Search

Heat exchanger is an important element of thermal systems. The wall fins patterns with different shape have strong effects on flue gas flow, which affects the performance of heat exchanger. A numerical model of heat exchanger was established based on computational fluid mechanics theory and the flow and heat transfer characteristics of flue gas were studied by the method of CFD and experiment. The optimal form of the wall fins patterns of flue gas channel was proposed. The results showed that the traditional circular fins reduce the effective contact time and lower the heat transfer efficiency between the flue gas and fin. When the optimal elliptical fins were used, the location of the detachment point was postponed, the effective heat transfer area was increased by 7.6% and the average heat transfer coefficient was increased by 12.1%. At the end, the fitting formula of convective heat transfer coefficient of Nu number was obtained in the optimized conditions. [ABSTRACT FROM AUTHOR]

When designing the indoor environment based on computational fluid dynamics (CFD), the artificial neural network (ANN) playing a role of surrogate model of CFD is involved to reduce the computational cost. To improve the performance of ANN, the training and normalization method of ANN are studied. An MD-82 aircraft cabin is used to test the proposed method, and different environmental parameters are used to evaluate the cabin environment. The results of different training methods are compared, and the parallel combination of genetic algorithm and particle swarm optimization shows better prediction accuracy than other training methods. A local logarithm normalization method is proposed to improve the success rate of ANN prediction. The success rate is increased by 2.5∼11.0% when the proposed local logarithm normalization method is adopted instead of local linear normalization one. [ABSTRACT FROM AUTHOR]

Over the past two decades, there has been a lot of discussion about the rapid increase of microplastics (MPs) due to their persistence, ubiquity, and toxicity. The widespread distribution of MPs in various freshwater ecosystems makes them available for different trophic levels biota. The ingestion and trophic transfer of MPs may induce potential impacts on freshwater food webs. Therefore, this systematic review is an in-depth review of 51 recent studies to confirm the spatial distribution of MPs in the Chinese freshwater ecosystem including water, sediment and biota, exposure pathways, and impacts on freshwater food webs. The result suggested the white, transparent and colored, Polypropylene (PP) and Polyethylene (PE) of <1 mm fibers were dominant in Chinese freshwaters. The uptake of MPs by various freshwater organisms as well as physiological, biological and chemical impacts on food webs were also elucidated. At last, some limitations were discussed for future studies to better understand the effects of MPs on food webs. [Display omitted] • Systematic review on MPs in Chinese freshwater and food webs has been performed. • Spatial distribution of MPs affects the ingestion by biota. • PE and PP, Fibres and <1 mm size were prominent among water, sediments and biota. • Ingestion, translocation, and elimination were observed in laboratory experiments. • MPs could induce physiological, biological and chemical impacts on food webs. [ABSTRACT FROM AUTHOR]

Abstract: The surface acoustic waves (SAWs) technique is becoming an attractive tool for accurately and nondestructively characterizing the mechanical property of the fragile low dielectric constant (low-k) thin film used in the advanced ULSI multi-layer interconnects. The dispersion features of SAWs propagating on the layered structure of low-k/SiO2/Si substrate and low-k/Cu/Si substrate are investigated in detail. The influence of the film thickness on the dispersion curvature is provided as an instruction for an accurate and facile fitting process. Numerical results indicate that the mechanical property of low-k films is expected to determine effectively when the broadband frequency is up to 300MHz. [Copyright &y& Elsevier]

The fine molecular structure of a flocculant fundamentally determines the internal flocculation mechanism and the final application property. In this work, three series of chitosan-based polymers (CTS-g-PAMD) with divergent charge densities and graft chain distribution were synthesized by graft copolymerization using acrylamide (AM) and acryloyloxyethyltrimethylammonium chloride (DAC). Meanwhile, flocculant with linear chain structure (CTS-CTA) was prepared by etherification using 3-chloro-2-hydroxypropyltrimethylammonium chloride (CTA). The characterization results confirmed that various monomers had been successfully introduced into chitosan. The reaction basically happened on —NH 2 at C 2 of chitosan, and the ring structure of chitosan was destroyed by free radical reaction. The obtained flocculants were used to flocculate bentonite and humic acid solution. Besides dose, the effects of chain structure, charge density and chain distribution on flocculation performance were systematically studied. Based on the fractal theory and flocculation kinetics, the effects of structural factors on floc characteristics were also investigated. The results showed that, flocculant with abundant graft chains exerts better flocculation performance and floc characteristic due to enhanced adsorption electrical neutralization and adsorption bridging effect. The effects of charge density and chain distribution on the flocculation performance were disparate in the range of insufficient and excessive doses. Furthermore, on the basis of the quadratic polynomial model, quantitative structure-effect relationships were established, which has guiding significance for the development and utilization of flocculants. Image 1 • Four chitosan-based flocculants with distinct molecular structures were prepared. • The cyclic structure of chitosan was destroyed by graft copolymerization. • Flocculants with "comb" branches exhibited better flocculation performance. • Chain distribution contributed differently under overdose and underdose. • The quantitative structure-activity relationships were established through model. [ABSTRACT FROM AUTHOR]