A series of studies in nucleate boiling phenomena on metal-graphite composite surfaces has been investigated by Prof. Wen-Jei Yang and their associates. It has been discovered that the unique micro-configured construction of the composite surfaces plays a crucial role in the enhancement of boiling heat transfer. The present paper focuses on the formation and growth processes of micro bubbles and the micro/nano scale boiling behavior to reveal the mechanism of boiling heat transfer enhancement on the unique surfaces. The growth processes of the micro and macro bubbles are analyzed and formulated followed by an analysis of bubble departure. Based on these analyses, the enhancement mechanism of the pool boiling heat transfer on the composite surfaces is clearly revealed. The micro-configured composite surfaces provide more even distribution of a great number of stable boiling active sites through the graphite fibers. Consequently, the heat conduction through the layers is increased, which provides the power of phase change at the interfaces on bubble bottoms. Experimental results convincingly demonstrate the enhancement effects of the unique structure of metal-graphite composite surfaces on boiling heat transfer.

This research is to fabricate μ-DMFC (micro direct methanol fuel cell) by using MEMS technology. A novel concept of design, compared with the traditional type of DMFC, has been designed and fabricated, which anode and cathode are made in the same plane so called coplanar type of DMFC. In this coplanar type of DMFC, we can also integrate the current collectors and catalyst layer on the flow channels. In order to improve the performance of entire system, we also integrate the fuel preheat device on the chip, so heater was put on the flow channels. By the heating effect, we apply voltage on both sides to increase operation temperature. The experiment results show that when we apply 41 volts on the pads, system average temperature will reach 70°C. Then the fuel (2M CH 3 OH / 2.5M H 2 SO 4 / H 2 O) was fed into anode, and (O 2 -sat. / 2.5M H 2 SO 4 / H 2 O) was fed into cathode, operating under 70°C. The maximum power was reached around 0.956mW/cm 2 at 4.978 mA/cm 2 .

This paper reports the design and simulation of thermal double-cantilever bimorph (TDCB) actuators that can be used to drive micromirrors efficiently. A TDCB actuator combines two paralleled bimorph actuators acting in opposite directions for rotational control of micromirrors. Each actuator is structured by nickel and silicon dioxide thin films with an embedded polysilicon line as a heat source. With a size of only 20 μ m width and 100 μ m length, TDCB actuators result in vertical displacement of 28 μ m at 11 volts DC which is a significant improvement, comparing to the conventional thermal bimorph actuators.

With the aim toward realizing polymerase chain reaction (PCR) of deoxyribonucleic acid (DNA) in plug-based capillary platforms, this paper reports the theoretical and experimental results of thermocapillary actuation for temperature cycling with an arbitrary ramping function. Two concepts were investigated: (a) actuation and spatial temperature cycling with three heaters and (b) actuation and temporal cycling with two heaters. The paper first describes the analytical models of both concepts. The model considers both the transient and coupling effect between heat transfer in the capillary wall and the surface tension driven movement of the plug. In the experiments, both temperature field and plug motion were measured and evaluated. The temperature field were captured by an infrared thermo tracer camera. The position of the plugs was automatically captured and evaluated with a CCD camera. Finally, analytical and experimental results are compared and discussed.

This study measures the thermal conductivity of the MWNT/epoxy bulk composite material to enhance the heat transfer rates of the high power LED device. In this study, three different weight percentages (0.0 wt%, 0.3 wt% and 0.5 wt%) of MWNT/Epoxy composite and five different heat generating rates were employed for the investigation. The case of pure epoxy resins (0.0 wt%) was used as a reference. The responding time and the thermal conductivity of the composites were evaluated. The results show that the response is the fastest for composite with 0.5 wt% MWNT among three composites studied herein. The responses of the 0.3%wt and 0.5%wt composite are increased by 14.3%∼26.7% relative to that of the pure epoxy. Compare with that of the pure epoxy, the thermal conductivities for the cases with 0.3 wt% and 0.5 wt% MWNT/epoxy composite are increased by 15.9%∼44.9%. Further, the thermal conductivity does not vary with temperature for the temperature range studied herein. In the present study, the thermal conductivity of the composite material is found to increase mildly with the increasing heat generation rate.

We fabricated bismuth-telluride based thin films and their in-plane thermoelectric micro-generators (4mm×4mm) on a glass substrate by using the flash evaporation method through shadow masks. We prepared fine powders of Bi 2.0 Te 2.7 Se 0.3 (n-type) and Bi 0.4 Te 3.0 Sb 1.6 (p-type). The shadow masks are fabricated by standard micro-fabrication processes such as nitridation of silicon, dry etching and wet etching. The output voltages of micro-generators are lower than that of a thermoelectric generator based on bulk materials. The main reason is because the temperature difference between cool and hot junctions of the micro-generator is small compared to a thermoelectric generator based on bulk materials. In this study, the micro-generators were fabricated on a silicon nitride substrate based thin film. By fabricating the micro-generator on the thin film substrate, a large temperature difference between cool and hot junctions is obtained due to the thin film effect and the heat radiation to air of the thin film substrate. At the silicon nitride substrate based thin films, the thermal conductivity is significantly reduced by 1.2 W/ (m K). The thin film substrate is prepared by applying the fabrication processes used for shadow masks. The silicon nitride substrate based thin film is fabricated by nitridation of silicon and then back etching the silicon wafer. The fabricated substrate thickness is 2.5 μm and 4.5 μm (4 mmx4 mm). The temperature between cool and hot junctions is measured by using the noncontact thermometer which senses the far-infrared radiation. The output voltage of the micro-generator based thin film is measured by giving a temperature difference by heating the bottom of the silicon nitride substrate based thin film.

Modeling of heat transfer in nanoscale multilayer solid-state structures is presented in this article to seek a potential design of thermoelectric materials. The phonon radiative heat conduction equation is used to describe the heat transport behavior in nanoscale multilayer solid-state structures and the diffuse mismatch model is utilized to simulate the interface condition between two dissimilar materials. In this paper, the thermal conductivity of thin film superlattices, nano wire superlattices and nano tube superlattices were calculated. Then, size effects on the performance of thermoelectric micro coolers were examined in detail. The results show that the effective thermal conductivity of thermoelectric materials in superlattice structures decreases as the layer thickness decreases. In addition, the thermal conductivities of nano wire and nano tube superlattices are less than that of thin film superlattices when they have the same layer thickness. It is noted that the restriction on the radial direction not only decreases the thermal conductivity in radial direction but also in axial direction. Thus, nano wire and nano tube superlattices are potential materials for high performance thermoelectric devices.

Heat dissipation is a very important subject when dealing with industrial application especially in modern semiconductor related applications. Several techniques have been developed to solve the heat generated problem, such as heat dissipation device in IC packaging, high heat conductivity materials, heat tube, force convection, etc. Porous material is used in this study. Porous material is known to have large interior surface, therefore, with proper force convection; it can easily carry heat away. Micro porous ceramic (porous size: 490 μm) is attached to uninterruptible power supply (UPS) power chips. The increase of the heat dissipation rate improves UPS performance. Heat transfer properties comparisons for power chip with and without micro porous materials attached are studies. Also, heat transfer rate under different fan speeds (force convection) is studied. The results show that, heat transfer increases with the use of micro porous materials, the effectiveness ranges between 2–22%. Also, the heat transfer rate varies with air flow rate, the increase of heat transfer is about 4–6%. The dust effect was also performed; experimental results show that heat transfer rate will not be affected by the accumulated dust if a micro porous material is applied.

Referring to regulation of ISO 9300, the discharge coefficients of 2mm, 5mm and 10mm nozzles with 2.5°, 4.0° and 6.0° diffuser angle were measured, respectively. Through comparisons among experimental results, simulation results and prediction results of empirical equations, it was clear that the discharge coefficients were the same for the nozzles with the same throat diameter and were in good agreement with the results of the empirical equations for 10mm nozzles, while that changed with different diffuser angle for other two sets of nozzles. The influence of throat diameter, surface roughness and entrance contour on discharge coefficient was analyzed one by one. The results showed the large out-of-roundness of entrance contour might be the most important reason resulted in the experimental results.