Papers by Keyword: Circular Tube

Abstract: This paper describes the failure modes and energy absorption capability of partially wrapped aluminium-glass/epoxy tubes, subjected to quasi-static loading. ‎These tubes are used in aircraft and automobiles applications. Aluminium tubes were partially wrapped with 4, 6 and 8 glass/epoxy layers, using filament winding process. The 90^◦ fiber orientation was used for glass/epoxy layers. Quasi-static loading of partially wrapped tubes was carried out at 5mm/min speed, using the universal ‎testing machine. The experimental results revealed that partially wrapped aluminium tubes are 42.54%, 47.77% and 28.91% more ‎efficient in energy absorption as compared to the simple aluminium tubes. Furthermore, the effect of glass/epoxy layers on ‎failure modes has also been described.

Abstract: Models are established for oval tube hole clad steel tube sheet and circular tube hole clad steel tube sheet. Finite element analysis software ANSYS Workbench is used. Stress distribution characteristics of tube sheet with oval tube hole are investigated. Stress distribution characteristics under different ellipticity are analyzed and the general law of stress distribution of oval tube hole clad steel tube sheet is summarized. Results show: effects of tube hole shape on stress of clad steel tube sheet mainly focus in the tube zone, oval tube hole could effectively improve the phenomenon of stress concentration at the connection of basic layer and clad layer. When tube hole is oval, the maximum values of thermal stress and mechanical stress increase comparing to clad steel tube sheet with circular tube hole. With the increase of ellipticity, the total stress of tube sheet increases, stress increases on the minor axis of tube hole and decreases on long axis, and the deviation between the two stresses increases. The results provide reference for the design of the clad steel tube sheet.

Abstract: The dynamic behavior of circular straight and stepped tubes made of aluminum alloy under high-velocity impacts was investigated by performing finite element analyses (FEA) and an experiment. The FEA and experiment on the straight tubes suggested that while an increase in the impact velocity enhanced the absorbed energy through compressive deformation just after impact, the peak load at the fixed end was not affected by the velocity. A stepped tube that was thicker near the impacted end was designed on the basis of the results for the straight tubes, and its dynamic behavior was investigated through FEA. The stepped tube absorbed a large amount of impact energy through compressive deformation at the thicker portion during the higher-velocity impact, without increasing the maximum fixed-end load from that of the straight tube.

Abstract: Effect of 30° rectangular-winglet vortex generators (WVGs) mounted in the central core of a circular tube on convection heat transfer and friction loss is experimentally investigated in the present work. The rectangular-WVGs with two different winglet-height to tube-diameter ratios (called blockage ratio, BR = b/D = 0.1 and 0.2) and three winglet-pitch to tube-diameter ratios (PR=P/D=0.5, 1.0, and 1.5) are introduced. In the experiment, air at ambient condition is passed through the uniform heat-fluxed circular tube for Reynolds numbers (Re) in a range of 500024,000. The use of WVGs is to generate longitudinal vortex flows in the tube. The experimental results of heat transfer and pressure loss presented in terms of Nusselt number and friction factor are compared between the inserted and the smooth tubes. It is found that the BR and PR provide a significant effect on the thermal performance of the test tube. The results reveal that at smaller PR, the WVG with BR=0.2 provides the highest heat transfer and friction factor but the one with BR=0.2, PR=1.5 yields the best thermal performance.

Abstract: A numerical investigation has been conducted to examine turbulent flow and heat transfer characteristics in a three-dimensional isothermal tube mounted with 60° angled rings (AR). The ARs with pitch spacing ratio, PR=1.0 and various blockage ratios (BR) ranging from 0.025-0.1 are introduced. The computations are based on a finite volume method and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds number (Re) ranging from 3000 to 12000. To generate a main counter-vortex pair flow in the tube, ARs at an attack angle of 60° are mounted repeatedly in the tube. Effect of different BRs at a single PR and nanofluid, Al₂O₃water, with volume fractions 1% and 5% on heat transfer and friction loss is investigated. It is apparent that two main vortex flows created by the ARs exist and help to induce impinging flows on the tube wall leading to drastic increase in heat transfer rate over the tube. The increment in the BR gives rise to the increase in the Nusselt number and friction factor. The computational results reveal that the maximum thermal enhancement factor for the AR with BR=0.025 is found to be 1.8 at Re =3000. The results show that nanofluid, Al₂O₃ water, can increase the thermal performance when increasing volume fraction to 5%.

Abstract: Thin-walled tubes are generally used as impact energy absorber in various application due to their ease of fabrication and installation, high energy absorption capacity and long stroke. However, the main drawback of plain tube is the high initial peak force. A concentric plunger in the form of tapered block is proposed to overcome this shortcoming while at the same time, improving the impact performance. Static and dynamic axial crushing were performed to determine the initial peak force (IPF), crush force efficiency (CFE) and specific energy absorption (SEA) for the concentric plunger with various taper angles. It was found that the concentric plunger affected the tube impact response. Comparison with plain circular tube was carried out and it was found that the concentric plunger improved the impact response of the tube especially in term of initial peak force.

Abstract: This work deals with periodic flow, friction loss and heat transfer characteristics in a constant temperature-surfaced circular tube fitted with rib vortex generators (RVG). The computations are based on the finite volume method with the SIMPLE algorithm implemented. The fluid flow and heat transfer behaviors are presented for Reynolds numbers ranging from 100 to 1000. To generate two main vortex flows through the tested section, the 45o RVGs are mounted repeatedly in in-line arrangements on the top and bottom walls and in the central area of the tested section. Effects of different RVG heights, BR in a range from 0.1D to 0.3D with a single pitch of 1.5D on heat transfer and friction losses in the test section are examined. It is apparent that the vortex flows created by the RVG exist and help to induce periodically impinging flows on a sidewall leading to drastic increase in the heat transfer rate over the test section. The computational results reveal that the optimum thermal performance is about 2.38 for using the RVG height of 0.2D for the RVG placed on the tube walls at the highest Re value.

Abstract: In this paper, the effects of the fillers in the rubber-filled circular tubes are investigated during the inversion process of the tubes under the axial loading, experimentally. For this purpose, a comparison between the experimental results of the empty and rubber filled circular tubes was performed. The inversion tests were carried out on the rubber-filled and empty brazen circular tubes. A pair of die and punch was prepared as the fixtures. All the inversion tests are performed under quasi-static axial loading. The experimental results of the filled tubes show a considerable increase in the energy absorption and the axial force comparing with the empty tubes, during the tube inversion process. The filler material in the circular tubes was supplied from the wastage of the tire producer companies. This is one of the best applications of the tire wastage that has good environmental and economical advantages. The tire wastage filled-tubes are introduced as a good energy absorber that can be used in the energy absorption mechanisms such as automobile bumpers, crashing barriers of roadsides, and aerospace.

Abstract: The entrance region flow of a Casson fluid in a tube has been investigated numerically without making prior assumptions on the form of velocity profile within the boundary layer region, which is determined by a cross sectional integration of the momentum differential equation for a given distance from the channel entrance. Using the macroscopic mass and momentum balance equations, the thickness of the core, the entrance length, and the pressure drop have been obtained at each cross section of the entrance region of the tube for specific values of Casson number.

Abstract: The experimental studies on the static and dynamic mechanical properties of aluminium foam material are presented first. Finite element models of four structures, including circular tube filled and bonded with aluminium foam, circular tube filled but unbonded with aluminium foam, single aluminium foam column and empty aluminium tube, under dynamic transverse compression are established by FEMB code. The dynamic mechanical behaviors of the structures are analyzed using LS-DYNA finite element code. The simulating results at certain cases are compared with experimental measurements and the satisfying consistency confirmed the validity of the model. The further numerical simulations are carried on the dynamic mechanical behaviors of four structures with outer tubes of different wall-thickness. It is found that aluminium foam filling can greatly improve the load-bearing capacity and energy-absorbing efficiency of structures. On the other hand, the effect of the aluminium outer tube on the structure is obvious compared with single aluminium foam column, in spite of the foam core and the tube are bonded together or unbonded. Another result can be seen that the bonding between the foam and outer tube affects the structure weakly for both thinner and thicker tubes. Finally, the simulating results show that the thicker wall of tube can improve the load-bearing capacity and energy-absorbing ability of the structure.