Changes in terrestrial surface dry and wet conditions on the Loess Plateau(China) during the last half century

This paper, using a revised Penman-Monteith model, computed the terrestrial surface humidity index of the Loess Plateau （China） based on climatic factors of monthly mean temperature, maximum temperature, minimum temperature, relative humidity, precipitation, wind speed and sunshine duration observed on the plateau from 1961 to 2008. The temporal-spatial distribution, anomaly distribution and sub-regional temporal variations of the terrestrial surface dry and wet conditions were analyzed as well. The results showed a decreasing trend in the annual average surface humidity from the southeast to the northwest in the research anna. Over the period of 1961-2008, an aridification tendency appeared sharply in the central interior region of the Loess Plateau, and less sharply in the middle part of the region. The border region showed the weakest tendency ol; aridification. It is clear that aridification diffused in all directions from the interior region. The spatial anomaly distribution of the terrestrial surface dry and wet conditions on the Loess Plateau can be divided into three key areas： the southern, western and eastern regions. The terrestrial annual humidity index displayed a significantly descending trend and showed remarkable abrupt changes from wet to dry in the years 1967, 1977 and 1979. In the above mentioned three key areas for dry and wet conditions, the terrestrial annual humidity index exhibited a fluctuation period of 3-4 years, while in the southern region, a fluctuation period of 7-8 years existed at the same time.

Asymmetric Drying and Wetting Trends in Eastern and Western China

As an important factor that directly affects agricultural production, the social economy, and policy implementation,observed changes in dry/wet conditions have become a matter of widespread concern. However, previous research has mainly focused on the long-term linear changes of dry/wet conditions, while the detection and evolution of the non-linear trends related to dry/wet changes have received less attention. The non-linear trends of the annual aridity index, obtained by the Ensemble Empirical Mode Decomposition(EEMD) method, reveal that changes in dry/wet conditions in China are asymmetric and can be characterized by contrasting features in both time and space in China. Spatially, most areas in western China have experienced transitions from drying to wetting, while opposite changes have occurred in most areas of eastern China. Temporally, the transitions occurred earlier in western China compared to eastern China. Research into the asymmetric spatial characteristics of dry/wet conditions compensates for the inadequacies of previous studies, which focused solely on temporal evolution;at the same time, it remedies the inadequacies of traditional research on linear trends over centennial timescales. Analyzing the non-linear trend also provides for a more comprehensive understanding of the drying/wetting changes in China.

Thermal–moisture dynamics and thermal stability of active layer in response to wet/dry conditions in the central region of the Qinghai–Tibet Plateau,China

The amount of rainfall varies unevenly in different regions of the Qinghai-Tibet Plateau, with some regions becoming wetter and others drier. Precipitation has an important impact on the process of surface energy balance and the energy-water transfer within soils. To clarify the thermal-moisture dynamics and thermal stability of the active layer in permafrost regions under wet/dry conditions, the verified water-vapour-heat coupling model was used. Changes in the surface energy balance, energy-water transfer within the soil, and thickness of the active layer were quantitatively analyzed. The results demonstrate that rainfall changes significantly affect the Bowen ratio, which in turn affects surface energy exchange. Under wet/dry conditions, there is a positive correlation between rainfall and liquid water flux under the hydraulic gradient;water vapour migration is the main form under the temperature gradient, which indicates that the influence of water vapour migration on thermalmoisture dynamics of the active layer cannot be neglected. Concurrently, regardless of wet or dry conditions,disturbance of the heat transport by conduction caused by rainfall is stronger than that of convection by liquid water. In addition, when rainfall decreases by 1.5 times(212 mm) and increases by 1.5 times(477 mm), the thickness of the active layer increases by 0.12 m and decreases by 0.21 m, respectively. The results show that dry conditions are not conducive to the preservation of frozen soil;however, wet conditions are conducive to the preservation of frozen soil, although there is a threshold value. When this threshold value is exceeded, rainfall is unfavourable for the development of frozen soil.

Study on potential evapotranspiration and wet-dry condition in the seasonal frozen soil region of northern Tibetan Plateau

This study was based on the CEOP/CAMP-Tibet observed data at AWS （Automatic Weather Station） of MS3478 in the seasonal frozen soil region of northern Tibetan Plateau from March 2007 to February 2008. The variation characteristics of PE （potential evapotransph＇ation） were analyzed based on the Penman-Monteith method recommended by FAO （the Food and Agriculture Organization of the United Na- lions）. The contributions of dynamic, thermal and water factors to PE were discussed, and the wet-dry condition of the plateau region was further studied. The results indicated that daily PE was between 0.52 mm and 6.46 mm for the whole year. Monthly PE was over 107 mm from May to September, but decreased to less than 41 mm from November to February. Annual PE was 1,037.8mm. In the summer, thermal PE was significantly more than dynamic PE, but conversely in the winter. Annual variation of thermal PE was of sine wave pattern. In addition, drought and semi-drought climate lasted for a long time while semi-humid climate was short. The effect of water and dynamic factors on PE varied considerably with the seasons. Annual variation of thermal PE was of sine wave pattern.

Pore-scale modeling of pore structure properties and wettability effect on permeability of low-rank coal

Permeability is a key parameter for coalbed methane development.Although the absolute permeability of coal has been extensively studied,wettability and pore structure properties continue to challenge the microscopic description of water-gas flow in coal.For this purpose,we reconstructed the microstructures of low-rank coal using micro-computed tomography(micro-CT)images.Pore geometry and pore-throat parameters are introduced to establish a relationship with absolute permeability.A dual-porosity pore network model is developed to study water-gas displacement under different wetting and pore structure properties.Results show that absolute permeability is significantly affected by pore geometry and can be described using a binary quadratic function of porosity and fractal dimension.Water-gas relative permeability varies significantly and the residual gas saturation is lower;the crossover saturation first decreased and then increased with increasing porosity under hydrophobic conditions.While the water relative permeability is lower and a certain amount of gas is trapped in complex pore-throat networks;the crossover saturation is higher under hydrophilic conditions.Models with large percolating porosity and well-developed pore networks have high displacement efficiency due to low capillary resistance and avoidance of trapping.This work provides a systematic description of absolute permeability and water-gas relative permeability in coal microstructure for enhanced gas recovery.

玉米半湿法提胚关键工艺与设备研究综述

对玉米半湿法提胚关键工艺与设备进行综述,阐述了玉米半湿法提胚原理;指出充分调质、高效脱胚和合理提胚是玉米半湿法提胚的三个关键工艺环节,水汽调节机、玉米脱胚机和玉米提胚机是玉米半湿法提胚的关键设备,并对各设备的优缺点进行了分析;最后指出必须研制具有自主知识产权且具有较高科技含量的玉米提胚关键设备,才能提高我国玉米深加工与综合利用的水平与质量。

坡地间隔覆盖配施土壤改良剂的实用性研究

本文采用间隔覆盖配施土壤改良剂方法,利用室内人工降雨实验与土柱实验研究该方法对土壤水分运动及分布的影响,进而为其实际应用奠定理论基础。结果表明:(1)间隔覆盖法可增加入渗区蓄水量,面积比为1:1时,土壤蓄水量可达到降雨量的1.83倍。配施土壤改良剂情况下,雨强I=60 mm/h,面积比1:1时,降雨入渗率可达到未施加改良剂处理的2.60倍。湿润锋分布较深,水分分布均匀程度也有所提高。(2)对土壤水分蒸发及吸持水能力的研究发现,在施加土壤改良剂条件下,水分蒸发受到抑制,而土壤吸持水能力增强,但两方面作用均与PAM用量密切相关。虽然研究结果证实此种方法的实用性,但土壤改良剂的适宜用量、间隔覆盖法的适宜面积比、水分的实际调控效果及其对作物的影响需进一步研究。

分体式蒸发空调器的设计与实验

设计研究了一种蒸发冷却与半导体制冷相结合的分体式蒸发空调器，探讨了其原理及三种运行模式。总结出该分体式蒸发空调器的主要设计步骤。对样机进行了实验，得出了该分体式蒸发空调器的出水、出风温度。结果表明，室外机出风温度高于室外湿球温度3-4℃。室外机出水温度低于室外湿球温度1-2℃，经过半导体制冷再次温降后，可低于室外湿球温度4-5℃。依据实验结果，结合气象数据，计算得出该分体式蒸发空调器在我国288个城市的出风、出水温度结果。计算得出，该分体式蒸发空调器可在我国西北地区等高温低湿地区广泛采用，适用率超过90％。

基于性能曲面特性的干湿球温度允差等级划分

在试验结果的基础上,分析制冷量和能效比随干湿球温度的变化特性。用赤池信息量准则(Akaike information criterion,AIC)选取制冷量和能效比最优拟合三维曲面方程,求解制冷量和能效比随干湿球温度变化的梯度极值区间,以两者梯度极值区间内干湿球温度允差范围的并集为A级、现行干湿球温度允差为C级,以各级最大(最小)能效比变化率相等原则,对允差进行三级非线性划分。实例表明随着允差等级的升高,能效比最大变化率由5.19%缩减至1.04%,分级允差能够更加准确地判别房间空调器的能效等级,并给国家标准的修订提供参考。

环境工况对家用空调器性能的影响

通过试验的方法定量研究了环境工况对制冷系统性能的影响,得出了相应的试验曲线,并根据试验结果分析了室内湿球温度及室外干球温度的变化影响空调性能的规律。

蒸发冷却与半导体制冷相结合分体式蒸发空调器的试验研究

设计制作了蒸发冷却与半导体制冷相结合分体式蒸发空调器的试验样机，在标准的空调焓差检测实验台上，模拟室内外侧空气温湿度，在室外侧干球温度34℃，湿球温度18—23℃之间的工况下，对该分体式蒸发空调器的冷水的温度、流量，冷风的温湿度进行了试验。结果表明，该分体式蒸发空调器在室外工况湿球温度20℃以下不开启半导体制冷装置即可满足需要；配合4组半导体制冷装置即可满足室外工况湿球温度23℃时需要，同时也保证了半导体制冷装置较高的能效比；得出了该分体式蒸发空调器的最佳气水比为2，亚湿球效率为110％。进而为分体式蒸发空调器的优化设计与产品开发奠定基础。

煤矿井下空调蒸发器对流传热特性试验

对恒定控制制冷剂R407C工作温度为9℃、额定制冷量为45k W条件下的蒸发器进行了模拟矿井条件湿空气的对流传热试验。研究结果表明:蒸发器的制冷量随进口空气温度的升高而增加,随进口空气相对湿度的增加而增加;出口空气温降随进口空气温度的升高而增加,随进口空气相对湿度的增加而缓慢降低;对流传热的Nu数随Re数的增加而增加,随进口空气相对湿度的增加而降低。

环境干湿球温度对空调器性能影响的试验研究

在一款整机型号为KFR-90WT1-520的某品牌空调器上,进行了环境干湿球温度对空调器性能影响的试验,得出了相应的试验结果与试验曲线。结果表明,空调器的性能受室外干球温度和室内湿球温度的影响,室内侧湿球温度和室外侧干球温度的变化对空调器运行性能影响较大,而室内侧干球温度和室外侧湿球温度的影响则稍小。

湿压缩-吸收式CO_2与R134a汽车空调系统性能实验比较

在现有汽车空调系统零部件的基础上,搭建了湿压缩-吸收式二氧化碳(CO2)循环汽车空调样机;并与采用同样零部件的R134a系统进行了对比性试验。实验结果显示:在相同的工况下,湿压缩-吸收式CO2系统的压力不超过3.5MPa,制冷量达到R134a系统的80%,COP达到了60%。显示了湿压缩-吸收式CO2汽车空调系统具有的潜在竞争力,为CO2汽车空调研发提供了新的思路。

二次回风系统节能及应用分析

净化空调系统中,送风量普遍较大,送风温差较小。二次回风空气处理系统在净化空调系统中有很好的实用意义。文章通过分析对比一次回风系统与二次回风系统,以求得到既节能又应用良好的空气处理系统。

空调室外机湿膜换热技术应用研究

面对夏季高温天气室外机密集安装的机房专用空调压缩机高压保护频发的问题,郑州联通动力维护人员一改只能被动地不断进行室外机冷凝器人工冲洗的方式,大胆采用室外机非接触式湿膜换热技术,主动、提前对室外机进风降温,有效解决了压缩机高压保护频发问题,节能效果良好。分析了此项技术的实现原理,总结了实施经验,并对经济效益进行了测算,具有较大的推广价值。

Corrosion Behavior of Weathering Test Steel for Bridge Under the Neutral Wet/Dry Alternate Condition

The corrosion behaviors of the high-performance weathering test steel for bridge and the reference (09CuPCrNi-A) were symmetrically studied under 3.5% NaCl neutral wet/dry alternate condition,revealing their dynamics line tendency of primary corrosion and the rusting flow in the simulative marine atmosphere environment.By observing the corrosion evolution of surface microstructures and composition by the scanning electronic microscope (SEM) and the energy dispersive spectrometer (EDS) at the different stages,the corrosion mechanism was further discussed in details.

基于湿帘蒸发冷却技术回收利用制冷冷凝水的分体式空调设计与实验应用

分体式空调在我国建筑中广泛使用,暖通空调能耗占建筑能耗可达到40%~50%,分体式空调的节能优化设计是空调节能的重要环节。分体式空调在湿负荷较大的场所,每1kW冷负荷每小时产生约0.8kg的冷凝水,冷凝水温度较低约为10~15℃。空气露点温度越高,含湿量越大,产生的冷凝水越多,而冷凝水需要设置排水管进行有组织排放,这既造成冷凝水冷量浪费又增加了排水管的管材使用。本文提出了一种基于湿帘蒸发冷却技术回收利用制冷冷凝水的分体式空调设计与实验应用。通过实验、计算和对比分析出利用制冷冷凝水后的实际节能效果,结果表明:通过利用湿帘蒸发冷却回收利用制冷冷凝水的分体式空调不仅可以提高制冷量约4.612%和能效比约9.302%,降低冷凝温度约4.685%,而且不需要设置排水管。

季铵盐阳离子调理剂在护发产品中的应用

本文介绍了市场上护发产品中常出现的几种季铵盐阳离子调理剂的性能,并结合具体配方,分析了护发产品中季铵盐阳离子调理剂的粘度特性、干湿发梳理性、干发体积、发束亮度、抗静电能力,为设计护发产品的配方提供了理论指导。

A CONSERVATIVE COUPLED FLOW/TRANSPORT MODEL WITH ZERO MASS ERROR

A fully conservative form applied to a coupled system of two-dimensional water flow and solute motion is presented. A cell-centred finite volume method based on Roe＇s approximate Riemann solver with unstructured grids is formulated. The bed slope source terms are discretized following an upwind approach and a semi-implicit treatment is used for the friction source terms. The centered discretization of the diffusion terms is in an implicit way. It is shown that this numerical technique reproduces almost exactly the steady state of still water and enables to achieve zero numerical errors in unsteady flow over configurations with strong variations on bed slope. The model ensures a global conservation and positive values of both water level and solute concentration. Numerical results show the effectiveness of the model in solute transport over real complex geometries.