检索结果-南通市图书馆

基于CO2混合工质的跨临界朗肯循环内燃机余热回收系统稳态性能分析

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

基于CO2混合工质的跨临界朗肯循环内燃机余热回收系统稳态性能分析

作者： muhammad zaman Shakir 天津大学

学位级别：硕士

内燃机是获得机械动力的主要来源之一,它被广泛应用于现代工业中的各个行业,尤其是交通运输领域,并且内燃机仍会在将来很长的一段时间作为主要动力源发挥其重要的作用,特别是在重型卡车和远洋货轮等重型运载工具中。目前中国是全球最大... 详细信息

内燃机是获得机械动力的主要来源之一,它被广泛应用于现代工业中的各个行业,尤其是交通运输领域,并且内燃机仍会在将来很长的一段时间作为主要动力源发挥其重要的作用,特别是在重型卡车和远洋货轮等重型运载工具中。目前中国是全球最大的内燃机制造商。2014年中国内燃机总产量超过8000万台,总功率超过20亿千瓦,占中国石油消耗总量的三分之二。但中国的石油储量较低,人均占有的石油量仅仅为世界平均值的大约11%,面临着严峻的资源紧缺问题。据国家中长期科技发展规划纲要专家组的估计,到2020年左右中国的总石油消费量至少高达4.5亿吨,同时石油对外依存度也会超过60%,这会对国家的能源供给和能源安全造成极大的压力。所以提高内燃机效率,减少石油消耗和污染物排放,对环境保护和国家能源安全具有十分重要的意义。然而,内燃机通常仅仅将30%-40%的输入燃料转变为有用功,大量的能量被烟气,缸套冷却水,机油等带走,造成了大量能量浪费。其中烟气和缸套冷却水是最重要的余热源,分别占输入能量的30%和20%左右。由于烟气和缸套冷却水所蕴含的巨大废热,余热回收成为一项有效提高内燃机效率的关键技术,受到了世界各国政府和各大主要相关企业的广泛重视。例如2014年8月,美国能源部投入5500万美元开展车辆节能减排技术的相关研究以降低车辆的整体油耗,其中就有两个专项是针对内燃机的余热回收技术。中国在2017年1月启动了与美国合作的为期五年的国际合作项目“超级卡车”,旨在将重载货车的燃油经济性在实际道路工况中提高至50%以上,而余热能回收技术是其中一项非常重要的专项课题。在各种不同的余热回收技术中,采用不同工质的朗肯循环因为对内燃机效率提升作用明显,而尤为受到关注。美国康明斯,德国宝马,奥地利AVL等汽车行业的公司都对各种结构和工质的朗肯循环开展了充分的研究,并认为它是进一步提升内燃机效率所必须采用的技术手段。大型船舶主机制造商MAN和瓦锡兰公司也都对内燃机余热回收技术投入了大量的研发力量。但是目前主流的采用有机工质的朗肯循环,存在着与内燃机多品位大温差的热源不相匹配的问题(缸套冷却水80-95℃,烟气500-700℃),既不能对烟气和缸套冷却水的热量同时进行完全的回收利用。另一方面,对于移动装置内燃机余热回收系统的小型化和轻量化至关重要。国际铝协的汽车轻量化研究结果表明,整车的重量每降低10%,大概可降低5%-9%的燃油消耗,尤其是重载卡车的油耗可平均降低高达9%。为了一步提升余热的回收利用率和内燃机的效率,近年来有学者提出CO跨临界朗肯朗循环。这种结构和工质的循环,仅仅通过单级循环就能实现烟气和缸套冷却水余热的完全回收,同时CO在系统小型化和轻量化方面有着非常明显的优势。因为超临界CO具有高气相密度和低液相粘度的物性特征,在微通道换热中可以显著减小流通阻力和减小压降,所以能够实现微通道换热器的在余热回收系统中的应用,从而显著减小系统尺寸;而另一方面超临界CO流体的膨胀比小,但同时单位体积的做功能力大,其膨胀机能够设计成简单的单级小型透平。但是CO跨临界朗肯循环也存在着自身的一些缺点,并在一定程度上限制了它的广泛应用。主要技术问题表现在以下几个方面:1.循环操作压力非常高,通常高达15MPa,给循环的正常运行带来了极大的安全隐患,同时也大大增加了系统的制造和运行成本。***的临界温度低,临界压力高(31℃,7.38MPa),因此在跨临界循环中用普通冷源冷凝CO非常困难,循环对冷源要求很高。***跨临界朗肯循环的热效率普遍低于其他制冷剂循环。为了解决纯CO跨临界朗肯循环的上述问题,提高系统的热力学和经济性能,通过在纯CO中添加其他工质而主动构建流体物性的方法是一种潜在的解决方案。因此,本研究选择了一些不同的有机工质R123,R161,R32,R1234yf,R22,R1234ze,R132a和R152a作为添加剂,以不同组分与CO混合作为系统工质。并广泛探索了以上述CO混合物为工质的跨临界循环系统性能。本文以改善循环性能,冷凝条件和操作压力为目标进行了模拟计算,从而为CO跨临界朗肯循环选择最合适的混合工质提供重要的参考依据,并通过实验研究验证了理论模拟工作。具体研究工作如下所述。在第三章中,本文首先基于本课题组的CO跨临界朗肯循环实验台架的结构形式,选取了带预热器和回热器的预回热循环系统为理论研究对象。详细的带预热过程和回热过程的预回热循环系统主要包括预热器、回热器、蒸发器、膨胀机、冷凝器、工质泵等部件。在这种结构的循环中,二氧化碳工质首先通过预热器回收缸套冷却水的大部分热量,然后流经回热器回收膨胀机出口的乏汽中所含的能量,从而进一步提高工质的温度,同时也减小了冷凝负荷,提升了系统能量利用率;在这之后工质进入蒸发器利用内燃机烟气余热对其进行最后的加热,从蒸发器出来的高温高

关键词：内燃机发动机余热回收跨临界朗肯循环 CO2混合物物理性质计算性能评估

Optimal Campaign in Leptospirosis Epidemic by Multiple Control Variables

同方学位论文库评论

在线全文

同方学位论文库

学校读者我要写书评

暂无评论

Applied Mathematics 2012年第11期3卷 1655-1663页

作者： muhammad Altaf Khan Gul zaman Saeed Islam muhammad Ikhlaq Chohan Department of Business Administration and Accounting Buraimi University College Al-Buraimi Oman Department of Mathematics Abdul Wali Khan University Mardan Pakistan Department of Mathematics University of Malakand Chakdara Lower Dir District of Khyber Pakhtunkhwa Pakistan

In this paper, we consider a leptospirosis epidemic model to implement optimal campaign by using multiple control variables. First, we show the existence of the control problem. Then we derive the conditions under which it is optimal to eradicate the leptospirosis infection and examine the impact of a possible educatioal/vaccinaction campaign using Pontryagin’s Maximum Principle. We completely characterize the optimal control problem and compute the numerical solution of the optimality system using an iterative method. The results obtained from the numerical simulations of the model show that a possible educational/vaccinaction combined with effective treatment regime would reduce the spread of the leptospirosis infection appreciably.

关键词： Mathematical Model Optimal Control Pontryagin’s Maximum Principle Numerical Results

Unsteady Incompressible Couette Flow Problem for the Eyring-Powell Model with Porous Walls

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

American Journal of Computational Mathematics 2013年第4期3卷 313-325页

作者： Haider zaman Murad Ali Shah muhammad Ibrahim Faculty of Numerical Sciences Islamia College University Peshawar Pakistan

This work is concerned with the influence of uniform suction or injection on unsteady incompressible Couette flow for the Eyring-Powell model. The resulting unsteady problem for horizontal velocity field is solved by means of homotopy analysis method (HAM). The characteristics of the horizontal velocity field and wall shear stress are analyzed and discussed. Pade approximants and Taylor polynomials are also found for velocity profile and are used to make the maximum error as small as possible. The graphs of the error for the Pade approximation and Taylor approximation are drawn and discussed. Convergence of the series solution is also discussed with the help of h-curve and interval of convergence is also found.

关键词： Unsteady Couette Flow Eyring-Powell Model Pade Approximants Porous Plates

<i>In Vitro </i>Antibacterial and Antifungal Activity of Methanol, Chloroform and Aqueous Extracts of <i>Origanum vulgare</i>and Their Comparative Analysis

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

International Journal of Organic Chemistry 2011年第4期1卷 257-261页

作者： zaman Ashraf Aun muhammad muhammad Imran Ahmad Hussen Tareq 不详

The work reports antibacterial and antifungal activity of different solvent extracts of Origanum vulgare. The antimicrobial activity of methanol, chloroform and aqueous extracts were determined against nine different gram negative and gram positive bacterial strains and three fungal stains. The bacterial strains were Bacillus subtilis (ATCC 6633), Staphylococcus aureus (ATCC 29213), Micrococcus luteus (ATCC 9341), Pseudo-monas aeruginosa (ATCC 33347), Escherichia coli (ATCC 25922), Salmonella typhi (ATCC 19430), Shig-ella flexneri (ATCC 25929), Salmonella para typhi A (ATCC 9150) and Proteus mirabilis (ATCC 49565) and fungal strains were Aspergillus flavus, Aspergillus nigar and Aspergillus pterus. Agar well diffusion method was followed in this study. The comparative analysis of antibacterial activity reflects that among these three extracts, chloroform and methanol extracts shows promising result by exhibiting maximum anti-bacterial activity, whereas aqueous extract is not active against most of these strains. The analysis of anti-fungal activity reveals chloroform extract as most efficacious unlike methanol and Aqueous extracts.

关键词： Origanum vulgare Antibacterial Activity Antifungal Activity

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

铅冷却快堆紧凑型热交换器流动换热计算

铅冷却快堆紧凑型热交换器流动换热计算

作者： muhammad Mubashar zaman 华北电力大学(北京)

学位级别：硕士

铅冷快堆是第四代反应堆,也称为“固态金属冷堆”。由于铅的密度很高,因此使用铅作为快中子堆的冷却工质是一项具有挑战性的任务。铅冷快堆主回路中的铅冷却是一个基本问题,为此已经提出了许多方法。一种最常见的方法是使用热交换器。... 详细信息

铅冷快堆是第四代反应堆,也称为“固态金属冷堆”。由于铅的密度很高,因此使用铅作为快中子堆的冷却工质是一项具有挑战性的任务。铅冷快堆主回路中的铅冷却是一个基本问题,为此已经提出了许多方法。一种最常见的方法是使用热交换器。但是由于温度高,无法使用简单的热交换器,因而提出一种新方法使用紧凑型热交换器。紧凑型热交换器可承受高温,更重要是尺寸较小,可提供更多的传热表面。因此,本研究的目的是设计一种用于铅冷快堆的热交换器。计算了紧凑型热交换器的流量和换热特性,并将其与其他不同种类的热交换器进行了比较,进而对紧凑型热交换器进行了优化,并比较了标称和优化结果。完成了热交换器流量和传热计算,分析了温度,压力和速度对铅冷快堆热交换器换热性能的影响。温度升高30℃,压降增加250Pa,反之亦然;流速增加0.2 kg/s,温度降低50℃。定义了两个不同的目标函数,包括年度总成本和熵产生单位,并在上述冲突目标之间找到最佳折衷。为此,采用了遗传算法进行多目标优化,评估了热交换器几何设计参数的一组最佳决策。主要优点是提供了一组最佳解决方案和策略,设计人员可以在满足所有约束条件（例如过程约束条件和可用投资）的情况下进行选择。将计算结果与文献调研数据进行了比较。研究结果表明,所设计出的该热交换器的总传热效果提高了 18.8%,年总成本降低了63.5%。与相同参数输入的管壳式热交换器相比较,可获得较低的年度总成本。

关键词：铅冷快堆换热器流量传热率

Molecular study of HCV detection,genotypes and their routes of transmission in North West Frontier Province,Pakistan

同方学位论文库评论

在线全文

同方学位论文库

学校读者我要写书评

暂无评论

Asian Pacific Journal of Tropical Biomedicine 2012年第7期2卷 532-536页

作者： Asher zaman Safi Yasir Waheed Joharia Sadat Solat-Ul-Islam Sadia Salahuddin Umar Saeed muhammad Ashraf Atta-ur-Rahman School of Applied Biosciences(ASAR) National University of Science and Technology(NUST) Lady Reading Hospital(L.R.H)Peshawar

Objective:To determine hepatitis C virus(HCV) genotypes and explore the associated risk factors in chronic HCY ***:A total of 116 patients with chronic hepatitis C were subjected to polymerase chain reaction(PCR) based detection out of which 112 chronic HCV patients[53 male(47.32%),59 female(52.68%);mean age(43.76±16.40) years;mean BMI(23.8± 3.9)kg]were enrolled in this *** frequency of 6 HCV genotypes and associated risk factors were evaluated from five districts of North West Frontier Province(NWFP).Results:Genotype 3was the most prevalent in 73 samples(65.17%) followed by genotype 1 in 24(21.42%) and genotype2 in 13(11.60%) ***3 had significantly high prevalence(P=0.0002).The results showed that 48(42.85%) samples were infected with HCV 3a:25(22.32%) with 3b;14(12.50%) with 1a;10(8.92%)with 1b;11(9.82%) with 2a;2(1.78%) with 2b;and 2 were *** distribution of HCV genotypes in ***,*** and Nowshehra districts was *** of unsterile equipment lor medication,barbers and previous history of hospitalization were the main risk factors for HCV ***:Cenotype 3a and 3b.1a.1b and 2a are the common genotypes in *** *** 6 can not be found in a single *** level of awareness about various modes ot transmission of HCV among the population is found to be verv low.

关键词： HCV Genotypes Subtype 3a Risk factors NWFP Transmission Molecular study PCR

Nucleus-acoustic solitary waves in self-gravitating degenerate quantum plasmas

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Physics B 2018年第4期27卷 191-197页

作者： D M S zaman M Amina P R Dip A A Mamun Department of Physics Jahangirnagar University Department of EEE Bangladesh University of Business and Technology(BUBT)

Nucleus-acoustic（NA） solitary waves（SWs） propagating in a self-gravitating degenerate quantum plasma（SDQP）system（containing non-relativistically degenerate heavy and light nuclei,and non-/ultra-relativistically degenerate electrons） have been theoretically *** modified Korteweg–de Vries（m K-d V） equation has been derived for both planar and non-planar geometry by employing the reductive perturbation *** is shown that the NA SWs exist with positive（negative） electrostatic（self-gravitational） *** is also observed that the effects of non-/ultra-relativistically degenerate electron pressure,dynamics of non-relativistically light nuclei,spherical geometry,*** modify the basic features（e.g.,amplitude,width,speed,etc.） of the NA *** applications of our results,which are relevant to astrophysical compact objects,like white dwarfs and neutron stars,are briefly discussed.

关键词： self-gravitational potential solitary waves

Four-dimensional parameter estimation of plane waves using swarming intelligence

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2014年第7期23卷 754-761页

作者： Fawad zaman Ijaz Mansoor Qureshi Fahad Munir Zafar Ullah Khan Department of Electronic Engineering Faculty of Engineering and Technology International Islamic University Sector H-10 Department of Electrical Engineering Air University

This paper proposes an efficient approach for four-dimensional （4D） parameter estimation of plane waves impinging on a 2-L shape array. The 4D parameters include amplitude, frequency and the two-dimensional （2D） direction of arrival, namely, azimuth and elevation angles. The proposed approach is based on memetic computation, in which the global optimizer, particle swarm optimization is hybridized with a rapid local search technique, pattern search. For this purpose, a new multi-objective fitness function is used. This fitness function is the combination of mean square error and the correlation between the normalized desired and estimated vectors. The proposed hybrid scheme is not only compared with individual performances of particle swarm optimization and pattern search, but also with the performance of the hybrid genetic algorithm and that of the traditional approach. A large number of Monte-Carlo simulations are carried out to validate the performance of the proposed scheme. It gives promising results in terms of estimation accuracy, convergence rate, proximity effect and robustness against noise.

关键词： amplitude estimation direction of arrival estimation frequency estimation genetic algorithm

Itopride for gastric volume,gastric emptying and drinking capacity in functional dyspepsia

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

World Journal of Gastrointestinal Pharmacology and Therapeutics 2017年第1期8卷 74-80页

作者： Shahab Abid Wasim Jafri Maseeh uz zaman Rakhshanda Bilal Safia Awan Aamir Abbas Department of Medicine Aga Khan University Department of Radiology Aga Khan University Pakistan Atomic Energy Commission

AIMTo study the effect of itopride on gastric accommodation, gastric emptying and drinking capacity in functional dyspepsia (FD). METHODSRandomized controlled trial was conducted to check the effect of itopride on gastric accommodation, gastric emptying, capacity of tolerating nutrient liquid and symptoms of FD. We recruited a total of 31 patients having FD on the basis of ROME III criteria. After randomization, itopride was received by 15 patients while 16 patients received placebo. Gastric accommodation was determined using Gastric Scintigraphy. 13C labeled octanoic breadth test was performed to assess gastric emptying. Capacity of tolerating nutrient liquid drink was checked using satiety drinking capacity test. The intervention group comprised of 150 mg itopride. Patients in both arms were followed for 4 wk. RESULTSMean age of the recruited participant 33 years (SD = 7.6) and most of the recruited individuals, i.e., 21 (67.7%) were males. We found that there was no effect of itopride on gastric accommodation as measured at different in volumes in the itopride and control group with the empty stomach (P = 0.14), at 20 min (P = 0.38), 30 min (P = 0.30), 40 min (P = 0.43), 50 min (P = 0.50), 60 min (P = 0.81), 90 min (P = 0.25) and 120 min (P = 0.67). Gastric emptying done on a sub sample (n = 11) showed no significant difference (P = 0.58) between itopride and placebo group. There was no significant improvement in the capacity to tolerate liquid in the itopride group as compared to placebo (P = 0.51). Similarly there was no significant improvement of symptoms as assessed through a composite symptom score (P = 0.74). The change in QT interval in itopride group was not significantly different from placebo (0.10). CONCLUSIONOur study found no effect of itopride on gastric accommodation, gastric emptying and maximum tolerated volume in patients with FD.

关键词： Itopride Gastric emptying Gastric accommodation Functional dyspepsia Dyspepsia