建筑窗体玻璃节能研究

本文对建筑中的外门窗在太阳辐射热的传递与利用,对几种玻璃光在不同波段情况有效光的传递等方面作了分析研究,得出了不同的太阳高度角下、建筑不同朝向的窗户应选用的建筑门窗玻璃。并特别指出Low-E玻璃对建筑节能有着突出的优势。     

垂直面太阳散射辐射计算方法研究

建筑设计必须考虑太阳辐射在建筑立面上的热作用,但气象台站仅观测水平面辐射数据,垂直面上的太阳辐射资料稀缺。为提出一种依据水平面辐射观测数据来计算垂直面散射辐射的方法,该文研究并建立辐射观测站,并进行长期辐射观测,积累了一定量的辐射数据。通过对垂直面上散射辐射主要影响因素的分析,提出基于晴空指数Kt和直射辐射与垂直面法线方向夹角φ的垂直面散射辐射计算方法。利用观测数据确定公式中的计算系数,并将该文研究提出的计算方法与国内外的5种太阳散射辐射计算模型进行比较分析。结果表明:1)该文提出的计算方法所需计算参数仅依据国内常规辐射观测数据即可。2)该方法能够实现对不同朝向垂直面散射辐射的计算。3)与国内外常用计算模型相比,该方法在不同天空晴朗度、不同朝向上整体精度更高。研究认为该文方法与国内气象部门的辐射观测数据相匹配,所需计算参数少、精度高、简单易用,可为建筑能耗计算和热环境分析提供新的垂直面散射辐射计算方法。     

不同玻璃对夏季炎热地区室内太阳辐射得热的影响分析

以夏季炎热的重庆地区为例,采用理论计算方法,深入分析不同玻璃类型对室内太阳辐射得热量的影响。通过建立太阳辐射模型,计算分析不同玻璃在不同朝向下的室内太阳辐射得热量,结果表明:当采用相同玻璃时,东、西向外窗全天阻挡的太阳辐射量约为南北向外窗全天阻挡量的2倍,东、西向外窗相比南北向外窗具有更大的隔热节能潜力;同时,透过Low-E中空玻璃和普通中空玻璃的室内平均太阳辐射得热量分别是透过单层玻璃的0.37倍和0.85倍,与实验测试分析结果基本一致;在进行不同玻璃外窗室内太阳辐射得热量计算时,不仅要考虑玻璃本身的隔热性能差异,还必须结合当地不同朝向外窗接收太阳辐射的时间分布规律。     

多朝向太阳能资源的测量与研究

设计一套多朝向太阳辐照与光伏发电效率测量系统,通过定时扫描不同朝向光伏组件的输出I-V曲线,采集最大功率点数据,检测光伏发电效率。配套开发的分析软件对实测数据进行校正、整理与挖掘,换算成各个朝向的太阳总辐照度,逐步形成多朝向太阳能资源数据库,为光伏发电系统的设计与安装、技术与效益评估提供重要依据。运行结果表明,系统状态稳定,实测数据不仅可初步揭示深圳地区多朝向太阳能资源状况,也可为实用太阳辐射模型的研究提供数据支持。     

太阳辐射吸收系数对围护结构夏季净得热量的影响

以上海地区的建筑围护结构夏季传热过程为研究背景,在分析太阳辐射作用下围护结构外表面热平衡关系的基础上,采用数值模拟方法,讨论在夏至日太阳辐射吸收系数对不同朝向围护结构表面温度和全天净得热量的影响。结果表明:吸收系数减小率相同时,南墙外表面温度下降率小于其他朝向,而其全天净得热量的减小率则大于其他朝向。不同朝向围护结构表面温度的下降率均小于吸收系数的减小率,但其全天净得热量的减小率均大于吸收系数的减小率,说明降低外墙外表面太阳辐射吸收系数可以有效减少因太阳辐射导致的传入围护结构内部的热量。     

深圳不同气象条件下各朝向太阳辐射分布特征

利用深圳地区搭建的多朝向太阳辐照与光伏发电效率测量系统2013—2017年120个朝向光伏组件实测数据,分析入射太阳辐射最佳朝向及其时间变化规律,不同气象条件下各朝向辐射的表现特征,以及方位角和倾角的差异对辐射影响的程度,得出:1)年均太阳辐射最大值的倾斜面为-15°/10°,即光伏发电最佳方位角南偏东15°,最佳倾角10°;3—10月份最佳倾角较低,在0°～20°之间,11月份—次年2月份最佳倾角在30°～50°之间,最佳朝向的月平均辐射量比水平面上要高出6.6%;对于可调倾角的光伏电站,每年可进行4次调节(4月份0°、7月份10°、9月份20°、11月份40°),就可达到较高的发电效率。2)深圳的多云天气最多,累计辐射值超过了1/3,因此多云天气时的太阳能利用也极具价值;3)深圳地区太阳辐射与气象条件关系密切,且东侧辐射值往往大于西侧。     

倾斜面太阳辐照度实用计算模型的研究

研究基于水平面上太阳辐照度数据计算任意倾斜面上对应太阳辐照度的方法,通过对直射、散射及反射现象的观察与分析,结合完整的实测数据,提出两种简单实用的计算模型。与经典模型相比,新模型所需的输入数据少,过程简单且结果准确。能够有效利用全国各地气象观测站的典型年太阳辐射数据,对不同朝向上的太阳能资源进行综合评价,建立相应的数据库,为太阳能发电系统的系统设计、工程安装和效益评估提供客观依据和科学指导。     

呼和浩特地区太阳辐射模型分析

依据太阳辐射相关理论,针对多种太阳辐射计算模型,运用MATLAB计算平台,分析计算了不同工况下,水平面上和任意朝向倾斜面上的太阳辐射量,并与呼和浩特地区太阳辐射实测值进行了比较.HOTTEL模型的计算值与实测值符合较好,可预测计算本地区太阳辐射量,并能为相近地区太阳辐射量计算提供参考.     

不同朝向玻璃窗太阳辐射得热系数模拟与实验研究

建立了太阳辐射得热系数的计算模型,并搭建了测量窗户太阳辐射得热系数的实验台,得到了玻璃窗的太阳辐射得热系数的实验值和模拟值,两者吻合度很好.结果表明:太阳辐射得热系数与太阳入射角密切相关,不同朝向玻璃窗的太阳辐射得热系数随着太阳入射角有规律地变化.当玻璃窗朝南时,一天之内太阳辐射得热系数先增大,中午时达到最大值而后减少;当玻璃窗朝西时,太阳辐射得热系数上午基本保持不变,而后减少(大概中午时分达到最小值),然后逐渐增大;玻璃窗朝东时太阳辐射得热系数变化情况与西向相反;当玻璃窗表面没有太阳直射辐射时,太阳辐射得热系数基本保持不变.     

浙江墙面太阳辐射的计算及其分布

引言墙面太阳辐射是直接影响室内温度、光照状况的重要环境因子之一。对建筑物朝向、间距、窗户开设面积的设计,和建筑采暖及降温的设计,以及空调负荷的计算,都必须考虑墙面太阳辐射这一因子。本文介绍墙面太阳辐射的计算方法,并对浙江省各朝向墙面上的太阳辐射值进行计算,为了解我省垂直面上的辐射分布情况提供参考依据。     

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.     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

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%.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

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.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

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.     

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.