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[en] This work presents a numerical and experimental investigation on the heat transfer and turbulent flow of cooling steam in a rectangular duct with 90 .deg. ribs and studies the effect of cooling conditions on the heat transfer augmentation of steam. In the calculation, the variation range of Reynolds is from 10,000 to 190,000, the inlet temperature varies from 300 .deg. C to 500 .deg. C and the outlet pressure is from 0.5MPa to 6MPa. The aforementioned wide ranges of flow parameters cover the actual operating condition of coolant used in the gas turbine blades. The computations are carried with four turbulence models (the standard k-ε, the renormalized group (RNG) k-ε, the Launder-Reece-Rodi (LRR) and the Speziale-Sarkar-Gatski (SSG) turbulence models). The comparison of numerical and experimental results reveals that the SSG turbulence model is suitable for steam flow in the ribbed duct. Therefore, adopting the conjugate calculation technique, further study on the steam heat transfer and flow characteristics is performed with SSG turbulence model. The results show that the variation of cooling condition strongly impacts the forced convection heat transfer of steam in the ribbed duct. The cooling supply condition of a relative low temperature and medium pressure could bring a considerable advantage on steam thermal enhancement. In addition, comparing the heat transfer level between steam flow and air flow, the performance advantage of using steam is also influenced by the cooling supply condition. Changing Reynolds number has little effect on the performance superiority of steam cooling. Increasing pressure would strengthen the advantage, but increasing temperature gives an opposite result.
[en] Mercury is a highly toxic non-essential element. The mercury cycling in natural environments is a complex process. In recent years, the stable mercury isotope tracer and related analytical techniques have been developed. They offer unique possibility to understand the biogeochemistry of mercury in various environmental conditions. So a new co-ordinated research project (CRP) on health impacts of mercury cycling in contaminated environments studied by nuclear techniques has been supported by the IAEA. This paper introduces the research project whose IAEA research contract number is CPR-10874. It includes the scientific background, scope of the project, methods, some results related to this CRP and the plans for future work. (author)
[en] In recent decades, the production and using of mercury was reduced, however, the mercury pollution and health impacts are still serious. It is because that China's economy was forging rapidly ahead in the past 20 years. The combustion of fossil fuels, in which of the coal is more than 70% in the total energy consumption, was increasing year after year, especially in some industrial cities. So a co-ordinated research project (CRP), on health impacts of mercury cycling in contaminated environments studied by nuclear techniques, has been supported by the IAEA. In the CRP that contract number is PRC-10874, some research techniques for understanding the behavior of mercury in terrestrial ecosystem were developed, and some problems about mercury pollution in terrestrial ecosystem and their impacts have been probed. The results indicated that because of the increasing of anthropogenic Hg emission, the Hg accumulation in terrestrial ecosystem was increasing with time in the research sites (Chongqing, China), which Hg in wet and dry deposition was sum 195.3 g/km2·yr in urban and 48.5 g/km2·yr in rural area. The bioaccumulation of Hg in plant was related to the concentration of atmospheric Hg and soil Hg. The Hg content of plant increased with the atmospheric Hg increasing. Hg contents in plant leaves increased with the increase of air-Hg, the correlation equation was: y 0.0173x-0.3204 Calculation from this equation showed that the accumulation of Hg in plants stemmed mainly from soil rather than atmosphere when air-Hg was lower than 18.5 ng/m3, however contribution of air-Hg to plant Hg accumulation was increasing with the increase of Air-Hg when its concentration was higher than 18.5 ng/m3. Furthermore, it was found that Hg content in some crops and livestock products had exceeded the limit of FHSV due to Hg accumulation in terrestrial ecosystem increasing gradually with the increasing Hg emission in Chongqing. It should be noted specially that the Hg concentration of milk was higher, some of it was in excess of the limit of Food Health Standard Value (FHSV) because of high Hg accumulation in forages. The investigation data of the mercury in fishpond systems in the research sites indicated that the accumulation of mercury in fishponds in polluted sites was much higher than that in control site. So the content of Hg in fish muscle in polluted sites was higher than in control site. The content of Hg in all the fish muscle in heavy pollution site exceeded the limit of FHSV for Hg in fish (0.3 mg/kg FW). The contents of mercury in muscle of fish from the Yangtze River were lower than the FHSV, but some data from the reservoirs were higher than the FHSV. All the I/O values, the ratios between the input of output of mercury in soil in vegetable land system in different acid deposition areas, in the acid deposition areas were more than 1, it means that there was accumulation of mercury in soil in the regions. The Hg content in surface soil increases average 0.567μg/kg a year in heavy pollution area, but only 0.00907μg/kg in control area. It implies that the Hg accumulated in soil more and more badly in heavy pollution area, it will influence the human health through the food chain. (author)
[en] Highlights: • A shaft cooling structure is designed based on loop thermosyphons. • A single loop thermosyphon is studied during heating and cooling of the same tube. • The optimal liquid filling ratio is obtained under the special condition. • Cooling effects of the cooling structure are simulated on the motorized spindle. - Abstract: In this paper, a shaft cooling structure of a grinding motorized spindle was designed based on loop thermosyphons. The evaporation and condensation sections of the loop thermosyphons were located on the same tube due to the thermal conductivity of the shaft. The experimental studies on both heat transfer performance and start-up characteristics of a single loop thermosyphon were performed under the special condition. Then, the cooling effect on the shaft was simulated depending on the obtained experimental data. Results demonstrated that the optimal liquid filling rate of a loop thermosyphon ranged between 50 and 60% under the special condition. Furthermore, a critical value of heating power between 20 W and 40 W was found. When the heating power exceeded this value, the temperature of the evaporation section increased rapidly without any fluctuation. The violent fluctuation of temperature at the upper evaporation section could be utilized as an indicator for the heat transfer limit. Finally, according to the simulation, the maximum temperature of the motorized spindle was reduced by approximately 28% under the effect of the designed cooling structure.
[en] Little is known about the relationships between Zn bioavailability in ZnO nanoparticle (NP)-spiked soil and the implications to crops. The present pot culture experiment studied Zn bioavailability in soil spiked with different doses of ZnO NPs, using the diethylenetriaminepentaacetic acid (DTPA) extraction method, as well as the toxicity and Zn accumulation in maize plants. Results showed that ZnO NPs exerted dose-dependent effects on maize growth and nutrition, photosynthetic pigments, and root activity (dehydrogenase), ranging from stimulatory (100–200 mg/kg) through to neutral (400 mg/kg) and toxic effect (800–3200 mg/kg). Both Zn concentration in shoots and roots correlated positively (P < 0.01) with ZnO NPs dose and soil DTPA-extractable Zn concentration. The BCF of Zn in shoots and roots ranged from 1.02 to 3.83 when ZnO NPs were added. In most cases, the toxic effects on plants elicited by ZnO NPs were overall similar to those caused by bulk ZnO and soluble Zn (ZnSO_4) at the same doses, irrespective of some significant differences suggesting a higher toxicity of ZnO NPs. Oxidative stress in plants via superoxide free radical production was induced by ZnO NPs at 800 mg/kg and above, and was more severe than the same doses of bulk ZnO and ZnSO_4. Although significantly lower compared to bulk ZnO and ZnSO_4, at least 16 % of the Zn from ZnO NPs was converted into DTPA-extractable (bioavailable) forms. The dissolved Zn"2"+ from ZnO NPs may make a dominant contribution to their phytotoxicity. Although low amounts of ZnO NPs exhibited some beneficial effects, the accumulation of Zn from ZnO NPs into maize tissues could pose potential health risks for both plants and human
[en] This paper deals with the optimization of a novel combined power system, which can effectively recover low-temperature waste heat and fully utilize the cold energy of LNG as well, based on the first thermodynamic law and the second thermodynamic law respectively. Parametric analysis has been performed to study the effects of heat source temperature, ammonia turbine inlet pressure, LNG turbine inlet and outlet pressures, as well as ammonia mass fraction of basic solution. The simulation results show that the system performance can be improved by applying optimization techniques. The optimization is conducted under a certain set of constraints by using the differential evolution (DE) algorithm to maximize the first and the second law efficiency respectively. Through parallel direct search over the whole feasible region, it is found that a maximum first law efficiency of 39.33% can be obtained when variable vector V1 = [423.70 K, 1.8 MPa, 3.904 MPa, 0.3 MPa, 0.52]; while a maximum second law efficiency of 55.62% can be obtained when variable vector V2 = [423.93 K, 1.874 MPa, 3.493 MPa, 0.8 MPa, 0.48]. In addition, the irreversibilities in various components of the cycle under typical operating conditions and exergy efficiency optimum condition have been compared through detailed exergy analysis. -- Highlights: • The combined power cycle utilizes low-temperature waste heat and LNG cold energy. • Parametric analysis results recommended that the cycle may be optimized. • Thermal and exergy efficiency were selected as objective functions separately. • Differential evolution algorithm was applied to reach the maximum efficiency. • Optimization of operating parameters improved the cycle performance significantly
[en] This paper has proposed a combined power system, in which low-temperature waste heat can be efficiently recovered and cold energy of liquefied natural gas (LNG) can be fully utilized as well. This system consists of an ammonia-water mixture Rankine cycle and an LNG power generation cycle, and it is modelled by considering mass, energy and species balances for every component and thermodynamic analyses are conducted. The results show that the proposed combined cycle has good performance, with net electrical efficiency and exergy efficiency of 33% and 48%, respectively, for a typical operating condition. The power output is equal to 1.25 MWh per kg of ammonia-water mixture. About 0.2 MW of electrical power for operating sea water pumps can be saved. Parametric analyses are performed for the proposed combined cycle to evaluate the effects of key factors on the performance of the proposed combined cycle through simulation calculations. Results show that a maximum net electrical efficiency can be obtained as the inlet pressure of ammonia turbine increases and the peak value increases as the ammonia mass fraction increases. Exergy efficiency goes up with the increased ammonia turbine inlet pressure. With the ammonia mass fraction increases, the net electrical efficiency increases, whereas exergy efficiency decreases. For increasing LNG turbine inlet pressure or heat source temperature, there is also a peak of net electrical efficiency and exergy efficiency. With the increase of LNG gas turbine outlet pressure, exergy efficiency increases while net electrical efficiency drops
[en] Mercury is a highly toxic non-essential element. The mercury cycling in natural environments is a complex process. In recent years, the stable mercury isotope tracer and related analytical techniques have been developed. They offer unique possibility to understand the biogeochemistry of mercury in various environmental conditions. So a new coordinated research project (CRP), on health impacts of mercury cycling in contaminated environments studied by nuclear techniques, has been supported by the IAEA. This paper introduces the research project which is IAEA research contract number CPR-10874. It includes the scientific background, scope of the project, methods, some results related to this CRP and the plans for future work. (author)