。夹卷作用同时也造成总体液态水中Ｓ（ＶＩ）、Ｈ＋等浓度的增加，在Ｓｍａｘ附近可达１个量级。如果考虑气溶胶粒子的夹卷，则可使气块内云滴污染物浓度随云滴大小的变化更加复杂化，如：不仅云滴污染物浓度随云滴大小而变化，即使对于相同大小的云滴之间，其污染物浓度也可相差很大。