Experimental studies on curling development of artificial soils

Soil curling is an important phenomenon associated with volume changes induced by increasing soil suction upon desiccation. The study of soil behaviors associated with drying in soils (e.g. soil shrinkage, desiccation cracks and curling) has received increasing attention over the last few years, which has been mainly driven by the forecast climate change that will warm up our planet. There are significant gaps in the current knowledge related to the factors that control the development of curling deformations in soils. For this, the curling phenomenon is investigated through laboratory desiccation tests on different mixtures of artificial soils. The effects of soil grain size distribution, mineralogy, soil microstructure, and soil water content on the curling deformation are analyzed. Digital photos were taken at regular time intervals during the tests to understand the volume changes in the soil samples during drying. It is found that soil fabric and soil water content have significant effects on curling scenario. It is observed that the percentage of sand particles and the initial water content play a critical role in the development of soil curling. Samples of pure clayey minerals experienced shrinkage without or with minor curling during drying.     

Relaxation nuclear magnetic resonance imaging (R-NMRI) of PDMS/PDPS siloxane copolymer desiccation

Relaxation nuclear magnetic resonance imaging (R-NMRI) was employed to study the effects of desiccation on SiO₂-filled and unfilled polydimethylsiloxane-polydiphenylsiloxane (PDMS/PDPS) copolymers. Uniform NMR spin-spin relaxation time (T₂) profiles were observed across the sample thickness indicating that the drying process is approximately uniform, and that the desiccation of the silicone copolymer is not a H₂O diffusion limited process. In a P₂O₅ desiccation environment, significant reduction of T₂ was observed for the SiO₂-filled and unfilled copolymer material for desiccation up to 225 days. A very small reduction in T₂ was observed for the unfilled copolymer between 225 and 487 days. The increase in relative stiffness with desiccation was found to be higher for the unfilled copolymer.     

Desiccation of adhering and biofilm Listeria monocytogenes on stainless steel: Survival and transfer to salmon products

The foodborne bacterial pathogen, Listeria monocytogenes, commonly contaminates foods during processing, where the microorganisms are potentially subjected to low relative humidity (RH) conditions for extended periods of time. The objective of this study was to examine survival during desiccation (43% RH and 15 °C) of biofilm L. monocytogenes N53-1 cells on stainless steel coupons and to assess subsequent transfer to salmon products. Formation of static biofilm (2 days at 100% RH and 15 °C) prior to desiccation for 23 days significantly (P < 0.05) improved survival of cells desiccated in initial low salt concentrations (0.5%) compared to the survival for non-biofilm cells also desiccated in low salt, indicating the protective effect of the biofilm matrix. Osmoadaptation of cells in 5% NaCl before formation of the static biofilm significantly (P < 0.05) increased long-term desiccation survival (49 days) irrespectively of the initial salt levels (0.5% and 5% NaCl). The efficiency of transfer (EOT) of desiccated biofilm cells was significantly (P < 0.05) lower than EOTs for desiccated non-biofilm bacteria, however, as biofilm formation enhanced desiccation survival more bacteria were still transferred to smoked and fresh salmon. In conclusion, the current work shows the protective effect of biofilm formation, salt and osmoadaptation on the desiccation survival of L. monocytogenes, which in turn increases the potential for cross-contamination during food processing.     

Modeling of Clay Liner Desiccation

The potential for the desiccation of clay liner component of composite liners due to temperature field generated by breakdown of organic matter in municipal solid waste landfills is examined using a model proposed by Zhou and Rowe. In these analyses, a set of fully coupled governing equations expressed in terms of displacement, capillary pressure, air pressure, and temperature increase are used, and numerical results are solved by using finite element method with a mass-conservative numerical scheme. The model results are shown to be in encouraging agreement with experimental data for a problem involving heating of a landfill liner. The fully coupled transient fields (temperature, horizontal stress change, suction head, and volumetric water content) are then examined for two types of composite liner system, one involving a geomembrane over a compacted clay liner (CCL) and the other involving a geomembrane over a geosynthetic clay liner (GCL). It is shown that there can be significant water loss and horizontal stress change in both the CCL and GCL liner even with a temperature increase as small as 20°C. The time to reach steady state decreases as boundary temperature increases. Under a 30°C temperature increase, it takes 5 years to reach the steady state water content with a GCL liner but 50 years with a CCL liner. The effects of various parameters, such as hydraulic conductivity and thickness of the liner, on the performance of the liner are discussed.     

真空冷冻干燥人参的物性测量

测定了人参的共晶点温度为-10~-15℃;导热系数为λ=0.041w/m·℃。可供人参冷冻干燥工艺和设备设计的基础物性数据。     

采用自励短路干燥法处理水轮发电机绕组绝缘下降问题

汾河水库水电站是一座结合工农业放水发电的季节性电站,全年间断性多年平均累计发电自然天数为122d,仅占全年的1/3。发电停机后,待再次开机时,绕组绝缘或多或少会有所下降,达不到正常开机并网的要求,电站多年来皆采用自励短路干燥法处理绕组绝缘下降问题     

Fiber Reinforcement for Waste Containment Soil Liners

The hydraulic properties of compacted clay liners can be adversely affected by desiccation cracking. Previous studies evaluated the use of soil additives (such as lime, cement, and sand) for crack reduction. Initial results indicated that soil shrinkage was reduced. However, in many cases, the additives resulted in an increased hydraulic conductivity and decrease in soil plasticity. As a result, there is an increasing interest in the use of fiber reinforcement, which has shown successful results in concrete and other material applications. The present investigation focused on the impact of fiber reinforcement on the development of desiccation cracks in compacted clay samples, as well as the impact of the fiber additives on soil workability, compaction characteristics and hydraulic conductivity. The results of this study indicate that, for the soils of this investigation, the optimum fiber content necessary to achieve maximum crack reduction and maximum dry density, while maintaining acceptable hydraulic conductivity, is between 0.4 and 0.5%. The observed crack reduction for this range of fiber content was approximately 50%, as compared to the unamended soil sample. The maximum observed crack reduction was approximately 90%, for a fiber content of 0.8%. Although the crack reduction could be increased further by increasing the fiber content, the sample hydraulic conductivity increased significantly and the practical limits of mixture workability were exceeded.     

充分发育烟叶失水特性及烘烤失水调控初报

对成熟烟叶采收后失水基本规律及烘烤过程失水与品质研究表明,烟叶失水干燥特征曲线表现出“近等速—减速—再减速”特征,烟叶失水明显减慢的临界含水率在３００％～３５０％区域。烘烤过程失水环境不同,烟叶失水速度可在４．３～２６．８ｇ．ｋｇ－１．ｈ－１之间变异。在皖北烟区若依靠自然通风进行排湿烘烤充分发育烟叶,绑竿密度以每标准竿６０～８０片为宜,而且采用低温低湿烘烤利于烤房内不同棚次烟叶协调失水。在变黄期,烤房底棚烟叶失水量下、中、上三个部位分别以占鲜烟重４０％、３０％、２７％为宜,失水速度平均值下、中、上三个部位可按１１．０、７．５、６．８ｇ．ｋｇ－１．ｈ－１左右调控。若变黄期烟叶失水适宜,定色期失水速度调控的关键是在升温适宜条件下将湿球温度控制在３７～３８℃。