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[en] Highlights: • A discussion on the influences of flow transition on heating capacity is proposed. • Flow transition is captured by intermittency factor within an IDDES method. • Meanwhile, flow physics behind aerodynamic performances are proposed. • The influences of evaporation and condensation temperature are discussed. - Abstract: This paper proposes a detailed discussion on the influences of flow transition on heating capacity of wind power heat pump system based on a novel improved delayed detached eddy simulation (IDDES) method and thermodynamic analysis. A numerical study of DU-212 airfoil flow field at high Reynolds number (up to 1.5 × 107) is first conducted. It is found that with high Reynolds number (Re = 1.5 × 107), flow transition is remarkably promoted and lower aerodynamic drag is achieved due to the decrease of momentum loss. Then, the influences of leading-edge trip on aerodynamic performances are studied and corresponding physical mechanisms are revealed. Furthermore, the heating capacity of a two-stage heat pump system is evaluated based on thermodynamic analysis. It is found that enhanced flow transition associated with leading edge trip could account for a reduction of heating capacity to at most 21.8% under certain circumstances. Eventually, the influences of evaporation and condensation temperature are briefly studied.
[en] The cholinergic M1 muscarinic receptors in brains of aged rats and the regulation effects of ZM (Anemarrhena asphodeloides Bunge) and its sapogenine ZMS were studied with autoradiography of 3H-pirenzepine. The mean grain densities in different brain areas were estimated by a computerized image-analysis system. The specific bindings of aged rats were decreased by 15% in cerebral cortex and striatum and by nearly 10% in hippocampus. Parallel experiments showed that chronic daily oral administration of ZM or its sapogenine ZMS to aged rats can attenuate the decrease of M1 receptor densities of the above three areas and keep them nearly normal for a long time
[en] Process simulation can help optimize the operating parameters aiming to improve the quality of rolled products. In this paper, software in Visual Basic language is developed to simulate the hot rolling process of a pair-crossed mill. The strip temperature is calculated by considering air cooling, water cooling, heat generation and conduction.The production parameters including rolling speeds, resistance to deformation, rolling forces, drive torques and powers are evaluated by mathematical models and their parameter identification support tools. The deformation of roll stack is calculated by influential function method. The roll temperature and expansion are calculated by finite differential method, and the roll wear is described by empirical formula. Based on these calculations as well as the effect of heredity is taken into account, the strip crown and flatness then can be obtained. The results show that the simulation software has friendly user interface, high accuracy and practicability. It can be served as a basis for the mill design and optimization of process parameters to acquire high quality of hot rolled strip. (author)
[en] Beacuse of the complex internal structure of wind turbine blades, there are many types of defects. There will be important significance to determine the type of defects to assess the blade residual life and feedback on the design and production process. At present the type of defects found by ultrasonic nondestructive testing (NDT) can't be determined. Physical models of several typical defects are constructed. The sound intensity reflection coefficients of different physical models are calculated seperately, and the calculation method of the sound intensity reflection coefficient of actual defect is presented. Combined the calculated coefficients with the defect information tested, a method of recognize the type of defects is presented. Actual specimen testing is used to verify the effectiveness of the method. (paper)
[en] A phosphorous–nitrogen containing cyclophosphazene derivative intumescent flame retardant with branched structures, named six(1-oxo-2,6,7-trioxa-1-phosphabicyclo[2,2,2]octane-4-methyl) cyclotriphosphazene (PEPAP), was synthesized by introducing caged phosphate to cyclotriphosphazene backbone. Then the PEPAP was applied to polypropylene (PP) by melt blending to improve the flame retardancy and thermal stability. Fourier transform infrared spectroscopy and proton nuclear magnetic resonance (1HNMR) were used to confirm the chemical structure of PEPAP. Thermal stability and flammability properties of PEPAP and PEPAP/PP composites were investigated by thermogravimetric analysis, limited oxygen index (LOI), vertical burning test (UL-94) and cone calorimetry tests. The flame-retardant mechanism was explored by thermogravimetric analysis/infrared spectrometry and thermogravimetry/mass spectrum analysis. The results showed that PEPAP had high thermal stability, and the addition of PEPAP greatly enhanced the carbonization process of PP. Also, the addition of PEPAP can dramatically improve the LOI value and UL 94 rating. For the 25% PEPAP/PP sample, the LOI value was increased to 29.4% and it can pass UL 94 V-0. The intumescent chars with an intact, multicellular structure formed from PEPAP/PP composites contain polyphosphoric acid, indicating a condensed flame-retardant mechanism of PEPAP.
[en] The Chinese government is paying considerable attention to the utilization of renewable energy, especially wind energy, because of problems such as low per capita energy consumption, heavy environment pollution, low energy efficiency, and small proportion of renewable energy. The utilization of wind energy, whose resources are very abundant in China, is undergoing rapid development; however, there are still a lot of barriers to overcome. Recently, the Chinese government made a series of policies to promote the wind power industry and the construction of wind farms, which accelerated the technology development simultaneously. The study presents a brief introduction to the resource, status and prospect of wind energy in China, which shows that with the support of the government, China will accelerate the cultivation of professionals, increase the investment of scientific research, establish a national public technical service platform to enhance self-innovation capability and to integrate domestic and oversea resources, and finally establish a complete industrial system that involves manufacture, consultation and service.
[en] A series of flame-retardant ethylene–vinyl acetate (EVA) composites with different contents of aluminum phosphate (AHP) and Trimer were prepared. The synergistic flame-retardant effects of the Trimer with AHP in EVA/AHP blends were studied by limiting oxygen index (LOI) tests, UL-94 tests, cone calorimeter tests, thermogravimetric analysis, and scanning electron microscopy (SEM). The LOI and UL-94 results showed that the system containing AHP and Trimer was very effective in improving the flame retardancy of EVA. When the mass ratio of AHP and Trimer was 3:1, the highest flame retardancy could be obtained, and when the flame-retardant loading was 30 wt%, the EVA/AHP/Trimer (7.5%) sample could achieve the V-0 rating in UL-94 tests, at the same time, its LOI value was 24.4%. The TG and DTG results showed that the addition of flame retardants catalyzes EVA decomposition in the first stage and generates a more stable char residue in the second stage. Consequently, an efficient reduction in the flammability parameters, such as heat release rate, total heat release, smoke production rate, and total smoke production could be observed. In addition, it was observed from the SEM observations of the morphological features that the AHP and Trimer combination, at the optimum proportion, could promote the formation of compact charred layers and prevent their cracking, which effectively protected the underlying materials from burning.
[en] Highlights: • Activated carbons were produced from reedy grass leaves by activation with phosphoric acid. • The activated carbons have a large number of oxygen- and phosphorus-containing surface groups. • The structure of activated carbons was bight fibers features on the surface and the external surface of the activated carbons was slightly corrugated and abundant pores. - Abstract: Activated carbons were produced from reedy grass leaves by chemical activation with H3PO4 in N2 atmosphere and their characteristics were investigated. The effects of activation temperature and time were examined. Adsorption capacity was demonstrated with BET and iodine number. Micropore volume and pore size distribution of activated carbons were characterized by N2 adsorption isotherms. The surface area and iodine number of the activated carbons produced at 500 °C for 2 h were 1474 m2/g and 1128 mg/g, respectively. Thermal decomposition of pure reedy grass leaves and H3PO4-impregnated reedy grass leaves have been investigated with thermogravimetric/mass spectroscopy (TG–MS) technique. It was found that the temperature and intensity of maximum evolution of H2O and CO2 of H3PO4-impregnated reedy grass leaves were lower than that of pure reedy grass leaves. This implies that H3PO4 as an activating reagent changed the thermal degradation of the reedy grass leaves, stabilized the cellulose structure, leading to a subsequent change in the evolution of porosity. The results of X-ray photoelectron spectroscopy and Fourier-infrared spectroscopy analysis indicate that the produced activated carbons have rich functional groups on surface
[en] Highlights: • Low-frequency dominant inflow leads to inner instability. • High-frequency mode is indispensable for inner instability. • Low-frequency mode highly affects the transition onset. • High-frequency mode highly affects the transition rate. • The frequency of laminar streaks is comparable with that of turbulent spot. - Abstract: The effect of free-stream turbulence (FST) on bypass transition in a zero-pressure-gradient boundary layer is investigated by means of Large Eddy Simulation (LES). The broadband turbulent inflow is synthesized to validate the feasibility of LES. Both a zero-thickness plate and one with super-ellipse leading-edge are addressed. The calculated Reynolds-averaged fields are compared with experimental data and decent agreement is achieved. Instantaneous fields show the instability occurs in the lifted low-speed streaks similar to earlier DNS results, which can be ascribed to outer mode. Various inflows with bi-/tri-mode interaction are specified to analyze effects of particular frequency mode on the instability pattern and multifarious transition or non-transition scenarios are obtained. Outer instability is observed in the cases with one low-frequency mode and one high-frequency mode inflow as reported by Zaki and Durbin (2005), and with one more high-frequency mode appended. Inner instability is observed in the case with a low-frequency dominant inflow, while the high-frequency mode is indispensable to induce the secondary instability. Furthermore, the results show that the transition onset is highly sensitive to low-frequency mode while the transition rate is highly sensitive to high-frequency mode. Finally, the formational frequency of turbulent spot (FFTS) is counted and the frequency of laminar streaks is demonstrated by spectral analysis
[en] The synergistic flame-retardant and smoke suppression properties of ammonium polyphosphate (APP) and activated carbon-supported Fe2O3 (AC-Fe2O3) on flame-retardant epoxy resin (EP) composites were studied. The fire behavior and smoke emission of EP composites were evaluated by limiting oxygen index (LOI), scanning electron microscopy, UL-94 vertical burning, and cone calorimeter test. LOI and UL-94 tests showed that the addition of appropriate amount of AC-Fe2O3 can effectively reduce the fly ash phenomenon, the dripping, and after-flame time. The thermogravimetric analysis and derivative thermogravimetry results showed that APP and AC-Fe2O3 can effectively decrease the maximum decomposition rate (Rmax) and promote the carbonization reaction of EP. As for the cone calorimeter test results, APP and AC-Fe2O3 clearly changed the decomposition behavior of EP, leading to the formation of a stable char layer on the surface of the composites. When flame-retardant loading was 4 mass%, the peak heat release rate and peak smoke production rate of the 3APP/1AC-Fe2O3/EP sample decreased 50.2% and 46.9%, respectively. The amount of char residual after test increased from 8.47 to 21.25%. In addition, it was observed from the macroscopic photographs of the char residue after the cone test that, at the optimum proportion, APP and AC-Fe2O3 could promote the formation of compact charred layers and prevent their cracking, which effectively protected the underlying materials from burning.