气膜防冰结构对发动机帽罩表面加热效果的影响

为改善发动机进口帽罩表面加热效果,针对气膜防冰结构开展了数值模拟研究,重点分析了不同吹风比和圆柱孔、腰形孔和气膜缝等3种开孔形状的气膜结构对帽罩表面加热效率的影响。数值研究结果表明：对于圆柱孔和腰形孔气膜结构,随着吹风比增大,气膜出现脱壁现象,最佳吹风比为0.8;对于气膜缝结构,随着吹风比的增大,整体气膜加热效率逐渐增大,在气膜口处有较好的加热效果。     

TR燃烧系统混合气形成过程的数值模拟

一种新型柴油机燃烧系统TR,是由收口深坑ω形燃烧室改进而成,在壁面设置导向圆弧,并与带中孔的多孔喷油嘴相匹配．为研究其气流运动规律和混合气形成机理,应用STAR-CD软件对TR燃烧系统进行三维数值模拟．结果表明,采用4×φ0．36mm 中心喷孔1×φ0．20mm的喷油器,并增加柱塞直径提高供油速率,可将TR 着火点控制在上止点附近,同时减小着火后的燃油喷射量．采用了导向圆弧和中孔喷射,燃烧室内气流运动剧烈, 燃油的空间分布更为合理,空气利用充分,减少壁面散热损失,实现TR系统的“快速燃油喷射、快速混合气形成和快速燃烧”设计思想,并具有良好的冷启动性能．     

旋转状态平板收敛缝形气膜孔改善 冷却效果的数值研究

数值研究了旋转状态下收敛缝形气膜孔结构的冷却特性，并与圆形孔对比，得到收敛缝形气膜孔具有改善气膜冷却效果的特性。结果表明：旋转条件下，气膜的偏移使得展向冷气覆盖的区域增大，收敛缝形气膜孔的展向冷却有效范围明显优于圆形孔，同时对主流的穿透率较低，说明旋转时收敛缝形气膜孔的贴壁性依然较好；各种转速条件下，圆形孔的气膜在大吹风比工况呈现脱离壁面的特点，而收敛缝形气膜孔可以更好地形成气膜保护壁面，从而增强冷却效果；研究范围内，随着吹风比的增加，收敛缝形气膜孔的优势越加明显，虽然气膜孔出口处出现冷却效率稍低的现象，但在冷却范围、冷却效率以及冷却均匀性等方面均优于圆形孔，从而可起到改善冷却效果的作用。     

叶片前缘波纹形气膜孔不同参数冷却特性研究

为了解决涡轮叶片前缘的冷却问题,提出结构简单的波纹形气膜孔的概念。对影响孔冷却特性的4个重要参数(吹风比、倾斜角、扩展角和后倾角),采用4因素4水平下的田口方法进行优化,并采用数值计算的方法将其冷却效率与参考孔型(圆柱形气膜孔)进行对比。其中,固定前缘孔间距30 mm,斜向倾角23°,并与试验保持一致。结果表明：吹风比为1、倾斜角为30°、扩展角为20°和后倾角为0°的波纹形气膜孔结构,壁面平均冷却效率达到0.36,冷却效果最佳;同时,随着吹风比的增大,该气膜孔结构前缘壁面平均冷却效率增长趋势明显,且在吹风比为2时冷却气流依旧具有良好的贴壁性能,壁面平均冷却效率超过圆柱形气膜孔82.96%。     

浅议空芯冲击钻头的设计制作及应用

对空芯冲击钻头和十字形冲击钻头在不同地层中的成孔效率比较，得出了空芯冲击钻头具有成孔进尺快，适用地层广泛，特别是在砂层、砾卵石层、强风化及浅部裂隙发育的中风化等地层中成孔效率更高，可降低施工成本，提高经济效益。     

新型缩放槽缝孔气膜冷却效率的数值研究

基于控制容积法对三维定常不可压缩N-S方程进行离散,采用分区域非结构化网格及两层k-ε湍流模型,在吹风比M=0.6～1.5的情况下,对新型缩放槽缝形气膜孔进行了详细的平板气膜冷却数值汁算,得到了在喷孔射流下游处及叶高方向上的气膜冷却效率,并研究了其孔长与孔径比L/D对冷却效率的影响.计算结果表明:高吹风比对缩放槽缝孔沿中心线冷却效率的影响较为复杂;缩放槽缝形气膜孔下游的冷却效率并不随吹风比的变化而单调变化,而是在吹风比为1.0时存在最佳值;在孔口下游较远区域,两个相邻孔之间沿叶高方向的气膜覆盖性较好;缩放槽缝孔的冷却效率随着其孔长与孔径比L/D的增大而增大,当L/D>8时,增加的幅度趋缓.     

锯片铣刀圆弧齿形的数控加工

本文介绍了活塞环铣油孔锯片圆弧铣刀齿形的加工方法,在原有锯片铣刀的基础上,采用全自动数控装置,进行圆弧加工。相对于手动加工方法进行了改进。即保证了圆弧齿的形状,又提高了加工效率。降低了劳动强度。     

蜂窝陶瓷蓄热体的热应力场数值模拟

对普通正方形格孔蜂窝蓄热体和夹角圆弧过渡正方形格孔蜂窝蓄热体的热应力场进行了数值模拟计算与对比分析.结果表明,夹角圆弧过渡正方形格孔蜂窝蓄热体的低应力区域更大,应力分布也更均匀;数值模拟结果能够指导蓄热体的结构优化设计.     

孔型对水雾/空气气膜冷却特性影响的数值模拟研究

在平板表面分别开设了圆柱孔、展向扩张孔和收缩扩张孔。对比研究了3种孔型的纯空气气膜冷却和水雾/空气气膜冷却特性。在3种吹风比：0.66、1.04、1.44下展开研究。将圆柱孔的数值计算结果与文献中的实验结果进行对照以验证水雾/空气冷却数值计算方法的正确性。对3种孔型下冷却气体混合物的无量纲速度矢量图和部分水雾颗粒的运动轨迹进行了比较和分析。对3种孔型中心线和展向平均气膜冷却效率进行了比较和分析。结果表明：圆柱孔和展向扩张孔射流形成的肾形涡将水雾颗粒抬离平板表面。收缩扩张孔射流形成的肾形涡增强了水雾颗粒的展向扩散并将靠近孔口两侧区域的水雾颗粒逐渐抬离平板表面。对于圆柱孔和展向扩张孔,其射流形成的肾形涡削弱了水雾颗粒对于展向平均气膜冷却效率的提高作用,收缩扩张孔水雾/空气冷却的展向平均气膜冷却效率在3种吹风比下均大于0.6,当吹风比为1.44时,收缩扩张孔的展向平均气膜冷却效率约为展向扩张孔的2倍,圆柱孔的4倍。2种冷却方式下,在吹风比从1.04增大到1.44时,展向扩张孔中心线气膜冷却效率降低0.3左右,而收缩扩张孔中心线冷却效率的降幅小于0.1。     

孔型对水雾/空气气膜冷却特性影响的数值模拟研究

在平板表面分别开设了圆柱孔、展向扩张孔和收缩扩张孔。对比研究了3种孔型的纯空气气膜冷却和水雾/空气气膜冷却特性。在3种吹风比:0. 66、1. 04、1. 44下展开研究。将圆柱孔的数值计算结果与文献中的实验结果进行对照以验证水雾/空气冷却数值计算方法的正确性。对3种孔型下冷却气体混合物的无量纲速度矢量图和部分水雾颗粒的运动轨迹进行了比较和分析。对3种孔型中心线和展向平均气膜冷却效率进行了比较和分析。结果表明:圆柱孔和展向扩张孔射流形成的肾形涡将水雾颗粒抬离平板表面。收缩扩张孔射流形成的肾形涡增强了水雾颗粒的展向扩散并将靠近孔口两侧区域的水雾颗粒逐渐抬离平板表面。对于圆柱孔和展向扩张孔,其射流形成的肾形涡削弱了水雾颗粒对于展向平均气膜冷却效率的提高作用,收缩扩张孔水雾/空气冷却的展向平均气膜冷却效率在3种吹风比下均大于0. 6,当吹风比为1. 44时,收缩扩张孔的展向平均气膜冷却效率约为展向扩张孔的2倍,圆柱孔的4倍。2种冷却方式下,在吹风比从1. 04增大到1. 44时,展向扩张孔中心线气膜冷却效率降低0. 3左右,而收缩扩张孔中心线冷却效率的降幅小于0. 1。     

The impact of disaggregated energy on productivity : A study of the US manufacturing sector, 1958–1985

The issue of the productivity slowdown of the 1970s and 1980s has received considerable analysis in the literature. However, the issue of the impact of energy on productivity is still debated. This study contributes to the debate, with the hope that some sight could be provided through disaggregating the factor input energy into two components; a petroleum component and a non-petroleum component. By analysing labour productivity growth, total factor productivity growth and labour intensity ratios, the disaggregated energy component can be viewed as a major influence in explaining the productivity decline.     

Forests for carbon sequestration or fossil fuel substitution? A sensitivity analysis

Among the proposals for mitigating the increase of atmospheric CO₂ are the possibility of reforesting degraded lands to sequester C or of using sustainable forest harvests to displace fossil fuels. Storing C on-site in forests and harvesting forests for a sustainable flow of forest products are not necessarily conflicting options if we recognize that their relative merits in mitigating net emissions of C will depend on site-specific factors, such as forest productivity and the efficiency with which harvested material is used. Since the land available for reforestation or development of forest plantations is limited, the relative merits of the different mitigation strategies need to be considered. We use a mathematical model of C stocks and flows to compare the net effect on C emissions to the atmosphere for the two approaches over a range of values of forest productivity and the efficiency of product use. When sustainably-produced forest products are used inefficiently to displace fossil fuels, the greater C benefit is achieved through reforestation and protection of standing forests, and increasing the rate of stand growth yields little gain. However, when forest products are used efficiently to displace fossil fuels, sustainable harvest produces the greater net C benefits, and the benefit increases rapidly with increasing productivity.     

An analysis of solar gain through externally shaded window of buildings

The development of computer software for analyzing the solar gain through windows of buildings is presented. The program which is capable of stating the hourly values of solar altitude angles, azimuth angles and extra-terrestrial intensity is written in the BASIC Language. The main feature of the program is that it can be used to determine the hourly values of normal solar intensity and solar energy incident on windows treated with reveals, over-hangs and side-fins. Application of the software in analyzing the solar gain through windows in some experiments yield results which are as consistent as those done manually. The experiments show that in every case, reveals have the effect of reducing the incident solar intensities, and hence incident solar energy on windows. Further analysis shows that over-hangs are much more effective in shading than vertical side-fins.     

基于常规测井资料的试油产能预测评价方法

针对HQ地区长6储层受多期沉积、成岩作用及构造等因素控制,影响储层渗流和产能的因素较多的情况,提出了一种基于储层常规测井资料预测试油产能的分析方法。依据达西产能预测基本方程,并结合油田区块地质特征和生产状况,选取储层自然电位、自然伽马、井径、密度、声波时差、俄罗斯阵列感应、双感应和微电极电阻率为该区油气储层试油产能评价参数,将目的层段储层划分为高、中、低三种产能类型,建立了储层试油产能预测的测井评价指标体系。采用灰色多元加权评价处理方法,对该区26口井31个试油层段进行了试油产能检验。检验结果表明,21口井26个试油产能层段预测评价结果与试油产能结果吻合,试油产能预测符合率达到83.9%;采用该方法克服了单一或局部参数值不能准确表征储层渗流及其产能的缺陷,有效提升了低渗储层产能预测的定量分析及评价能力。     

The effects of electricity reforms on productivity and efficiency of China's fossil-fired power plants: An empirical analysis

This paper investigates the effects of electricity reforms on productivity and efficiency of China's generation plants, based on the third industrial census data and the first economic census data. Partial factor productivity (PFP) analysis indicates that the productivity improvements in labor and capital inputs associated with the reforms are approximately 26% and 45% respectively. The effect of the reforms on fuel expense is weakly significant, but there is evidence of significant productivity improvement in fuel usage. Further total factor productivity (TFP) analysis shows that the efficiency gain from the reforms is still significant when the substitution effect of labor and capital inputs are considered, though the magnitude is much lower than that of the PFP analysis. The effect of the reforms on technical efficiency becomes weakly significant when fuel expense is further included in TFP analysis, but a significant positive effect is expected if fuel input is measured in physical quantity.     

Managing chipper knife wear to increase chip quality and reduce chipping cost

Wood biomass is turned into industrial fuel through chipping. The efficiency of chipping depends on many factors, including chipper knife wear. Chipper knife wear was determined through a long-term follow-up study, conducted at a waste wood recycling yard. Knife wear determined a sharp drop of productivity (>20%) and a severe decay in product quality. Dry sharpening with a grinder mitigated this effect, but it could not replace proper wet sharpening. Increasing the frequency of wet sharpening sessions determined a moderate increase of knife depreciation cost, but it could drastically enhance machine performance and reduce biomass processing cost. Since benefits largely exceed costs, increasing the frequency of wet sharpening sessions may be an effective measure for reducing overall chipping cost. If the main goal of a chipper operator is to increase productivity and/or decrease fuel consumption, then managing knife wear should be a primary target.     

Recent advancements in condensers to enhance the performance of solar still: A review

Pure drinking water sources are continuously decreasing day by day in the world and in contrast requirement is continuously increasing. Solar still is a device, which converts the saline water into pure form at a lower cost and is useful in the remote areas. But its less productivity and low efficiency is a significant issue to use it as potable water provider. Solar still productivity can be increased by using flat plate collectors, fins, evacuated tubes, different absorbing, and nanomaterials, but the major problem on its productivity is heat loss from glass cover to the ambient. Condenser reduces the temperature of the water vapor and maintain the condensation to enhance the productivity. This review shows different modification in the design of condenser attached with solar still to enhance the yield. At last the future work on the condenser is also discussed here.     

Solar-control films

The magnitude of the transmittance of solar radiation through glass is dependent upon its angle of incidence, the emissivity of the glass surface and the length that the light beam travels through the glass. To alter the emissivity of a glass surface a solar-control film can be attached to it. However, none of the present generation of ‘solar’ films that are applied to transparent glass surfaces is able to inhibit insolation gain during the summer while providing satisfactory thermal-radiation insulation with respect to energy leaving the building during the winter. This is because different wavelengths of radiation need to be inhibited for these two processes to be successful, namely short-wave radiation in the case of insolation and long-wave radiation for thermal insulation. Neither of these films inhibits glare satisfactorily. As expected, the energy transmittance and rate of heat gain by the affected room decrease as the angle of incidence (of the energy source, i.e. the sun, with respect to the glass) increases. Also the magnitude of this rate of heat gain depends upon the type (reflective, insulating or absorptive) of solar-control film applied to the glass.     

Investigation into a catalytically controlled reaction gasifier (CCRG) for coal to hydrogen

Energy demands will increase as industrialized nations strive to maintain progress and productivity gains and as developing nations increase their consumption and productivity. One direction that is evolving to satisfy the demand while minimizing environmental impacts is to move toward a hydrogen economy. For the foreseeable future, the majority of these demands will be met through the increased usage of fossil fuels. One of the most abundant and readily available fuels is coal. This realization has raised some questions about the responsible use of such a fuel and as such it is critical that a Greenhouse Gas Management strategy/technology be developed to forestall projected global warming and its impacts.     

Dynamic modelling of a two-phase thermofluidic oscillator for efficient low grade heat utilization: Effect of fluid inertia

In this paper, a promising heat engine technology capable of utilizing low grade heat is examined. Based on a two-phase thermofluidic oscillator concept, the novelty and advantage of this particular system lie in its use of phase change and its lack of reliance on inertia to sustain oscillations, though it is recognized that inertia will always be present in any physical manifestation of the engine. The system is analysed using lumped linearized one-dimensional network models, both with and without inertia, based on thermoacoustic principles and extending these to account for phase change. The gain (temperature difference between source and sink heat exchangers) and frequency at which marginal stability (desirable continuous oscillations) can be achieved is calculated. The effects of the load resistance (fluid drag) and fluid inertia, as well as of the flow resistance due the feedback valve on the marginal stability gain, frequency and exergetic efficiency of the system are investigated. It is found that an increase in feedback resistance leads to a need for a higher gain for oscillatory behaviour to be achieved. In addition, even though an increase in either the resistance or inertia in the load, or the feedback resistance at low values of these variables has almost no effect on the required gain and the oscillation frequency of the system, an increase in these variables can lead at higher values to increased gains and reduced frequencies. A reduced feedback resistance and greater load inertia can also lead to considerably higher efficiencies, while increasing the load resistance allows for an increase in efficiency until a maximum is reached, after which the efficiency decreases again. The validity of certain approximations made previously is considered, and it is shown that these must be made with care. The results from this study can be used for the improved design and optimization of such oscillators, and similar systems.