The speed, reflection and intensity of waves propagating in flexible tubes with aneurysm and stenosis: Experimental investigation

A localized stenosis or aneurysm is a discontinuity that presents the pulse wave produced by the contracting heart with a reflection site. However, neither wave speed ( c) in these discontinuities nor the size of reflection in relation to the size of the discontinuity has been adequately studied before. Therefore, the aim of this work is to study the propagation of waves traversing flexible tubes in the presence of aneurysm and stenosis in vitro. We manufactured different sized four stenosis and four aneurysm silicone sections, connected one at a time to a flexible ‘mother’ tube, at the inlet of which a single semi-sinusoidal wave was generated. Pressure and velocity were measured simultaneously 25 cm downstream the inlet of the respective mother tube. The wave speed was measured using the PU-loop method in the mother tube and within each discontinuity using the foot-to-foot technique. The stenosis and aneurysm dimensions and c were used to determine the reflection coefficient ( R) at each discontinuity. Wave intensity analysis was used to determine the size of the reflected wave. The reflection coefficient increased with the increase and decrease in the size of the aneurysm and stenosis, respectively. c increased and decreased within stenosis and aneurysms, respectively, compared to that of the mother tube. Stenosis and aneurysm induced backward compression and expansion waves, respectively; the size of which was related to the size of the reflection coefficient at each discontinuity, increases with smaller stenosis and larger aneurysms. Wave speed is inversely proportional to the size of the discontinuity, exponentially increases with smaller stenosis and aneurysms and always higher in the stenosis. The size of the compression and expansion reflected wave depends on the size of R, increases with larger aneurysms and smaller stenosis.

On the Influence of Cold Rolling Parameters for 14CrW-ODS Ferritic Steel Claddings

Oxide dispersion strengthened (ODS) steels, produced by powder metallurgy, are considered as promising material for high burn up cladding tubes for future Sodium Cooled Fast reactors. They present superior radiation resistance compared with austenitic steels and high creep strength due to reinforcement by the homogeneous dispersion of hard nano-sized particles. While the manufacturing route of 9Cr-based martensitic ODS steels are relatively well mastered thanks to the alpha  gamma phase transformation, the cold processing of ferritic ODS steels is more complicated because the material recovery after amounts of cumulative plastic strain is quite difficult. The aim of this study is to investigate several possible cold rolling routes for a Fe-14Cr-1W-0,3Ti-0,3Y2O3 ODS ferritic grade comparing the effects of annealing temperature on cold-workability, microstructure evolution and mechanical properties. A three-roll type HPTR rolling mill was used to manufacture ODS steel claddings. Cold rolling passes and intermediate annealing were repeated until reaching the final geometry: 10.73mm external diameter and 500µm thick. Depending of the cold rolling routes, different annealing temperatures of 1150°C, 1200°C and 1250°C were applied on the mother tube. Each pass was conducted using cross-section reduction ratio varying from at least 15% up to 25%. In each case, intermediate annealing at 1200°C for 1 hour were applied between one or several passes. The optical and SEM observations, hardness measurements, tensile tests were conducted to characterize the manufactured cladding tubes. The highest annealing temperature used on the mother tube enhances the recovery which leads to the lowest hardness level. The intermediate heat treatments applied in the course of the cold processing induces relatively low decrease of hardness. Microstructure characterization of hot extruded mother tubes shows highly anisotropic structures with equiaxed grains in the transverse direction but with significant elongation in the longitudinal direction. The elongated grain structure produced during hot extrusion is retained during cold rolling processes. Tensile tests are carried out on both longitudinal and circumferential directions by mean of respectively tile and ring tensile specimens for temperatures between 20°C and 700°C. The lowest is the annealing temperature applied on the mother tube the highest is the ultimate strength and the lowest is the uniform elongation. For the lowest annealing temperature, the UTS values measured at room temperature are ~1500MPa and ~1300MPa in the longitudinal direction and the circumferential direction, respectively. UTS values around 1000MPa in the both directions are found in case of lower annealing temperature showing a less pronounced anisotropy. For each test temperature, the uniform elongation values are relatively low compared to values obtained by other authors on 12%Cr-ODS ferritic steels. The lowest values of elongation are measured around 400°C.

Multi-branching flows from one mother tube to many daughters or to a network

Multiply branching fluid flows are modelled in two contexts. The first (type I) is for one-to-many branching. Computations are described for flow through a channel, with fully developed motion upstream, which branches abruptly into a number of subchannels downstream. The differences in pressure between the upstream end of the channel and the downstream ends of the subchannels are substantial. Comparisons with recent analytical predictions show fair agreement for Reynolds numbers in the low tens and above. The second context (type II) has successive generations of bifurcation in a network. Modelling, computations and analysis include the effects of many bifurcations.

Pulsatile Flow Into a 45-Degree Tube Bifurcation

In this study, we use numerical simulation to investigate the pulsatile flow into a 45°-tube bifurcation. There is a well-known analytical solution for the pulsatile flow in a straight pipe. However, to study the pulsatile flow into a branched pipe only numerical solution or experimental techniques are available. The unsteady, three-dimensional, incompressible Navier-Stokes equations are solved using a finite volume solver. A time periodic flow is established. As compared to the straight tube flow case, it is found that the introduction of bifurcation changes the periodic flow structure upstream and downstream of the bifurcation. The periodic flow in the forward flow and the reverse flow part of the cycle are very different. The forward flow part of the cycle is a problem of splitting the mother tube flow into the two daughter tubes. The reverse flow part of the cycle is the problem of two jets coming out of the daughter tubes mixing in the mother tube chamber.