森林对二氧化碳循环的影响

假定安徽地区为封闭系统，用大气中ＣＯ２源汇理论，估算森林固定ＣＯ２的效益及安徽地区大气中ＣＯ２的增量，结果表明：安徽地区以各种途径释放到大气中ＣＯ２总量为１８．４２５×１０７ｔ，其中森林、农作物、荒山、水体的吸收率分别为４０．３２％，４７．６４％，５．９９％，５．２５％。滞留量为０．１５３２×１０７ｔ，ＣＯ２浓度的年增量为０．７８μｇ·ｇ－１，低于世界年平均增量（１．０～１．２μｇ·ｇ－１），若ＣＯ２释放量不变，全省只要在原有森林覆盖率的基础上，营造阔叶林６．９７×１０４ｈｍ２或针叶林９．０３×１０４ｈｍ２。

光合作用就是碳汇

光合作用就是碳汇,这既是诠释生命的历程又是讲述碳循环的故事。大约在46亿年前,频繁的火山活动喷发出H2O、CO2、CO、H2、CH4、N2、H2S、NH3、SO2和He等气体,在紫外线、宇宙射线、闪电、高温等自然条件的长期作用下,产生了许多简单的有机物,然后随雨水进入原始水域,在一定的条件下,形成了许多不同性质的生物大分子,继而演化为原始单细胞。大约在35~38亿年前,不生氧光合细菌就开始了初始的光合作用。数亿年后,以蓝细菌为代表的生氧光合生物出现,地球进入了生氧光合作用时代,并逐渐形成了现在的大气圈和水圈。在O2充足的环境下生命大量出现,最后演变进化出草、木、虫、鱼、鸟、兽及人类。不管光合作用怎样变化,CO2一直是这个伟大生化反应的原料。光养生物通过光合作用释放O2,并将大气中的CO2和热量源源不断地转运储存到由植物、动物、微生物构成的食物网中;生物氧化消耗O2,同时向大气中释放CO2和热量;演绎着“碳热氧”在大气圈、生物圈、水圈和岩石圈中循环往复、周而复始的变化过程;驱动着能量流动、物质循环和信息传递,产生了风雨雷电、龙腾虎跃、五彩缤纷、气象万千的生态世界。

微管壳式换热器在能量转换循环中的应用

目前,超临界二氧化碳(S-CO_(2))布雷顿循环普遍采用印刷电路板换热器(PCHE)来保证其相对其他能量转换循环的紧凑性优势。PCHE芯体为整体结构,若内部出现泄漏或结垢等问题,很难进行维护与检修。本文提出了一种微管壳式换热器(MSTE),其结构与传统管壳式换热器类似,但其管径缩小至微通道级。由于MSTE的流道横截面积占总截面积之比较PCHE大,在典型的回热器与冷却器设计工况下,相对PCHE而言,采用MSTE可将体积与质量均减小30%以上。灵敏性分析结果显示,采用本文设计的MSTE结构的回热器与冷却器,回热器冷热流道入口温度升高20℃左右,压缩机入口温度变化均不超过1℃,说明该种结构换热器的换热能力足够支撑能量转换循环的一般工况波动。

Carbon Turnover in a Crop Rotation Under Free Air CO_2 Enrichment (FACE)

Mostly based on assumptions derived from controlled-environment studies, predicted future atmospheric CO2 concentrations [CO2] are expected to have considerable impacts on carbon （C） turnover in agro-ecosystems. In order to allow the in situ examination of C-transformations in the plant-soil system of arable crop rotations under future [002], a free air carbon dioxide enrichment （FACE） experiment （550 μmol mol^-1 CO2） was started at Braunschweig, Germany in 1999. The crop rotation under investigation comprised winter barley, a cover crop （ryegrass）, sugar beets and winter wheat. Assessments of CO2 effects included the determination of above- and belowground biomass production, measurements of canopy CO2- and H2O- fluxes, soil microbial biomass and in situ soil respiration. The results obtained during the 1st crop rotation cycle （3 years） showed that for the selected crops elevated [CO2] entailed significant positive effects （P 〈 0.05） on aboveground （6%-14% stimulation） and belowground biomass production （up to 90% stimulation）, while canopy evapotranspiration was reduced. This resulted in increased soil water content. Also, depending on crop type and season, high CO2 stimulated in situ soil respiration （up to 30%）, while soil microbial biomass did not show significant respouses to elevated [CO2] during the first rotation cycle.

Characters of the P_(CO)_2 and CO_2 Flux in the East China Sea in Autumn

P CO 2 of air and seawater samples from the East China Sea (ECS) were measured in situ in autumn, 1994. Ocean currents, terrestrial fluviation, biological activities, etc.,P CO 2 characters in air and seawater were investigated. CO 2 flux and its character in the East China Sea are discussed on the basis of theP CO 2 profiles of air and seawater. It was clear that the nearshore was the source of CO 2; and that the outer sea area was the sink of CO 2; and that the shelf area of the ECS is a net sink for atmospheric CO 2 in autumn.

Methane Dynamics in Northern Peatlands: A Review

Northern peatlands store a large amount of carbon and play a significant role in the global carbon cycle. Owing to the presence of waterlogged and anaerobic conditions, peatlands are typically a source of methane (CH4), a very potent greenhouse gas. This paper reviews the key mechanisms of peatland CH4 production, consumption and transport and the major environmental and biotic controls on peatland CH4 emissions. The advantages and disadvantages of micrometeorological and chamber methods in measuring CH4 fluxes from northern peatlands are also discussed. The magnitude of CH4 flux varies considerably among peatland types (bogs and fens) and microtopographic locations (hummocks and hollows). Some anthropogenic activities including forestry, peat harvesting and industrial emission of sulphur dioxide can cause a reduction in CH4 release from northern peatlands. Further research should be conducted to investigate the in fluence of plant growth forms on CH4 flux from northern peatlands, determine the water table threshold at which plant production in peatlands enhances CH4 release, and quantify peatland CH4 exchange at plant community level with a higher temporal resolution using automatic chambers.

Theoretical Study on CO_2 Transcritical Cycle Combined Ejector Cycle Refrigeration System

Chlorofluorocarbons(CFCs) or hydrochlorofluorocarbons(HCFCs) are as main refrigerants used in traditional refrigeration systems driven by electricity from burning fossil fuels, which is regarded as one of the major reasons for ozone depletion (man-made refrigerants emission) and global warming (CO 2 emission). So people pay more and more attention to natural refrigerants and energy saving technologies. An innovative system combining CO 2 transcritical cycle with ejector cycle is proposed in this paper. The CO 2 compression sub-cycle is powered by electricity with the characteristics of relatively high temperature in the gas cooler (defined as an intercooler by the proposed system). In order to recover the waste heat, an ejector sub-cycle operating with the natural refrigerants (NH 3, H 2O) is employed. The two sub-cycles are connected by an intercooler. This combined cycle joins the advantages of the two cycles together and eliminates the disadvantages. The influences of the evaporation temperature in CO 2 compression sub-cycle, the evaporation temperature in the ejector sub-cycle, the temperature in the intercooler and the condensation temperature in the proposed system performance are discussed theoretically in this study. In addition, some unique features of the system are presented.

System design and analysis of the trans-critical carbon-dioxide automotive air-conditioning system

As an environmentally harmless and feasible alternate refrigerant, CO 2 has attracted worldwide attention, especially in the area of automobile air conditioning (AAC). The thermal property of CO 2 and its trans critical refrigeration cycle is very different from that of the traditional CFC or HCFC system. The detailed process of CO 2 system thermal cycle design and optimization is described in this paper. System prototype and performance test bench were developed to analyze the performance of the CO 2 AAC system.

Scenario Formation of Energy Demand and CO_2 Emissionsfor Sustainable China

Co-integration theory has been employed in this paper and Granger causes are found between urbanization rate and GDP, between capital stock and GDP. Scenario analysis of GDP is performed using the GDP model established in the paper. The energy consumptions in Germany, Japan and other developed countries are analyzed and compared with the energy consumption in China. Environmental friendly scenario of energy demand and CO2 emissions for sustainable China has been formed based on the results of comparison. Under environmental friendly scenario, the primary energy consumption will be 4.31 billion ton coal equivalence （tee） and CO2 emissions will be 1.854 billion t-c in 2050; energy per capital will be 3.06 tee that is 1.8 times of energy consumed in 2005 in China and 51% of consumed energy per capital in Japan in 2003. In 2050, the energy requirement of unit GDP will be 20% lower than that of Germany in 2003, but will be still 37% higher than that in Japan in 2003. It is certain that to fulfill the environmental friendly Scenario of energy demand and CO2 emissions is a difficult task and it needs long term efforts of the whole society, not only in production sectors but also in service and household sectors,

Second Law of Thermodynamics Analysis of Transcritical Carbon Dioxide Refrigeration Cycle

In order to identify the locations of irreversible loss within the transcritical carbon dioxide refrigeration cycle with an expansion turbine, a method with respect to the second law of thermodynamics based on exergy analysis model is applied. The effects of heat rejection pressures, outlet temperatures of gas cooler and evaporating temperatures on the exergy loss, exergy efficiency and the coefficient of performance (COP) of the expansion turbine cycle are analyzed. It is found that the great percentages of exergy losses take place in the gas cooler and compressor. Moreover, heat rejection pressures, outlet temperatures of gas cooler and evaporating temperatures have strong influence on the exergy efficiency, COP and the exergy loss of each component. The analysis shows that there exists an optimal heat rejection pressure corresponding to the maximum exergy efficiency and COP, respectively. The results are of significance in providing theoretical basis for optimal design and the control of the transcritical carbon dioxide system with an expansion turbine.

Thermo economic evaluation of oxy fuel combustion cycle in Kazeroon power plant considering enhanced oil recovery revenues

Oxy fuel combustion and conventional cycle(currently working cycle) in Kazeroon plant are modeled using commercial thermodynamic modeling software. Economic evaluation of the two models regarding the resources of transport and injection of carbon dioxide into oil fields at Gachsaran for enhanced oil recovery in the various oil price indices is conducted and indices net present value(NPV) and internal rate of return on investment(IRR) are calculated. The results of the two models reveal that gross efficiency of the oxy fuel cycle is more than reference cycle(62% compared to 49.03%), but the net efficiency is less(41.85% compared to 47.92%) because of the high-energy consumption of the components, particularly air separation unit(ASU) in the oxy fuel cycle. In this model, pure carbon dioxide with pressure of 20×105 Pa and purity of 96.84% was captured. NOX emissions also decrease by 4289.7 tons per year due to separation of nitrogen in ASU. In this model, none of the components of oxy fuel cycle is a major engineering challenge. With increasing oil price, economic justification of oxy fuel combustion model increases. With the price of oil at $ 80 per barrel in mind and $ 31 per ton fines for emissions of carbon dioxide in the atmosphere, IRR is the same for both models.

Exergetic Comparative Analysis of Ammonia and Carbon Dioxide Two-Stage Cycles for Simultaneous Cooling and Heating

The paper deals with the comparative analysis of the performance of cooling and heating systems operating with NH3 （ammonia） or CO2 （carbon dioxide）, both natural refrigerants. The study is based on the exergetic analysis that points out the location and the magnitude of a system malfunction. Both systems, with NH3 or CO2 operate in two stages. The exergetic analysis gives the direction of the structural optimization. The exergetic analysis has shown that the best structural schematic is not the same for the two agents. The exergetic analysis points out that the largest exergy destruction in the CO2 cycle is due to the throttling process and offers solutions to diminish it.

Brayton Power Cycles for Electricity Generation from Fusion Reactors

Brayton power cycles for fusion reactors have been investigated, using Helium in classical configurations and CO2 in a recompression layout. Thermal sources from the reactor have strongly constrained the cycle configurations, hindering use of a recuperator in Helium cycles and conditioning the outlet turbine temperature in CO2 ones. In both cycles, it is possible to take advantage of the exhaust thermal energy by coupling the Brayton to a Rankine cycle, with an organic fluid in the helium case （iso-butane has been investigated） and steam in the CO2 case. The highest efficiency achieved with Helium cycle is 38.5% using Organic Rankine Cycle and 32.6% with Helium alone. The efficiency changes from 46.7% using Rankine cycle to 41% with CO2 alone. The Helium cycle is highly sensitive to turbine efficiency and in a moderate way to compressor efficiency and pressure drops, being nearly insensitive to thermal effectiveness in heat exchangers. On the other hand, CO2 is nearly insensitive to all the parameters.

Thermodynamic Analysis and Comparison on Low Temperature CO_2-NH_3 Cascade Refrigeration Cycle

This paper is focused on the cascade refrigeration cycle using natural refrigerant CO 2-NH 3. The properties of refrigerants CO 2 and NH 3 are introduced and analyzed.CO 2 has the advantage in low stage of cascade refrigeration cycle due to its good characteristics and properties. The thermodynamic analysis results of the CO 2-NH 3 cascade refrigeration cycle demonstrates that the cycle has an optimum condensation temperature of low stage and also has an optimum flow rate ratio.By comparing with the R13-R22 and NH 3-NH 3 cascade refrigeration cycles, the mass flow rate ratio of CO 2-NH 3 is larger than those of R13-R22 and NH 3-NH 3, the theoretical COP of CO 2-NH 3 cascade refrigeration cycle is larger than that of the R13-R22 cascade cycle and smaller than that of the NH 3-NH 3 cascade cycle. But the real COP of CO 2-NH 3 cascade cycle will be higher than those of R13-R22 and NH 3-NH 3 because the specific volume of CO 2 at low temperature does not change much and its dynamic viscosity is also small.

Assessment of Sustainable Energy Strategy with Long-Term Global Energy Model Incorporating Nuclear Fuel Cycle

This paper investigates long-term energy strategy compatible with significant reduction of world carbon dioxide （CO2） emissions, employing a long-term global energy model, Dynamic New Earth 21 （called DNE21）. The model seeks the optimal energy mix from 2000 to 2100 that minimizes the world total energy system cost under various kinds of energy and technological constraints, such as energy resource constraints, energy supply and demand balance constraints, and CO2 emissions constraints. This paper discusses the results of primary energy supply, power generation mix, CO2 emission, CCS （carbon capture and storage） and total system costs for six regions including world as a whole. To evaluate viable pathways forward for implementation of sustainable energy strategies, nuclear power generation is a viable source of clean and green energy to mitigate the CO2 emissions. Present research shows simulation results in two cases consisting of no CO2 regulation case （base case） and CO2 REG case （regulation case） which halves the world CO2 emissions by the year 2050. Main findings of this research describe that renewable and nuclear power generation will contribute significantly to mitigate the CO2 emission worldwide.

天体Ⅰ型X射线暴中的核物理

X射线暴(X-ray burst)是指天体的X射线亮度突然增强10~50倍的天文现象.它是发生在由一颗中子星(或者黑洞)和一颗伴随的“捐赠者”伴星(通常为红巨星)所构成的密近双星系统里的剧烈核过程.作为宇宙中发生最频繁的热核爆炸事件,X射线暴已广泛为国际上众多基于卫星的X射线观测站所观测和研究,其中包括2017年中国发射的“慧眼”硬X射线调制望远镜.核物理学家需要提供精确的核物理输入量,例如原子核质量、衰变寿命、核反应率等,结合天体物理模型,进而深入理解X射线暴中天文观测到的光变曲线、双星系统相应的天体物理环境参数,以及爆炸灰烬中的核素丰度分布等重要科学问题.本文针对天体Ⅰ型X射线暴中关键核反应研究进行了系统的阐述,详细介绍了X射线暴中的一些主要核合成过程,以及所需的关键核物理输入量,总结了相关研究方向的具体目标,为研究者指出了未来可能的研究方向.

Component Exergy Analysis of Solar Powered Transcritical CO_2 Rankine Cycle System

In this paper,exergy analysis method is developed to assess a Rankine cycle system,by using supercritical CO2 as working fluid and powered by solar energy.The proposed system consists of evacuated solar collectors,throttling valve,high-temperature heat exchanger,low-temperature heat exchanger,and feed pump.The system is designed for utilize evacuated solar collectors to convert solar energy into mechanical energy and hence electricity.In order to investigate and estimate exergy performance of this system,the energy,entropy,exergy balances are developed for the components.The exergy destructions and exergy efficiency values of the system components are also determined.The results indicate that solar collector and high temperature heat exchanger which have low exergy efficiencies contribute the largest share to system irreversibility and should be the optimization design focus to improve system exergy effectiveness.Further,exergy analysis is a useful tool in this regard as it permits the performance of each process to be assessed and losses to be quantified.Exergy analysis results can be used in design,optimization,and improvement efforts.

Efficient reversible CO/CO_(2) conversion in solid oxide cells with a phase-transformed fuel electrode

The reversible solid oxide cell(RSOC)is an attractive technology to mutually convert power and chemicals at elevated temperatures.However,its development has been hindered mainly due to the absence of a highly active and durable fuel electrode.Here,we report a phase-transformed CoFe-Sr_(3)Fe_(1.25)Mo_(0.75)O_(7)-δ(CoFe-SFM)fuel electrode consisting of CoFe nanoparticles and Ruddlesden-Popper-layered Sr_(3)Fe_(1.25)Mo_(0.75)O_(7)-δ(SFM)from a Sr_(2)Fe_(7/6)Mo_(0.5)Co_(1/3)O_(6)-δ(SFMCo)perovskite oxide after annealing in hydrogen and apply it to reversible CO/CO_(2)conversion in RSOC.The CoFeSFM fuel electrode shows improved catalytic activity by accelerating oxygen diffusion and surface kinetics towards the CO/CO_(2)conversion as demonstrated by the distribution of relaxation time(DRT)study and equivalent circuit model fitting analysis.Furthermore,an electrolyte-supported single cell is evaluated in the 2:1 CO-CO_(2)atmosphere at 800℃,which shows a peak power density of 259 mW cm^(-2)for CO oxidation and a current density of-0.453 A cm^(-2)at 1.3 V for CO_(2)reduction,which correspond to 3.079 and3.155 m L min-1cm^(-2)for the CO and CO_(2)conversion rates,respectively.More importantly,the reversible conversion is successfully demonstrated over 20 cyclic electrolysis and fuel cell switching test modes at 1.3 and 0.6 V.This work provides a useful guideline for designing a fuel electrode through a surface/interface exsolution process for RSOC towards efficient CO-CO_(2)reversible conversion.