微通道换热器不同风速下换热及其流动特性研究

以微通道换热器为研究对象,搭建微通道换热器性能测试实验台,利用控制变量法研究分析不同入口风速对出口空气温度、湿度、压降、凝水生成量等参数的变化规律,计算换热器表面凝水生成速率、凝水排除速率、换热量和空气侧传热系数,从而分析表面凝排水特性及其对换热性能的影响。实验结果表明,风速对微通道换热和流动特性影响显著。出口空气温度和空气侧压降均随风速的提高而增加,压降增幅随风速的增加有所减缓。风速为2.5m/s时,换热量和空气侧传热系数最佳。

牵引电动机绝缘烘干新方法

牵引电动机的可靠性,很大程度上取决于它的绝缘的技术状态。在冬季,牵引电动机的绝缘会受潮,以致使绝缘电阻大大降低,往往导致绝缘被击穿。 绝缘受潮是由以下两个原因引起的。一是冷却空气中的潮气或通过风道间隙进入的雪花直接附着到绝缘上;二是环境温度突然下降时,在绝缘的表面上会出现凝露现象。特别是当牵引电机的温度比车间温度低得多时,如把电力机车停放在有供暧设备的车间里,则上述凝露现象将更为严重。

Lead Removal from Aqueous Solutions Using Novel Gel Adsorbent Synthesized from Natural Condensed Tannin

Lead has caused serious environmental pollution due to its toxicity, accumulation in food chains and persistence in nature. In this paper, removal of lead from aqueous solutions is investigated using a novel gel adsorbent synthesized from natural condensed tannin. The novel adsorbent performs in aqueous solutions as a weak base with valid basic groups of 1.2mmol·g-1 tannin gel particles and therefore results in the elevation of pH value of aqueous solutions. Even when initial pH is 3.6, final pH at equilibrium can climb up to 6.5 that is above the pH value for Pb(OH)2 precipitation formation and then lead can be removed from wastewater by this so-called surface precipitation. The adsorption isotherm can be expressed by the Langmuir equation and the maximum capacity for adsorption of Pb is up to 92 mg·g-1 (based on dry adsorbent) when initial pH value is 3.6. Hence, the adsorbent does offer favorable properties in lead removal with respect to its high adsorption capacity at low initial pH value, which is advantageous to lead removal from acidic wastewater. A model is put forward to describe the individual adsorption phenomenon of the tannin gel adsorbent.

Fuzzy Based Auto-coagulation Control Through Photometric Dispersion Analyzer

The main role of water treatment plants is to supply high-quality safe drinking water. Coagulation is one of the most important stages of surface water treatment. The photometric dispersion analyzer(PDA) is a new optical method for flocculation monitoring, and is feasible to realize coagulation feedback control. The on line modification of the coagulation control system' s set point( or optimum dosing coagulant) has influenced the application of this technology in water treatment plant for a long time. A fuzzy control system incorporating the photometric dispersion analyzer was utilized in this coagulation control system. Proposed is a fuzzy logic inference control system by using Takagi and Sugeno' s fuzzy if-then rule for the self-correction of set point on line. Programmed is the dosing rate fuzzy control system in SIEMENS small-scale programmable logic controller. A 400 L/min middle-scale water treatment plant was utilized to simulate the reaction. With the changes of raw water quality, the set point was modified correctly in time, as well as coagulant dosing rate, and residual turbility before filtration was eligible and stable. Results show that this fuzzy inference and control system performs well on the coagulation control system through PDA.

Digital speckle pattern interferometric measurement of diffusion coefficients in hydrogels

The technique of real-time digital speckle pattern interferometry is p roposed to study diffusion of surfactants in hydrogel. The diffusion coefficient is simply and directly determined from the interferograms. An example of diffus ion coefficient measurement of surfactant in agarose gel demonstrates the useful ness of the method. The results obtained are compared with the theoretical simul ating values.

Super-tough and strong nanocomposite fibers by flow-induced alignment of carbon nanotubes on grooved hydrogel surfaces

Nanocomposite fibers have attracted intensive attentions owing to their promising applications in various fields. However, the fabrication of nanocomposite fibers with super toughness and strong strength under mild conditions remains a great challenge. Here we present a facile flow-induced assembly strategy for the development of super-tough and strong nanocomposite fibers with highly ordered carbon nanotubes (CNTs), which can be induced by directional and fast flow on a grooved hydrogel surface. The prepared nanocomposite fibers show excellent mechanical properties, with a tensile strength up to 643±27 MPa and toughness as high as 77.3±3.4 MJ m^-3 at ultimate strain of 14.8±1.5%. This versatile and efficient flow-induced alignment strategy represents a promising direction for the development of high-performance nanocomposites for practical applications.

Preparation of stable micropatterns of gold on cell-adhesion-resistant hydrogels assisted by a hetero-bifunctional macromonomer linker

Surface patterning is very useful in biomaterial studies, yet it is not easy to prepare a micropattern with cell-adhesion contrast that is stable in a wet environment. Recently, a platform technique of transfer photolithography was invented to fabricate stable metal microarrays on the surface of a cell-adhesion resistant and mechanically biomimetic poly（ethylene glycol） hydrogel; the linker is the key chemical in such a transfer strategy. This article reports the design and synthesis of a hetero-bifunctional macromonomer linker with a thiol group at one end and an acryloyl group at the other end. The bifunctional linker was char- acterized by GPC and ~H NMR, and the average number of thiol groups in the bifunctional linker was detected by Ellman＇s reagent. The regent stability under wet conditions was also confirmed by the model reactants. The resultant micropatterned surfaces are meaningful for future studies of cell behaviors on mechanically biomimetic matrixes.

Vortex fluidic mediated one-step fabrication of polyvinyl alcohol hydrogel films with tunable surface morphologies and enhanced self-healing properties

Previous strategies for controlling the surface morphologies of polyvinyl alcohol(PVA)-based hydrogels,including freeze-drying and electrospinning,require a posttreatment process,which can affect the final textures and properties of the hydrogels.Of particular interest,it is almost impossible to control the surface morphology during the formation of PVA hydrogels using these approaches.The strategy reported in this study used the novel vortex fluidic device(VFD)technology,which for the first time provided an opportunity for one-step fabrication of PVA hydrogel films.PVA hydrogels with different surface morphologies could be readily fabricated using a VFD.By also reducing the crosslinking agent concentration,a self-healing gel with enhanced fracture stress(60%greater than that of traditionally made hydrogel)was achieved.Interestingly,the associated selfhealing property remained unchanged during the 260-s mechanical testing performed with the strain rate of 5%s-1.The VFD can effectively tune the surface morphologies of the PVA-based hydrogels and their associated properties,particularly the self-healing property.