Artificially roughened solar air heater: A comparative study

Artificially roughened solar air heater has been topic in research for the last 30 years. Prediction of heat transfer and fluid flow processes of an artificially roughened solar air heater can be obtained by three approaches: theoretical, experimental, and computational fluid dynamics (CFD). This article provides a comprehensive review of the published literature on the investigations of artificially roughened solar air heater. In the present article, an attempt has been made to present holistic view of various roughness geometries used for creating artificial roughness in solar air heater for heat transfer enhancement. This extensive review reveals that quite a lot of work has been reported on design of artificially roughened solar air heater by experimental approach but only a few studies have been done by theoretical and CFD approaches. Finally this article presents a comparative study of thermo-hydraulic performance of 21 different types of artificial roughness geometries attached on the absorber plate of solar air heater in terms of thermo-hydraulic performance parameter. Heat transfer and friction factor correlations developed by various investigators for different types of artificially roughened solar air heaters have also been reported in this article.     

Optimal heat rejection pressure for transcritical CO2 refrigeration cycle with an expander

Heat rejection pressure plays an important role in designing a transcritical CO₂ refrigeration system, and it has an optimal value to maximize the system’s coefficient of performance (COP). With a thermodynamic simulation model, the optimal heat rejection pressure is studied in the paper for an expander cycle, as well as conventional throttle valve cycle. The effects of compressor efficiency, expander efficiency, gas cooler outlet temperature, and evaporation temperature on the optimal heat rejection pressure are analyzed. It is the first time for a transcritical CO₂ expander cycle that the optimal heat rejection pressure is correlated with the gas cooler outlet temperature and the evaporation temperature at given compressor efficiency and expander efficiency. The average deviation from the correlation to simulation results is less than 1.0%. The correlation provides a guideline to system development and performance optimization of a transcritical CO₂ expander cycle.     

Experimental investigation on engine performances,combustion characteristics and emission of exhaust gases of VCR engine fuelled with cottonseed oil methyl ester blended with diesel

This research work investigates the engine performances, combustion characteristics, and emission of exhaust gases of variable compression ratio engine fuelled with cottonseed oil methyl ester (COME) and diesel at different blends. The analysis showed that heat release rate and cylinder pressure is higher for diesel than COME blends. Higher BTE is obtained at the maximum load condition. The higher BTE and lower SFC are obtained for blend B15 as 42.17% and 0.2 kg/kW-hr at brake mean effective pressure (BMEP) of 4.64 bar. Also it is found that the peak cylinder gas pressure and combustion duration increases when the BMEP increases. At the BMEP of 3.51 bar, higher HRR is observed as 18.12 J/deg. Increase in HRR is obtained as 6.07% for B30 at BMEP of 4.64 bar when compared to diesel. Ignition delay decreased by 13.16% for B100, by the increment of blend proportions when compared to diesel, at BMEP of 4.64 bar. Lower smoke, HC and CO emissions are observed when increasing the blend proportions, whereas the nitric oxide emissions increases due to the better combustion resulted in higher temperatures. At BMEP of 4.64 bar, the CO emissions are reduced to 25.24% for neat biodiesel when compared with the diesel.     

中原经济区能源消费视角下的大气环境压力评估

研究以能源消费模式为切入点,分析中原经济区能源消费总量、消费结构和利用效率的现状水平,并分析能源消费引起的大气环境压力状况。基于经济发展速度调控及节能减排力度的不同,设置2020年三种能源消费情景,使用区域能源消费总量优化模型模拟预测不同情景下的能源消费总量,并分析不同情景下的大气环境压力。结果表明,快速发展和适度发展Ⅰ情景下,2020年区域能源消费总量将比2012年增加4.2×10~8tce和2.4×10~8tce,煤炭消费总量将增加3.1×10~8tce和1.2×10~8tce,大气污染物排放压力增加30%和50%;适度发展Ⅱ情景下,能源消费总量将增加0.2×10~8tce,煤炭消费总量将下降0.3×10~8tce,大气污染物排放压力将降低20%。因此,要实现经济发展稳步增长(年均增长率7.7%)和大气污染物排放总量削减10%目标,重中之重是实现煤炭消费总量"零增长"或"负增长",同时力争能源消费总量控制在5×10~8~6×10~8tce,凭借煤炭占比大幅下降(降至65%左右)最大限度发挥能源供给领域节能效应,依靠产业结构升级节能效应和技术节能拓展能源消费领域节能空间,将能效水平提高至0.6tce/万元以下。     

湖北省耕地非农化压力的时空演变格局

耕地非农化压力及其区域差异是建设用地指标区际配置的基础。湖北省社会经济发展与城镇化水平存在显著的区域差异,耕地非农化压力区际差异明显。通过对比人均建设用地指标的理论值与实际值之间的差异开展湖北省耕地非农化压力的时空格局研究,结合重心迁移模型,采用Arc GIS空间分析方法揭示了湖北省耕地非农化压力的时空演化路径。结果表明:(1)湖北省耕地非农化压力存在显著的区域差异,西部地区中恩施市的耕地非农化压力较大,其他城市耕地非农化压力较小且相对变化较小;东部地区的耕地非农化压力较大且相对变化较大;(2)2000~2011年,湖北省耕地非农化压力的重心总体向东北方向迁移,表明湖北省东部一些城市的耕地非农化压力相对西部一些城市的增长较大。(3)重心迁移距离为17.37 km,相对较小,表明湖北省耕地非农化压力于2000~2011年整体变化相对稳定。     

上流式厌氧污泥床反应器处理饮料废水

通过监测西安可口可乐饮料有限公司污水处理站的上流式厌氧污泥床(UASB)反应器,探讨饮料废水厌氧处理过程中COD去除率、沼气组分、氢分压、出水挥发性脂肪酸、产甲烷活性以及污泥形态。结果表明,UASB反应器对饮料废水中的COD去除率达到84.55%,产生的沼气中甲烷组分含量高达74.5%。反应器内的氢分压仅2.5 Pa,为水解发酵和产氢产乙酸过程创造了良好的条件。UASB反应器中污泥具有较高的产甲烷活性,以乙酸、丙酸和丁酸为基质时,最大比产甲烷活性分别为407.14、331.74和241.27 m L CH4/(g VSS·d)。UASB反应器中的污泥形态主要为絮状,甲烷菌中的优势菌为甲烷丝菌,同时存在少量甲烷杆菌。针对该厂UASB反应器中污泥的现状,提出了影响颗粒化的因素和控制措施,为后期的运行和管理提供了参考依据。     

新型低气阻高效除尘器的研究与应用

为了提高除尘器对细颗粒物的捕捉效率,制备了一种由蜂窝陶瓷、聚酰胺材质扭线刷和缚尘剂组成的除尘模块。其中填充了聚酰胺扭线刷的蜂窝陶瓷为除尘模块的主体,该主体独有的结构将拦截尘粒的滤料纤维分布在与气流方向垂直的平面上,有利于含尘气体的捕捉。缚尘剂为除尘模块的增强因子,它可以在除尘模块表面形成液膜,用来抑制除尘时的二次扬尘,提高除尘效率。通过对涂覆有缚尘剂的除尘模块的除尘效率的研究表明,含尘气体通过除尘模块,对粒径2μm的颗粒除尘效率最高可达到97.08%,表明了除尘模块去除细颗粒物的潜力;另外,在实验中设定的条件下,系统的压降保持在85 Pa以下。总体而言,该除尘模块在保持较低压降的同时对细颗粒物有较高的去除效率,有应用在工业除尘的潜力。     

不干胶废弃物热重分析

为了探索不干胶类包装废弃物的热解特性,采用热重分析手段分析了不同升温速率条件下不干胶类废弃物的失重特点,并且采用Ozawa法和KAS法比较分析不同转化率条件下的表观活化能分布.热重分析结果表明,不干胶类废弃物的热解主要分为3个阶段:第1阶段(室温～ 200℃)为不干胶类废弃物的干燥阶段,第2阶段(200 ～ 590℃)为热解的主要阶段,第3阶段(590 ～800℃)为热解半焦的深度热解阶段.升温速率对热解失重率有重要影响,Ozawa法和KAS法计算结果表明,2种方法计算的热解活化能比较接近,Ozawa法得到的活化能为349.9 kJ/mol,KAS法得到的活化能为336.9kJ/mol;并且不干胶类废弃物的热解表观活化能呈现出阶段性分布.     

变压吸附技术分离模拟油田火驱尾气中的CO_2

采用变压吸附技术分离模拟油田火驱尾气(CO_2-N_2-CH_4混合体系)中的CO_2。考察了吸附压力、吸附温度和气体流量对吸附效果的影响。实验结果表明:在吸附温度为25℃、吸附压力为0.6 MPa、气体流量为2 000m L/min、初始CO_2体积分数为13.01%的条件下,CO_2的穿透吸附量为60.34 m L/g,CO_2吸附率为78.92%,碳分子筛对CO_2的分离因子为8.233;在床层利用率为0.523的条件下进行降压解吸,当吸附压力降至0.1 MPa时,出口CO_2体积分数约为80%,CO_2的回收率可达96.38%。     

汽轮机回热系统安全运行与节能降耗

通过对300 MW汽轮机回热加热系统运行现状调查,分析了加热器端差异常和易发生泄漏原因,并制定了相应的对策。探索了远场涡流检测技术在高压加热器检验中的应用规律,通过高低水位调整试验确定了其最佳运行方式,对高压加热器的设计、制造及运行具有借鉴意义。