Catalytic Cracking and Heat Sink Capacity of Aviation Kerosene Under Supercritical Conditions

Catalytic cracking of China no. 3 aviation kerosene using a zeolite catalyst was investigated under supercritical conditions. A three-stage heating/cracking system was specially designed to be capable of heating 0.8 kg kerosene to a temperature of 1050 K and pressure of 7.0 MPa with maximum mass flow rate of 80 g/s. Sonic nozzles of different diameters were used to calibrate and monitor the mass flow rate of the cracked fuel mixture. With proper experiment arrangements, the mass flow rate per unit throat area of the cracked fuel mixture was found to well correlate with the extent of fuel conversion. The gaseous products obtained from fuel cracking under different conditions were also analyzed using gas chromatography. Composition analysis showed that the average molecular weight of the resulting gaseous products and the fuel mass conversion percentage were a strong function of the fuel temperature and were only slightly affected by the fuel pressure. The fuel conversion was also shown to depend on the fuel residence time in the reactor, as expected. Furthermore, the heat sink levels due to sensible heating and endothermic cracking were determined and compared at varying test conditions. It was found that at a fuel temperature of similar to 1050 K, the total heat sink reached similar to 3.4 MJ/kg, in which chemical heat sink accounted for similar to 1.5 MJ/kg

Performance of supersonic model combustors with distributed injection of supercritical kerosene

Supersonic model combustors with two-staged injections of supercritical kerosene were experimentally investigated in both Mach 2.5 and 3.0 facilities with the stagnation temperatures of approximately 1750K. Supercritical kerosene at temperatures of approximately 760K and various pressures was prepared using a two-staged heater developed in Ref. 1 and injected at equivalence ratios of 0.98 to 1.46. Two pairs of integrated injector/flameholder cavity models in tandem were used to facilitate the fuel-air mixing and stabilize the combustion. Combustor performances with different fuel injection locations, injector numbers, combinations of injection stages, and combustor entry Mach numbers were investigated systematically and discussed based on the measured static pressure distributions and the specific thrust increments due to combustion. With two-staged fuel injections the overall performance of the combustors was shown to be improved and fuel injections at equivalence ratio higher than unity could be reached without combustor-inlet interaction. Reducing the number of injectors while increased its diameter was very effective to increase the pressure rise in the combustor with single-stage injections but had little effect on the combustor performance with two-staged fuel injections. Increasing the entry Mach number resulted in lower combustion levels, in particular, with fuel injections at locations close to the combustor exit but was balanced with two-staged fuel injections

Thermal cracking of aviation kerosene for scramjet applications

Thermal cracking of China No.3 aviation kerosene was studied experimentally and analytically under supercritical conditions relevant to regenerative cooling system for Mach-6 scramjet applications. A two-stage heated tube system with cracked products collection/analysis was used and it can achieve a fuel temperature range of 700-1100 K, a pressure range of 3.5-4.5 MPa and a residence time of approximately 0.5-1.3 s. Compositions of the cracked gaseous products and mass flow rate of the kerosene flow at varied temperatures and pressures were obtained experimentally. A one-step lumped model was developed with the cracked mixtures grouped into three categories: unreacted kerosene, gaseous products and residuals including liquid products and carbon deposits. Based on the model, fuel conversion on the mass basis, the reaction rate and the residence time were estimated as functions of temperature. Meanwhile, a sonic nozzle was used for the control of the mass flow rate of the cracked kerosene, and correlation of the mass flow rate gives a good agreement with the measurements

Heat Transfer of Aviation Kerosene at Supercritical Conditions

The heat transfer characteristics of China no. 3 kerosene were investigated experimentally and analytically under conditions relevant to a regenerative cooling system for scramjet applications. A test facility developed for the present study can handle kerosene in a temperature range of 300-1000 K, a pressure range of 2.6-5 MPa, and a mass How rate range of 10-100 g/s. In addition, the test section was uniquely designed such that both the wall temperature and the bulk fuel temperature were measured at the same location along the flowpath. The measured temperature distributions were then used to analytically deduce the local heat transfer characteristics. A 10-component kerosene surrogate was proposed and employed to calculate the fuel thermodynamic and transport properties that were required in the heat transfer analysis. Results revealed drastic changes in the fuel flow properties and heat transfer characteristics when kerosene approached its critical state. Convective heat transfer enhancement was also found as kerosene became supercritical. The heat transfer correlation in the relatively low-fuel-temperature region yielded a similar result to other commonly used jet fuels, such as JP-7 and JP-8, at compressed liquid states. In the high-fuel-temperature region, near and beyond the critical temperature, heat transfer enhancement was observed; hence, the associated correlation showed a more significant Reynolds number dependency

牛姆林自然保护区常绿针阔叶混交林群落特征初探

对福建省牛姆林自然保护区常绿针阔叶混交林的区系组成、地理成分、垂直结构、物种多样性等特征研究结果表明,该混交林群落维管植物种类组成丰富,600m~2样地内有38科62属119种,其中以常绿高位芽植物占绝对优势;种子植物地理成分中热带性质属37属占64.91％,温带成分19属占33.33％;群落分层现象明显,乔木层可分4个亚层,乔、灌木及藤本植物种类和数量均丰富,草本植物较少;比较群落各部分多样性水平为灌木层>乔木层>草本层>层间植物

低龄DDH患儿初次开放复位术中股骨截骨必要性的前瞻性随机对照试验研究方案

回顾性研究发现,股骨截骨术并非低龄DDH患儿手术治疗所必须的,而应根据患儿具体情况合理选择;本研究通过多中心前瞻性研究进一步探讨对于18个月至3岁DDH患儿是否要行股骨截骨术。FSODDH项目为一项多中心前瞻性随机对照临床试验研究。研究设计拟招募200名单侧低龄DDH患儿,随机分成股骨截骨组(n=100)和股骨不截骨组(n=100)。股骨截骨组患儿全部采取髋关节开放复位术、骨盆截骨术及股骨截骨术治疗;股骨不截骨组患儿全部采取髋关节开放复位术及骨盆截骨术治疗;术后定期随访至少2年。收集术前、术后1周、术后1个月、术后3个月、术后6个月、术后1年及术后2年的髋关节正位X线影像资料,比较两组患儿的髋臼指数、股骨头坏死率、再脱位率、术中出血量、手术时间和住院天数等临床指标。这一多中心前瞻性研究将能为低龄DDH患儿是否需行股骨截骨术提供循证医学证据

Flow rate analyses and calibrations of kerosene cracking for supersonic combustion

Measurements of kerosene conversion due to thermal cracking and mass flow rate through a sonic nozzle have been made under supercritical conditions. Based on the temperature dependency of mole fraction of gaseous products from kerosene cracking, a one-step cracking model has been proposed to correlate the kerosene conversion and the mass flow rate through a sonic nozzle. In this model, the cracked kerosene was described as a three-component ideal gas mixture (IGM) of unreacted kerosene, gaseous products after cooled to room temperature and residuals. The composition of unreacted kerosene and gaseous products were determined by a gas chromatography, while the approximate chemical formula of the residuals was derived from the average molecular weight of cracked kerosene mixture at high temperature. The mass flow rate of cracked kerosene was then calculated from ideal gas law for the three-component mixture. Agreement was obtained when comparing the calculated mass flow rate with the measurements. Kerosene residence time and the rate constant of conversion inside a heater were also discussed based on this global cracking model

航空煤油超声速稳定燃烧贫富油极限实验研究

本文采用了直联式超燃实验平台，以凹腔稳定器为例，在入口马赫数2.35燃烧室中，研究了来流总温1950-2250 K范围内，单侧凹腔底部喷注超临界态煤油的超声速燃烧特性及火焰稳定性，获得了贫油和富油熄火极限的实验数据，并通过单一的参数Damkohler数对熄火极限实验数据进行了拟合

Cloud-Based Per formance Testing Service

云计算作为一种新型的计算资源交付模型，为软件性能测试带来了新的机遇。设计了一种四层架构的性能测试服务平台，实现传统性能测试软件向云计算环境的迁移，同时设计一种准入控制和任务调度算法，实现负载发生资源的共享管理和动态分配，满足多租户性能测试需求。基于上述工作，完成已有性能测试工具 Bench4Q的迁移。 Cloud computing has emerged as a new paradigm for delivery of computing resources. It has brought great opportunities to performance testing. A four layer model for cloud-based performance testing is proposed. At the same time, an admission control and scheduling algorithm is also designed. All this can achieve the flexible management and dynamic dispatch of shared resources, which are pooled for load generation. The requirements of multi-tenancy can also be implemented. Based on the above mentioned proposition, an available tool, Bench4Q is migrated to the cloud

某水库及水系林丹污染对食品与饮水的影响

目的　为探讨某水库及周围水系大面积水域农药(林丹)污染是否对相关生物的食物链、生活饮用水造成污染。方法　1998～2 0 0 1年对该水系的浅层地下水、粮食、奶、蛋类和鱼进行了跟踪调查。结果　该水系周围食物链、生活饮用水中有不同程度的林丹检出。结论　林丹有较强的生物富集作用,该污染水平对人体健康的影响应给予高度重视