Showing papers by "Ephraim M Sparrow published in 2011"

Numerical simulation of fluid flow around a vertical-axis turbine

Abstract: A novel, vertical-axis turbine has been designed to meet a specific power-generation need. It is intended that the turbine will provide local electricity to off-grid cellular communication towers. It is intended that the turbine will reduce or eliminate the use of diesel-power generation for these towers and result in a reduction of operating costs and greenhouse gas emissions. The design effort has had two main stages. First, a prototype turbine blade was designed and tested in a large-scale wind tunnel. The initial design was based on available literature information. Subsequently, numerical simulations of the fluid flow patterns around the turbine blade were used to create improvements to the design. These improvements include the use of venting apertures in the turbine blade to reduce negative drag and thrust loading and the use of caps to improve power-generation efficiency. Through numerical modeling, significant improvements in performance were achieved resulting in a viable turbine design.

An Archive of Skin-Layer Thicknesses and Properties and Calculations of Scald Burns With Comparisons to Experimental Observations

Abstract: A numerical model has been constructed to assess the depth of injury incurred when skin is exposed to heated water. The model includes an extended duration that occurs when clothing, saturated with hot water, is kept in contact with the skin after the direct exposure has ended. The model takes data from a broad summary of literature, which examines the ranges of reported tissue thicknesses, tissue thermophysical properties, and blood perfusion. Water temperatures ranging from 60°C to 90°C and total exposure durations up to 110 s were modeled. As expected, longer durations and elevated temperatures lead to a greater extent of tissue injury. For lower values of temperatures (60°C), burns range from mild (0.1 mm) to severe (2.2 mm) depending on the exposure duration. On the other hand, for higher exposure temperatures (90 °C), all durations led to burns that extended at least halfway through the dermal layer. As expected, burn depths with intermediate temperatures fell between these ranges. Calculated values of tissue injury were compared with prior injury reports. These reports, taken from literature, reinforce the present calculations. It is seen that numerical models can accurately predict burn injury as assessed by clinical observations; in fact, the calculations of burn injury presented here provide more information for the appropriate treatment of burn injuries compared with visual observation. Finally, literature values of a number of skin-layer thicknesses, thermophysical properties, and burn-injury parameters were collected and presented as an archival repository of information.

Optimal Techniques with the Diamondback 360° System Achieve Effective Results for the Treatment of Peripheral Arterial Disease

Abstract: The Diamondback 360® Orbital PAD System (DB360) is a novel orbital atherectomy system for the treatment of calcified lower extremity lesions associated with peripheral arterial disease (PAD). This percutaneous, endovascular system incorporates the use of centrifugal force and differential sanding to modify plaque morphologies. The mechanism of differential sanding discriminates between compliant arterial tissue and diseased fibro-calcific or calcific plaque. An eccentrically mounted diamond-coated crown orbits at high speeds and removes a thin layer of calcific plaque with each pass of the crown. The crown creates a more concentric, smooth vessel lumen with increased diameter, increased lesion compliance and improved blood flow while protecting the vessel media. As a result, the risk for post-procedure thrombus formation and potential for restenosis may be reduced. The risk of intra-procedural events (slow flow, hemolysis, spasm and pain) may be reduced due to the design of this orbital sanding system along with proper technique. Extensive benchtop, in vivo, and clinical testing has confirmed these results and is presented within this paper. In addition, guidelines for selecting the most appropriate crown size and type (solid versus classic) and step-by-step procedural technique and pharmacology information are presented. The DB360 System provides a safe, efficacious, and cost-effective endovascular method for PAD treatment. Careful understanding of procedural methods, use of pharmacological drugs, and understanding of device operation contributes to improved treatment success.

High-frequency pulsatile pipe flows encompassing all flow regimes

Abstract: Time-varying pipe flows driven by a harmonically pulsating inlet velocity and spanning all flow regimes have been investigated by means of numerical simulations. The Reynolds number varied from 1000 to 5000 in response to the inlet velocity oscillations. The frequency of the pulsations was varied from 1 to 10 Hz. These frequencies are markedly higher than those previously studied (maximum value of 0.025 Hz). The motivation for the use of the elevated frequency range was engendered by practical applications such as cardiovascular and respiratory systems of mammals in addition to numerous industrial applications. The simulations made use of the modified Menter transitional model. The key conclusion found here is that the use of a quasi-steady model for the prediction of fully developed friction factors is not applicable for the higher frequencies considered here. The deviations between the actual and quasi-steady friction factor values increase markedly with increasing frequency. Backflow occurs near the wa...

Particle Trajectories and Agglomeration/Accumulation in Branching Arteries subjected to Orbital Atherectomy.

Abstract: Background: The transport of particles in surrogate and actual arterial geometries has been investigated syner- gistically by experimentation and numerical simulation. The motivating application for this work is orbital atherectomy which spawns a particle cloud in the process of debulking plaque from arterial walls. Methods: Paired simulations and experiments were performed to prove the capability of the simulation model to predict both fluid and particle motions in branched arterial geometries. The verified model was then employed to predict the pat- tern of fluid flow in an actual multi-branched arterial geometry, including the flowrates passing through each of the indi- vidual branches. These predictions are in very good agreement with experimental data. Focus was then shifted to the is- sues of particle agglomeration within the flowing fluid and particle accumulation on the vessel walls. Once again, a syn- ergistic approach was used. Flow visualization was employed to track the particle motions and to identify possible particle agglomeration within the fluid. Results and Conclusions: Accumulation of particles on walls was identified by measuring size distributions of effluent and residue within the artery. Scanning Electron Microscopy (SEM) evaluation showed evidence of a size-based sorting as the particles passed through vessels. It was found that plaque-facsimile particles resisted particle-particle agglomera- tion. They also did not accumulate to the wall of the facsimile artery. In addition, simulations showed that if particle-wall accumulation were to occur, it would be limited to very small regions in the artery branches.

Bioreactor for the reconstitution of a decellularized vascular matrix of biological origin

Abstract: Acellular matrices derived from animal and human cadaveric donor vessels or other tubular matrices are appropriate candidates for the creation of tissue- en-gineered, small-diameter, muscular arteries. Engi-neering principles have been used to design a bio-reactor and the necessary auxiliary systems for the reconstitution of a previously decellularized vascular matrix. The bioreactor enables the attachment of cells to the luminal and/or exterior surfaces of the matrix. For the recellularization procedure, the matrix is situated within a sealed compartment in order to maintain a sterile environment. The matrix is rotated continuously to assure a spatially uniform re-constitution. The auxiliary systems that serve the bioreactor are: (a) an oxygenator, (b) peristaltic pumps, one for conveying the internal cell medium and the other for conveying the external cell medium, (c) motor and gearing to create steady and controlled rotation, (d) reservoirs for the containment of the two media, and (e) tubing to convey the respective fluids and to interconnect the bioreactor culture chamber to the various auxiliary components. A recellularized matrix produced by the bioreactor demonstrated its capabilities to reconstitute a previously decellularized scaffold.

Simulation of helically wrapped, compact heat exchangers

Abstract: A new category of heat exchanger has been invented which fulfills the dual requirements of compactness and high thermal efficiency. The underlying principle of the exchanger is the helical intertwining of the tubes which carry the participating fluids. To ensure a thermal bridge of high conductivity between the tubes, silver braze was introduced into the interstitial space. Numerical simulation was used to characterize the performance of this category of heat exchanger. The simulation model is three-dimensional for both fluid flow and heat transfer and is also conjugate in that it encompasses two flow passages, their walls, and the interconnecting silver braze. A fabrication means was also developed. Numerical results were obtained for two general classes of heat exchange situations, one of which dealt with single-phase flows while the other related to two-phase flows. The single-phase situation investigated here is a water-water heat exchanger. The heat exchange effectivenesses evaluated from the numerical simulations demonstrated a level of enhancement of 84% compared to a baseline case consisting of straight flow passages. This level of enhancement is substantially higher than that achieved by other modes of augmentation. The results also showed that further enhancements can be achieved by increasing the number of helical turns per unit length. Experimentation was used to validate the basic computational model. For a given physical situation, the measured relationship between volumetric fluid flow and pressure drop was compared with that predicted by the numerical simulation. The excellence of the agreement lends strong support to the physical principles that underlie the simulation model

Numerical simulation of fluid flow around a

Abstract: FIG. 7. Simulated power generated on a two-dimensional, three-stage wind turbine positioned in a simulated wind tunnel.Approach air speed¼8.7 m=s.FIG. 8. Comparison of a simulated two-dimensional turbine with experimentally determined results. The data are takenwith an approach wind speed of 8.7 m=s and a three-stage rotor. Experiments were completed with a capped and ventedrotor, shown in Fig. 9.

Secondary wave phenomena following an underwater explosion

Abstract: Underwater explosions produce apowerful shockwave followedbya secondarypressurewave,which results from the contraction of the gaseous products created by the explosion. Analytical tools were employed in order to find the variation of the secondarywave pressure as a function of time for 60 lbs of HBX-1 explosive at a 7.315m (24 ft) depth of detonation. These tools included the Navier–Stokes equations, the volume-of-fluid model of two-phase flow, and the so-called similarity equations, which are experimentally derived and embody the behavior of the shockwave and the period of the secondary wave. Heat-transfer phenomena were carefully assessed, and it was found that both the magnitude of the maximum pressure and the time of its occurrence are highly insensitive to heat transfer. During its evolution, the shape of the bubble created by the explosion passes through a range of significantly different geometries. At a time equal to half the bubble period, the shape ismore or less spherical. At the end of a full period, the bubble is toroidal in shape. Owing to the buoyancy of the bubble, it experiences a vertical rise as a function of time. The maximum rise is approximately 2 m. The rising bubble causes the displacement of the surface of the water.