Characterization of Thermal Striping in Liquid Sodium With Optical Fiber Sensors

This study characterized the magnitude, spatial profile, and frequency spectrum of thermal striping at a junction using a novel sodium-deployable optical fiber temperature sensor. Additionally, this study revealed for the first time the capability of performing cross correlation velocimetry (CCV) with an optical fiber to acquire fluid flow rates in a pipe. Optical fibers were encapsulated in stainless steel capillary tubes with an inert cover gas for high-temperature sodium deployment. Plots of temperature oscillation range as a function of two-dimensional space highlighted locations prone to mechanical failure for particular flow momentum ratios. The effect of inlet sodium temperature differential and bulk flow rate on thermal striping behavior was also explored. The power spectral density (PSD) revealed that the striping temperature oscillations occurred at frequencies ranging from 0.1 to 6 Hz. Finally, the bulk flow rate of liquid sodium was calculated from thermal striping's periodic temperature oscillations using cross correlation velocimetry for flow rates of 0.25–5.74 L/min.

Effects of bileaflet mechanical heart valve orientation on fluid stresses and coronary flow

The effects of the orientation of a bileaflet mechanical heart valve on the viscous and turbulent stresses in the flow past it and on the flow rate in the right coronary artery were investigatedin vitroin a mock circulation loop, using a fluid that matched the kinematic viscosity of blood and the refractive index of the aorta model. Measurements were made past the valve mounted in three orientations at the base of an anatomical aorta model, within physiological aortic flow conditions. At peak flow, the turbulent stresses were on average 21 % higher and viscous stresses exceeding 10 Pa (namely of a level that has been associated with blood cell damage) were 30 % more frequent when the valve was oriented with its plane of symmetry normal to the aorta’s plane of curvature than when it was parallel to it. This was attributed to the impingement of a lateral jet on the concave wall of the aorta and to steeper velocity gradients resulting from the geometrical imbalance of the sinuses relative to the valve’s central jet when the valve was in the ‘normal’ orientation. Very high levels of turbulent stresses were found to occur distal to the corners of the valve’s lateral orifices. The bulk flow rate in the right coronary artery was highest when the valve was positioned with its central orifice aligned with the artery’s opening. The coronary flow rate was directly affected by the size, orientation and time evolution of the vortex in the sinus, all of which were sensitive to the valve’s orientation.

Simplified Explicit Flow Equations for Herschel-Bulkley Fluids in Couette-Poiseuille Flow—For Real-Time Surge and Swab Modeling in Drilling

Summary Simplified flow equations are developed for Herschel-Bulkley (HB) fluids in laminar Couette-Poiseuille (CP) flow. Such flow problems are encountered in drilling when the drillstring is moved longitudinally (surge and swab operations). The new equations give the frictional-pressure gradient explicitly as a function of the bulk-flow rate. This makes them very well-suited for applications in fast, robust dynamic models for real-time applications. Incorporating these equations in a dynamic model based on ordinary differential equations (ODEs) enables coupling with system identification and control-system theory. This is a great advantage in drilling applications where there are many uncertain parameters and few measurements. Thorough analysis of relevant analytical solutions is performed to replace the most complex (implicit) parts of the solution with simpler approximations. The accuracy of the new equations, in comparison with numerical simulations and available analytical solutions, is shown to be acceptable for most practical applications.

Wall Shear Stress Measurements in an Arterial Flow Bioreactor

Physiological flow parameters such as pressure and stress inside the vascular system strongly influence the physiology and function of vascular endothelial cells [1]. Variations in the shear stress experienced by endothelial cells affect morphology, alignment with the flow, mechanical strength, rate of proliferation, and gene expression [2]. Although it is known that these factors are dependent on the hemodynamics of the flow, the relationship has not been accurately quantified. In vitro bioreactor flow loops have been developed to simulate vascular flow for tissue conditioning and measurement of the endothelial cell response to varying shear [3–5]; however, wall shear stresses (WSS) have been estimated from the bulk flow rate by assuming Poiseuille flow [2, 6]. Due to the pulsatility of the flow, biochemical interactions, and the typically short vessel length, this assumption is fundamentally incorrect; however, the level of inaccuracy has not been quantified.

Axisymmetric creeping motion of drops through circular tubes

The axisymmetric creeping motion of a neutrally buoyant deformable drop flowing through a circular tube is analysed with a boundary integral equation method. The fluids are immiscible, incompressible, and the bulk flow rate is constant. The drop to suspending fluid viscosity ratio is arbitrary and the drop radius varies from 0.5 to 1.15 tube radii. The effects of the capillary number, viscosity ratio, and drop size on the deformation, the drop speed, and the additional pressure loss are examined.Drops with radius ratios less than 0.7 are insensitive to substantial variation in capillary number and viscosity ratio, and computed values of drop speed and extra pressure loss are in excellent agreement with small deformation theories (Hestroni et al. 1970; Hyman & Skalak 1972a). For this drop size range, significant deformation will result only for Ca > 0.25. The onset of a re-entrant cavity is predicted at the trailing end of the drop for Ca ≈ 0.75. Drop speed and meniscus shape become independent of drop size for radius ratios as small as 1.10. The extra pressure loss can be positive or negative depending mainly on the viscosity ratio, however a relatively inviscid drop can cause a positive extra pressure loss when capillary forces are significant. Computed values for extra pressure loss and drop speed are in good agreement with the experimental data of Ho & Leal (1975) for drops of sizes comparable with the tube radius.

Computation of Annular, Turbulent Flow With Rotating Core Tube

Numerical predictions are presented of fully-developed turbulent flow through a concentric annulus in which the core tube rotates about its axis. Comparisons are drawn with the extensive experimental data of Kuzay and Scott [1] which span Reynolds numbers from 1.7 to 104 to 6.5 × 104 and with rotational speeds of the core tube varying from zero to nearly 2.8 times the bulk axial velocity. Predictions have been obtained by means of an adapted version of the Patankar-Spalding [5], numerical procedure employing, as turbulent transport model, the version of the mixing length hypothesis applied by Koosinlin, Sharma and Launder [2] to flows on spinning cones and cylinders. Agreement with experiment is generally close at the higher relative swirl rates but the predictions of the swirling velocity profile deteriorate as the bulk flow rate is increased. The discrepancy seems to be due to the experimental data requiring a greater development length as the magnitude of the rotational velocity is reduced relative to that of the mean flow. Demonstrative developing-flow predictions are provided which exhibit closer agreement with the experimental data.