太阳能对热泵循环性能的影响

利用太阳能-土壤源复合热泵实验平台进行太阳能热泵运行实验,分析提高蒸发器进口水温对热泵性能的影响。实验结果表明:随着蒸发器进口水温的升高,热泵吸热量和制热量增速较大,输入功率增速较小,因而机组COP和系统COP也随之升高。压缩机排气压力和吸气压力也随之升高,但排气压力的增速小于吸气压力的增速,压缩比逐渐减低。提高蒸发器进口水温可以提高蒸发温度,进而明显改善热泵的性能状态。     

采用喷水降温螺杆压缩机的水蒸气热泵性能研究

为拓宽水蒸气热泵在余热回收中的工作温区,降低水蒸气压缩机的排气温度,对采用喷水降温螺杆压缩机的水蒸气热泵系统及其主要部件建立热力学模型,研究了螺杆压缩机喷水温度,及最佳喷水温度下蒸发温度、冷凝温度对系统性能的影响。结果表明:喷水可以有效降低压缩机排气温度,喷水温度在73～87℃之间可保证压缩机运行在报警温度之下;压缩机耗功和冷凝器放热量随喷水温度的升高先增加后降低,在喷水温度为80℃时系统性能系数(EER)最佳;最佳喷水温度下,蒸发温度提高,蒸发器吸热量、压缩机耗功、冷凝器放热量及EER增大,压缩机压比降低;冷凝温度提高,压缩机耗功、压比增大,冷凝器放热量和EER降低。     

热泵辅助太阳能中央热水系统年运行特性研究

提出采用热泵来取代传统的电加热器,构成热泵辅助太阳能中央热水系统,可有效地降低能源消耗.结合2005年西安地区气象数据,建立了合适的数学模型,并用现有的试验数据对模型进行了校准,通过模型模拟了该年热泵辅助和电辅助太阳能中央热水系统的性能系数,输入功耗,出水温度等运行参数,并对两者进行了对比.     

太阳能热泵的性能分析

分析了工作温度对太阳能集热器和热泵的影响:降低太阳能集热器的集热温度和提高热泵的蒸发温度,有利于改善太阳能热泵系统的工作性能;设定了太阳能热泵的一些参数,计算和说明其性能;指出了太阳能热利用技术与热泵技术的有机结合,是解决"全天候工作"和"太阳能建筑一体化"问题的有效方式.     

直膨式太阳能热泵系统的模型仿真

考虑了集热器中制冷剂压降的存在,利用平衡均相理论建立了太阳能集热/蒸发器的两相流模型,同时建立了压缩机、冷凝器的数学模型.从理论上分析了集热器中制冷剂的压降、集热器的类型、集热面积、太阳能辐照度、环境温度、压缩机容积以及冷凝温度等因素对直膨式太阳能热泵系统热工性能的影响,并在此基础上给出了改善系统性能的建议.     

太阳能热泵系统的试验研究与分析

为研究以太阳能为低温热源的供热运行特点,建立了太阳能热泵系统试验台及试验台测量系统,使用数据分析软件处理不同工况下的试验数据,分析了蒸发和冷凝温度对吸热量、制热量、压缩机状态、系统COP的影响。结果表明,太阳能热泵系统在运行期间节能效果明显,蒸发温度的增大有利于提高太阳能热泵系统的工作性能。     

真空管直膨式太阳能热泵系统性能分析

该文将真空管集热器与直膨式太阳能热泵结合,提出一种真空管直膨式太阳能热泵系统。实验研究典型工况下太阳辐照度、循环水温度对系统性能的影响,并探讨压缩机变频条件下系统的动态性能。结果表明,提高太阳辐照度、降低循环水温度有利于提高系统性能,在太阳辐照度为850 W/m2,循环水温度为55℃时系统取得最大COP,为5.36。压缩机频率为42 Hz的系统COP为4.08,较45、47、50 Hz分别提高1.23%、8.5%、13.6%。     

CO_2热泵干燥的运行工况分析

在对CO2跨临界循环进行热力学研究的基础上,运用EES软件对CO2热泵干燥系统进行仿真模拟。结果表明:随着蒸发温度的上升,系统的COP和SMER上升,但压缩机排气温度下降;随着压缩机排气压力的上升,系统的COP和SMER下降,压缩机排气温度上升。因此,为了保证热泵干燥系统正常工作,应当保证系统运行参数维持在以下范围内:蒸发温度存在一个上限,而且在满足干燥过程正常运行所需要的压缩机排气温度前提下,应当尽量降低压缩机的排气压力。     

转子式压缩机吸气带液时排气状态的变化

滚动转子式压缩机具有较好的抗湿压缩性能,利用少量吸气带液可有效降低压缩机排气温度,且不造成额外的系统成本.对滚动转子式压缩机少量吸气带液时,排气温度、排气比焓的变化趋势进行了实验研究,并对压缩机功耗、吸气比焓和机壳散热量等三个排气比焓的影响因子进行了分析.结果表明:少量吸气带液能有效降低排气温度,且压缩机运行性能良好;当吸气干度x为0.9x1.0时,三个影响因子均趋向定值,且机壳散热所占比例很小(低于1%).     

太阳能-热泵辅助加热热水系统运行的经济性分析

通过建立太阳能集热设备和水箱温度模型,模拟仿真太阳能-空气源热泵辅助加热热水系统的系统性能。并以南京地区家用热水器全年供热水为例,对三种供热水系统的经济性能进行比较分析,从而得出采用太阳能-空气源热泵辅助加热供热水系统具有良好的经济效益。     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

Contents in Volume 23,2014

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汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.