Numerical Analysis of Pressure Gradient along Casing in Helical Turbulent Flow of Power Law Fluid in Eccentric Annulus

With the use of casing running tool (CRT), casing can be rotated and reciprocated at the same time with circulation of drilling fluid. Thus the flow in well bore was eccentric annular helical. Pressure exerted on casing was important for casing buckling analysis. A numerical model of eccentric annular helical flow of power law fluid was built in this paper. The relationship between average pressure gradient on pipe and some influence factors (pipe axial velocity, rotating angular velocity, drilling fluid circulation velocity, and axial coordination) was analyzed. Results showed that average pressure gradient caused by shear stress was only affected by average annular flow velocity, and it didn’t change along pipe length. Effect of rotating angular velocity on average pressure gradient on pipe was very small and could be negligible. A fitting function between average pressure gradient and average annular flow velocity was obtained in this end.

Hydrodynamic Evaluation of a Minimally Invasive Heart Valve in an Isolated Aortic Root Using a Modified In Vitro Model

Implantation methods for commercially available heart valve prostheses require open-chest access to the heart to perform the suturing process. In order to alleviate this complicated surgical implant technique, a “stent-valve” design was developed that will provide a less cumbersome implantation method and therefore a less invasive access to the heart. The purpose of this study is to verify its hydrodynamic performance and migration characteristics to assess its feasibility for use as a replacement heart valve. Hydrodynamic evaluation of the novel stent-valve combination device was carried out using a Vivitro left heart simulator and by setting up a comparison with the same 19 mm trileaflet valve under a traditional implantation (suture) method. To assess implantation ability under normal physiological conditions, porcine aortic root tissue was mounted into the left heart simulator to replace the original glass sinus. A comparison experiment was conducted to study the change in the total compliance and resistance of the testing system using the modified Windkessel model. For the range of test conditions investigated, the stent-valve combination device produced an average pressure gradient of 41.2 mm Hg(±19.6 mm Hg), an average effective orifice area (EOA) of 1.06 cm2(±0.08 cm2), and an average regurgitation percentage of 4.5% (±3.3%), while the sutured valve produced an average pressure gradient of 48.7 mm Hg(±17.4 mm Hg), an average EOA of 0.88 cm2(±0.14 cm2), and an average regurgitation percentage of 0.8% (±0.4%). The total compliance and resistance of the system was 0.37 ml/mm Hg(±0.01 ml/mm Hg) and 1.1 mm Hg/ml/s(±0.29 mm Hg/ml/s), with the original Windkessel model, and 0.33 ml/mm Hg(±0.01 ml/mm Hg) and 1.1 mm Hg/ml/s(±0.24 mm Hg/ml/s) for the system with the aortic tissue. The stent-valve combination device has demonstrated favorable hydrodynamic performance when compared with the same trileaflet valve under the traditional suturing method, and the arterial stent makes it possible to secure the valve at its required position without migration.

A model of the injection moulding process

This paper is concerned with the injection moulding process, in which hot molten plastic is injected under high pressure into a thin cold mould. Assuming that the velocity and temperature profiles across the mould maintain their shape, a simple steady state model to describe the behaviour of a Newtonian fluid during the filling stage is developed. Various phenomena of the process are examined, including the formation of a layer of solid plastic along the walls of the mould, and the relationship between the flux of liquid plastic through the mould and the average pressure gradient along the mould. In any given situation, it is shown that there is a range of pressures and injection temperatures which will give satisfactory results.