Experiments were conducted on the investigation of the electroosmotic flow with five different electric field strength, four kinds of buffer solution concentration, six different pH values, and three kinds of microchannel geometry. Joule heating effects were also taken into consideration. Experiments were performed using a microparticle image velocimetry (MPIV) for full field velocity distributions and micro laser-induced fluorescent (£gLIF) for full field temperature distributions. It is found that the presence of Joule heating and flow area change could have a great impact on the microfluidic transportation, e.g. dispersion. Furthermore, data were presented and the relation between zeta potential and pH value were discussed in detail. It is found that, as pH > 7.5, all silanol sites are deprotonated.

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.

The aim of this study was to explore the properties of thermal field in spray cooling via experiments. The nozzle diameter (dj) used herein was 200 £gm and the heating surface measured 45 mm ¡Ñ 45 mm. The study was divided into two parts for experiments and analyses. In the first part, with DI water and FC-72 (dielectric liquid) as the working media, the changes in the liquid film thickness on the heater surface under different values of heating power were observed; heat input (Q) and value of gauge pressure (£GP) were taken as the main parameters for discussing the influence of these two parameters on the liquid film thickness in spray cooling. The second part, with DI water as the working medium, adopted the £gLIF system (fluorescent dye: Rhodamine B; concentration: 1.5¡Ñ10-4 M) to measure the effect of different working medium temperatures (23 ¢XC, 30 ¢XC, and 40 ¢XC) on the global temperature distribution, liquid film temperature changes on the heater surface and the thermal field condition of spray cooling, with an aim of exploring the internal physical phenomena of the droplets during cooling.

Experiments were investigated on passive mixing enhancements in different geometric microchannels with roughened surfaces and flow was driven by electroosmotic flow (0.027 ≤ Re ≤ 0.081). Experiments were perform using micro particle image velocimetry (MPIV) technology for velocity measurements and relative analysis. Iodine and DI water mixing experiments were captured by common optical microscope for flow visualization, and rhodamine B and buffers mixing experiments were measured by micro laser-induced fluorescence (µLIF) technology for concentration field measurements and analysis. The experimental results showed that the Twr and Tcdr micromixers can generate chaotic flow and enhance the mixing performance in the short channel length. Finally, the mixing length was developed in terms of within accuracy between the experimental data and prediction data.

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.

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.