The effect of compression work on free convection in gases

Summary This paper attempts to investigate the influence of compression work on free convective flows in gases. Since this effect is usually small a dimensional analysis using the complete set of governing equations is presented first, in order to recognize the cases for which compression work is not negligibly small in comparison with other effects. Among other things it is shown that in gases viscous heating is always of a much lower order of magnitude than compression work. Next a case of boundary layer flow that possesses similarity is studied in some detail. For various degrees of importance of compression work a numerical integration of the governing ordinary differential equations is carried out. For very strong compression work an asymptotic solution can be found. In all cases the boundary layer shows oscillatory behaviour of both the temperature and velocity profile.     

On formation of carbon clusters on a substrate in plasma pyrolysis of hydrocarbon gases

The influence of nanoparticles of soot precipitated onto a catalytic metal substrate from a flow on the formation of carbon clusters in a supersaturated solid solution on the substrate boundary is considered. The free energy and the probability of the formation of critical clusters are considered.     

Combined equation of state for liquids and gases, which includes the classical and scaling parts

A new equation of state is suggested, which describes the P-ρ-T data for ⁴He and SF₆ in the ranges of reduced densities ?1 < (ρ?ρ _c )/ρ _c < 1 and of reduced temperatures ?0.3 < (T-T _c )/T _c < 0.3 (ρ _c and T _c are the critical values). This equation includes the regular equation of state approximating the P-ρ-T data outside of the critical region and the nonparametric scaling equation of state adequately describing the P-ρ-T data in the vicinity of the critical points, which are combined by the crossover function. The classical function of damping of fluctuations of density and temperature when moving away from the critical point is suggested as the crossover function. Two equations of state are used for the regular part of combined equation, namely, the new cubic equation of state suggested by us and the equation of state of Kaplun and Meshalkin. The nonparametric scaling equation of state with three system-dependent constants is used as the scaling part of the combined equation. The conditions (?P/?v) _T = 0 and (?² P/?v ² ) _T = 0 are valid for the combined equation at the critical point; binodal and spinodal are present, as is the case in classical equations of state. The approximation of the most exact data on ⁴He and SF₆ using the new equation reveals that the latter equation correctly describes the P-ρ-T data with mean-square error with respect to pressure of ±0.5%.     

裂解气相色谱-质谱法研究双酚A型聚砜的热裂解机理

在热重分析测试结果的基础上,采用裂解气相色谱-质谱联用仪(Py GC-MS)分析双酚A型聚砜在500~700℃范围内不同温度下热裂解形成的产物种类及其相对含量。通过对比不同温度下的裂解产物,发现500℃时PSU裂解形成的主要产物是苯酚,550℃时才检测到SO2。随着裂解温度升高,裂解产物的种类增多,SO2的相对含量逐渐升高,直到700℃取代苯酚成为最主要的裂解产物。最后,该文根据不同温度下产生的裂解产物的种类及其相对含量推测PSU产生热裂解的机理。     

Methodological Foundations for the Prevention of Technical Failures

An analysis is made of the methodological foundations for setting up a system of procedures for preventing failures of complex technical objects during their operation.     

Forging of blades for gas turbines

Abstract

Forging technology has been developed to the point where wrought nickel alloy turbine blades can be manufactured to accurate dimensional tolerances and consistent metallurgical characteristics. Metallurgists and engineers have utilized theoretical knowledge and practical understanding of nickel superalloys and the forging process to meet the ever-increasing temperature and stress demands of turbine engines. New materials, forging techniques, and the use of computer-aided design and manufacturing systems are being developed to compete with advanced casting technology.

MST/259     

Extrapolation of the emissivity of gases

A new simple equation for the emissivity of gases is derived. This is used in order to extrapolate the emissivity of water vapor to high temperatures, great optical thicknesses, and an effective pressure differing from unity.     

Development of vertical axis wind turbines

This paper summarises the work done at the National Aeronautical Laboratory (NAL) between 1975 and 1977 on the development of vertical axis wind turbines based on the Darrieus rotor. On the analytical side, a performance analysis was developed which permits the estimation of the characteristics of such machines. A 5 m high wind turbine using curved wooden blades was designed, fabricated and tested. Both the theory and initial tests confirmed the low starting torque of the turbine. Wind tunnel tests were performed on model Savonius rotors to determine optimum starter bucket configurations. Finally a straight-bladed turbine was designed and constructed. It is concluded from our experience that darrieus burbines are likely to be useful in large systems used to generate electrical power for the grid; for direct water pumping purposes, however, these turbines are unlikely to be suitable.     

铁道车辆减速顶构件失效断口的SEM分析

本文采用扫描电镜（ＳＥＭ）对实际使用中的Ｔ．ＤＪ型减速顶的失效断口进行了宏观、微观形貌观察，发现断口具有典型疲劳条纹。分析了裂纹的产生、扩展机制，并对如何延长工件的使用寿命，提出一些建议。     

Failures of welded titanium aircraft ducts

An in-service failure of a thin-walled titanium bleed-air duct from a wide-bodied commercial aircraft has been investigated. Cracking had occurred in the heat-affected zone (HAZ) adjacent to a circumferential weld joining two sections of the duct which was manufactured from commercially pure (grade 3) titanium sheet. Specimens were cut from the duct to include an intact weld and tested under known conditions (overload, fatigue, sustained loading) for comparison with the failed duct. Metallographic observations showed that cracking occurred through an acicular HAZ, and fractographic observations revealed brittle, cleavage-like cracking with occasional areas of fatigue striations for both the failed duct and fatigued specimens. These observations, and the absence of sustained-load cracking in test specimens, suggested that the in-service failure had occurred primarily by fatigue. Observations also indicated that small, cleavage-like cracks had been present in the ducts prior to service, although whether these cracks were caused by overload tearing, stress-corrosion cracking, hot-salt cracking or fatigue was not clear. Other possible causes of cleavage-like cracking, e.g. the presence of hydrides as proposed for previous failures, contamination of HAZs by oxygen/nitrogen, are discussed. Possible ways of preventing further failures are then outlined.     

出租车计价器电源部分常见故障

本文介绍了计价器电源部分的原理及常见故障分析。     

Investigation of Conveyor Pulley Shaft Failures

The cause for failures of shafts in a conveyor pulley in iron-making unit at JSW Steel has been investigated. Visual, metallographic, chemical, and fractographic studies were carried out in this study. Fracture studies of the shaft revealed shear failure because of overload. Detailed investigation revealed that the source of overload and cause of failure to be the end disk of the pulley drum, which is not considered a critical component. The disk material complies with the required material specification but failed because of changes in metallurgical characteristics during welding. Severe centerline segregation in the end disk drastically reduced its strength and service life, leading to premature failures. It was found that end disk welding failures led to overloaded bending stresses, thereby causing an imbalance in the shaft rotation and leading to failure.