John Elsnab

Sea ice floes dissipate the energy of steep ocean waves

A laboratory experimental model of an incident ocean wave interacting with an ice floe is used to validate the canonical, solitary floe version of contemporary theoretical models of wave attenuation in the ice-covered ocean. Amplitudes of waves transmitted by the floe are presented as functions of incident wave steepness for different incident wavelengths. The model is shown to predict the transmitted amplitudes accurately for low incident steepness but to overpredict the amplitudes by an increasing amount, as the incident wave becomes steeper. The proportion of incident wave energy dissipated by the floe in the experiments is shown to correlate with the agreement between the theoretical model and the experimental data, thus implying that wave-floe interactions increasingly dissipate wave energy as the incident wave becomes steeper.

Endocapsular carousel technique phacoemulsification.

&NA; We describe an approach to cataract phacoemulsification that uses the carouseling technique within the capsular bag. This is made possible by a newly designed phacoemulsification tip with 3 unique modifications: a 20‐degree right bend in the tip, a semicircular opening, and a third irrigation port. These 3 features facilitate the carouseling technique of phacoemulsification without expressing the lens into the anterior chamber. The method decreases corneal endothelial injury by maximizing the distance between the delivered thermal energy and the corneal endothelium. The preoperative and postoperative pachymetry and endothelial cell counts in the first 8 patients treated using this technique are reported. Financial Disclosure: G.J. Jardine, G.C. Wong, J.R. Elsnab, and B.K. Gale have no financial or proprietary interest in any material or method mentioned. Additional disclosure is found in the footnotes.

Estimation of Kinetic Energy Dissipation from Breaking Waves in the Wave Crest Region

AbstractWave-induced turbulence due to breaking in the absence of surface shear stresses is investigated experimentally. A high-fidelity particle image velocimetry (PIV) technique is used to measure the turbulence near the water surface, inside the wave crests. The spatial velocity vector fields of the breaking waves acquired from PIV provide accurate vertical velocity profiles near the air–water interface, as well as wavenumber velocity spectra beneath the breaking waves at different depths. These velocity spectra exhibit a Kolmogorov interval at high wavenumbers, indicating the presence of isotropic turbulence and permitting an estimation of energy dissipation rates. The depth dependence of dissipation rates of the breaking waves generated in the laboratory shows a scaling similar to that found in wind-forced breaking waves in the field. A phase dependence in the dissipation rates of turbulence kinetic energy is also observed, which should be considered to improve the accuracy of the estimated and model...

Experimental investigation of mixing in a t-channel for asymmetric inlet conditions

An experimental investigation of water flow in a rectangular T-channel with inner dimensions of 20 × 20 mm (inlet channel) and 20 × 40 mm (outlet mixing channel) has been conducted. The inlet Reynolds number Re, based on inlet hydraulic diameter, ranged from Re1 = 90 to 775. Inlet flow conditions were asymmetric, and inlet Re ratios of Re1/Re2 = 1.24, 1.65 and 2.45 were obtained by varying volumetric flow rate. Dynamical conditions and T-channel geometry are directly applicable to microscale mixing. Planar laser induced fluorescence (LIF) was used to characterize flow regimes and behaviors, including periodicity, in the inlet and outlet channels. Two distinct flow regimes were identified and characterized for asymmetric inlet Re. For low inlet Re, Re1 ≤ 150, and all Re1/Re2, flows were steady. For higher Re and all Re1/Re2, a jet flow regime, characterized by two counter rotating vortices and increasingly turbulent at higher Re dominated the flow in the junction. Qualitative mixing characteristics for all flow regimes, based on LIF visualizations in the outlet channel, are also presented.Copyright

Contraction/Expansion Effects in 90° Miter Bends in Rectangular Xurographic Microchannels

Xurography is an inexpensive rapid prototyping technology for the development of microfluidic systems. Imprecision in the xurographic tape cutting process can result in undesired changes in channel dimensions near features that require a change in cutting direction, such as 90° miter bends. An experimental study of water flow in rectangular xurographic microchannels incorporating 90° miter bends with different channel widths in each leg is reported. A set of twelve microchannels, with channel depth approximately 105 micrometers and aspect ratio ranging from 0.071 to 0.435, were fabricated from double-sided adhesive Kapton® polyimide tape and two rectangular glass plates. The channels were reinforced with a mechanical clamping system, enabling high Reynolds number, Re, flows (up to Re = 3200) where Re was based upon hydraulic diameter and average velocity. Reported data include friction factor and critical Reynolds number for straight microchannels and loss coefficients for flow through 90° miter bends that contain either a contraction or expansion with cross-sectional area ratios of 0.5, 0.333 and 0.2. The critical Reynolds number, Recr , ranged from 1750 to 2300 and was found to be dependent on channel defects such as sidewall roughness, adhesive droplets, and corner imperfections. Loss coefficients through 90° miter bends with expansion decrease rapidly for Re Recr . For 90° miter bends with contractions, loss coefficients gradually decrease with increasing Re for 150 < Re < 1400. In addition, the loss coefficient decreases with decreasing area ratio through the contraction or expansion. The minor loss coefficient data were found to be dependent on Reynolds numbers and area ratio of contraction/expansion at the bend. The results suggest that the effect of the contraction/expansion was the dominant mechanism for minor losses in the 90° miter bend.Copyright

Sample to answer: a fully integrated nucleic acid identification system for bacteria monitoring

A fully integrated microfluidic system was developed and incorporates an EC-MWCNT (electrochemical multiwalled carbon nanotube) sensor for the detection of bacteria. Sample metering, reagent metering and delivery was implemented with microvalves and pumps embedded inside the microfluidic system. The nucleic acid extraction was performed using microchannels controlled using automated platforms and a disposable microfluidic silica cartridge. The target samples were flowed and hybridized with probe ssDNA (single strand DNA) across the MWCNT-EC sensor (built on a silicon chip), which was embedded in a microfluidic cell. The 9-pad sensor was scanned before and after hybridization to measure the quantity of RNA (Ribonucleic acid) bound to the array surface. A rapid and accurate sample-in answer-out nucleic acid system was realized with automated volume metering, microfluidic sample preparation, and integrated nano-biosensors.

Isothermal microtube heat transfer with second-order slip flow and temperature jump boundary conditions

Two analytical models are presented in which the continuum momentum and energy equations, coupled with second-order slip flow and temperature jump boundary conditions, are solved. An isothermal boundary condition is applied to a microchannel with a circular cross section. The flow is assumed to be hydrodynamically fully developed and thermal field is either fully developed or thermally developing from the tube entrance. A traditional first-order slip boundary condition is found to over predict the slip velocity compared to the second-order model. Heat transfer increases at the upper limit of the slip regime for the second-order model. The maximum second-order correction to the first-order Nusselt number is on the order of 18% for air. The second-order effect is also more significant in the entrance region of the tube. The Nusselt number decreases relative to the no-slip value when slip and temperature jump effects are of the same order or when temperature jump effects dominate. When temperature jump effects are small, the Nusselt number increases relative to the no-slip value. Comparisons to a previously reported model for an isoflux boundary condition indicate that the Nusselt number for the isoflux boundary condition exceeds that for the isothermal case at all axial locations.Copyright

An experimental comparison of velocities underneath focussed breaking waves

Abstract Nonlinear wave interactions affect the evolution of steep wave groups, their breaking and the associated kinematic field. Laboratory experiments are performed to investigate the effect of the underlying focussing mechanism on the shape of the breaking wave and its velocity field. In this regard, it is found that the shape of the wave spectrum plays a substantial role. Broader underlying wave spectra leads to energetic plungers at a relatively low amplitude. For narrower spectra waves break at higher amplitudes but with a less energetic spiller. Comparison with standard engineering methods commonly used to predict the velocity underneath extreme waves shows that, under certain conditions, the measured velocity profile strongly deviates from engineering predictions.

Microtube Gas Flows With Second-Order Slip Flow and Temperature Jump Boundary Conditions

Second-order slip flow and temperature jump boundary conditions are applied to solve the momentum and energy equations in a microtube for an isoflux thermal boundary condition. The flow is assumed to be hydrodynamically fully developed, and the thermal field is either fully developed or developing from the tube entrance. In general, second-order boundary conditions assuming an effective mean free path model predict a lower slip velocity than a first-order model assuming a hard sphere mean free path model. Heat transfer effects associated with rarefied flow are reduced for the second-order model. The effect of the second-order terms is most significant at the upper limit of the slip regime. For airflow at standard conditions, the maximum second-order change to the Nusselt number is on the order of 15%. The second-order effect is also more significant in the entrance region of the tube. Nusselt numbers are found to increase relative to their no-slip values when temperature jump effects are small. In cases where slip and temperature jump effects are of the same order, or where temperature jump effects dominate, the Nusselt number decreases when compared to traditional no-slip conditions.

Microtube Fluid Dynamic Characteristics With MTV Qualified Flow Conditions

Deionized water flows in fused silica microtubes, with nominal diameters of 100, 320, and 1000-μm were studied. Flow conditions produced Reynolds numbers in the range 150 < Re < 11,000. Critical Reynolds number was found to be in the range of 2180 < Recr < 2450 for the three tube sizes. The average Poiseuille number was 76.9 ± 5%. Experimental turbulent data was in excellent agreement with the Colebrook equation. Molecular tagging velocimetry was used to further validate transition; Recr was in agreement with that determined by the integral technique.Copyright