Extrusion of pastes with a piston extruder for the determination of the local solid and fluid concentration, the local porosity and saturation and displacement profiles by means of NMR imaging

 Nuclear Magnetic Resonance (NMR) was used to investigate the extrusion behaviour of PTFE pastes in a ram extruder. By means of ¹H-NMR imaging (MRI) it is possible to determine the local proton density and therefore, the local fluid concentration. The ¹⁹F-MRI provides the local solid concentration. Thus the local saturation and the local porosity can be calculated with the information of the local fluid and solid concentration. Furthermore displacement profiles can be derived from NMR images by means of correlation techniques without any preparation or marking of the pastes. Received: 8 May 2000   Accepted: 1 May 2001     

柴油机活塞环组-缸套润滑状态和摩擦功耗的分析方法和应用(英文)

本文研究了表面粗糙度对柴油机活塞环—缸套摩擦副润滑性能的影响。文中考虑了温度效应,从而克服了以往分析这类问题的数学模型所存在的缺陷。此外,文中还介绍了本文作者在S195柴油机内按装的测量油膜厚度的遥测新方法。测量结果和分析计算结果一致。最后,文中还定量地给出了S195柴油机活塞环组摩擦功耗的大小。     

一类二热源热机的有限时间热力学分析

应用有限时间热力学理论研究一类以理想气体为工质,热交换过程是不可逆的活塞式二热源热机,探讨热阻及活塞运动对热机性能的影响,导出其基本优化关系,并应用它讨论热机的优化性能,得到一些有意义的新结论。     

Obturator and detonation experiments in the subdetonative ram accelerator

An experimental investigation has been undertaken to improve understanding of the role of the obturator and detonations in the subdetonative ram accelerator starting process. Ram accelerator start experiments were conducted with various obturator geometries to determine the obturator dynamics and assess its effect on the outcome of a start attempt. The obturator rapidly decelerates upon entrance and then moves backwards. Reversal of direction occurs more rapidly after propellant ignition, for less massive obturators, and solid geometries. Perforated geometries and decreasing obturator mass are less conducive to igniting a given propellant, as evidenced by the flowfield and start attempt outcome data presented. Wave unstarts were observed to occur with and without detonations, indicating more than one mechanism responsible for this type of start failure. Piston-initiated detonation experiments were conducted by firing the obturators without the ram accelerator projectile. The piston experiments identified the detonation limits for a wide range of propellants, but were found to not always be indicative of the upper Mach number at which a ram accelerator can be successfully started. In some instances a successful start or wave fall-off would occur at Mach numbers above which a piston alone detonated the propellant. Thus, the projectile can play a mitigating role in detonation initiation and use of piston detonation limits to quantitatively define a detonation wave unstart limit was not realized. Received 6 April 1998 / Accepted 15 January 1999     

Similarity solutions for the flow behind an exponential shock in a non-ideal gas

Similarity solutions for the flow of a non-ideal gas behind a strong exponential shock driven out by a piston (cylindrical or spherical) moving with time according to an exponential law are obtained. Similarity solutions exist only when the surrounding medium is of constant density. Solutions are obtained, in both the cases, when the flow between the shock and the piston is isothermal or adiabatic. It is found that the assumption of zero temperature gradient brings a profound change in the density distribution as compare to that of the adiabatic case. Effects of the non-idealness of the gas on the flow-field between the shock and the piston are investigated. The variations of density-ratio across the shock and the location of the piston with the parameter of non-idealness of the gas are also obtained.     

Experimental investigation on tunnel sonic boom

Upon the entrance of a high-speed train into a relatively long train tunnel, compression waves are generated in front of the train. These compression waves subsequently coalesce into a weak shock wave so that a unpleasant sonic boom is emitted from the tunnel exit. In order to investigate the generation of the weak shock wave in train tunnels and the emission of the resulting sonic boom from the train tunnel exit and to search for methods for the reduction of these sonic booms, a 1300 scaled train tunnel simulator was constructed and simulation experiments were carried out using this facility.In the train tunnel simulator, an 18 mm dia. and 200 mm long plastic piston moves along a 40 mm dia. and 25 m long test section with speed ranging from 60 to 100 m/s. The tunnel simulator was tilted 8° to the floor so that the attenuation of the piston speed was not more than 10 % of its entrance speed. Pressure measurements along the tunnel simulator and holographic interferometric optical flow visualization of weak shock waves in the tunnel simulator clearly showed that compression waves, with propagation, coalesced into a weak shock wave. Although, for reduction of the sonic boom in prototype train tunnels, the installation of a hood at the entrance of the tunnels was known to be useful for their suppression, this effect was confirmed in the present experiment and found to be effective particularly for low piston speeds. The installation of a partially perforated wall at the exit of the tunnel simulator was found to smear pressure gradients at the shock. This effect is significant for higher piston speeds. Throughout the series of train tunnel simulator experiments, the combination of both the entrance hood and the perforated wall significantly reduces shock overpressures for piston speeds ofu _p ranging from 60 to 100 m/s. These experimental findings were then applied to a real train tunnel and good agreement was obtained between the tunnel simulator result and the real tunnel measurements.     

EQ6100汽油机活塞销偏置的研究

本文从理论上分析了发动机活塞销偏置的目的,提出将EQ6100汽油机活塞销由原来向主推力面偏置改为向次推力面偏置。实验结果表明,活塞销改为向次推力面偏置后,发动机的经济性及动力性均得到了改善。     

Propagation of converging and diverging shock waves under isothermal condition

In this article the flows of perfect gas behind converging and diverging strong shock waves under isothermal condition in the cases of spherical and cylindrical symmetry are examined. A diverging shock wave is formed by energy supply according to a power law. These waves propagate in a uniform medium at rest and all conservation laws hold at the fronts of these shock waves. It was established that in the case of converging waves for any value of the ratios of specific heats the solution of the problem under consideration exists and is unique. When the problem has more than one solution. In the case of diverging shock waves the solution exists and is unique for any from the interval and any value of power in the energy input law. Received 4 August 1996 / Accepted 28 May 1996     

Exact solution of a boundary value problem describing the uniform cylindrical or spherical piston motion

In this paper, we construct the exact solution for fluid motion caused by the uniform expansion of a cylindrical or spherical piston into still air. Following Lighthill [1], we introduce velocity potential into the analysis and seek a similarity form of the solution. We find both numerical and analytic solutions of the second order nonlinear differential equation, with the boundary conditions at the shock and at the piston. The results obtained from the analytic solutions justify numerical solution and the approximate solution of Lighthill [1]. We find that although the approximate solution of Lighthill [1] gives remarkably good numerical results, the analytic form of that solution is not mathematically satisfactory. We also find that in case of spherical piston motion Lighthill’s [1] solution differs significantly from that of our analytic and numerical solutions. We use Pade′ approximation to extend the radius of convergence of the series solution. We also carry out some local analysis at the boundary to obtain some singular solutions.     

双级制冷压缩机配置的节能优化

通过对国产典型产品比较发现,双级螺杆式压缩机COP值高于双级活塞式压缩机。在-35℃/35℃典型工况下,平均COP值高11.4%,最大增加了18.3%。实例分析表明,不同方案配置的电机功率差别很大。活塞机比螺杆机方案电机总功率明显偏大,平均大20%,差别最大的总功率增加了42%。因此,在制冷系统设计选型阶段,应对压缩机不同选型方案COP及电机功率进行优化,应认真核算实际需要的电机功率。对于年运行≥3000小时的系统,应选用Y2-E或者YX系列高效节能型电动机。