On the characteristics of tubular materials for hydroforming—experimentation and analysis

Increasing acceptance and use of hydroforming technology within the automotive industry demands a comprehensive understanding of related issues such as material characteristics, tribology, part and tooling design. Among these issues, characterization and specification of tubular material properties under hydroforming conditions is the main concern of this paper. Analytical improvements and their comparison with experimental findings on measurement of material properties of tubes under hydraulic bulging conditions are explained. With these improvements, ‘on-line’ and continuous measurement of flow stress for tubular materials become possible, and are proven to be in good agreement with previous ‘off-line’ measurements presented by the authors.     

Studies on 10kg alloy mass metal hydride based reactor for hydrogen storage

A 10 kg alloy mass metal hydride reactor, with LaNi₅ alloy was designed. Heat transfer enhacement in the reactor was achieved by including embedded cooling tubes and an external water jacket. Detailed parametric study has been carried to understand the performance of the system. The effect of both geometrical and operational parameters was studied in simulations. The optimized geometrical parameters were used for fabricating the reactor. Experimental studies were carried on the fabricated reactor. Absorption studies were carried out for different supply pressure and different cooling fluid temperatures. Storage capacity of 1.13 wt% was found in 1620 s at a supply pressure of 25 bar and with a flow rate of 20 LPM. Similarily, desorption studies were carried out for varying heat transfer fluid temperatures. Complete and fastest desorption was observed at 80 °C with the reaction completion time of 2700 s.     

Characterization of the two-phase flow regimes and liquid dispersion in horizontal and vertical tubes by using coloured tracer and non-intrusive optical detector

The monitoring of heat exchangers on duty with respect to flow mal-distributions needs the development of inlet-outlet experimental techniques in order to perform a fault diagnosis. Within this framework and as a first attempt to solve this problem in the case of multi-phase heat exchangers, we propose to use a non-intrusive optical sensor associated to a liquid phase tracer experiment. In order to check the capabilities of this technique, we present here the results that we have obtained for the characterization of two phase flows in horizontal and vertical tubes. The difference between refractive index of the two phases allows estimating the void fraction on the section illuminated by the optical sensor and permits to characterize two-phase flow regime from the signal characteristics. Signal analysis and treatment of the absorbance variation due to the coloured tracer injected in the liquid phase permit to estimate the real liquid phase averaged velocity and consequently the real gas phase average velocity. We also calculated volumetric void fraction and compared it to usual correlations with a good agreement. Finally, the evolution of the experimental liquid phase Peclet number with the two-phase flow regime has been observed and qualitatively explained.     

Heat transfer asymptote in laminar flow of non-linear viscoelastic fluids in straight non-circular tubes

The fully developed thermal field in constant pressure gradient driven laminar flow of a class of non-linear viscoelastic fluids with instantaneous elasticity in straight pipes of arbitrary contour ∂D with constant wall flux is investigated. The non-linear fluids considered are constitutively represented by a class of single mode, non-affine constitutive equations. The driving forces can be large. Asymptotic series in terms of the Weissenberg number Wi are employed to expand the field variables. A continuous one-to-one mapping is used to obtain arbitrary tube contours from a base tube contour ∂D₀. The analytical method presented is capable of predicting the velocity and temperature fields in tubes with arbitrary cross-section. Heat transfer enhancement due to shear-thinning is identified together with the enhancement due to the inherent elasticity of the fluid. The latter is to a very large extent the result of secondary flows in the cross-section but there is a component due to first normal stress differences as well. Increasingly large enhancements are computed with increasing elasticity of the fluid as compared to its Newtonian counterpart. Order of magnitude larger enhancements are possible even with slightly viscoelastic fluids. The coupling between inertial and viscoelastic non-linearities is crucial to enhancement. Isotherms for the temperature field are discussed for non-circular contours such as the ellipse and the equilateral triangle together with the behavior of the average Nusselt number Nu, a function of the Reynolds Re, the Prandtl Pr and the Weissenberg Wi numbers. Analytical evidence for the existence of a heat transfer asymptote in laminar flow of viscoelastic fluids in non-circular contours is given for the first time. Nu becomes asymptotically independent from elasticity with increasing Wi, Nu = f(Pe, Wi) → Nu = f(Pe). This asymptote is the counterpart in laminar flows in non-circular tubes of the heat transfer asymptote in turbulent flows of viscoelastic fluids in round pipes. A different asymptote corresponds to different cross-sectional shapes in straight tubes. The change of type of the vorticity equation governs the trends in the behavior of Nu with increasing Wi and Pe. The implications on the heat transfer enhancement is discussed in particular for slight deviations from Newtonian behavior where a rapid rise in enhancement seems to occur as opposed to the behavior for larger values of the Weissenberg number where the rate of increase is much slower. The asymptotic independence of Nu from elasticity with increasing Wi is related to the extent of the supercritical region controlled by the interaction of the viscoelastic Mach number M and the Elasticity number E, which mitigates and ultimately cancels the effect of the increasingly strong secondary flows with increasing Wi to level off the enhancement. The physics of the interaction of the effects of the Elasticity E, viscoelastic Mach M, Reynolds Re and Weissenberg Wi numbers on generating the heat transfer enhancement is discussed.     

Composite Tube Hinges

This paper is concerned with self-powered, self-latching tube hinges, made by cutting three parallel slots in a thin-walled carbon fiber reinforced plastic tube with a circular cross section. Thus, a hinge consists of two short tubes connected by three transversally curved strips of material (known as tape springs). A particular tube hinge design is considered, with a diameter of about one-third that of the hinges used previously; this requires the tape springs to reach strains close to failure when the hinge is folded. Three analyses of the peak strains in a tube hinge are presented. The first analysis obtains general analytical expressions for the longitudinal fold radius of a tape spring and the associated peak fiber strains. The second analysis is a finite-element simulation of the folding of a single tape spring and the third analysis is a simulation of a complete tube hinge. It is found that the largest fiber strains in one- and two-ply hinges can be predicted analytically with very good accuracy. It is also found that the contact and interaction between the three tape springs that form a tube hinge, modeled in the third analysis, do not affect the peak strains significantly.     

耳型折叠波导慢波结构W波段行波管

毫米波行波管具有大功率、宽频带、高增益等特点，广泛用于雷达、高速通信、电子对抗等现代军事装备中。为提高折叠波导耦合阻抗并考虑工程应用性，提出一种耳型折叠波导新型慢波结构。与常规矩形波导相比，工作频带内耦合阻抗提高30%以上，损耗降低10%。研制的耳型折叠波导W波段行波管，在工作电压21.9 kV，电流210 mA，占空比为5%时，10.8 GHz带宽内输出功率大于192 W，峰值功率达278 W，电子效率和增益分别达到6.3%和44.6 dB，行波管工作稳定。     

Degradation and collapse of square tubes under cyclic bending

This paper presents the results of an experimental investigation of the elastic–plastic degradation and collapse of steel tubes with square cross-section under cyclic pure bending in a curvature symmetric fashion. The results indicate that the structural performance of the tubes degrades due to the growth of periodic, transverse deflections in their flanges. The wavelength of these deflections is equal to the wavelength of the buckling mode of the tubes under monotonic pure bending. Persistent cycling induces localization of the amplitude of these deflections and leads to the formation of a kink in one of the flanges. This causes collapse of the tube.     

Analytical Models for Concrete Confined with FRP Tubes

Concrete columns encased in fiber-reinforced polymer (FRP) tubes offer an attractive solution to enhance behavior of concrete in terms of strength as well as ductility. Analytical models for development of stress-strain curves for concrete confined with FRP are proposed in this paper. The predicted stress-strain curves for confined concrete using the proposed models are compared with those of tests for concrete specimens confined with FRP. It is demonstrated that the proposed models predict the stress-strain behavior of confined concrete very well. Based on the confidence gained in the proposed models, the effects of using different fibers, the presence of voids, and the number of layers are established.     

氯化聚乙烯橡胶及其在汽车胶管中的应用

本文叙述了氯化聚乙烯橡胶的性能及其在汽车胶管中的应用。     

循环机压力表导管断裂原因分析

通过宏观、微观等金相组织分析方法，分析了循环机压力表导管的失效原因。结果表明，导管破裂裂纹起源于角焊缝熔合区的焊接微裂纹及粗大的魏氏组织，并在随后的试车中不断扩展而造成导管环状断裂。