The measurement of the temperature field at the tool-chip interface in machining has been demonstrated. The key elements in the measurement technique are the use of an optically transparent sapphire tool, which has enabled direct images of the tool-chip contact area in the infra-red to be obtained at high spatial and temporal resolution; and radiation intensity measurements in two wavelength windows which have enabled the temperature field to be accurately derived from these intensity values. The principal characteristics of the temperature field such as the variation of temperature with position along the interface and the location of the region of highest temperature are identified. The implications of this measurement to our understanding of the tribology of the tool-chip interface and machining process models are briefly discussed.

This paper presents global and point-wise comparisons of experimental measurements and numerical simulation results of electroosmotically driven flows in grooved micro-channels. The micro-channels are made by photolithography using poly-dimethyl-siloxane (PDMS), a type of silicon product, which is transparent, permeable to a variety of liquids and vapors. Experiments are performed using a micro-scale particle image velocimetry (μ-PIV) system developed for measurement of flows in micro-channel geometries. Full field velocity distributions are measured in Eulerian viewpoint by tracking the fluorescence images. The numerical algorithm is based on the spectral element formulation of incompressible Navier-Stokes equations with electroosmotic forcing. The algorithm utilizes modal expansions in mixed quadrilateral and triangular meshes, enabling complex geometry discretizations with spectral accuracy. Comparisons of experimental and numerical results show good agreements, validating both numerical and experimental methodologies.

Cooling of surfaces is often carried out in devices consisting of arrays of round nozzles, through which coolant impinges vertically upon the surfaces. To enhance the heat transfer coefficient and save the amount of coolant, two-phase jets were applied to the cooling of copper surface of 30mm in diameter. Experiments were conducted with using water and air at atmospheric pressure. The heat transfer coefficient by single-phase water jets was well described with an empirical correlation. The experimental heat transfer coefficient increased with addition of air. When the volumetric air flow ratio β is less than 0.2, the heat transfer coefficient by air/water two-phase jets was larger than the prediction where the volumetric two-phase velocity and the physical properties of water were used in the empirical correlation for single phase heat transfer. However, the experimental data gradually decreased with increase of gas phase at β > 0.2. To study the enhancement and degradation mechanism of impinging two-phase heat transfer, the flow pattern in a capillary tube such as the nozzle tube and the impinging behavior on a transparent glass plate were observed with a high-speed video camera. When β was small, numerous air micro bubbles of very small diameter were impinging on the heat transfer surface. When β was large, impinging micro bubbles could not be observed. Gas and water phases intermittently impinged on the glass plate as the heat transfer surface. In the observed photograph, a hexagonal pattern resulting from interference among the adjusting two-phase jets could be recognized. The enhancement of heat transfer at β < 0.2 is considered to be due to the micro bubbles sweeping on the surface. The degradation at β > 0.2 is mainly due to the lower thermal capability of gas-phase than that of liquid-phase. The gas-phase intermittently impinged on the surface and its heat transfer was relatively low.

Optical breakdown by ultrashort laser pulses in dielectrics presents an efficient method to deposit laser energy into materials that otherwise exhibit minimal absorption at low laser intensities. During optical breakdown, a high density of free electrons is formed in the material, which dominates energy absorption, and, in turn, the material removal rate during ultrafast laser-material processing. Classical models assume spatially uniform electron population and constant laser intensity in the focal region, which results in a time-dependent expressions only, i.e., the rate equations, to predict electron evolution induced by nanosecond and picosecond pulses. For femtosecond pulses, however, the small spatial extent of the pulse requires that the pulse propagation be considered, which results in inhomogeneous plasma and localized electron formation during optical breakdown. In this work, a femtosecond breakdown model is combined with the classical rate equations to determine both time- and position -dependent electron density during femtosecond optical breakdown in water. The model exhibits good agreement when compared with experimental results. For other transparent or moderately absorbing dielectric media, the model also shows promise for determining the time- and position-dependent electron evolution induced by ultrashort laser pulses. Another interesting result is that the maximum electron density formed during femtosecond-laser-induced optical breakdown can exceed the conventional limit imposed by the plasma frequency.

Liquid crystal is one of homogeneous ER (Electrorheological) fluids in some range of temperature. Transient responses of pressure drop are examined when liquid crystal flows between two parallel-plate electrodes for constant flow rates. When voltages are applied on the liquid crystal and removed, the pressure responses of the inlet of electrodes are measured with the pressure transducer. At the same time, liquid crystal between the transparent electrodes made of glass is visualized with the high-speed video camera to investigate the time history of the director of the liquid crystal. Outlet of the flow channel with two parallel-plate electrodes is atmosphere. Relation between the flow visualization results and changes of pressure drop is investigated especially for transient period. In the present experiment the flow rates change from 0.001cc/sec (velocity is 1mm/sec) to 0.003cc/sec and the electric field intensity is from 0.2kV/mm to 1kV/mm. The gap of the electrodes is 0.2mm. The isotropic-nematic transition is 35.5°C and smectic-nematic transition is 23.1°C. The open-loop test facility with the liquid crystal is set in a pyrostat to keep the temperature constant.

Future gun-launched projectiles will have higher muzzle velocities. There currently exists a need for RF transparent radome solutions with muzzle velocities near Mach numbers equal to 3 (M = 3). Future Combat System (FCS) requirements may push these velocities as high as M = 5. Assessments of aerothermal heating requirements for specific radome geometries need to be studied. Trade-off studies involving aerodynamic shape, antenna location, materials, and RF characteristics also need to be made. The final product of this report is twofold. The first is a short-term solution using the extruded/molded plastics to manufacture a radome. The other is a guideline for a more extensive study to find several solutions for high speed, RF transparent radomes for ballistic projectiles.

Phase-resolved PIV measurements were performed to reveal the detailed flow features within a triple impeller stirredtank. Two tests were performed: low and high rotational speeds, 175 and 575 RPM, respectively. The tests used an optically transparent mixing vessel to measure the 2D flow field characteristics along a vertical plane passing through the tank center. The measurements disclosed interesting in-plane vortical behavior that when measured at two angular positions with respect to the blade passage further indicated the three-dimensional flow behavior. For the low RPM case, a laminar flow nature was apparent, whereby vortical toroidal structures spanned around the stirrer vertical axis. Six such structures were dominant. For the high RPM case and for θ = 0° six dominant vortical structures were apparent. Their r-z plane location and size were different from that for the low RPM case. With blade passage four of these vortical structures appeared to merge into two, suggesting that constant toroidal vortical structures spanning around the stirrer axis were absent from the high RPM case. A switch between six distinct and four distinct in-plane vortical structures as the blades pass through the measurement plane further suggested a transitional flow field at 575 RPM.

A micro heat sink comprising 10 microchannels integrated with a local heater and a temperature microsensor array has been fabricated on a silicon wafer using standard micromachining techniques. A glass wafer was anodically bonded to the silicon wafer in order to cap the trapezoidal microchannels, about 14μm in depth and 120μm in average width. DI water was pressurized through the heat sink serving as the working fluid. Boiling curves of device temperature, at a few locations along the centerline, were measured as a function of the input power. In contrast to previously reported results, the boiling plateau associated with latent heat of phase change from liquid to vapor was detected. The transparent glass ceiling allowed the visualizations of flow phenomena dominated by surface effects. The classical bubble dynamics of bubble formation, growth, and detachment was observed at relatively low input power. However, this mode was completely suppressed at moderate power levels. Further increase of the input power resulted in a clear separation between the upstream vapor and the downstream liquid. The average location of the vapor/liquid interface shifted downstream with the input power, and near the critical heat flux condition the interface was located at the channel outlet. Thus, the added heat resulted in increased quality of the two-phase flow rather than increasing the mixture temperature.

This paper presents a technique to fabricate MEMS from a novel, optically transparent polysilazane material. Polysilazane is a hybrid organic/inorganic polymeric glass that is highly transparent in the infrared to ultraviolet range and exhibits thermal stability superior to that of organic glasses such as polycarbonate and PMMA at temperatures up to 230 °C without losing optical transparency. In addition, the UV absorption of the polysilazane is closer to that of silicate glass than to pure organic polymeric glasses. This paper is the first reported work on fabricating MEMS out of this novel material, which has many potential applications in optical MEMS. The fabrication process based on casting in micro molds made photolithographically from SU8 photoresist is described, and a fundamental study of the cure depth of the polysilazane is reported. A polysilazane phase transmission grating is fabricated and demonstrated as a proof of concept optical device.

A novel device-level micropackaging that may encapsulate functional devices in post packaging has been developed. The encapsulation is formed with a metallic microcap like a dome shape to shield necessary micro devices from external impact or contamination. The metal cap is initially fabricated on a carrier glass and then transferred onto a host substrate. In this micropackaging, the micro assembly transfer and cap leg-snapped techniques are utilized in successfully demonstrating the transferred cap on the selected area of the host substrate that is aligned through the transparent glass. The low temperature solder bonding also allows this technique to be compatible with existing integrated circuit and micromachined devices. Furthermore, the robustness of the electroplated micro cap is even superior to the reported surface micromachining technique due to the high stiffness of a thicker structure by controllable electroplating. With the effective aid of the numerical analysis of the cap leg, the fracture can be expected at a desirable spot in which the stress concentration occurs under pulling forces for separation of the carrier glass and the cap. As a result, the micro encapsulation presents a successful, new packaging technique with advantages of selective 3D micro packaging, sealing, robustness, back-end process compatibility and potentially low cost.

Internet technology opens up another domain for building future CAD/CAM environment. The environment will be global, network-centric, and spatially distributed. In this paper, we present a new approach to network-centric virtual prototyping (NetVP) in a distributed design environment. The presented approach combines the current virtual assembly modeling and analysis technique with distributed computing and communication technology for supporting virtual prototyping activities over the network. This paper focuses on interoperability, shape representation, and geometric processing for distributed virtual prototyping. STEP standard and CORBA-based interfaces allow the bi-directional communication between the CAD model and virtual prototyping model, which makes it possible to solve the problems of interoperability, heterogeneity of platforms, and data sharing. STEP AP203 is utilized as a means of transferring and sharing product models. In addition, Attributed Abstracted B-rep (AAB) is introduced as 3D shape abstraction for transparent and efficient transmission of 3D models and for the maintenance of naming consistency between CAD models and virtual prototyping models over the network. Further, this paper discusses geometric processings needed for distributed virtual prototyping activities such as collision detection and interactive assembly modeling.

New heat transfer correlations were developed for two-phase heat transfer in a horizontal pipe for different flow patterns. Flow patterns were observed in a transparent circular pipe (2.54 cm I.D. and L/D = 96) using an air/water mixture. Visual identification of the flow patterns was supplemented with photographic data, and the results were plotted on the flow regime map proposed by Taitel and Dukler and agreed quite well with each other. A two-phase heat transfer experimental setup was built for this study and a total of 150 two-phase heat transfer data with different flow patterns were obtained under a uniform wall heat flux boundary condition. For these data, the superficial Reynolds number ranged from 640 to 35,500 for the liquid and from 540 to 21,200 for the gas. Our previously developed robust two-phase heat transfer correlation for a vertical with modified constants predicted the horizontal pipe air-water heat transfer experimental data with good accuracy. Overall the proposed correlations predicted the data with a mean deviation of 1.0% and an rms deviation of 12%.

In this paper, calculations of mixed-mode heat transfer in beds of randomly-packed cylinders are presented. An unstructured finite volume method is employed. Random packing is addressed by meshing a periodic module, and creating the bed by stacking and random lateral translation of modules. The ability of the finite volume scheme to employ arbitrary polyhedra is exploited in addressing the resulting non-conformal interfaces. Conduction and radiation are considered, but convection is ignored. Results are presented for conducting and semi-transparent cylinders for a range of fluid and solid conductivities and solid refractive indices and establish the viability and versatility of the method.

A two-channel architecture is presented for the control of a bilateral telemanipulation system. The use of two channels enables the authors to cast the control problem in a classical unity-feedback control loop form, which in turn enables the use of frequency-domain loop shaping techniques. Specifically, the human-manipulators-environment loop can be supplemented with a compensator of a lead/lag form, which can be utilized to simultaneously increase the stability robustness and the transparency bandwidth of the system. This design approach is illustrated with a single-degree-of-freedom example.

Past studies of dynamic failure in sandwich structures have mostly been concerned with post-mortem investigations of failure patterns resulting from the dynamic loading of such structures through projectile impact. The final fracture patterns have typically been very complex and their time sequence, interdependence, and detailed nature (opening versus shear) were unclear. In the present work we concentrated on the real-time investigation of the generation and the subsequent evolution of dynamic failure that occurred within microseconds after impact. Model sandwich structures involving a combination of transparent polymers and metals (typically tri-layers bonded together by weak or strong adhesives) were designed and subjected to impact loadings to study the failure evolution mechanism. High-speed photography and dynamic photoelasticity were utilized to study the nature and the sequence of failure modes. A series of complex failure modes was observed. In most cases, interfacial cracks (dynamic delamination) appeared first. These cracks were shear dominated and were often intersonic. Thus, initial delamination was found to be shear driven and happen at extremely short time scales even at moderate impact speeds ranging between 20 to 50 m/s. The transition behavior between interlayer crack growth and intralayer crack formation was also observed. Opening (subsonic) intralayer cracks kinking from the dynamic shear delamination propagated into the core layer of the model sandwich structure and eventually branched as they reached a high enough growth speed.

Heat transfer measurements and photographic studies were performed to capture the detailed evolution of liquid-vapor interfacial behavior near critical heat flux (CHF) for a 90-degree downward-facing convex surface. The test surface, with a width of 3.2 mm and a 102.6-mm radius, consisted of a series of nine heaters which dissipated equal power. Instrumentation within each heater facilitated localized heat flux and temperature measurements along the convex surface, and transparent front and back windows enabled optical access to a fairly two-dimensional liquid-vapor interface. Near CHF, vapor behavior along the convex surface was cyclical in nature and somewhat similar to that observed in pool boiling on horizontal downward-facing flat surfaces. The vapor repeatedly formed a stratified layer at the bottom of the convex surface, which stretched as more vapor was generated, and then departed from the surface. Subsequently, the bottom (downward-facing) heaters, followed by the other heaters, were wetted with liquid before the nucleation/coalescence/stratification/release process repeated itself. Prior to CHF, the surface was adequately cooled by the liquid wetting. At CHF, the surface was still wetted for a brief period, but the wetting time was too short to allow adequate cooling of the downward-facing heaters, and the temperature of these heaters began to rise. This study proves that despite the pronounced thickening of the vapor layer as it propagates upwards along the convex surface, CHF always commences on the downward-facing heaters.

Sealed fluidic microchannels were fabricated from SU-8 epoxy, sandwiched between glass and silicon substrates. The process flow for fabricating microfluidic devices, including packaging, is described. Features integrated in the packaged device include sealed channels, electrical circuits, membrane for thermal isolation and pressure sensing, as well as interconnects for fluids and electrical signal. The resulting channel is optically transparent from all sides. The objective is to introduce a new fabrication technique for microfluidic systems that is both flexible and cost-effective, allowing new designs and mass-production capabilities.

Accurate estimation of turbulent stresses in pulsatile flows is very important in the design of mechanical heart valves to reduce thromboembolism and hemolysis. The flow within the lumen of a fully transparent bileaflet mechanical heart valve model, in the “mitral” position of an in-vitro pulsatile flow loop, is characterized using digital particle image velocimetry (DPIV). A phase-averaging technique is used to obtain the mean velocities and turbulent stresses. The results are compared with those obtained using laser Doppler anemometry which shows good agreement between the two measurement techniques, thereby validating the integrity of the DPIV measurements in the conditionally sampled time dependent flow. Convergence and accuracy issues involving turbulent stress measurements with DPIV in pulsatile flows are addressed in this paper.

The use of ultrasound (US) probes in the emulsification and removal of cataracts has the side effect of corneal and scleral burning. In order to quantify the effects of burning on these tissues, experiments were conducted using bovine corneas to determine the activation energy (E) and frequency factor (A) from an Arrhenius damage model. Bovine corneas were heated on a constant temperature copper stage set at the desired temperature (ranging between 40–70°C). The damage criterion set was the loss of transparency of the tissue and the time required to reach the opacity was used to construct an Arrhenius injury model. Results yielded an activation energy of 98.56 kJ/mole and a frequency factor of 2.9×10 13 s −1 . After determining the parameters for the Arrhenius damage integral, a numerical model was developed to simulate the damage based on variations of the temperature at the ultrasound probe tip with time. Results indicate that as much as 39% of the cornea (in area) can be damaged irreversibly (Ω>1) for temperatures reaching 65°C for a time period of 3 minutes. An intermittent procedure which does not allow temperatures to reach beyond 60°C for more than a minute was found to be optimal for treatment purposes. These results show that the sensitivity of the corneal tissue during US heating can be quantitatively measured and predicted. It is therefore important to optimize the treatment procedure to minimize thermal injury during the procedure.

An inverse solution technique is used to predict the necessary temperature and heat flux distributions of the heater section of a two-dimensional enclosure so the heater satisfies the specified heat flux and temperature distributions of design surfaces, while satisfying one thermal boundary condition for the other walls. Radiation is the dominant mode of heat transfer in systems where high temperatures are present; therefore, it is considered as the only mode of heat transfer in this study. The two-dimensional enclosures considered in this study are made up of straight segments, positioned so that they form irregularly shaped enclosures approximating situations for many of the real cases in industrial applications. The enclosure walls are gray, emitting diffusely and reflecting either diffusely or specularly. The medium inside the enclosure may be transparent, absorbing-emitting or absorbing-emitting and isotropically scattering. For the participating medium cases, the gray medium is considered as isothermal, homogeneous and isotropically scattering. The Monte Carlo method is used for formulation of radiative heat transfer. The method is preferred for its accuracy and ease of handling complex geometries and various surface and medium properties. The main contribution of this study is to solve inverse design problems for complex geometries that contain blockage and shading effects, as could be the case in many real industrial applications. The resulting system of equations, which includes Fredholm equations of the first kind, is known to be highly ill-conditioned in nature. The solution for this ill-conditioned system is handled by the conjugate gradient method, an iterative solution method, which obtains smooth and very accurate solutions in a few steps for linear systems.