海水淡化喷嘴分布特性的实验研究

为验证国产喷嘴性能,对低温多效海水淡化用进口M5型工程喷嘴和一种国产研制型蓝色喷嘴做了单喷嘴的喷淋布液分布实验,对比分析了这2种喷嘴的全周向喷淋布液分布特性以及喷淋流量和盐水浓度对其布液分布的影响。实验结果表明：研制型蓝色喷嘴与M5型喷嘴的喷淋布液分布规律基本一致;单喷嘴喷淋布液规律并不随流量的增大而发生大的变化;盐水浓度对喷嘴的喷淋布液分布规律影响不大。实验证明国产喷嘴性能良好,满足工程应用要求。     

Triethylamine as an initiator for cracking of heptane

Triethylamine was found to be effective in promoting the cracking of heptane at the temperature of 550–650 °C. The experimental yields of ethylene and propylene are more than twice as high as the calculated values on hypothesis of no interaction between triethylamine and heptane, when the mass fraction reaches 6% at the most notable temperature of 550 °C. The accelerating mechanism is studied by gas chromatography–mass spectrometry (GC–MS) and it shows that the accelerating effect is mainly attributed to the initiative release of CH₃CH₂ from triethylamine by the scission of the C–N bond.     

Concept for on orbit liquid hydrogen test bed

There is growing interest in the utilization of cryogenic propellants for future space missions. The utilization of these propellants for long duration in space presents substantial challenges in fluid management in the low g environment. Lockheed Martin (LM) is developing the concept for a space borne system for demonstration of long term storage, various fluid management tests involving control of tank pressure, location and identification of vapor and liquid phases, venting in low g, mass gauging, and extension of life with cryocoolers and location of liquid for transfer. In addition the concept includes autonomous coupling and hydrogen transfer from tank to tank. The concept is based on a flight qualified flight proven hydrogen Dewar design from a previous program The concept for this system is described.     

An experimental study on flow patterns and heat transfer characteristics during cryogenic chilldown in a vertical pipe

In the present paper, the experimental results of a cryogenic chilldown process are reported. The physical phenomena involve unsteady two-phase vapor–liquid flow and intense boiling heat transfer of the cryogenic fluid that is coupled with the transient heat conduction inside pipe walls. The objective for the present study is to compare the chilldown rates and flow patterns between the upward flow and downward flow in a vertical pipe. Liquid nitrogen is employed as the working fluid and the test section is a vertical straight segment of a Pyrex glass pipe with an inner diameter of 8 mm. The effects of mass flow rate on the flow patterns, heat transfer characteristics and interface movement were determined through experiments performed under several different mass flow rates. Through flow visualization, measurement and analysis on the flow patterns and temperature variations, a physical explanation of the vertical chilldown is given. By observing the process and analyzing the results, it is concluded that pipe chilldown in a vertical flow is similar to that in microgravity to some extent.     

Study on steam-carrying effect in static flash evaporation

Study on steam-carrying effect in static flash of both pure water and aqueous NaCl solution was present. Properties, including steam-carrying ratio, waterfilm height drop and equilibrium concentration of waterfilm, were measured in experiments. Their dependences on separating height, initial waterfilm concentration and mean pressure difference were analyzed. Particularly, steam-carrying ratio was defined as the mass ratio of be-carried liquid and generated steam. Results suggested that this ratio increased with the decreasing of separating height or the rising of initial waterfilm concentration, and a peak value existed in its evolution versus mean pressure difference. At last, according to experimental results and basic principles a calculating model for steam-carrying effect in static flash was built.     

槽式太阳能电站集热管热性能测试

采用硅碳棒加热技术和热平衡法测试了桑普生产的具有自主知识产权的槽式太阳能电站集热管的热性能。在40～300℃温度范围内,共测试8个工况下集热管热性能。实验结果显示,集热管中低温性能与肖特公司的PTR70相差不大,完全满足中低温槽式太阳能电站和其他太阳能中低温利用领域的应用。红外图像结果表明,玻璃-金属封接温度明显高于玻璃外管温度,对集热管进行理论分析时不能忽略此部分漏热量。实验数据的获得为国内太阳能槽式电站的设计、建设提供了实验参数,为集热管漏热测试相关标准的制定提供了基础。     

Electromagnetic and microwave-absorbing properties of magnetite decorated multiwalled carbon nanotubes prepared with poly(N-vinyl-2-pyrrolidone)

The magnetite (Fe₃O₄) decorated multiwalled carbon nanotubes (MWNTs) hybrids were prepared by an in situ chemical precipitation method using poly(N-vinyl-2-pyrrolidone) (PVP) as dispersant. The structure and morphology of hybrids are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron-microscopy (TEM). The TEM investigation shows that the Fe₃O₄/MWNTs hybrids exhibit less entangled structure and many more Fe₃O₄ particles are attached homogeneously on the surface of MWNTs, which indicated that PVP can indeed help MWNTs to disperse in isolated form. The electromagnetic and absorbing properties were investigated in a frequency of 2–18 GHz. The results show that the Fe₃O₄/MWNTs hybrids exhibit a superparamagnetic behavior and possess a saturation magnetization of 22.9 emu/g. The maximum reflection loss is ?35.8 dB at 8.56 GHz, and the bandwidth below ?10 dB is more than 2.32 GHz. More importantly, a new reflection loss peak occurs at the frequency of 14.6 GHz, which indicates that the Fe₃O₄/MWNTs hybrids have better absorption properties in the high-frequency.     

采用不同膨胀机构的跨临界CO2循环性能分析

运用热力学第一定律和第二定律对跨临界CO2基本循环、膨胀机循环、喷射器循环和涡流管循环进行了分析,计算了各循环各个部件的损失,比较了各循环性能系数和总损失。计算结果表明,采用膨胀机、喷射器和涡流管等膨胀设备代替基本循环中的节流阀后,由于这些改进膨胀设备的损失小于基本循环节流阀的损失,同时改进循环中压缩机的损失小于基本循环的压缩机损失,从而减小了循环总损失,提高了循环的COP。膨胀机循环的COP远大于其它跨临界CO2循环,其次为喷射器循环和涡流管循环。     

Correlations and optimization of a heat exchanger with offset-strip fins

The thermo-flow characteristics of a heat exchanger with offset-strip fins are numerically investigated for various fin geometries and working fluids. Previous correlations underestimate f values in the laminar and turbulent regimes and overestimate j values in the laminar regime, as the blockage ratio increase. Therefore, new correlations, which apply to offset-strip fins with blockage ratios of greater than 20%, are presented. Even though the working fluid was changed, the f values did not vary. However, the j values differed according to the working fluid. New j correlations were suggested as functions of the Prandtl number. Design variables of the offset-strip fins in a fuel cooler were optimized by using the correlations and the design of experiment. As a result, the JF factor of the optimized offset-strip fin was enhanced by 24% compared with that of the reference offset-strip fin.     

Combustion and emission characteristics of a diesel engine fuelled with diesel–propane blends

In this paper, the combustion and emission characteristics of a direct injection diesel engine operating on diesel–propane blends were investigated. The results showed that under the same operating condition, the effective thermal efficiency increased with the increase of propane proportion in the blends. Ignition delay and combustion durations of diesel–propane blends were decreased with the increase of propane proportion in the blends. Maximum cylinder pressure, maximum rate of pressure rise, maximum rate of heat release and maximum mean combustion temperature of the diesel–propane blends increased with the increase of propane proportion in the blends. Simultaneous reduction in exhaust CO, HC and smoke emissions could be realized when operating on the diesel–propane blends. Exhaust NO_x emission gave an increasing trend when operating on the diesel–propane blends.