One-step measurements of powder resistivity as a function of relative humidity and its effect on charging

A new one-step technique to measure the effect of ambient humidity on powder resistivity has been previously presented. In this article, we provide more experimental data obtained with five different powders. One-step measurements and traditional multi-step measurements were performed. Also, additional measurements were performed using standard resistivity cell. Results were compared and it could be concluded that the new technique provided meaningful results although significant hysteresis was observed during humidification and drying cycles. Finally, charging of the powder was also measured and it was noticed that it decreases with decreasing resistivity and increasing humidity.     

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.     

相对湿度对空调中翅片管蒸发器性能的影响

基于换热器几何结构参数以及流路布置等相同的3HP商用空调,在空调工况下,研究了相对湿度对R22替代制冷剂R407C、R410A、R32以及R290在蒸发器内的流动和传热性能的影响规律。研究表明:在一定的条件下,增加环境相对湿度,这五种制冷剂对应蒸发器换热量、压降和质量流量均增加,其中R407C蒸发器换热量最大,R290和R32蒸发器压降和制冷剂质量流量均小于R22蒸发器。在低湿度环境下(约20—30%相对湿度),显热换热占主导因素。随着相对湿度的增加,显然换热减少,潜热换热增强且起主导因素。在满足换热量的要求下,R290在协调压降与质量流量具有一定的优势且满足现行工质替代理念,可以作为现有商用空调的环保型替代工质。     

A detection of atmospheric relative humidity profile by UV Raman lidar

A new spectroscopic filter constructed with a high-spectral-resolution grating and two narrow-band mirrors is designed to separate the elastic scattering and the vibrational Raman scattering spectra in an ultraviolet (UV) Raman lidar system. The density of humidity and water vapor mixing ratio are calculated from the vibrational Raman scattering signals of N₂ and H₂O. Water vapor mixing ratio is retrieved from this development. With this measured water vapor mixing ratio, the relative humidity is calculated with atmospheric temperature profile obtained by another Raman temperature lidar. Preliminary experiments and comparison results between lidar and radiosonde showed that the UV Raman lidar system has the capability for profiling the water vapor mixing ratio up to a height of 2 km with less than 10% of the uncertainty under the conditions of laser energy of 300 mJ and signal-averaging time of 10 min.     

Temporal-spatial diversities of long-range correlation for relative humidity over China

Long-range correlations of daily relative humidity anomaly records from 191 weather stations over China during 1951-2000 are analyzed by means of fluctuation analysis (FA) and detrended fluctuation analysis (DFA). The information about trends in the relative humidity records can be obtained by comparing the FA curve with DFA curves. The daily relative humidity fluctuations are found to be power-law correlated and their average scaling exponent is higher than that of the temperature fluctuations, indicating that the relative humidity fluctuations take different statistical behavior from other meteorological quantities and there exists a stronger persistence in the relative humidity fluctuations. Furthermore, it is also found that these power-law scaling properties vary from station to station and show both spatial and temporal diversities, which may be explained by a proposed mechanism.     

汽车座椅局部散热除湿研究

车内空气的温度和相对湿度是影响人体舒适性的重要因素。特别是在高温条件下,高湿对人体的影响更加明显。使用计算流体力学和计算传热学的方法,对座椅和人体接触面温湿度较高的问题进行分析。根据人体及汽车座椅的相关尺寸,建立座椅的计算模型,然后进行数值计算。从改变结构的方面考虑解决问题的途径,即在座椅与人体接触面下开槽,并强制通风。使用FLUENT软件进行数值模拟,选择k-ε模型求解温度场和湿度场。计算结果表明,这种方法可以降低汽车座椅与人接触区域的温度和相对湿度,提高局部热舒适性。所得数据为车室内人体局部热舒适性评价提供理论依据。     

Particle charging characteristics with the low-speed mixed fluid under high electric field

Air pollution caused by particles with small size has been a global concern because of threats to human health. A feasible way to remove these super fine suspended particles is using electrostatic precipitation technology. Herein, the PIV was used to measure the particle velocity distribution. By analyzing the particle motion trend in high electric field, a process of particle charging loss was observed. This phenomenon cannot be explained by current particle charging theories. Our conclusions may improve the understanding of particle charging processes.     

Relative humidity sensor based on SMS fiber structure with polyvinyl alcohol coating

A novel relative humidity (RH) sensor based on single-mode–multimode–single-mode (SMS) fiber structure is presented. The sensors are created through coating a thin layer of polyvinyl alcohol (PVA) on the multimode fiber deleted the cladding trough HF solution cauterization as the sensitive cladding film, whose refractive index varies as a function of humidity level. Due to the SMS fiber structure's sensitivity to ambient refractive index, the transmission spectra of SMS fiber structure coated PVA film are modified under exposure to different ambient humidity levels ranging from 30% to 80% RH. The related numerical simulations of transmission spectra of SMS fiber structure with different surrounding refractive index are also proposed. The sensitive of the RH measurement of 0.09 nm/% RH in the range from 30% to 80% RH is experimentally achieved. Meanwhile the intensity of wavelength at 1543 nm is decreasing as the humidity increasing. The experimental results obtained are consistent with the conclusion obtained by numerical simulating.     

充电参数对聚丙烯蜂窝膜驻极体压电性的影响

通过接触法充电、恒压电晕充电，以及开路热刺激放电技术，对充电参数(例如充电电压，充电时间和充电温度等)对聚丙烯蜂窝膜(PP cellular)驻极体的压电性及其热稳定性的影响的研究，并从孔洞型薄膜压电体的材料结构和理论模型出发，讨论了这些参数对其影响的原因，分析了与压电活性密切相关的空间电荷的动态特性.结果表明，合理地优化充电参数，能使这类呈闭合孔洞的聚合物蜂窝膜驻极体的压电性及其稳定性得以改善，为拓宽这类新型压电功能膜应用领域，推动其产业化进程提供了一定的理论和技术依据. 关键词： 聚丙烯蜂窝膜 压电性 充电参数 电荷输运     

恒流电晕充电对聚四氟乙烯多孔薄膜驻极体驻极态的影响

利用常温下恒流和恒压电晕充电、充电后的等温表面电位衰减、热刺激放电和扫描电镜等实 验手段研究了恒流和恒压电晕充电技术对聚四氟乙烯多孔薄膜驻极体驻极态的影响.与恒压电晕充电相比较，恒流电晕充电时由于流过薄膜的电流恒定，增加了注入电荷在多孔结构厚度方向界面处的俘获概率，使沉积电荷密度上升，改善了驻极体的储电能力.然而，这些位于不同层深多孔界面处的俘获电荷在这类功能膜储存或使用过程中，经外激发从脱阱位置 以跳动（hopping）模式输运至背电极的路径相对缩短将导致脱阱电荷衰减较快. 关键词： 恒流电晕充电 聚四氟乙烯多孔膜 驻极体 电荷稳定性     

水介质形成线泄漏电阻对充电效率的影响

研制了一种基于直线变压器技术的脉冲功率系统,采用水介质脉冲形成线并联充电作为脉冲形成装置。分析了给形成线充电时泄漏电阻对充电电压效率和能量效率的影响,给出了泄露电阻的能量损耗率计算公式;结合实验参数计算了本实验中水介质形成线的泄漏电阻,介于8.2 kΩ与3 kΩ之间。根据泄露电阻取值范围,分析了双模块和四模块实验中水介质形成线充电过程中的电压效率与能量效率,结果表明水介质形成线的能量损失占其获得能量的5%～12%;计算结果同时表明：随着实验模块数增加,能量损失逐渐增大。     

The influence of particle size on separation and dustiness in powder mixtures during nonelectrostatic and electrostatic coating

Common food powders and their mixtures, consisting of two powders with the same composition but different in particle size: fine (51–95 μm) and coarse (244–401 μm) NaCl, KCl, sucrose, rice starch, maltodextrin, whey protein, casein and soy protein, were coated on a target at 0 and −25 kV. Over half of the mixtures showed separation due to a difference in particle size. Separation was caused by the difference in individual transfer efficiency of the powders and interactions during coating. Both composition and differences in size were found to be important. Being in a mixture did not change the amount of dust formed.     

水介质形成线泄漏电阻对充电效率的影响

研制了一种基于直线变压器技术的脉冲功率系统,采用水介质脉冲形成线并联充电作为脉冲形成装置。分析了给形成线充电时泄漏电阻对充电电压效率和能量效率的影响,给出了泄露电阻的能量损耗率计算公式;结合实验参数计算了本实验中水介质形成线的泄漏电阻,介于8.2kΩ与3kΩ之间。根据泄露电阻取值范围,分析了双模块和四模块实验中水介质形成线充电过程中的电压效率与能量效率,结果表明水介质形成线的能量损失占其获得能量的5%～12%;计算结果同时表明:随着实验模块数增加,能量损失逐渐增大。     

量子尘埃等离子体中尘埃充电对尘埃声波的影响

采用流体动力学方程组和尘埃充电方程组成的自洽模型系统,对量子尘埃等离子体中的尘埃声波波动性质进行了研究。通过线性理论分析方法得到系统的尘埃声波波动方程及其色散关系,并对色散关系进行了数值分析。研究表明：充电效应定性地修正了尘埃声波的色散特性,引起尘埃声波的耗散,其耗散强度主要与尘埃等离子体的参数有关。最后,分析了引起尘埃声波耗散的物理原因。     

充电不均匀对脉冲形成系统输出方波脉冲平顶的影响

在对脉冲形成线进行充电时,由于充电时间较短,以及形成线具有一定的长度,往往会使得充电电压在脉冲形成线上存在一定的不均匀性,从而影响到负载输出电压。对此进行了理论和模拟研究,分析了引起充电不均匀的原因和机制;在此基础上,通过求解不均匀充电初始条件下的电报方程,得到负载输出电压,并进行了模拟。结果表明,充电不均匀会引起负载输出电压平顶的起伏。     

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.     

入射电子能量对低密度聚乙烯深层充电特性的影响

高能带电粒子与航天器介质材料相互作用引起的深层带电现象, 一直是威胁航天器安全运行的重要因素之一. 考虑入射电子在介质中的电荷沉积、能量沉积分布以及介质中的非线性暗电导和辐射诱导电导, 建立了介质深层充电的单极性电荷输运物理模型. 通过求解电荷连续性方程和泊松方程, 可以得出不同能量 (0.1–0.5 MeV) 电子辐射下, 低密度聚乙烯 (厚度为1 mm) 介质中的电荷输运特性. 计算结果表明, 不同能量的电子辐射下, 介质充电达到平衡时, 最大电场随入射能量的增加而减小; 同一能量辐射下, 最大电场随束流密度的增大而增加. 入射电子能量较低时 (≤ 0.3 MeV) , 最大电场随束流密度的变化趋势基本相同. 具体表现为: 当束流密度大于3× 10^-9 A/m²时, 最大场强超过击穿阈值2×10⁷ V/m, 发生静电放电 (ESD) 的可能性较大. 随着入射电子能量的增加, 发生静电放电 (ESD) 的临界束流密度增大, 在能量为0.4 MeV时, 临界束流密度为6×10^-8 A/m². 当能量大于等于0.5 MeV时, 在束流密度为10^-9–10^-6 A/m²的范围内, 均不会发生静电放电 (ESD) . 该物理模型对于深入研究深层充放电效应、评估航天器在空间环境下 深层带电程度及防护设计具有重要的意义. 关键词： 高能电子辐射 低密度聚乙烯(LDPE) 介质深层充电 电导特性     

微波测湿技术引进物理实验教学的探讨

提出了将微波测湿技术引进物理实验教学的设想,在分析该设想可行性基础上设计了实验方案。     

Effect of process parameters on the recovery of lactose in an antisolvent acetone/acetone-ethanol mixture: A comparative study based on sonication medium

Recovery of lactose from the whey using sonocrystallization was studied experimentally. The effect of sonication medium and irradiation power levels was evaluated using three different ultrasonic equipments. Effects of various parameters such as sonication time, pH of the medium, antisolvent (acetone and acetone-ethanol mixture) and concentration of lactose were determined. The optimal parametric conditions were analyzed using differential scanning calorimetry, thermogravimetric analysis, particle size distribution, and zeta potential measurements. Overall, the highest lactose recovery was obtained using a mixture of acetone and ethanol as antisolvent in bath sonication as well as atomization process.