Influence of numerical and viscous dissipation on shock wave reflections in supersonic steady flows

Numerical simulations are investigated to describe precisely the shock wave reflections in supersonic steady air flow field. The main objectives are to study the influence of the wedge trailing edge corner angle, of the numerical methods and of the viscous effects on the shock wave reflections and on the hysteresis behavior. The computations are done with different MUSCL-TVD finite volume schemes and the corresponding results are compared. The flow viscosity is also taken into account and comparisons are made between inviscid and viscous flow simulations. The results display the non-negligible influence of the numerical scheme accuracy on the results, mainly on the position and height of the Mach stem, and the relatively weak influence of the flow viscosity on these parameters. Comparisons between numerical results and experimental data have also been done and a good agreement is only observed for small wedge angles mainly due to the three-dimensional effects in the experimental setup.     

Measurement of interfacial area concentration in subcooled liquid-vapour flow

In two-fluid modelling, accurate prediction of the interfacial transport of mass, momentum and energy is required. Experiments were carried out to obtain a database for the development of interfacial transport models, or correlations, for subcooled water-steam flow in vertical conduits. The experimental data of interest included the interfacial area concentration, interfacial condensation heat transfer and bubble relative velocity. This paper focuses on the interfacial area concentration. The interfacial area concentration was obtained by measuring the distributions of bubble volume and surface area as well as the area-averaged void fraction at various axial locations in subcooled water-steam condensing vertical upward flow under low flow rate and low pressure conditions. The bubble size and surface area were determined using high-speed photography and digital image processing techniques. The area-averaged void fraction was measured by a single-beam gamma densitometer. The results were compared with existing correlations, which were developed on the basis of data obtained for air-water adiabatic flows. Poor agreement between the present data and the existing correlations was obtained. Accordingly, new correlations suitable for subcooled liquid-vapour bubbly flow are proposed.     

Implications of variable fluid resistance caused by start-up flow in microfluidic networks

Electrical circuit analogies are often used to design microfluidic systems because they simplify device design, providing simple relationships between fluid flow rate, driving forces, and channel dimensions. However, such approximations often significantly overestimate flow rates in situations where start-up energy losses from establishing kinetic head are similar in magnitude to the energy required to overcome viscous shear stresses, as is often the case within complex microfluidic networks. These reduced flows can be more accurately predicted within an electrical analogy framework that accounts for the nonlinear flow resistance generated on the transient regime of start-up flow. In this work, standard flow resistance expressions are modified to account for such effects, and the onset of nonlinear resistance is predicted by a dimensionless parameter, $\xi = Re\frac{D}{L},$ which is dependent on the Reynolds number and the channel length. As a demonstration, variable fluid resistance is shown to dramatically affect the flow performance of common microfluidic units such as T-junctions and serpentine channels, and the change in performance is accurately predicted. Experimental and theoretical analysis of T-junctions further shows that variable flow resistance causes the ratio of flows through the junction to converge toward unity with respect to an increasing total flow rate. In addition, serpentine channels are shown to exaggerate these start-up effects, owing to compounded energetic demand associated with changing a flow’s direction. As a result, serpentine channels cause the ratio of flow rates exiting a T-junction to diverge from unity with respect to an increasing flow rate.     

Gaseous ammonia as a refining agent for cottonseed oils

In this investigation the application of gaseous ammonia to cottonseed oil refining was explored. The ammonia reacted quantitatively with the free fatty acids in the oil; its solubility in coftonseed oil was determined as a function of pressure. In “degumming” it was more efficient in removing phosphatides than other agents. A reduction in refining loss resulted for oils refined with gaseous ammonia as outlined and compared with the standard AOCS cup loss analysis. However, the oil colors were substantially higher even though the ammonia treated oils were re-refined with caustic solution. Results using cottonseed oil-hexane “miscellas” containing less than 70% oil showed low refining losses, but the colors were estremely high. Above 70% oil content the losses were higher, but the colors were lower. The colors never equalled “standard cup” results. This study was sponsored by the Texas Engineering Experiment Station and the Cotton Research Committee of Texas.     

Views necessary for the traumatic wrist

Wrist injuries are an extremely common occurrence. The origin of these injuries may be due to a fracture of the two bones of the forearm or the wrist bones, which may sometimes require specific X-rays views. They are rarely responsible for a dislocation of the wrist. Strains wrists may be misdiagnosed and may result in instability of the wrist. The initial examination of all wrist injuries should systematically include the following four views: (1) a PAview of the wrist in pronation (with the palm facing downward). (2) a lateral view according to the Meyrueis technique. (3) an oblique view. (4) a scaphoid view. An additional, fifth view with the wrist in supination (with the palm facing upward) may be required. If there is clinical evidence of instability of the wrist or if the initial examination results in a probably strained wrist, a further more complete radiological examination can then be undertaken. This examination, known as "the instability examination" includes stress views, which can allow detection of a discrete instability of the wrist. Finally, it is sometimes necessary to carry out this examination in a bilateral and comparative manner.     

Performance Characteristics of Alpha-Particle Corona-Streamer Counter

Alpha-particle wire-plate corona counters in air can be operated either in the spark or in the corona-streamer modes. The streamer mode is preferred over the spark mode since it has the advantages of low dead time and the absence of electrode corrosion by sparking. An analysis of the alpha-particle corona-streamer counter is described. The alpha-particle triggered corona pulse characteristics (e.g., pulse shape, amplitude, repetition rate, etc.) are calculated. Not only the pulse characteristics but also the inception voltages of the corona-mode regime are determined. For each wire diameter, a transition gap length between corona and spark modes exists, which is termed ``critical gap length.' The counting rate characteristics have been obtained for wire diameters 0.05-0.1 mm. All the theoretical findings are confirmed by experiment.     

Colorectal lesions predisposing to cancer

Precursors of colorectal carcinoma are adenomatous polyps, sporadic or arising in familial adenomatous polyposis and Lynch syndrome and chronic inflammatory lesions related to ulcerative colitis and Crohn's disease. The adenoma-carcinoma sequence is well established and early detection and removal of colorectal adenomas is thought to prevent colorectal cancer in high risk asymptomatic persons, i.e. subjects over 45 years, with personal or familial history of adenomas and colorectal cancers. The precancerous potential of adenomatous polyps varies according to tissue type, with increased risk with the extent of the villous component, high grade of dysplasia, large size greater than 1 cm and multiple adenomas. The development of de novo colorectal cancer from normal mucosa with flat adenomas has been recently emphasized. The risk of colonic cancer in patients with ulcerative colitis and Crohn's disease is controversed.