定形相变贮能式地板辐射采暖系统的实验研究

作者在北京采暖季节对相变贮能式地板辐射采暖系统进行了实验研究。该系统采用厚度为2cm，熔点和潜热分别为21．6℃和37J／g的定形相变材料。作为比较，也对普通地板采暖系统进行了对比实验研究，发现：相变贮能式地板辐射采暖系统在实验期间基本上每天开启8～10h，在维持室内温度高于对比试验的情形下，运行费用低于对比试验中的普通地板采暖系统。此外，由于相变材料具有较好的贮热能力，电加热系统的启停造成的室内温度波动较小，变化平缓；试验房间内各壁面温度较高，且波动很小，从而提高了室内的平均辐射温度，这也是地板辐射采暖舒适和节能的原因之一。     

电加热相变材料蓄热地板采暖的热性能模拟

为消除电采暖引起的电网峰谷差并降低采暖运行费用，该文提出了一种带有相变材料潜热贮能板的地板电采暖系统，并建立了分析此系统热性能的地板和房间理论模型，对给定的电加热相变蓄热地板采暖房间，模拟了室内空气温度和地面温度的变化，藉此分析了我国几个气候地区冬季该系统的应用效果，结果证明此采暖方式在使房间热负荷不大的建筑和气候条件下，基本能满足人的热舒适性要求，有较好的应用前景。     

低温热水型相变蓄能地板采暖房间动态热性能研究

提出一种采用相变材料蓄能的低温热水地板采暖系统形式。建立反映该采暖地板在应用房间中动态传热过程的数学模型,该模型可用于模拟研究不同材料蓄能地板在房间中的热性能;对比研究低温热水型相变材料潜热蓄能式采暖地板与混凝土显热蓄能式采暖地板的热性能差异。分析相变材料的相变温度、相变潜热和导热系数等因素对该地板采暖房间热性能的影响。研究结果显示相变材料潜热蓄能式地板具有蓄热效率高、室内温度波动小和室内平均温度高等特点。     

相变蓄热板材用于电加热地板采暖的节能效果研究

采用等效比热法和全隐式有限差分格式,编程对影响相变蓄热板材(PCTSP)作为电加热地板采暖系统填充层节能效果的因素(加热方式、相变温度、相变半径、潜热及热导率)进行参数化研究。结果表明:将20mm厚的PCTSP用作填充层,相对于40mm厚碎石混凝土作为填充层来说:①当PCTSP的热物性给定时,采用不同的加热模式,基于总能耗的节能率是完全不同的,同时能够取得节能效果的相变温度范围也不同;②对于第一种加热模式,热导率、相变半径和潜热越大,能够取得节能效果的相变温度范围越宽,即相变材料的选择自由度越大。     

结合太阳能空气集热器的定形相变蓄能地板采暖系统实验研究

提出了一种与太阳能空气集热器结合的定形相变蓄能地板采暖系统充分利用太阳能.白天,由太阳能空气集热器加热后的热空气通过保温管道输送到相变地板夹层,相变材料(PCM)蓄热;夜间,房间的冷空气进入相变地板夹层,被加热后送入房间,相变材料放热.可行性实验研究表明,此采暖系统安全可靠,能显著提高窒内温度,房间各处受热均匀,热舒适性较好,有一定的应用前景.     

地板下送风式相变蓄热电采暖系统

提出了一种利用定形相变材料蓄存夜间廉价电热，并能控制放热速率的地板下送风式相变蓄热电采暖系统。可有效利用夜间廉价电并提高室内环境热舒适性，搭建了应用此采暖系统的实验房间，测量了系统和室内空气的温度变化，分析了此采暖方式的使用效果。结果表明，该系统蓄放热性能较好。白天的电热负荷全部转移到夜间低谷电价时段，白天供热量可借送风量调节，冬季采用该系统供暖可满足热舒适的要求。     

金属基相变材料的研究进展及应用

金属基相变材料由于具有储能密度高、热稳定性好、热导率高等优点,在潜热热能储存系统中具有极大的优势。本文回顾了金属基相变材料的发展历程,归纳了金属基相变材料的性能参数,总结了各种热物性的测量方法,探讨了金属基相变材料与容器材料的相容性问题,分析了金属基相变材料在太阳能热发电、工业余热回收和电力削峰填谷中的应用前景。金属基相变材料的高温腐蚀性是目前限制其在热控制中应用的主要因素。为了实现金属基相变材料的广泛应用,需要重点解决金属基相变材料的封装问题。     

RT6/纳米铝相变蓄冷材料的热物性研究

石蜡类相变材料RT6相变潜热高,相变温度低,化学性质稳定,但其具有导热系数低,蓄能时间长的缺点,固采用纳米粒子强化换热。通过粒度观测法选取分散稳定性较好的纳米Al粒子制备纳米相变材料,实验分析强化后的相变过程、纳米流体石蜡/纳米铝的导热性和相变特性。实验结果表明,复合材料稳定性好,相变温度基本不变为4～8℃,相变焓值略有下降,但导热系数明显提高,可以作为蓄冷系统的新型蓄冷材料广泛应用。     

相变材料和隔热材料在不同地区建筑中应用效果之比较分析

利用典型气象年逐时数据,讨论了5个热工分区中典型城市的建筑采用外保温或相变材料后,全年室温和采暖空调能耗的变化情况,并分别采用"全年累计满足舒适度小时数"和"单位面积耗电量"作为两种材料在被动式和主动式建筑中应用效果的评价指标,结合"峰谷电价"、采暖或空调运行费用和材料的初投资,对其在不同地区的应用进行了可行性分析。研究发现:外保温随采暖能耗在整个建筑能耗中比例的增大而愈显重要;内墙为相变材料可使被动式建筑夏季具有较好的舒适度,使主动式建筑夏季空调能耗降低,但其成本较高,北京、上海和广州地区投资回收期至少为15a;在仅需考虑采暖需求的哈尔滨地区,相变蓄能式地板采暖系统节能效果较好,投资回收期可控制在5a,但采用外保温比相变材料更具经济性,投资回收期仅为1.5a。     

基于分时电价的热泵供热系统相变储热应用研究

中国提出“双碳”战略,推进可再生能源利用和供热电气化,降低电供热成本已成为迫切需求。本文提出了一种新型含相变储热的热泵供热系统。供热系统利用富余的可再生能源发电量或谷电储热,在可再生能源间歇期或峰电时段放热,实现热电解耦、削峰填谷,提高系统经济性。基于相变储热装置使用的灵活性,控制策略可根据可再生能源发电特性或分时电价时段动态调整。本研究测试以谷电为主要驱动能源的系统运行特性,分析不同储热时间和储热容量对系统经济性的影响,在青海高海拔地区进行供热实验。结果表明,含相变储热的热泵供热系统比热泵直接供热耗电量成本降低5.28%;储能容量为75 kWh时,通过调节控制策略改变储热时间可使系统能耗和运行成本分别降低5.69%、13.5%;增加储能容量至150 kWh可调节峰谷电用量,谷电占比最高可达84.52%,运行成本可再降低10.04%。含相变储热的热泵供热系统具有良好的经济效益,合理利用其热电解耦特性可助力可再生能源消纳和电网稳定运行。     

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%.     

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.     

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.     

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。