Thread-annular flow in vertical pipes

Abstract

Thread injection is a promising method for different minimally invasive medical applications. This paper documents an experimental study dealing with an axially moving thread in annular pipe flow. Mass flow and axial force on the thread are measured for a 0.46 mm diameter thread in pipes with diameters between 0.55 and 1.35 mm. The experiments with thread velocities of up to 1.5 ms−1 confirm the findings of theoretical studies that for clinical requirements the radius ratio between thread and pipe is crucial for the adjustments of mass ow and force on the thread.In both regimes, laminar and turbulent flow, the thread shows a characteristic oscillatory behaviour without touching the pipe wall. Resonance-like oscillations indicate circular thread motions around the pipe centre. The oscillating eccentricities may arise from longitudinal inhomogeneities of the thread shape and flow disturbances which cause non-stationary lateral momenta. According to established findings on annular flow with eccentric cylinders we assume that the mass flow, which is high compared to the concentric model, is caused by the temporary thread eccentricities. These findings should be considered in clinical applications to avoid possible thread blockage due to resonance-like vibrations.

Mathematical modeling of axial flow between two eccentric cylinders: Application on the injection of eccentric catheter through stenotic arteries

“…A simplified version of the injection process can be modeled mathematically by considering the axial flow between concentric cylinders with the inner cylinder (representing the thread or catheter) moving at a constant velocity. The first study was that of Frei et al [4], who examined the problem experimentally and theoretically. They modeled the thread injection process by using a cylindrical rubber filament to represent the catheter.…”

Single Fiber Transport in a Fracture Slit: Influence of the Wall Roughness and of the Fiber Flexibility

“…Except for the numerical work of [Frei et al 2000], all studies of moving cylinders in confined geometry were restricted to the case of cylindrical objects normal to the flow [Bouard 1997, Zovatto et al 2001, Richou et al 2005. Finite element simulations were thus undertaken to determine the velocity V f of a fiber parallel to the flow; particular attention was given to the dependence of V f on the distance of the axis of the cylinder from the mid-plane of the fracture.…”

Flows in annuli with longitudinal grooves

“…Progress in modelling of the effects of surface roughness is well summarized by Valdes et al (2007). The thread-annular flow found in minimally invasive surgical applications has been studied by Freai, Lüscher & Wintermantel (2000).…”