太阳能热泵相变蓄热供暖系统参数影响研究

针对寒冷地区的气候特点及建筑负荷特点,提出利用相变蓄热的太阳能热泵系统,介绍该系统的运行原理,建立系统各部分的数学模型,针对哈尔滨地区(45.8°N,126.8°E)的气象条件,编制系统动态运行模拟程序,研究太阳集热器面积及相变蓄热水箱参数对整个系统运行性能的影响。研究结果表明,当设计热负荷为10 k W时,系统所需太阳集热器面积约为60 m2,对应相变蓄热水箱中相变材料最佳质量分数约为70%,相变材料封装尺寸减小有助于提高太阳能集热量,且该效果在供暖初期和末期更为显著。     

土壤源热泵复合系统太阳能集热器面积的选择方法

针对以太阳能集热系统恢复埋管周围岩土温度的土壤源热泵建筑供暖的复合系统,研究该系统太阳能集热器面积的合理选择方法。在西安市气候条件下,针对10000 m~2的住宅建筑面积,应用TRNSYS软件建立该复合系统的动态运行换热模型。根据太阳能集热系统是否在冬季联合供暖运行分2种工况进行多种条件的仿真计算,得到对应不同岩土导热系数值的相对最佳集热器面积,从而得到这2种工况的单位建筑面积相对最佳集热器面积与岩土导热系数的关系。     

寒冷地区户用大平板太阳能集热器-空气源热泵系统性能研究

针对太阳能难以单独稳定供暖和空气源热泵供暖成本高的问题，提出空气源热泵辅助太阳能稳定供暖构想，在甘肃省兰州市七里河区魏岭乡绿化村研发搭建大平板太阳能集热器-空气源热泵系统，对比研究晴天、多云和阴天3种典型工况下大平板太阳能集热器的集热效率、太阳能热泵和空气源热泵COP、太阳能保证率、系统总供热量和系统能效比等性能参数。结果表明：晴天、多云和阴天系统集热效率分别为44.9%、38.7%和20.6%,3种工况下太阳能热泵COP均为4.0，空气源热泵COP分别为3.5、3.3和3.1，太阳能保证率分别为38.1%、32.3%和12.9%，系统全天供热量分别为142.52、135.22和120.96 kWh，系统能效比分别为3.5、3.4和2.7。研究结果证明大平板太阳能集热器-空气源热泵系统用于寒冷地区单体建筑供暖的可行性，可为寒冷地区农村单体建筑的供暖提供一种新途径。     

一种太阳能空气源/水源热泵系统的仿真分析

针对空气源热泵在低温环境下的低效问题与太阳能系统因依赖于天气状况而呈现的不稳定性等问题,提出了一种由太阳能水集热器、太阳能空气集热器、水源热泵和空气源热泵等4种装置组成的复合供暖、供热水系统,并根据日间与夜间的不同的气候条件,提出了5种运行模式。建立了系统的仿真模型,对系统在整个供暖季的运行仿真表明:该系统能够应对严寒天气并正常高效运转,在全供暖季的平均能效为4.21,各种工作模式的平均能效均在3以上,月平均能效为4~6。     

太阳能辅助地源热泵系统运行模式研究

利用Trnsys软件建立了太阳能辅助地源热泵系统仿真模型,通过试验验证了模型的准确性。试验结果显示,地源侧循环水先流经地埋管后经过集热器的串联模式是复合系统的最佳连接方案,COP值可达到4.56,比单一热泵系统提高了8.83%。基于最优模式,进一步研究太阳能集热器面积和地埋管换热器长度对复合系统的影响表明,在联合供暖工况下太阳能集热器面积每增加1 m2,可以减少换热器地埋管长度4.09 m。     

SIMULATION OPTIMIZATION RESEARCH ON SOLAR ENERGY-PHASE CHANGE THERMAL STORAGE-FRESH AIR HEATING SYSTEM

构建太阳能-相变蓄热-新风供暖系统用于承担建筑新风负荷,以全玻璃真空管集热器作为系统集热组件,以相变蓄热装置作为系统蓄热组件,以空气-水换热器作为系统供暖末端.通过使系统运行不同模式的方式达到将不稳定的太阳能变为稳定供暖热源的目的.建立耦合系统动态仿真模型并对其进行实验验证.依据此模型对系统最佳设计参数(集热系统流量、相变材料质量、相变温度等)和运行策略进行研究.     

一种主、被动结合的太阳能空气采暖模拟研究

主、被动结合的太阳能双效集热器空气采暖系统,可同时解决南向房间和北向房间的供暖问题。借助TRNSYS仿真平台,编写双效集热器的嵌入模块,对应用在太阳能示范建筑上的主、被动式双效集热器空气采暖进行模拟研究。模拟结果显示在合肥地区,木质结构的示范房只需白天供暖情况下,整个采暖期的太阳能保证率为38%,而同样条件下在拉萨和上海地区,太阳能保证率分别达到77%和58%;若示范建筑采用有蓄热能力的混凝土砖墙结构,在拉萨地区全天供暖条件下太阳能保证率达到64%;晴朗天气,南向房间和北向房间白天均可达到20℃舒适性温度。同时讨论集热器倾角、出口温度、集热面积等对主动式空气采暖太阳能保证率的影响。     

基于能量分析和分析的太阳能热泵系统优化研究

以热力学第一、二定律为基础,对太阳能热泵系统的各主要部件进行分析,给出系统各环节的能量分析模型和分析模型。选取北京某典型别墅作为太阳能热泵系统的应用对象,模拟系统效率随太阳能集热器面积和储水箱体积的变化,获得相应参数的最佳配比。结果表明:COP分析和代价效率分析一致,系统在集热器面积为127.98 m~2,水箱体积为9.08 m~3时达到最优;集热器面积为127.98 m~2,水箱体积为3.936 m~3时系统效率最大。     

基于TRNSYS的空气源热泵辅助太阳能热水系统优化研究

为实现空气源热泵辅助太阳能热水系统中关键参数的优化匹配,基于TRNSYS动态模拟平台建立完整的空气源热泵辅助太阳能热水系统模型。以系统生命周期成本为目标函数,以集热器面积、集热器倾角、水箱容积及热泵功率为优化变量,借助GENOPT软件调用Hooke-Jeeves算法对系统各变量进行同步优化,并对各优化变量进行敏感性分析。以西昌市某学生宿舍的空气源热泵辅助太阳能热水系统为研究对象进行优化。研究结果表明,优化后的COPsys普遍提高,系统性能得到明显改善,系统全年运行费用缩减,全年节电率高达9.11%。并在此基础上提出关键参数的推荐匹配原则:单位集热面积水箱容积为70 L/m~2,单位集热面积热泵功率为60 W/m~2,最佳集热器倾角为φ-6°(φ为当地纬度)。对空气源热泵辅助太阳能热水系统进行设计时,可依据以上匹配原则对热泵功率、集热器面积、水箱容积、集热器倾角按照先后顺序进行优化。研究结果可为空气源热泵辅助太阳能热水系统的优化设计提供理论依据。     

晋北地区村镇住宅建筑供暖系统优化及经济性研究

以晋北地区某村镇住宅建筑为例，对太阳能与电锅炉供暖系统进行设计方案优化及经济性研究。根据晋北地区气候特征，分析村镇住宅建筑负荷特性；采用模拟研究方法，分别对太阳能系统供暖、电锅炉系统供暖以及太阳能与电锅炉耦合系统供暖进行建筑能耗模拟；针对面积为60 m²、100 m²、200 m²村镇住宅建筑，考虑不同热源承担的建筑负荷比例、供热系统初投资及运行费用，优化不同面积村镇建筑的供暖模式以及不同热源承担的负荷占比。结果显示：太阳能系统初期投资高，电锅炉系统运行费用高。长期运行时，太阳能供暖系统的经济性优于电锅炉供暖系统。太阳能供暖系统与电锅炉供暖系统单独运行时，太阳能供暖系统不能很好地满足供暖条件，而电锅炉供暖系统运行费用较高；太阳能+电锅炉供暖系统的太阳能和电锅炉的供暖占比分别为50%时，前期投资和系统运行费用比较经济。     

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.     

Contents in Volume 23,2014

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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%.     

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.     

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.     

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.     

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.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

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.