Effect of bent inlet pipe on the flow instability behavior of centrifugal compressors

Bent inlet pipes are often used in centrifugal compressors due to limited installation space, and an understanding of the effect on compressor stability is essential for safety and durability. This paper firstly investigates flow instability behaviors in two compressors, one with a straight inlet pipe and the other with an S-shaped bent pipe. In detail, it analyzes the resulting flow fields, instability evolution paths and surge boundaries. The results show that the S-shaped pipe obviously affects the flow field at high mass flow rates, while reverse flow mainly influences the flow field at low mass flow rates. Reverse flow first occurs at certain flow passages with a high pressure difference that is predominantly decided by the volute rather than the S-shaped bent pipe. In addition, centrifugal compressors can tolerate reverse flow to some extent so that surge would not occur immediately if reverse flow occurs unless the reverse flow region extends circumferentially and radially to a sufficiently large size. Since the S-shaped pipe is not dominant in the creation and extension of reverse flow, it does not exacerbate the stability of the central compressor to a great extent. Last but not least, the S-shaped pipe is noted to delay the occurrence of surge at 90% rotating speed, which suggests the possibility of improving compressor stability with bent inlet pipes. This result differs from the conventional understanding that inlet distortion usually deteriorates compressor stability and emphasizes the particularity of centrifugal compressors.     

闭式脉动热管启动性能的实验研究

实验研究了以乙醇为工质的闭式脉动热管在不同工况下的启动性能,分析了充液率、倾斜角、热负荷对脉动热管启动性能的影响。研究发现脉动热管具有两类启动方式:温度飞升式启动和温度渐进式启动。脉动热管启动性能最优的最佳充液率范围在41%～52%之间。相同热负荷下,随着倾斜角在0°～90°范围内逐渐增大,热管启动性能将得到改善。随着热负荷的增大,启动时间缩短但最高启动温度随之升高。     

计算机辅助设计在高层建筑物采暖设计中的应用

介绍了高层建筑采暖设计中 ,应用计算机辅助设计对单管顺流式、三通调节阀跨越式及单、双管系统利用不等温降法进行准确的水力计算、热力计算 ,提出主要的数学模型及编程的基本技巧。     

Thermal protection mechanism of heat pipe in leading edge under hypersonic conditions

Sharp local structure, like the leading edge of hypersonic aircraft, confronts a severe aerodynamic heating environment at a Mach number greater than 5. To eliminate the danger of a material failure, a semi-active thermal protection system is proposed by integrating a metallic heat pipe into the structure of the leading edge. An analytical heat-balance model is established from traditional aerodynamic theories, and then thermal and mechanical characteristics of the structure are studied at Mach number 6–8 for three refractory alloys, Inconel 625, C-103, and T-111. The feasibility of this simple analytical method as an initial design tool for hypersonic aircraft is assessed through numerical simulations using a finite element method. The results indicate that both the isothermal and the maximum temperatures fall but the von Mises stress increases with a longer design length of the leading edge. These two temperatures and the stress rise remarkably at a higher Mach number. Under all investigated hypersonic conditions, with a 3 mm leading edge radius and a0.15 m design length, the maximum stress exceeds the yield strength of Inconel 625 at Mach numbers greater than 6, which means a material failure. Moreover, both C-103 and T-111 meet all requirements at Mach number 6–8.     

长征系列液体火箭发动机导管锉修技术

导管锉修是发动机装配工作中一项重要操作技能,根据液体火箭发动机的装配特点,从导管锉修流程中导管比试、导管锯切和导管锉修3个环节进行论述,深入剖析了发动机导管锉修技术的关键和难点,得出了导管锉修技术方法。从实际装配经验中归纳总结了4条导管的比试准则,归纳总结了6条影响导管锯切位置的关键影响因素,并详细说明了导管锉修应满足的5项要求以及各项控制参数。     

Experimental study on effect of inclination angles to ammonia pulsating heat pipe

In this paper, a novel study on performance of closed loop pulsating heat pipe（CLPHP）using ammonia as working fluid is experimented. The tested CLPHP, consisting of six turns, is fully made of quartz glass tubes with 6 mm outer diameter and 2 mm inner diameter. The filling ratio is50%. The visualization investigation is conducted to observe the oscillation and circulation flow in the CLPHP. In order to investigate the effects of inclination angles to thermal performance in the ammonia CLPHP, four case tests are studied. The trends of temperature fluctuation and thermal resistance as the input power increases at different inclination angles are highlighted. The results show that it is very easy to start up and circulate for the ammonia CLPHP at an inclining angle.The thermal resistance is low to 0.02 K/W, presenting that heat fluxes can be transferred from heating section to cooling section very quickly. It is found that the thermal resistance decreases as the inclination angle increases. At the horizontal operation, the ammonia CLPHP can be easy to start up at low input power, but hard to circulate. In this case, once the input power is high,the capillary tube in heating section will be burnt out, leading to worse thermal performance with high thermal resistance.     

冬季自来水管冻断破坏问题的研究

我国大量高层建筑的水箱在严冬容易冻断破坏，给人民生活带来了许多困难，为了探讨这一普遍存在的问题，本文应用线弹簧模型，从断裂力学的角度分析了冬季自上而下为水管冻断破坏的原因，得到了自来水管的应力强度因子计算式，理论计算结果与实际情况相符合。     

测地线缠绕90°弯管的运动方程

用纤维缠绕90°弯管主要有两种方法:计算机控制缠绕或摆动缠绕弯管机控制缠绕。本文分别讨论在上述方法中测地线缠绕时丝嘴运动规律。 在用计算机缠绕90°弯管时,由于芯模回转,丝嘴既可在三维空间也可在二维空间运动。文中分別给出了在这两种情况下测地线缠绕时丝嘴运动方程。 本文还讨论了实现整螺旋缠绕的条件和最优参数的选取。在缠绕受内压的弯管时,推荐取弯管曲率半径与弯管半径比值近似为4。为实现测地线缠绕90°弯管提供了依据。     

The Mercury Dual Imaging System on the MESSENGER Spacecraft

The Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft will provide critical measurements tracing Mercury’s origin and evolution. MDIS consists of a monochrome narrow-angle camera (NAC) and a multispectral wide-angle camera (WAC). The NAC is a 1.5° field-of-view (FOV) off-axis reflector, coaligned with the WAC, a four-element refractor with a 10.5° FOV and 12-color filter wheel. The focal plane electronics of each camera are identical and use a 1,024×1,024 Atmel (Thomson) TH7888A charge-coupled device detector. Only one camera operates at a time, allowing them to share a common set of control electronics. The NAC and the WAC are mounted on a pivoting platform that provides a 90° field-of-regard, extending 40° sunward and 50° anti-sunward from the spacecraft +Z-axis—the boresight direction of most of MESSENGER’s instruments. Onboard data compression provides capabilities for pixel binning, remapping of 12-bit data into 8 bits, and lossless or lossy compression. MDIS will acquire four main data sets at Mercury during three flybys and the two-Mercury-solar-day nominal mission: a monochrome global image mosaic at near-zero emission angles and moderate incidence angles, a stereo-complement map at off-nadir geometry and near-identical lighting, multicolor images at low incidence angles, and targeted high-resolution images of key surface features. These data will be used to construct a global image base map, a digital terrain model, global maps of color properties, and mosaics of high-resolution image strips. Analysis of these data will provide information on Mercury’s impact history, tectonic processes, the composition and emplacement history of volcanic materials, and the thickness distribution and compositional variations of crustal materials. This paper summarizes MDIS’s science objectives and technical design, including the common payload design of the MDIS data processing units, as well as detailed results from ground and early flight calibrations and plans for Mercury image products to be generated from MDIS data.     

矢量喷管六分量测力试验台的研制

为用于矢量喷管试验而研制的新型六分量天平试验台选择台式天平作为测力天平设计方案、对称全弹性波纹管作为连接试验台和固定管道的引气管道 ,采用地轴单元校和地轴多元校获取天平工作公式 ,并采用试验修正消除波纹管的影响。根据天平静校和标准收敛喷管的动校检验 ,该天平性能达到了设计要求 ,说明天平的研制是成功的。