Chen-Kang Huang

Experimental Investigation of Vapor Chamber Module Applied to High-Power Light-Emitting Diodes

This article experimentally investigates the thermal performance of the vapor chamber module applied to the high-power light-emitting diodes in natural convection. The flat-plate-type vapor chamber and the lamp-type vapor chamber are provided to solve the heat dissipation problem of the high-power light-emitting diodes. The results show that the spreading resistance and the corresponding temperature difference of the flat-plate-type vapor chamber at 30 W are lower than those of the copper plate by 34% and 4°C, respectively, and are lower than those of the aluminum plate by 56% and 6°C, respectively. Compared with the copper and aluminum plates, the lamp-type vapor chamber at 15 W is reduced about 8% and 12% for the total thermal resistance, respectively. In addition, it is also about 3°C and 5°C lower for the central wall temperature of the lighting side, respectively. This study provides a new thermal management method to solve the heat dissipation of the high-power light-emitting diodes. Furthermore, the vapor chamber can effectively lower the spreading resistance and diminish the hotspot effect.

Performance Analysis and Optimized Design of Backward-Curved Airfoil Centrifugal Blowers

In this study, backward-curved airfoil centrifugal blowers were numerically simulated and compared with experimentally measured data. Simulation settings and boundary conditions are stated, and the measurements follow ANSI/AMCA Standard 210-07/ANSI/ASHRAE Standard 51-07, Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating (AMCA/ASHRAE 2007). Comparing simulation results with measured data, it was found that the deviation of the static pressure curve at each specified flow rate was within 4.8% and the deviation of the efficiency curve was within 15.1%. After the simulation scheme was proven valid, the effects of blade angle, blade number, tongue length, and scroll contour were discussed. Several parameter changes are suggested based on these simulations. An optimized design is presented with a 7.9% improvement in static pressure and a 1.5% improvement in efficiency. Overall, the whole process simulates backward-curved airfoil centrifugal blowers effectively and is a powerful design tool for blower development and improvement.

The Effects of Vapor Space Height on the Vapor Chamber Performance

The performance of vapor chambers, also known as flat heat pipes, was studied experimentally. Five vapor chambers with different vapor space heights were intentionally fabricated and tested. The hydraulic diameter ratio was created to be the dimensionless parameter to represent the variation of the vapor space height. The parameter was further used to derive the optimum vapor chamber height. It was found that the vapor chamber achieved the optimum design when the hydraulic diameter ratio of non wick vapor space to chamber interior was greater than 0.6. It is believed that the results are valuable for future vapor chamber design.

The application of UV-LEDs to printed circuit board process

This study investigated using high power UV light emitting diode (LED) to replace the traditional UV lamp in printed circuit board process. It was expected to take the advantages of energy conservation, long life and quick response of UV-LEDs. The feasibility of this replacement was evaluated.

The Estimation of Thermal Conductivity for Alumina-Epoxy Composite Material with High Filling Volume Fraction

In this study, the transport theorem of phonons and electrons is utilized to create a model to predict the thermal conductivity of composite materials. By observing or assuming the dopant displacement in the matrix, a physical model between dopant and matrix can be built, and the composite material can be divided into several regions. In each region, the phonon or electron scattering caused by boundaries, impurities, or U-processes was taken into account to calculate the thermal conductivity. The model is then used to predict the composite thermal conductivity for several composite materials. It shows a pretty good agreement with previous studies in literatures. Based on the model, some discussions about dopant size and volume fraction are also made.

Adsorption Cooling With Multi-Stage Desiccant Processes

For traditional adsorption cooling systems using silica-gel-like desiccant wheels, the moisture is removed from the air and stored in the desiccant wheels. The subsequent reactivation process is to dry the wheel by blowing hot air. The moisture is added to the dried air to take the advantage of evaporative cooling. Currently, the two processes are performed on the different sections of a wheel. However, the temperature of the reactivated part will be higher, and the residual heat will be dissipated into the air-conditioning space. Some researchers have reported to add another section to cool down the regenerative part. Unfortunately, the addition of cooling section decreases the working durations of other two sections.In this study, a novel desiccant-evaporative cooling process is proposed. The wheel is now stationary. Fans and air doors were designed to adjust various air flows to pass through the wheel to perform the dehumidifying, reactivation, and cooling inside the wheel. Most importantly, for each period, the desiccant wheel was used only to dehumidify, reactivate, or cool down. The air to cool the desiccant wheel was released outside, so no residual heat went to the air-conditioning space. The outdoor air was acquired to be heated and reactivate the desiccant wheel. The indoor was used to cool the wheel to achieve better cooling effects.An experimental prototype was designed and established. The air could be directed through the desiccant wheel. A controller was installed. The duration of the dehumidifying, reactivation, and cooling process could be set on the panel. The evaporative cooling process was performed by ten ultrasonic humidifiers. The hot air was from a liquid-to-air heat exchanger, and the hot water can be from a solar heater or any waste heat sources.Optimized sets of period durations were suggested. The criteria to end each process have been proposed for future automation. It is shown that the novel design is able to deliver cooler air. Although the cool air output is currently intermittent, a solution has been figured out and will be improved soon.Copyright

Boiling Enhancements by Anodizing and Pre-Boiling in Nanofluid

Numerous methods, such as sintered or machined surface, have been proposed to enhance the boiling performance. On the other hand, nanofluids are also reported to increase the convective heat transfer and become attractive in many engineering applications. In this study, anodizing was tried to produce porous structure on the heater surface to enhance the boiling performance. Two electrolyes, phosphoric acid and oxalic acid, were used. It was found the anodized pores prepared by oxalic acid were smaller. However, the phosphoric acid anodized surface exhibited a CHF increment by 40% with almost no superheat increment. A nanofluid pre-boiling process was also proposed. An aluminum wire was used as the heater to boil nanofluid for a certain time at a certain heat flux. 0.1 wt% TiO2 nanofluid was used as the working fluid during the pre-boiling process. The wire then went on being the heater for pure water. It is found that aluminum wires exhibit boiling enhancement after preboiling in nanofluid. The most effective process heat flux and duration were found experimentally. The experimental results showed an 11° decrease of the surface superheat. According to SEM photos, two layers were deposited on the aluminum surface. The top layer is more like clusters of deposited nanoparticles, and the layer could be dissolved into water when perform subsequent pure water boiling. The other layer located beneath is more condensed and reliable. It is believed that the second layer could be the main mechanism to exhibit the boiling enhancement.Copyright