THERMOMECHANICAL APPROACH TO SHRINKING AND CRACKING PHENOMENA IN DRYING

The thermomechanics of partly saturated porous materials is presented as a basis for the construction of mechanistic theory of drying. Based on the balance of mass, momentum, energy, entropy, and the thermodynamics of irreversible processes the constitutive laws for heat and mass transfer and the physical relations between stresses, strains, moisture content and the temperature are developed. Using the London-Heitler's formulas for cohesion and the Condon-Morse curve performing the bond energy of two atoms versus their distance, a theoretical strength of material during drying process is estimated. By analogy to Griffith's concept, a fracture criterion is formulated. Finally, the acoustic emission as a possible method for detection of fracture process in dried materials is discussed.     

High performance airbrush spray coated organic solar cells via tuning the surface tension and saturated vapor pressure of different ternary solvent systems

In this work, thieno [3,4-b] thiophene/benzodithiophene (PTB7): [6,6]-phenyl C71-butyric acid methyl ester (PC₇₁BM) based organic solar cell (OSC) with a new record of power conversion efficiency (PCE) of ∼7.62% has been realized using airbrush spray (AS) coating method in air ambient which can be well compatible with large-scale fabrication. By investigating the physical mechanism of AS coated blend films, a series of ternary solvent systems (TSS) are used to simultaneous optimize the surface tension and the saturated vapor pressure of solution. Therefore, different TSS further controls the morphology of PTB7:PC₇₁BM blend films precisely and systematically. It is elucidated that the chlorobenzene (CB)/o-Xylene (o-Xy)/1, 8-diiodoctane (DIO) TSS with a ratio of 37:60:3 vol.% could lead to a homogeneous surface morphology with a decreased aggregation domain size of active layer. In addition, the high fill factor, increased PC₇₁BM absorption and internal quantum efficiency indicate the formation of bicontinuous interpenetrating and fully percolated networks with nanostructured phase separation in BHJ blend films. Ultimately, the AS coated OSCs based on the TSS of CB/o-Xy/DIO gains a 34% enhancement in PCE, compared with the conventional CB/DIO solvent based OSCs.     

Effect of trace contaminants on cold soak filterability of canola biodiesel

A cold soak filtration test (CSFT; ASTM D 7501-09b) was included in B100 specifications under ASTM D 6751-09, bringing new challenges to biodiesel producers and researchers investigating B100 quality. For a plant breeding program evaluating canola biodiesel quality traits, rapid assessment of biodiesel quality is important. Typically, a limited amount of seed from new canola lines is available; therefore, obtaining the required volume of biodiesel for evaluating cold soak filterability (300 mL) is not possible. In order to rapidly screen canola breeding lines for B100 quality, cold soak filterability must be assessed with reduced volumes of biodiesel. The primary objective of this study was to evaluate the impact of saturated monoglycerides, glycerin, and soap on cold soak filterability. Biodiesel filtration time rapidly escalated when the SMG concentration was above 0.28%. The influence of saturated monoglycerides (0.04-0.46% w/w) on biodiesel precipitate formation was also evaluated. A regression model was generated to predict the filterability of biodiesel against the concentrations of trace contaminants. The results will be instrumental to scaling down biodiesel CSFT for a canola breeding program.     

Preparation and properties of polyurethane acrylates modified by saturated alcohols

Polyurethane acrylates (PUAs) modified by saturated alcohols were synthesized by saturated alcohols, isophorone diisocyanate (IPDI), 2-hydroxyethyl acrylate (HEA) and polycaprolactone triol (PCL). The molecular structures were identified by Fourier transform infrared (FTIR) spectroscopy. Real time infrared (RTIR) spectroscopy was used to investigate the conversion vs. irradiation time plots of photopolymerization of synthesized PUAs. The volume shrinkage was measured by using laser displacement sensor (LDS). The adhesion in the glass, polycarbonate (PC) and polyvinyl chloride (PVC) substrates was tested by the laser micrometer and universal testing machine. The glass-transition temperature (Tg) and storage modulus (E′) were measured by dynamic mechanical analysis (DMA). The pendulum hardness, pencil hardness and flexibility were also tested. The results showed that the synthesized PUAs had low volume shrinkage and excellent adhesion in glass, PC and PVC substrates.     

Preparation of organic and carbon xerogels using high-temperature–pressure sol–gel polymerization

To prepare organic gels at temperatures higher than normal boiling point of solvent, a method was developed using sol–gel polymerization in atmosphere saturated by vapor of solvent. To illustrate the advantages of proposed method, two series of gels were prepared using the conventional (T_curing = 70 °C) and the high temperature (T_curing = 140–170 °C) sol–gel polymerization. While no drying shrinkage was observed in our proposed method, 5–18% linear shrinkage occurred in conventional method depending on resin concentration in sol. Moreover, rising of curing temperature reduced the required time for preparation of organic gels from 5 days to lower than 5 h. The effects of processing parameters were investigated on physical and mechanical properties of organic xerogels. The results revealed that resin concentration significantly affects both density and compressive strength of final xerogels. While the curing temperature had no obvious effect on density, the raising of curing temperature significantly enhance the strength of organic xerogels. Carbon xerogels prepared by pyrolysis of novolac aerogels in inert atmosphere. The textures of the carbon xerogels were denser than corresponding organic xerogels, as evidenced by scanning electron microscopy (SEM) images. N₂ adsorption tests indicated that carbon aerogels were mainly meso or macroporous depending on resin concentration in initial sol.     

Effect of pore water pressure on tunnel support during static and seismic loading

The support of underground structures must be designed to withstand static overburden loads as well as seismic loads. New analytical solutions for a deep tunnel in a saturated poroelastic ground have been obtained for static and seismic loading. The static solution accounts for drainage and no-drainage conditions at the ground–liner interface. Linear elasticity of the liner and ground, and plane strain conditions at any cross-section of the tunnel are assumed. For tunnels in which ground stresses and pore pressures are applied far from the tunnel center, the drainage conditions at the ground–liner interface do not affect the stresses in the liner. The analytical solution shows that the stresses in the liner are exactly the same whether there is drainage or not at the ground–liner interface. Hence, if the drainage conditions in the tunnel are changed from full drainage to no-drainage or vice versa the stresses in the liner are not affected. However, the stresses and displacements in the ground change significantly from drainage to no-drainage conditions. For seismic loading a new analytical formulation is presented which provides the complete solution for the ground and the liner system for both dry and saturated ground conditions. The formulation is based on quasi-static seismic loading and elastic ground response; for a saturated ground, undrained conditions are assumed which indicate that the excess pore pressures generated during the seismic event do not dissipate. The results show that the racking deformations of a liner in dry or saturated ground are highly dependent on the flexibility of the liner.     

直接蒸发冷却器用填料性能评价指标诠释

本文对直接蒸发冷却器用填料种类及性能作了简单的概述,并详细介绍了填料性能评价指标,阐明了蒸发冷却效率、饱和效率及加湿效率的概念,并指出三者之间的关系.     

Saturated steam process with direct steam generating parabolic troughs

The direct steam generation (DSG) in parabolic trough collectors is an attractive option regarding the economic improvement of parabolic trough technology for solar thermal electricity generation in the multi Megawatt range. The European DISS project has proven the feasibility of the direct steam generation under real solar conditions in more than 4000 operation hours. Within the European R&D project INDITEP the detailed engineering for a pre-commercial DSG solar thermal power plant with an electrical power of 5 MW is being performed. This small capacity was chosen to minimise the risk for potential investors.In regards to DSG solar thermal power plants, only steam cycles using superheated steam have been investigated so far. The paper will investigate the advantages, disadvantages, and design considerations of a steam cycle operated with saturated steam for the first time. For near term applications, saturated steam operated DSG plants might be an interesting alternative for power generation in the small capacity range due to some specific advantages:

• Simple set up of the collector field.

• Proven safe collector field operation.

• Higher thermal efficiency in the collector field.

Evaluation of the reliability of transport networks based on the stochastic flow of moving objects

In transport networks, human beings are moving objects whose moving direction is stochastic in emergency situations. Based on this idea, a new model—stochastic moving network (SMN) is proposed. It is different from binary-state networks and stochastic-flow networks. The flow of SMNs has multiple-saturated states, that correspond to different flow values in each arc. In this paper, we try to evaluate the system reliability, defined as the probability that the saturated flow of the network is not less than a given demand d. Based on this new model, we obtain the flow probability distribution of every arc by simulation. An algorithm based on the blocking cutset of the SMN is proposed to evaluate the network reliability. An example is used to show how to calculate the corresponding reliabilities for different given demands of the SMN. Simulation experiments of different size were made and the system reliability precision was calculated. The precision of simulation results also discussed.     

An Experimentally Simple Method for Measuring Sorption Isotherms

Abstract

We describe a simple, yet practical and precise, way of measuring sorption isotherms with each sample in its own glass jar with a saturated salt solution. The measurements are done with below-balance weighing and with the sample kept inside the closed jar during the whole measurement period, providing constant relative humidity (RH) conditions. The technique has been tested on microcrystalline cellulose and bentonite clay. The agreement with literature values was good; the differences seen for bentonite at high RH are discussed in terms of the slow attainment of equilibrium for this material.