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In this paper, we describe high-precision experimental and numerical characterization of the positioning forces acting on Drosophila embryos that have self-assembled onto 2-D arrays of hydrophobic sites on a silicon substrate in water. The forces measured using a surface micromachined optical-encoder force sensor operating in reflection, are in good agreement with numerical simulations based on an extended surface energy model for the oil-based fluidic system. The positioning forces of ellipsoidal embryos on flat sites show a linear-spring-like relationship between the force and displacement on rectangular as well as cross-shaped sites. An average detachment force of 8.9 /spl mu/N/spl plusmn/1.3 /spl mu/N was found for the immobilized embryos on 250 /spl mu/m/spl times/100 /spl mu/m sites. The cross-shaped site has only 19.85% of the area of the rectangular site, but provides a comparable positioning force with a significant reduction in embryo clustering. In contrast, the positioning forces of flat silicon chips, similar in size to the embryos, are linear in the displacement only over a limited range (0/spl sim/40 /spl mu/m), and are then constant up to the detachment force (25.0 /spl mu/N/spl plusmn/3.5 /spl mu/N). Our measurements also show significant hysteresis in the force vs. displacement, indicating that variations in the surface properties play an important role in the self-assembly process.

We describe high precision experimental and numerical characterization of the positioning forces acting on Drosophila embryos that have self-assembled onto two-dimensional arrays of hydrophobic sites on a silicon substrate in water. The forces measured using a surface micromachined optical-encoder force sensor operating in reflection, are in good agreement with numerical simulations based on an extended surface energy model for the oil-based fluidic system. The positioning forces of ellipsoidal embryos on flat pads show a linear-spring-like relationship between the force and displacement on rectangular as well as cross-shaped pads. In contrast, the positioning forces of flat silicon chips, similar in size to the embryos, are linear in the displacement only over a limited range, and are then constant up to the detachment force. The optical force characterization method and the associated surface energy model for the self-assembly process can potentially be used for design optimization of fluidic self-assembly for a wide range of applications in biology.

We present a micrograting-based force sensor integrated with a surface micromachined silicon-nitride probe for penetration and injection into Drosophila embryos. The probe is supported by springs of a known spring constant, and the penetration force is determined from displacement measurements using a high-resolution, miniaturized optical encoder that is designed to only be sensitive to axial deflections of the probe. The optical-encoder force sensor exhibits configurable sensitivity and dynamic range, allowing monitoring over a wide range of forces. The periodicity of the encoder response can be used for calibration of the injector displacement and to obtain information about the localized elastic properties of the target. We used an force sensor with a measured spring constant of 1.85 N/m for penetration experiments on Drosophila embryos, and found a penetration force of 52.5 μN (±13.2%) and a membrane displacement of 58 μm (±5.2%).

Laser Doppler velocimetry (LDV) measurements are presented of turbulent flow in a two-pass square-sectioned smooth duct simulating the coolant passages employed in gas turbine blades under rotating and nonrotating conditions. For all cases studied, the Reynolds number characterized by duct hydraulic diameter and bulk mean velocity was fixed at 1×104. The rotation number Ro was varied from 0 to 0.2. It is found that as Ro is increased, both the skewness (SK) of streamwise mean velocity and magnitude of secondary-flow velocity increase linearly, SK=2.3 Ro and U2+V2¯/Uh=2.3 Ro+0.4, and the magnitude of turbulence intensity level increases exponentially. As Ro is increased, the curvature induced symmetric Dean vortices in the turn for Ro=0 is gradually dominated by a single vortex most of which impinges directly on the outer part of leading wall. The high turbulent kinetic energy is closely related to the dominant vortex prevailing inside the 180-deg sharp turn. The size of separation bubble immediately after the turn is found to diminish to null as Ro is increased from 0 to 0.2. A simple correlation is developed between the bubble size and Ro. A critical range of Ro responsible for the switch of faster moving flow from near the outer wall to the inner wall is identified. For both rotating and nonrotating cases, the direction and strength of the secondary flow with respect to the wall are the most important fluid dynamic factors affecting local the heat transfer distributions inside a 180-deg sharp turn. The role of the turbulent kinetic energy in the overall enhancement of heat transfer is well addressed.

Heat transfer measurements using a transient liquid crystal thermometry (TLCT) are presented to study the eAect of rotation on the local heat transfer distributions around a sharp 180∞ turn of a two-pass smooth square duct for the first time in open literature. The duct has a dimensionless divider wall thickness of 0.25. Detailed local Nusselt number distributions on the leading and trailing walls are given for rotation numbers ranging from Roa 0 to 0.20 at a Reynolds number of 1:0 10 4 . The results show informative spanwise variations of heat transfer enhancement or abatement resulting from rotation. A critical range of Ro is identified, below which the regional averaged Nusselt number ratios of the regions after the 180∞ sharp turn in a rotating two-pass cooling passage are rather insensitive to the rotation eAect. Laser‐Doppler velocimetry (LDV) measurements within the turn are further performed to explain the local heat transfer distributions. Under rotating conditions, the curvature induced symmetric Dean vortices in the turn for the stationary case change greatly and are dominated by a single vortex most of which impinges directly on the leading wall’s outer part, resulting in a high heat transfer enhancement on the leading wall in the turn. ” 2001 Elsevier Science Ltd. All rights reserved.

The effect of divider thickness on fluid flows in a two-pass smooth square duct with a 180 deg straight-corner turn is an important issue to the turbine blade internal cooling but has not been explored in the past. Laser-Doppler velocimetry measurements are thus presented for such a study at a Reynolds number of 1.2 × 104 and dimensionless divider thicknesses (Wd*) of 0.10, 0.25, 0.50. Results are presented in terms of various mean velocity components in two orthogonal streamwise planes and three cross-sectional planes, the local and regional averaged turbulent kinetic energy and resultant mean velocity distributions, and complemented by the liquid crystal measured heat transfer coefficient contours. The measured velocity data are able to reasonably explain published and present measured heat transfer results. Wd* is found to have profound effects on the flow features inside and immediately after the turn. The turbulence level and uniformity in the region immediately after the turn respectively decrease and increase with increasing Wd*.

Measurements are presented of the distributions of heat transfer coefficients along the leading and trailing walls of a rotating two-pass rectangular channel with through flow. The channel has a 180° rectangular turn and a cross-sectional aspect ratio of 1.25. The Reynolds number and rotational number were varied from 5.0×103 to 5.0×104 and 0 to 0.44, respectively. Complementary flow visualization and laser-Dopper velocimetry measurements were also performed to facilitate interpretation of the measured heat transfer distributions. The results show that the secondary flow induced by the curvature and turbulence enhancement associated with unsteadiness of separation bubble downstream of the sharp turn are responsible for the significant heat transfer augmentation attained in the first part of the second pass. Moreover, the quantitative effects of the Coriolis force on the skewness of streamwise mean velocity profiles and in turn different local and average heat transfer features in the radially outward and inward flows are demonstrated and addressed.

We present a high-speed microfluidic cell sorter employing embedded heaters and nozzles to generate deflecting jets to change the movement of the cells. We simulated the transient flow fields to validate the concept and optimize the sorter design. The simulation demonstrates a spatial switching window corresponding to 1.1 times the switching chamber length. Experimental verification was obtained using micromachined devices characterized by stroboscopic measurements. With a 4.9 /spl mu/s working period for the 20/spl times/20 /spl mu/m/sup 2/ heaters that generate the deflecting jets, the sorter can potentially attain a working frequency of 50 kHz or higher. We built a scattered-light based optical system to detect moving particles and successfully performed sorting of 20 /spl mu/m microspheres. This type of sorter is promising for micromanipulation of a variety of biological cells and inorganic particles.

We present a micrograting-based injection force sensor integrated with a surface micromachined silicon-nitride injector. The injector is supported by springs of known spring constant, and the injection force is determined from displacement measurements using a high-resolution, miniaturized optical encoder. The sensor exhibits configurable sensitivity and dynamic range, allowing monitoring over a wide range of forces. The periodicity of the encoder response can be used for calibration and to obtain information about the deformation of the target. We used an injector with a measured spring constant of 1.85 N/m for penetration experiments on Drosophila embryos, and found a penetration force of 52.5/spl plusmn/13.2% /spl mu/N and a membrane displacement of 58/spl plusmn/5.2% /spl mu/m.

Detailed local Nusselt number distributions, streamwise mean flow patterns and cross-sectional secondary flow patterns, and friction factors in the first pass of a sharp turn two-pass square channel with various configurations of longitudinal vortex generator arranged on one wall were measured using transient liquid crystal thermography, laser-Doppler velocimetry, and pressure transducer probing, respectively. The Reynolds number, based on channel hydraulic diameter and bulk mean velocity, was fixed at 1.2 × 104. The vortex generator height-to-hydraulic diameter ratio and pitch-to-height ratio were 0.12 and 10, respectively. Comparisons in terms of heat transfer augmentation and uniformity and friction loss are first performed on 12 configurations of longitudinal vortex generator. The fluid dynamic mechanisms and wall confinement relevant to heat transfer enhancement are then documented for three-selected vortex generator models. In addition, the differences in fluid flow and heat transfer characteristics between a single vortex generator and a vortex generator array are addressed for the delta wing 1 U and 45° V U models which provide better thermal performance. The direction and strength of the secondary flow with respect to the heat transfer wall are found to be the most important fluid dynamic factors affecting the heat transfer promotion through the channel wall, followed by the convective mean velocity, and then the turbulent kinetic energy. Furthermore, the effects of the two-dimensional heat conduction near the vortex generator edge and unseen heat transfer areas on the Nusselt number estimation are documented in detail.Copyright © 1999 by ASME

In view of lacking in velocity field data for the flow through turbine blade internal cooling passages, laser Doppler velocimetry measurements are presented for the flow development in a two-pass smooth rectangular duct of 1.1 aspect ratio with a 180 deg straight-corner turn with and without duct rotation. The test duct had a curvature axis normal to the rotational axis. The Reynolds number based on the bulk mean velocity and hydraulic diameter was 1.4 × 104 and the rotation numbers were 0 and 0.082. Characteristics, such as the upstream and downstream extents of the sharp-turn effect on the main flow profile, curvature induced Dean vortices inside the turn, turning geometry-induced separating bubble immediately downstream of the turn, and the resulting double-peak mean velocity profiles in the second pass are used to describe the developing mean flow for the case without rotation. High turbulence levels and significantly more non-uniform flow after the sharp turn in the front part of the second pass explain previously reported work showing higher but non-uniform heat transfer after that turn. Rotating the duct augments and shifts the peaks of the streamwise mean velocity and turbulence intensity profiles towards the trailing and leading walls of the first and second passes, respectively. In addition, the duct rotation skews the separating bubble and reduces its size to about 75% of its stationary counterpart.