腔增强拉曼技术下的过饱和硫酸镁液滴蒸发动力学初探(英文)

本文通过单光束梯度力光学镊子-拉曼光谱系统,对硫酸镁单液滴随着相对湿度变化的反应进行了探究。当硫酸镁单液滴被光镊捕获之后,通过相对湿度的梯度变化探究了捕获液滴的蒸发动力学变化。发生在与耳语回音模相称波长的受激拉曼散射可以用来准确地确定液滴半径,因此,可以通过腔增强拉曼散射得到在不同湿度下处于平衡的液滴半径信息。本研究通过光镊对硫酸镁单液滴的实时监测,阐述了在某个相对湿度范围内该液滴的粒径变化的过程和结果,在此之前的硫酸镁吸湿性研究中没有先例。研究结果表明在相对湿度逐渐降低至40%的过程中硫酸镁液滴半径的变化速率逐渐变小。而当相对湿度低于40%时,液滴半径的减小会被严重抑制。这种现象表示在高浓度条件下硫酸镁液滴中水的蒸发扩散速率会降低。另一方面,在蒸发过程后的相对湿度上升过程中,硫酸镁液滴尺寸的增加明显缓慢于湿度增长速度。这一现象显示液滴的尺寸变化是不可逆的。说明胶态的形成导致了传质受阻,从而阻碍了液滴中水分子的交换。     

水平均质表面上液滴聚合过程的可视化实验研究

对水平均匀表面上液滴的聚合过程及特性进行了可视化实验研究,获得了液滴半径和液滴物性等参数对液滴聚合过程中液滴液桥半径和接触角变化特性的影响规律。实验结果表明:液滴聚合中液桥半径和接触角都呈衰减振荡变化; 聚合前液滴半径越小,液桥半径振荡频率越大,振幅越小,振荡时间越短;液滴的粘度越大,液桥半径的振荡频率越小, 振幅越小,振荡时间越短;液滴聚合前的接触角明显大于聚合液滴静止后的接触角,其差值与固体界面状况和气、固、液物性相关。     

基于改进格子Boltzmann焓法模型的液滴凝固数值研究

为了研究不同冷壁面特性上液滴的结晶过程以及凝固速率的规律,利用通过加入对流换热和辐射换热项,使用固相体积分数修正流场的改进的焓-LB方法,使得模型模拟的结果更加精确.分析了液滴在6种不同的壁面特性下,凝固过程平均固相体积分数随时间的变化.分析了凝固后接触角及接触面积与半径的比值随亲疏水性不同的变化.结果表明:壁面的亲水性越好,液滴凝固成核后与壁面的接触角越小,接触面积与半径之间的比值越大;反之,壁面的疏水性越好,液滴凝固成核后与壁面的接触角越大,接触面积与半径之间的比值越小.在超疏水表面存在粗糙元间距较大时,凝固速率最慢,且与粗糙元的接触面积较小,有利于抑霜除霜.     

丁二酸钠和硫酸铵混合气溶胶的光镊受激拉曼光谱研究

采用光镊悬浮技术捕获颗粒尺寸3～8μm的丁二酸钠/硫酸铵混合气溶胶液滴,控制湿度条件、温度条件,通过调节不同相对湿度(RH)并采集氢-氧振动带的受激拉曼峰位信息,利用非弹性米氏散射理论计算实时液滴半径尺寸。计算结果表明,当液滴尺寸响应完湿度的变化后在RH恒定时,液滴半径仍持续减小,这说明丁二酸钠和硫酸铵之间发生了反应,释放出氨气使得液滴半径减小。     

含盐脱硫废水液滴群在低温烟道蒸发特性数值模拟研究

以含盐脱硫废水在某燃煤电厂330 MW机组空气预热器后烟道的喷雾蒸发过程为研究对象,采用离散相模型研究气液两相流动、传热传质和雾化液滴的蒸发,分析了烟气温度、烟气流速、脱硫废水含盐量、液滴直径对蒸发时间,喷雾含水量、蒸发质量的影响。研究表明:含盐脱硫废水蒸发末期,由于水与结晶盐的相互作用,蒸发速率减小;脱硫废水含盐量越高,蒸发越快,盐分由1.0增加至2.0%,蒸发时间减少0.02 s;液滴直径越大,蒸发结晶的固体越大,相同直径下含盐液滴蒸发时间比不含盐液滴蒸发越短;与不含盐液滴相比,液滴直径为60μm时两者完全蒸发时间基本相当,但液滴粒径180μm时,含盐液滴完全蒸发时间比不含盐液滴缩短0.3 s;温度越高,不同含盐量的液滴完全蒸发时间越接近。     

真空型FTIR对硫酸铵/柠檬酸混合体系气溶胶吸湿性研究

采用真空型傅里叶变换红外光谱仪结合压力方波控制系统研究硫酸铵/柠檬酸混合体系气溶胶的吸湿性。相对湿度缓慢变化时,硫酸铵气溶胶的潮解点和风化点分别在相对湿度~80%和~35%,当OIR(柠檬酸与硫酸铵的摩尔比例)=1∶3时,柠檬酸的加入使硫酸铵潮解点降低至~76%,风化点也降低至~28%;相对湿度发生脉冲变化时,随着脉冲相对湿度的最低点逐渐降低,硫酸铵的结晶量台阶式增加,最后完全结晶。在硫酸铵/柠檬酸混合气溶胶中,柠檬酸始终保持液滴状态,随脉冲相对湿度变化,硫酸铵台阶式结晶幅度变小,风化范围变宽。     

润湿梯度作用下液滴在倾斜表面向上运动的格子Boltzmann模拟

采用基于Shan-Chen伪势模型的格子Boltzmann方法,对液滴在存在润湿梯度的倾斜表面上克服重力、自下而上运动的过程进行模拟。探究润湿梯度、液滴尺寸、Bond数以及表面倾斜角度对液滴运动的影响。计算结果表明：液滴在运动过程中,内部会出现沿斜面向上的速度矢量,润湿梯度越大,液滴运动速度越快,润湿长度也越长,且动态接触角减小速率越快。液滴尺寸和Bond数对液滴运动的影响较小,但存在临界Bond数,超过该临界Bond数时,液滴将沿梯度润湿表面向下运动。表面倾角对液滴运动有显著影响,倾角增大,液滴运动速度和润湿长度都明显减小。     

利用不同的湿度调节方法研究醋酸镁气溶胶中水的传质过程

利用一种自制的湿度调节设备与真空红外光谱仪相结合, 提出了一种研究醋酸镁气溶胶的吸湿性和传质动力学的新方法。湿度调节装置通过改变纯水汽压力来调节样品室的相对湿度,这样可以实现湿度以不同的速度发生变化。与红外光谱手段相结合,湿度缓慢变化,让气溶胶时刻处于准稳态过程,可以研究气溶胶在热力学稳态的吸湿性质。湿度脉冲式改变,可以研究气溶胶的动态吸湿性质以及传质动力学过程。红外光谱的扫描方式随着湿度的改变速度进行调节。由于实验中的相对湿度由纯水气提供,因此通过对红外方光谱中纯水气的特征吸收峰面积的定量计算获得与光谱同步的相对湿度值。研究发现,当湿度稳定在一个高湿度时,醋酸根和液态水的峰面积在持续下降。并且首次发现经过一个准稳态的湿度循环后(1.05×104 s),在80%RH条件下,水峰面积由1.5降低至1.1。通过改变实验方案并对其结果进行对比可知,在高湿度条件下,醋酸镁发生水解,生成的醋酸由于样品室内的负压而挥发,因此引起气溶胶含水量下降。采用脉冲发式快速改变样品室的湿度,一个湿度脉冲循环需要10 s。计算脉冲循环过程中气溶胶的含水量发现,在湿度高于70%RH时,气溶胶含水量没有减少。但是加湿过程的水传输比去湿过程的水传输快。这些现象说明醋酸镁的水解速率小于湿度的脉冲改变速率。在湿度快速变化的过程中,气溶胶液滴表面难溶物的形成引起水传输发生受阻现象。     

微通道内光热相变驱动流体运动特性研究

本文通过可视化实验,对微通道内光热效应致相变驱动流体运动特性进行了研究,通过红外聚焦激光跟随微通道内液柱气液界面进行加热持续产生的蒸发冷凝-聚合过程对液柱进行连续驱动。实验研究了激光功率、加热点位置对相变过程中的界面行为、冷凝液滴分布、驱动速率的影响规律。结果表明,激光功率越高,光斑距离界面越近,液柱蒸发速率越大,蒸汽浓度高,冷凝液滴分布越密集,驱动流体流动速度越快。     

利用不同的湿度调节方法研究醋酸镁气溶胶中水的传质过程（英文）

利用一种自制的湿度调节设备与真空红外光谱仪相结合,提出了一种研究醋酸镁气溶胶的吸湿性和传质动力学的新方法。湿度调节装置通过改变纯水汽压力来调节样品室的相对湿度,这样可以实现湿度以不同的速度发生变化。与红外光谱手段相结合,湿度缓慢变化,让气溶胶时刻处于准稳态过程,可以研究气溶胶在热力学稳态的吸湿性质。湿度脉冲式改变,可以研究气溶胶的动态吸湿性质以及传质动力学过程。红外光谱的扫描方式随着湿度的改变速度进行调节。由于实验中的相对湿度由纯水气提供,因此通过对红外方光谱中纯水气的特征吸收峰面积的定量计算获得与光谱同步的相对湿度值。研究发现,当湿度稳定在一个高湿度时,醋酸根和液态水的峰面积在持续下降。并且首次发现经过一个准稳态的湿度循环后(1.05×10~4 s),在80%RH条件下,水峰面积由1.5降低至1.1。通过改变实验方案并对其结果进行对比可知,在高湿度条件下,醋酸镁发生水解,生成的醋酸由于样品室内的负压而挥发,因此引起气溶胶含水量下降。采用脉冲发式快速改变样品室的湿度,一个湿度脉冲循环需要10s。计算脉冲循环过程中气溶胶的含水量发现,在湿度高于70%RH时,气溶胶含水量没有减少。但是加湿过程的水传输比去湿过程的水传输快。这些现象说明醋酸镁的水解速率小于湿度的脉冲改变速率。在湿度快速变化的过程中,气溶胶液滴表面难溶物的形成引起水传输发生受阻现象。     

单滴醋酸钠和醋酸镁的过饱和溶液的拉曼光谱研究(英文)

应用拉曼光谱和电动态平衡技术研究了单滴醋酸钠和醋酸镁的过饱和溶液,特别是对在不同相对湿度条件下的结构变化以及接触离子对的形成进行了详细讨论。     

共焦拉曼光谱对疏水基底上Mg(CH3COO)2液滴与CO2非均相反应动力学过程的观测

本文利用共焦拉曼光谱在球形液滴的表面和中心可聚焦两次的特性, 观测了不同RH(relative humidity, 相对湿度)下疏水基底上Mg(CH3COO)2液滴与CO2在液滴表面和中心的反应情况。结果表明, 反应生成的产物为碱式碳酸镁。当RH约73%时, 液滴表面和中心生成的产物的量差别不大; 当RH约65%时, 表面和中心的差别较RH约73%时明显; 而当RH降至约58%时, 表面和中心的差别则变得非常明显。由于Mg(CH3COO)2液滴在较低相对湿度下会形成胶态结构, 引起传质受阻, 从而使得CO2由液滴表面扩散到内部变得越来越困难, 最终导致液滴表面生成的产物比中心多。     

共聚焦拉曼光谱研究ZnSO_4微液滴的风化过程

通过共聚焦拉曼原位光谱技术在分子水平上研究了沉积在聚四氟乙烯基底上的ZnSO_4微液滴的风化过程.根据获得的高信噪比的Raman光谱,详细探讨了湿度降低时ZnSO_4微液滴中Zn~(2+)和SO_4~2离子的缔合行为,即经由单齿、双齿最终转化为复杂的链状或网状接触离子对.利用曲线拟合技术对其光谱的ν1-SO_4~2峰进行分峰,获得了不同湿度下ZnSO_4微液滴中各组分的量化信息:高湿度时,液滴中主要包含自由的水合SO_4~(2-);随着湿度降低,自由SO_4~(2-)逐渐向单齿、双齿接触离子对转化,并在湿度为66%和34%时分别达到其最大值;继续降低湿度,复杂的链状或网状接触离子对逐渐成为液滴中的主要成分.     

Confocal Raman imaging and atomic force microscopy of the surface reaction of NO2 and NaCl(100) under humidity

Polarized confocal Raman imaging combined with non‐contact atomic force microscopy (AFM) was used to study the three‐dimensional evolution of the NaCl(100) surface during its reaction with NO₂ at low pressure as a function of relative humidity (RH) from 0% to nearly 80%. Sea salt particles containing NaCl as the main constituent are believed to be the major source of reactive tropospheric chlorine and nitrate fallouts. At an RH of 0%, the reaction of dry NO₂ generates surface conversion to NaNO₃ monolayer capping the NaCl(100) surface and releases NOCl. The subsequent exposure of this NaNO₃ layer to RH below ∼45% induces the formation of rare NaNO₃ tetrahedral crystals less than 0.5 µm in size. The crystallization occurs through two‐dimensional NO₃⁻ migration under the H₂O monolayer regime. After another subsequent exposure to RH above 45% and below 75%, supermicrometric NaNO₃ rhombohedral plates were obtained under the H₂O multilayer regime. On the other hand, the simultaneous exposure of NaCl(100) to NO₂ and H₂O below ∼45% RH rapidly generates numerous submicrometric NaNO₃ tetrahedra on the NaCl(100) surface. The dramatic increase of NaNO₃ production in the presence of water vapour is explained by the formation of HNO₃ and its easy reaction with the NaCl(100) surface. For RH above 45% and below 75%, the tetrahedra evolve to rhombohedral plates of supermicrometric size. The exposure of NaCl(100) to NO₂/H₂O mixtures under RH above 75% induces the coexistence of both solid‐state NaNO₃ and dissolved NO₃⁻ in droplets. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of surface energy and relative humidity on AFM nanomechanical contact stiffness

The effects of surface functionality and relative humidity (RH) on nanomechanical contact stiffness were investigated using atomic force acoustic microscopy (AFAM), a contact scanned-probe microscopy (SPM) technique. Self-assembled monolayers (SAMs) with controlled surface energy were studied systematically in a controlled-humidity chamber. AFAM amplitude images of a micropatterned, graded-surface-energy SAM sample revealed that image contrast depended on both ambient humidity and surface energy. Quantitative AFAM point measurements indicated that the contact stiffness remained roughly constant for the hydrophobic SAM but increased monotonically for the hydrophilic SAM. To correct for this unphysical behavior, a viscoelastic damping term representing capillary forces between the tip and the SAM was added to the data analysis model. The contact stiffness calculated with this revised model remained constant with RH, while the damping term increased strongly with RH for the hydrophilic SAM. The observed behavior is consistent with previous studies of surface energy and RH behavior using AFM pull-off forces. Our results show that surface and environmental conditions can influence accurate measurements of nanomechanical properties with SPM methods such as AFAM.     

(NH4)2SO4，NH4NO3和(NH4)2SO4/NH4NO3混合气溶胶吸湿质量增长因子的快速测量方法

气溶胶颗粒的吸湿性决定了其尺寸、浓度、化学组成以及相态,从而显著影响着全球气候、大气异相化学以及人类健康。运用在线、原位、连续扫描衰减全反射傅里叶变换红外光谱（ATR-FTIR）技术, 结合线性湿度（RH）控制系统,实现了RH连续变化条件下气溶胶FTIR-ATR光谱的快速测量。根据水弯曲振动谱带（~1 640 cm-1）峰面积随RH的变化,得到了(NH₄)₂SO₄,NH₄NO₃和(NH₄)₂SO₄/NH₄NO₃混合气溶胶的质量增长因子（MGFs）、潮解点（DRH）和风化点（ERH）。与气溶胶的E-AIM模型预测值相比较,实验结果表现出良好的一致性,证实该方法是一种测量大气气溶胶MGFs,ERH和DRH的快速测量方法。     

Sorption isotherm measurements by NMR

An experimental setup is described for the automated recording of sorption isotherms by NMR experiments at precisely defined levels of relative humidity (RH). Implementation is demonstrated for a cotton fabric; Bloch decays. T1 and T2* relaxation times were measured at predefined steps of increasing and decreasing relative humidities (RHs) so that a complete isotherm of NMR properties was obtained. Bloch decays were analyzed by fitting to relaxation functions consisting or a slow- and a fast-relaxing component. The fraction of slow-relaxing component was greater than the fraction of sorbed moisture determined from gravimetric sorption data. The excess slow-relaxing component was attributed to plasticized segments of the formerly rigid cellulose matrix. T1 and T2* sorption isotherms exhibit hysteresis similar to gravimetric sorption isotherms. However, correlating RH to moisture content (MC) reveals that both relaxation constants depend only on MC, and not on the history of moisture exposure.     

An experimental study of relative humidity and air flow effects on positive and negative corona discharges in a corona-needle charger

In this paper, the effects of inlet air RH and air flow rate on positive and negative corona discharges in a corona-needle charger have been experimentally studied and discussed. Its corona discharge characterizations in terms of current-to-voltage relationships of the corona-needle charger on the effects of inlet air RH and air flow rate were evaluated at applied corona voltages between 0 and 3.1 kV, an air flow rates between 5 and 15 L/min, a relative humidity between 20 and 90%, and an operating pressure of about 101.3 kPa. Experimental results were shown that discharge current is strongly affected by the RH level of the inlet air. The positive discharge current was found to be decreased with increasing RH value at RH values below 60% and increased with increasing RH value at RH value above 60% in the same corona voltage. The negative discharge current was found to be stable with increasing RH value at RH values below 40% and increased with increasing RH value at RH value above 40% in the same corona voltage. For the air flow rate effects, the positive discharge current was found to slightly decrease when the air flow rate increased at RH value below 90% and to increase with the air flow rate at RH value of 90%. For the negative corona, the discharge current was also found to monotonically decrease when the air flow rate increased.     

Graphene oxide thin film coated quartz crystal microbalance for humidity detection

In this paper, we demonstrated that chemically derived graphene oxide (GO) thin film as a humidity sensitive coating deposited on quartz crystal microbalances (QCMs) for humidity detection. By exposing GO thin film coated QCMs to various relative humidity (RH) environments at room temperature, the humidity sensing characteristics of the QCMs such as sensitivity and linearity, response and recovery, humidity hysteresis were investigated. The experiment results show that GO thin film coated QCMs exhibit an excellent humidity sensing performance. Moreover, the possible humidity sensing mechanism of GO thin film coated QCMs was also investigated by monitoring the crystal's motional resistance change. It is suggested that the frequency response of the QCMs is dependent on water molecules adsorbed/desorbed masses on GO thin film in the low RH range, and on both water molecules adsorbed/desorbed masses on GO thin film and variations in interlayer expansion stress of GO thin film derived from swelling effect in the high RH range.