Jin-Cherng Shyu

An Experimental Investigation of Micro Pulsating Heat Pipes

Si-based micro pulsating heat pipes (μPHP) charged with HFE-7100 were tested at several heating powers with two orientations, θ = 0° and 90°. The width of the channel is 0.8 mm in a μPHP having uniform channels, and 1.0 mm or 0.6 mm in the other μPHP. The depth of each channel is 0.25 mm. The overall size of each μPHP is 60 mm × 10 mm × 1.25 mm. Both visual observation and temperature response of the present μPHPs at various conditions were performed. The performance was compared between two μPHPs having either uniform channels or non-uniform channels at difference heating powers. Results showed that both μPHPs could not start the pulsating two-phase flow in the channel of μPHPs as the μPHPs were operated horizontally at heating power ranging from 1 W to 7 W, except when the μPHP having non-uniform channels was tested at heating power of 7 W. Unlike the failure start-up for horizontal arrangement of μPHPs, μPHPs with a vertical arrangement shows a significant start-up phenomenon for both μPHPs with uniform and non-uniform channels due to the assistance in the start-up of both μPHPs arising from gravity force.

A comparative study of nozzle/diffuser micropumps with novel valves.

This study conducts an experimental study concerning the improvement of nozzle/diffuser micropump design using some novel no-moving-part valves. A total of three micropumps, including two enhancement structures having two-fin or obstacle structure and one conventional micro nozzle/diffuser design, are made and tested in this study. It is found that dramatic increase of the pressure drops across the designed micro nozzles/diffusers are seen when the obstacle or fin structure is added. The resultant maximum flow rates are 47.07 mm3/s and 53.39 mm3/s, respectively, for the conventional micro nozzle/diffuser and the added two-fin structure in micro nozzle/diffuser operated at a frequency of 400 Hz. Yet the mass flow rate for two-fin design surpasses that of conventional one when the frequency is below 425 Hz but the trend is reversed with a further increase of frequency. This is because the maximum efficiency ratio improvement for added two-fin is appreciably higher than the other design at a lower operating frequency. In the meantime, despite the efficiency ratio of the obstacle structure also reveals a similar trend as that of two-fin design, its significant pressure drop (flow resistance) had offset its superiority at low operating frequency, thereby leading to a lesser flow rate throughout the test range.

Performance of the LED array panel in a confined enclosure

This study performs an experimental study concerning performance of an LED array under natural convection. A total of 270 1-W LEDs having an efficiency of 75% are used to simulate a large LED panel. The size of the cooling heat sink is 348 mm × 558 mm having vertical plate fin configuration with a fin spacing of 9.33 mm. The effect of shrouding, including shrouding above the heat sink and the blockages being placed at the entrance and exit are investigated. For the shrouding effect above heat sink, the heat transfer coefficient is first slightly increased with the rise of shroud distance and peaks at a shroud distance of 20 mm, followed by a marginal decrease of heat transfer coefficient with the shroud distance. On the other hand, a continuous but a very small increase of the heat transfer coefficients with the inlet or outlet blockage distance is seen, yet no plateau is seen as opposed to the effect of shroud distance above heat sink. For the same blockage distance, normally the heat transfer coefficient for those being blocked at the exit is slightly higher than that of inlet blockage. The maximum temperature within the heat sink does not take place at the central position; rather it peaks at the quarter position of the heat sink due to edge effect and likely higher air flow at the center position. The average heat transfer coefficient reaches 6 W/m K as the upper shield is removed.

An experimental investigation of micro pulsating heat pipes

Si-based micro pulsating heat pipes (μPHP) charged with HFE-7100 were tested at several heating powers with two orientations, θ = 0° and 90°. The width of the channel is 0.8 mm in a μPHP having uniform channels, and 1.0 mm or 0.6 mm in the other μPHP. The depth of each channel is 0.25 mm. The overall size of each μPHP is 60 mm × 10 mm × 1.25 mm. Both visual observation and temperature response of the present μPHPs at various conditions were performed. The performance was compared between two μPHPs having either uniform channels or non-uniform channels at difference heating powers. Results showed that both μPHPs could not start the pulsating two-phase flow in the channel of μPHPs as the μPHPs were operated horizontally at heating power ranging from 1 W to 7 W, except when the μPHP having non-uniform channels was tested at heating power of 7 W. Unlike the failure start-up for horizontal arrangement of μPHPs, μPHPs with a vertical arrangement shows a significant start-up phenomenon for both μPHPs with uniform and non-uniform channels due to the assistance in the start-up of both μPHPs arising from gravity force.

Heat transfer of vapor chamber with different types of microchannels

ABSTRACT Two 40-mm × 35-mm × 1.525-mm micro vapor chambers were fabricated by inductively coupled plasma etching on silicon substrates and tested in this study. One vapor chamber exhibited convergent microchannels, whose widest and narrowest width were 0.3 mm and 0.1 mm, respectively, and the other exhibited discontinuous microchannels having width of 0.3 mm. Those micro vapor chambers that were filled with deionized water in a filling ratio of approximately 48% were tested with various titled angles and input powers. The results showed that the thermal performance of the vapor chamber having discontinuous microchannels was inferior because the spacing between microchannelend and the micropostin both condensing and evaporating sections was too far to return the condensed fluid from condensing section to the evaporating section of the vapor chamber. On the contrary, the convergent microchannel in the other vapor chamber enhanced capillary force, so that the condensed liquid could be successfully forced from the condensing section to the evaporating section even with top heating mode (–90°). The thermal resistance of the vapor chamber having convergent micro channels with top heating mode was 2.08°C/W at 22 W, while the thermal resistance of the vapor chamber with horizontal heating mode was 1.46°C/W at 28 W.

Design and fabrication of a passive microfluidic mixer with dynamic disturbance produced by catalytic chemical reactions

We report a novel passive microfluidic mixer design for mixing enhancement based on dynamic disturbances due to bubble generation produced by catalytic decomposition of hydrogen peroxide. A Y-shaped passive microfluidic mixer with a width and depth of 1 mm and 50 µm, respectively, with platinum deposition on the partial undersurface of the mixing channel for H 2 O 2 catalytic decomposition, is demonstrated. Various Reynolds numbers (0.06 to 63.5) and H 2 O 2 concentrations are tested to investigate their effects on the mixing. The experimental results show that mixing can be significantly improved either with the decrease of volumetric flow rate at a given H 2 O 2 concentration or with the increase of H 2 O 2 concentration at intermediate Reynolds numbers based on the present design. The mixing index scatters between 0.8 and 1.0 at x ≥ 15 mm for all H 2 O 2 concentrations if Re =0.06 in the mixing channel. However, the H 2 O 2 concentration has no significant effect on mixing provided Re ≥ 63.5. In addition, the maximum mixing enhancement for Q L =1, 10, 100, and 1000 µL/min ( Re =0.06, 0.63, 6.35, and 63.5) at x ≥ 15 mm are 5.7, 11.85, 6.27, and 4.8, respectively, with 0.1 M 2 O 2 ]<8.8 M in this study.

A numerical study on the performance of air-breathing microfluidic fuel cells

In this study, computational modeling and numerical simulation used to investigate the characteristics and the effects of both the electrode conditions and operating conditions on the performance of air-breathing direct formic acid microfluidic fuel cells by performing steady state and 3-D simulations of the microfluidic fuel cells. Firstly, a three-dimensional microfluidic fuel cell model was established using COMSOL Multiphysics 5.1 to simulate the fuel cell performance. Subsequently, both V-I curves obtained from simulation and published experimental data under similar operating condition were compared to assure the validity of the simulation. The transport phenomena in the microfluidic fuel cells were formulated with continuity equation, momentum equation, species transport equation, and charge equation. The porous media flow in the gas diffusion layer was described by Brinkman equation. The Butler-Volmer equations were applied to get the V-I curves. Besides, numerical simulation model can be used for further optimization, to analyze the current density distribution and the reactant concentration on both electrodes were also discussed.

The photodiodes based on thin film organic electronic device

In this study, we propose the detection of the black shutter using thin film organic photodiodes. The device structure include hole transporting layer, polyethylenedioxythiophene: Poly-styrenesulphonate (PEDOT:PSS), active layer, poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM), indium tin oxide anode (ITO), and Al or LiF/Al cathode. The optimal opto-electronics effect of device structure was it had 150 °C heating process, active layer had 105 nm thicknesses and had LiF/Al cathode. The output voltage test used 1000W simulator and 20W fluorescent light, we got the 0.5V and 0.25V difference, respectively. Output voltage difference is 10 times more than the dye-sensitized photovoltaic cell [1]. Obviously, thin film organic photodiodes can be expected applications in the wearable eye-gaze tracking systems. It is expectation to measure the signs of thin film organic photodiodes array and make the relative devices or systems in future.

A study of hydrogen peroxide microfluidic fuel cells

This study investigated various effects, including reactant concentrations, volumetric flow rates and microchannel width, as well as the electrode distance, on the performance of microfluidic fuel cells employing hydrogen peroxide dissolved in alkaline and acid electrolytes as both fuel and oxidant, respectively. Three concentrations ranging from 0.1 M to 0.6 M and five volumetric flow rates ranging from 0.01 mL/min to 1.0 mL/min were tested in the present study for cell performance measurement and discussion. Three microfluidic fuel cells were tested here. Two of them have rectangular microchannel of 0.5 mm and 1.0 mm in width with electrode distance of 0.4 mm. An additional 0.5-mm-wide microchannel fuel cell was also tested with a shorter electrode distance of 0.2 mm. Results show that cell performed at either larger volumetric flow or with smaller microchannel width usually had higher current output at a given cell voltage. The highest cell output at 0.1 V and 0.1 M among the present cells was approximately 100 mA/cm2 produced by the cell whose microchannel width and electrode distance are 0.5 mm and 0.2 mm, respectively. However, with a higher reactant concentration of 0.6 M, the highest cell output at 0.1 V and 0.1 M among the present cells was 2.5 times higher than the abovementioned value, namely 250 mA/cm2, produced by the cell with microchannel width and electrode distance of 0.5 mm and 0.4 mm, respectively.

A visualization study of venting gas via hydrophobic nanoporous membrane

This study examines the venting gas characteristics in a microchannel through a hydrophobic nanoporous membrane with a pore size of 0.22 μm and a porosity of 70%. A total of three microchannels were made and tested, including a serpentine, a parallel and a contraction-expansion configuration. The mass flux (G) is 5, 7.5 and 10 kg/m2s with the quality (x) ranging from 0 to 0.1. Flow visualization is also performed to observe the bubbles movement under different experimental conditions. The tested results show that the amount of venting gas is strongly related to the contact time and configuration of gas slug and the development of flow pattern in the channel.