间接膨胀式太阳能多功能热泵系统换热性能的实验研究

间接膨胀式太阳能多功能热泵系统(indirect expansion solar assisted multifunction domestic heat pump,IESA-MDHP)的运行性能受到多种因素影响,利用带有太阳模拟发射器的焓差实验室可定量检测热泵系统的运行性能,并对不同条件下的运行性能进行比较。该文在稳定的外界条件下,对IESA-MDHP系统在太阳能制热水模式和太阳能制热模式下运行的换热性能进行实验研究。结果表明,在太阳能制热水模式中,随着水箱初温升高,蒸发侧和冷凝侧换热功率均会提高,在制热水的同时,向系统输入太阳辐照,与无辐照时相比,辐照强度从0 W/m~2上升到500 W/m~2时,系统在蒸发侧和冷凝侧的平均换热功率可分别提高30.11%和37.46%,平均COP可提高32.27%;在太阳能制热模式中,水箱作为系统的蒸发热源,水箱初始温度越高,蒸发侧换热功率越大,对应的冷凝侧换热功率随之增大。     

辐照强度对直膨式太阳能热泵性能影响的研究

文章搭建了直膨式太阳能热泵热水系统实验装置,研究了辐照强度对直膨式太阳能热泵性能的影响。结果表明,在环境温度及冷凝温度不变的情况下,蒸发温度及性能系数(COP)值随着辐照强度的增大而升高,且辐照强度增加200 W/m2,蒸发温度升高3~5℃,COP值升高0.8~1.2;得热效率随着辐照强度的增大而降低,其降低速率随着辐照强度的增大而逐渐减小。     

R290直膨式太阳能热泵供暖系统实验研究

为分析直膨式太阳能热泵耦合地板辐射供暖系统在北方寒冷地区的实际运行特性,设计并搭建以丙烷(R290)为工质的直膨式太阳能热泵供暖实验平台,分析冬季不同运行工况下环境参数对系统热力性能的影响。实验结果表明：系统可实现室内供暖的稳定性,实验测试期间平均室温保持在16.1～20.8℃之间,热泵系统性能系数(COP)保持在2.57～4.30之间,供暖系统COP保持在2.24～3.98之间。太阳辐照度每增加50 W/m²,热泵系统COP提升4.9%;环境温度每升高1℃,热泵系统COP提升2.4%。太阳辐照度对热泵系统的电子膨胀阀开度和工质质量流量影响较为显著。当终止水温从45℃提升至55℃时,热泵系统COP降低12.2%;而在终止水温为50℃时,供暖系统COP达到最大值3.37。     

不同调节方式对循环加热式CO2热泵性能影响的实验研究

为研究膨胀阀开度和压缩机频率对循环加热式CO₂热泵制热性能的影响,采用实验的方法研究了阀开度35%,37%,40%和频率75,80,85 Hz工况下制热量和制热系数COP瞬时值和平均值以及加热时间的变化。结果表明：随着压缩机频率增加,平均制热量和最大瞬时制热量增加,平均COP和最大瞬时COP减小,加热时间缩短;随着阀开度增大,平均制热量和平均COP减小,最大瞬时制热量和COP增大,加热时间延长;当压缩机频率一定时,在不同的水箱温度范围采用合适的膨胀阀开度可以有效提高热泵的平均COP;以本文75 Hz工况为例,当水温小于25.9℃时采用40%开度,当水温在25.9～35.4℃之间时采用37%开度,当水温大于35.4℃时采用35%开度;合理匹配开度和频率可以最大程度提高平均制热量,同时抑制平均COP的减小。     

EXPERIMENTAL RESEARCH ON TWO NATURAL WORKING FLUIDS OF MODERATELY HIGH TEMPERATURE HEAT PUMP

以筛选适合中高温热泵工况,环境性能优良的自然工质为目标,在理论循环分析基础上,采用指定工质侧参数的循环性能对比实验评价研究方法,在水-水蒸气压缩式热泵实验台上,对理论循环性能优良、样品可得的自然工质HC600(丁烷)、HC600a(异丁烷),在蒸发温度为30 ～ 50℃,冷凝温度为60 ～95℃范围进行实验研究.研究结果表明,两种自然工质中高温热泵循环性能优良,两者在较低温度工况循环性能差别不大,在较高温度工况HC600的循环性能优于HC600a,在蒸发温度为44℃,冷凝温度为90℃时,丁烷和异丁烷COP分别为3.84和3.33,但两种工质的可燃性应引起足够重视.     

变工况下跨临界二氧化碳空气源热泵系统性能的实验研究

以跨临界二氧化碳空气源热泵系统为研究对象,研究了电子膨胀阀开度、压缩机频率对系统COP以及制热量的影响,并提出更高效的热泵运行方案。实验结果表明:在不同的阀开度下,系统COP均出现先上升后下降的趋势,随着加热过程进行,阀开度越大COP下降的幅度越大;压缩机频率的提升会使系统最大COP下降;系统在75 Hz下加热水箱温度至38 ℃后,将系统频率调节至85 Hz可以使系统在保持高COP运行的同时减少加热时长,加热速率提升约18%。     

工质为R415b的空气源热泵热水器性能实验研究

通过对工质为R415b的空气源热泵热水器的性能实验,给出了环境温度和相对湿度不同时,随着水箱内水温的升高,热泵系统内蒸发压力、冷凝压力、压比、吸气温度、液管温度、冷凝侧过热度和过冷度、蒸发侧过热度以及COP的变化规律,指出了空气源热泵热水器的COP不仅随水温动态变化,而且与气温及湿度有关。同时,还对水箱内水的升温规律以及与热泵循环参数的关联进行了研究。     

超临界补气增焓高温CO2热泵热风机实验研究

针对工业上循环加热工况下,CO₂热泵气体冷却器出口温度过高、能效显著降低的问题,文章提出了带有超临界补气的高温CO₂热泵循环,并对系统进行了实验研究。主要分析了主路膨胀阀开度、压缩机频率、气体冷却器的风机频率对出风温度、性能系数COP等参数的影响。实验结果表明:出风温度随着主路膨胀阀开度的增大呈现降低趋势而COP呈升高趋势;降低气体冷却器的风机频率对出风温度的提升效果最为明显,风机频率每调低1%,出风温度最大提升5.07%。以得到最高出风温度为目标的实验数据表明,该系统在气体冷却器出口温度为75℃以上时,出风温度可达130℃以上,对应COP为1.40~1.50。     

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%。     

直膨式太阳能热泵制热性能的对比研究

直膨式太阳能热泵(direct expansion solar assisted heat pump,DX-SAHP)可直接吸收利用太阳能,进而提高热泵的蒸发温度和性能系数(COP),有利于改善热泵的热性能和结霜。本文在带有太阳模拟发射器的焓差实验室中建立直膨式太阳能热泵和常规直彭热泵的对比实验,对不同条件下的热泵系统参数进行测量并进行性能对比和分析。实验结果显示,直膨式太阳能热泵能够吸收太阳能,在辐照度分别为100和200 W/m~2的工况下,系统制热功率比无辐照时的制热功率分别提高9.8%和21.8%,COP分别提高11.7%和23.7%,且除霜启动延迟23 min;辐照度为200 W/m~2时,直膨式太阳能热泵在环境温度5℃下的制热功率比1℃下的制热功率提高16.92%;在室外温度为1℃,相对湿度为95%的工况下,提高太阳辐照度,可有效减小涂层蒸发器进出口温度的波动,提高蒸发器运行的稳定性。此外,直膨式太阳能热泵在运行过程中吸收的太阳辐射被用来蒸发液态制冷剂工质,导致压缩机进气量增加,系统的制热功率和COP提高。     

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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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.     

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.