A microparticle image velocimetry (MPIV) system has been used to measure streamwise and spanwise velocity fields along a 100 ¡Ñ200 ¡Ñ20 mm microchannel with a hydraulic diameter of 133.3 at 10¡ØRe¡Ø421.4. The measuring technique uses 1 diameter orange fluorescent polystyrene flow tracing particles, a pulsed Nd: YAG double resonant tube laser with a micro electroscope, and a high resolution CCD camera to record particle-image fields. Local velocity profiles as flow proceeds downstream were measured at particular positions to examine the entrance effect and hydrodynamically fully developed length as well as velocity slip at wall for liquid flow in a microchannel. Velocity slip exists with a considerable value over the entire range of Re under study. Moreover, the friction factors were calculated and compared with those of previous study. Good agreement was found which also assesses the accuracy of the present results.

Abstract In this study, we use microfabrication processes on silicon to produce a rectangular microchannel. The fabrication technology includes exposing, dry etching, and anodic bounding technologies. After fabrication finished, we use AFM and alpha-step to secure surface roughness. It is found a relatively low surface roughness about 3.34¢H with dimension of 0.5£gm¡Ñ100£gm¡Ñ5000£gm microchannel. A theoretical study and calculations, we also made with continuity equation and proper slip condition to analyze fluid behavior in microchannel. At present, several fluid informations in microchannel that incloud pressure drop, fluid velocity, and fluid mass flow rate were obtained.

A numerical prediction using the Direct Simulation Monte Carlo method (DSMC)has been performed on low speed gas flows through a short parallel plate microchannel(L/Dh=6). Computations were carried out for nitrogen, argon, and helium gas. Micro pressure driven flows are simulated with the inlet value of the Knudsen numbers ranging from 0.09 to 0.2. The effects of varying pressure, wall temperature, inlet flow and gas transport properties on the wall heat transfer, pressure and velocity distribution were examined. Friction factors and heat transfer from the channel were also calculated and compared with those of previous studies. Finally, the averaged Nusselt number was correlated in a simple form of the averaged Peclet number and Knudsen number in the transition flow regime.

In this study, high-fidelity conjugate heat transfer simulations are used to model a micro-channel heat exchanger (MCHE) in a crossflow to study its thermal-hydraulic performance. This study considers three different microchannels (internal flow) geometries (circular, triangular, and square) with louver-shaped fins. The local flow field showed a strong coupling between the microchannel flow, solid domain, and crossflow. The flow separation and wake regions formed near MCHE resulted in a large variation in the velocity field and temperature in the crossflow. The wake region had a significant spanwise variation due to its interaction with fins, which also causes variations in the thermal boundary layer. The heat conduction in the solid structure provided a non-uniform temperature field with a higher temperature near the microchannel and a slightly lower temperature near the surface exposed to the crossflow. The microchannel flow analysis showed that the internal geometry affects the pressure drop, which is highest for the triangular MCHE and lowest for the circular MCHE. However, the microchannel flow temperature change was relatively similar for all microchannels. Results showed that for the same volume of the microchannel, the circular shape microchannel has a higher performance index value than the triangular and square shapes. This study also considers three different fin (external flow/crossflow) geometries (louver, step, and saw) with the same tube and circular shape microchannel and identifies the corrosion hot spot. Crossflow shows higher temperatures near the boundary layer of the tube, which results in higher corrosion rates. A predicted flow field also identifies crevices between fins and tube surfaces as critical corrosion hot spots often associated with low-velocity regions. Electrochemical impedance spectroscopy (EIS) analysis was done on AA3102 (Alloy used in the circular channel and louver fin) alloy in corrosive environments containing low and high concentrations of the combination of sodium chloride and ammonium sulfate. Electrolytes used in this research have pH values ranging from 4.0 to 5.8, closer to nearly neutral environments encountered in many atmospheres. EIS results are presented, including Rsol, Rpore, and Rct of AA3102 with very thin arc evaporated porous Zinc film on AA 3102 along with their equivalent circuit.

In this thesis, a new model is formulated for a piezoelectric membrane and fluid motion in a microchannel heat engine. A new slug flow model is developed for droplet motion in a circular cross-section channel. The model includes friction, pressure, viscous and thermocapillary forces on the droplet. This thesis examines the concept of a piezoelectric device at one end of the channel to generate electricity from thermocapillary pumping of the droplet within the microchannel. The slug flow model is used to predict the flow energy needed to convert the thermocapillary pumping into electrical energy. A thin membrane design of a piezoelectric device is developed and modelled with the slug flow approximation. The deformation of the piezoelectric membrane is analyzed. The deformation is found to be a function of the air pressure in the closed microchannel and the displacement of the droplet along the microchannel. This was formulated based on the bending of a thin plate (representing the membrane). The displacement relates to the final output voltage of the design. The direct piezoelectric effect was also examined to determine a relationship between the output voltage and induced stress on the membrane by the force of air. Results are presented for a micro heat engine configuration containing a single membrane on one side of the droplet. It was found that the deformation of the membrane and the output voltage were directly proportional to the displacement of the droplet. A relatively small output voltage was gained from a complete cycle of the droplet. A sensitivity study was performed by varying the channel dimensions along with the dimensions of the piezoelectric membrane. The coupling factor of the piezoelectric membrane was varied to examine its effect on the output voltage. It was found that a larger channel and thinner membrane resulted in a larger output voltage. Materials with a large piezoelectric constant were found to have the largest output voltage, as opposed to those with a lower dielectric constant. / UOIT

Entropy based design is a novel design method that incorporates the second law of thermodynamics with computational and experimental techniques to achieve the upper limits of performance and quality in engineering technologies. As the emerging technologies are pressing towards the theoretical limits of efficiency, the concept of entropy and entropy based design will have an increasing role of performance. Measuring entropy generation is a valuable diagnostic tool from which the areas with high destruction rates of available energy may be determined and re-designed. In this work, a general model is developed, based on previous analytical expressions for pressure drop and heat transfer, for predicting entropy generation in a microchannel. The model includes the effects due to developing and fully developed flow, entrance and exit geometries, cross-sectional shapes, aspect ratio, and different thermal boundary conditions. An experimental technique is presented that enables the measurement of the spatial istribution of entropy generation in a microchannel. The experimental method is a combination of Micro Particle Image velocimetry to measure the spatial distribution of velocity and Micro Laser Induced Fluorescence to determine the temperature data. This method provides certain advantages over conventional anemometry techniques. This method, offers the whole-field non-intrusive, and instantaneous measurement of entropy generation in the device; while, previous techniques are limited to single point, averaged measurements.

Entropy based design is a novel design method that incorporates the second law of thermodynamics with computational and experimental techniques to achieve the upper limits of performance and quality in engineering technologies. As the emerging technologies are pressing towards the theoretical limits of efficiency, the concept of entropy and entropy based design will have an increasing role of performance. Measuring entropy generation is a valuable diagnostic tool from which the areas with high destruction rates of available energy may be determined and re-designed. In this work, a general model is developed, based on previous analytical expressions for pressure drop and heat transfer, for predicting entropy generation in a microchannel. The model includes the effects due to developing and fully developed flow, entrance and exit geometries, cross-sectional shapes, aspect ratio, and different thermal boundary conditions. An experimental technique is presented that enables the measurement of the spatial istribution of entropy generation in a microchannel. The experimental method is a combination of Micro Particle Image velocimetry to measure the spatial distribution of velocity and Micro Laser Induced Fluorescence to determine the temperature data. This method provides certain advantages over conventional anemometry techniques. This method, offers the whole-field non-intrusive, and instantaneous measurement of entropy generation in the device; while, previous techniques are limited to single point, averaged measurements.

Experiments were performed using a microparticle image velocimetry (MPIV) for full field velocity distributions of electroosmotically driven flows in a 40 mm long microchannel with a square cross section of 200 µm ¡Ñ 200 µm. Electroosmotic flow bulk fluid velocity measurements were made in a range of streamwise electric field strengths from 5 to 25 kV/m. A series of seed particle calibration tests can be made in a 200 µm x 200 µm x 24000 µm untreated PDMS channel incorporating MPIV to determine the electrophoretic mobilities in aqueous buffer solutions of 1 TAE, 1 TBE, 10 mM NaCl, and 10 mM borate, respectively. A linear/nonlinear (due to Joule heating) flow rate increase with applied field was obtained and compared with those of previous studies. A parametric study, with extensive measurements was performed with different electric field strength and buffer solution concentration under a constant zeta potential at wall for each buffer. The characteristics of electroosmotic flow in square microchannels were thus investigated. Finally, a composite correlation of the relevant parameters was developed within accuracy for 99% of the experimental data.

Microchannel plate (MCP) detectors have been the detector of choice for ultraviolet (UV) instruments onboard many NASA missions. These detectors have many advantages, including high spatial resolution (<20 mu m), photon counting, radiation hardness, large formats (up to 20 cm), and ability for curved focal plane matching. Novel borosilicate glass MCPs with atomic layer deposition combine extremely low backgrounds, high strength, and tunable secondary electron yield. GaN and combinations of bialkali/alkali halide photocathodes show promise for broadband, higher quantum efficiency. Cross-strip anodes combined with compact ASIC readout electronics enable high spatial resolution over large formats with high dynamic range. The technology readiness levels of these technologies are each being advanced through research grants for laboratory testing and rocket flights. Combining these capabilities would be ideal for UV instruments onboard the Large UV/Optical/IR Surveyor (LUVOIR) and the Habitable Exoplanet Imaging Mission (HABEX) concepts currently under study for NASA's Astrophysics Decadal Survey.

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