Experiments were conducted in electroosmotic flow (EOF) with 0.005≤Re ≤ 0.039 on mixing enhancement in 3-D helical microchannels. Both inlet velocity and concentration distribution along the flow channel were measurement via £gPIV and £gLIF technique respectively. The experimental results showed that the helical channels can generate nearly fully chaotic flow and achieve the complete mixing in a relatively short channel with three different helical channels (3, 4, and 6 inlet channels), and the four-inlet channel found to have the best mixing efficiency. Finally, the mixing length was correlated into a form of £f/Dh = 2.8Pe0.35 within ¡Ó8% accuracy between the experiments and prediction.

In this study, we design different inscribed/circumscribed circular torus-type microchannels to investigate the stretching behavior of DNA molecules. Strain rate and relaxation time play an important role in DNA stretching. In order to perform an analysis of the coil-stretch transition of DNA, we develop a method of stretching DNA molecules by using £gPIV and CLSM measurements. £gPIV is designed to measure the velocity distribution, after which the local strain rate can be estimated. The hydrodynamic stretching of DNA molecules in the elongation flow is observed using a confocal laser scanning microscope (CLSM). The relaxation time of the DNA molecules is then estimated according to the CLSM images analysis. At present, our experiments using the electro-osmotic flow (EOF) driven at various electric fields and viscosities to stretch DNA molecules show how one can investigate the influence of hydrodynamic interactions in the case of stretching of DNA molecules.

This study proposed a Y-type mixer which was driven by electroosmotic flow (Ex = 5 - 25 kV/m) with 7 different mixing angles (30¢X, 60¢X, 90¢X, 120¢X, -120¢X, -90¢X, -60¢X) to enhance mixing efficiency . The mixing performance of the device was demonstrated by using micro laser-induced fluorescence (£gLIF) technology to quantify the concentration distribution in the microchannel. Also, micro particle image velocimetry (£gPIV) was used for velocity measurements and analysis. It was found that the negative mixing angle could induce larger dead zone area than the positive one. The joule heating effect was found when electric field strength was larger than 15 kV/m. The combined dead zone and joule heating effect could enhance the mixing performance slightly. Although it has only a marginal effect on the mixing length for the positive mixing angles. Negative mixing angles allow a reduction of mixer size, which means a more efficient use of material and space. Finally, the best mixing angle was found to be -60¢X.

In this study, an electrokinetics-induced elongation flow was created inside a gradual converging-diverging microchannel with different temperature (25, 35, 45, 55¢XC). The conformation of DNA molecules, local strain rate, and the relaxation time play important roles in determining the extent of DNA stretching. By using £gPIV/£gLIF measurements, the velocity/temperature distributions in microchannels can be secured. The local strain rate was estimated by £gPIV measurements. We observe the hydrodynamic stretching DNA molecules in elongation flow by confocal laser scanning microscope (CLSM). Through CLSM images analysis, relaxation time of DNA molecules was estimated. Finally, dynamic properties and stretching ratio of DNA molecules stretched by EOF driven at various electric field and temperature ware measured. The thermal effect and the electric field on the conformation were also studied and discussed.

An experimental investigation was carried to examine the flow/ thermal field characteristics with/without phase change in the microchannels and compared with the traditional results. There are three parts in this study. The first part investigated the 2-D flow field measured by the micro particle image velocimetry (£gPIV) in a single PMMA microchannel fabricated by an ArF excimer laser. The slip boundary condition in the microchannel wall was also discussed. The second part studied the influence of surface condition (hydrophilic vs hydrophobic) on the flow/thermal field in a micro cooling device which included twenty parallel microchannels, which was fabricated by SU-8 microfabrication technique and replicated by the PDMS replica technique. The UV/ozone device was used to change the PDMS microchannels¡¦ surface condition from hydrophobic to hydrophilic and the £gPIV/£gLIF system was also used to measure the velocity and temperature distribution. The third part investigated the two-phase subcooled flow boiling phenomena (onset of nucleate boiling, boiling curve, flow patterns, bubble departure diameter and frequency) in the seventy-five parallel microchannels fabricated by SU-8 microfabrication technique, and aimed to raise the critical heat flux (CHF) and heat transfer coefficient to enhance the cooling efficiency. Three major methods were used in this study, as follows: (1) To add the cavity angle of £c = 60¢X, 90¢X, and 120¢X on the microchannel side walls. (2) To coat 2 £gm diamond film on the Cu heated surface. (3) To add 1 vol. % Multi-walled Carbon Nanotube (MCNT) into the working medium (deionized water). The goal of this paper is to develop a high heat flux cooling technique and apply the experimental results to solve the cooling problem resulting from the exceedingly high heat flux from the electronic component.

Abstract This study aims to measure the flow field distribution in a microchannel with different heights adjusted. Two different materials, PDMS and Coverglass, were used to observe the flow velocity distribution change resulting from the difference in Zeta potential. The velocity distribution data were also obtained. In the experiment, 1¡Ñ TBE buffer solution with viscosity of 1 cp was used with the electric field intensity controlled under 5, 7.5 and 10 kV/m, respectively. Micrometer resolution Particle Image Velocimetry (£gPIV) was used to measure partial velocity distribution in order to explore the hydrodynamic stretch effect on DNA molecules when the microchannel, where the solution was placed, was adjusted to different heights. This study also statistically analyzed the stretch length distribution of DNA molecules in the microchannel and calculated the time of DNA molecule deformation and stress relaxation time in order to understand the stretch condition under different heights as well as the stretch and deformation of DNA molecules in microchannels.

By focusing on the cooling requirement of high power LED, the study aims to explore the spray cooling method and analyze its cooling performance. The ultrasonic micro-nozzle plate made of piezoelectric ceramic material was used in this experiment in order to establish a spray cooling system. The nozzle plate array (3 ¡Ñ 2) was used to carry out a cooling test for 24 LEDs with high power (6 ¡Ñ 4). Three different watts (1 W, 3 W, 5 W) of LED were tested, the total input power was 24W, 72W and 120 W, respectively, and the working medium was DI water. The goal is to understand the variance in performance caused by nozzle plates of different nozzle diameters (dj = 7, 35 £gm) in varied nozzle distances (z = 10, 20, 30, 40, 50 mm). The experiment used thermocouples to measure the slug temperature of LED. By applying thermal resistnace to the LED to calculate its chip temperature, and using micrometer resolution particle image velocimetry (£gPIV) to observe the spray flowfield inside the LED chamber, this study analyzes the influence of flowfield change on cooling performance.

This study aims to explore the use of an ultrasonic micro-nozzle plate, made of piezoelectric ceramic material, as a core material to establish a set of spray cooling system for high power LED. The system uses a single nozzle plate to implement a cooling test for 4 high power LEDs (2 ¡Ñ 2). The total input power was 4 W, 12 W and 20 W, and working medium was DI water. In order to understand the performance variance introduced by utilizing nozzle plates with differing nozzle diameters (dj = 7, 35 £gm) across various nozzle exit to test distance (z = 10, 20, 30, 40, 50 mm). By using micrometer resolution particle image velocimetry (£gPIV) to observe the spray flowfield inside the chamber, and using thermocouples to measure the temperature of LED slug and thermal resistance was used to calculate the LED junction temperature , Tj, for analyzing the influence of flowfield change spread in chamber on its cooling performance. The possibility of an LED spray cooling system is also explored.