Hsiao-Kang Ma

Study of an LED device with a honeycomb heat sink

Previous studies show that the lighting quality of LED largely depends on operating temperature. LED without thermal management may fail early due to thermal runaway, epoxy degradation, and thermal stress under high-operating temperatures. In this study, the performance of a honeycomb heat sink was investigated by experimentation and three-dimensional numerical models. Two kinds of honeycomb models were proposed to demonstrate the performance of a heat sink with single and multiple heat sources for LED thermal management. The performances of innovative honeycomb heat sinks depend on the number of cells, aspect ratio, and the rib-space ratio. The simulated results indicated that the performance varies a little when the conductivity is over 50W/mK. Compared to the simulated heat flux ratio 0.95, the measured heat flux ratio 0.93 at θ=30° was slightly lower. The measured performance of the lump and stack (5 pieces) honeycomb heat sink can respectively keep 13.761W and 13.338W under the dummy heater at 67°C and the ambient temperature at 27°C. The innovative design with nine pieces of layers that are drilled to reduce their weight can effectively dissipate the heat by natural convection in the application of a high-power LED street lamp.

Effect of BFG cofiring on unburned carbon formation in a coal-fired boiler

Abstract One of the China Steel Corporation (SCS) 55MWe tangentially fired boilers, uses Australia Woodland (bituminous) coal as the fuel, cofiring with Blast Furnace Gas (BFG) caused a serious carbon burnout problem. The experimental works and numerical computations were both carried out to examine the potential impacts of BFG cofiring on flow pattern, flue gas residence time and temperature. In experimental studies, an isothermal flow model with a 1 12 scale factor of CSC boiler which use air as working fluid is established to investigate the flow phenomena. The Reynolds number based on burner diameter is keeping above the critical value (25,000) to sustain the turbulence in the model. A five-hole pitot tube is used to measure the mean velocity. And, monosize helium bubbles are led into the model as tracers for the qualitative observation of flow field. In numerical computations, a 2-D furnace heat transfer and combustion model was applied to analyze the furnace performance. Boiler operational parameters, which affect the final carbon burnout levels, were identified and analyzed by model predictions.

Investigation of a multiple-vibrating fan system for electronics cooling

The previous study presented a novel multiple-vibrating fan cooling system actuated by both the piezoelectric (PZT) effect and magnetic force. The thermal performance of the system was demonstrated by checking the temperature drop of the thermocouples adhered to the fin surface. In this study, the convection heat transfer coefficient of an internal multiple-vibrating fan cooling system was calculated by simulation model to verify the accuracy of the theoretical model. Furthermore, the applications of multiple-vibrating fan cooling systems were demonstrated by an external multiple-vibrating fan cooling system, and a T-shape multiple-vibrating fan cooling system. The experimental result showed that the external multiple-vibrating fan cooling system consuming 0.086W, and was able to decrease the core temperature of dummy heater B dissipating 25W from 110.1°C to 80.5°C while the ambient temperature was 27.4°C. The T-shape multiple-vibrating fan cooling system consuming 0.15W, was able to decrease the core temperature of dummy heater B dissipating 25W from 86.9°C to 55.6°C while the ambient temperature was 27.4°C.

Study of multiple magnetic vibrating fins with a piezoelectric actuator

An innovative cooling technology, multiple magnetic vibrating fins system with only one piezoelectric actuator, is investigated for the thermal management in this study. The vibrating driving force is generated by a piezoelectric actuator and then transfer to multiple magnetic fins by the magnetic forces. The multiple magnetic vibrating fins system in this study uses only one piezoelectric actuator to drive ten fins to vibrate simultaneously which means that it not only decrease the cost but also distinctly increase the application value. In this study, the resonance frequency and the vibration amplitude of the multiple magnetic vibrating fins is investigated to optimize its thermal performance. Compare to traditional fixed fins, the experiment results show that the improved thermal performance of the vibrating fins cooling system (η) can be improved up to 34.7%, 38.5%, 37.4% and 25.9% under the pitch of vibrating fins of 6 mm, 8 mm, 10 mm, and 12 mm, respectively, with the power consumption of 0.2 W.

Development of One-sided Actuating Piezoelectric Micropump Combined with Cold Plate in a Laptop

We investigated a new one-sided actuating piezoelectric micropump combined with a cold plate (OAPCP-micropump) in a liquid cooling system to solve heat dissipation problems and to improve electronic device reliability for a laptop. The OAPCP-micropump, which is composed of a PDMS diaphragm, a 45 mm times 28 mmtimes 4 mm pump chamber with added fins, a rectangular piezoelectric device, and two check valves, can allow a thinner design and drive liquid in one direction. The results show that the shape of the fins has a strong effect on the pressure drops and flow profiles. The fluid in the pump chamber may impinge on the fins and increase the heat dissipation rate due to the oscillation by the actuator. When the fins are shorter than 1.25 mm, they have a negligible effect on the performance of the OAPCP-micropump. In addition, increasing the number of fins from 6 to 12 can enhance the heat dissipation rate but has no influence on the flow rate. The measured maximum flow rate of the OAPCP-micropump is 4.1 ml/s, and its maximum pump head reaches 9807 Pa. In general, the new cooling system with an OAPCP-micropump design shows a stable performance on total thermal resistance due to the high flow rate.

The novel modularized multiple fans system with a piezoelectric actuator

Previous studies proposed the multiple fans system with a piezoelectric actuator (MFPA), which combined the piezoelectric effect, magnetic effect and resonance effect to drive the passive fans vibrating simultaneously. In this study, the thermal performance of a modularized MFPA was investigated, in which the housing design was applied. Performance of the MFPA system (η) is defined to describe the improvement of the thermal performance. The results indicate that the geometry of the housing can significantly influence the thermal performance of the modularized MFPA. The results show that can be improved from 30.26 % to 37.55 % when dimensionless width number (Z*) and dimensionless length number (Y*) are decreased from 1.5 to 1.25 and from 0.92 to 0.42, separately. Moreover, in the investigation the nozzle angle (θ), the results indicate that η can be further improved to 46.61 % when θ is increased from 0 to 63.43 .

A multiple vibrating-fan system using interactive magnetic force and piezoelectric force

A vibrating fan system is being pursued as a means to create a heat dissipation system. To improve the efficiency of a heat dissipation system, a novel multiple vibrating-fan system that is actuated by both piezoelectric effect and magnetic force has been developed. The performance of the system is affected by the geometry of the fans and the distance between the fans and the heat sink. The surface temperature of a 20W heat sink can be reduced from 67°C to 50°C using this multiple vibrating-fan cooling system; The power consumption of this system is only 0.027 W, which is lower than a single piezoelectric (PZT) fan. Thus, the novel design of a cooling system with multiple fans shows effective thermal dissipation as well as low power consumption.

The development of a valveless piezoelectric micropump

Previous studies have indicated that the performance of the micropump is influenced by the driving voltage, frequency, valves, and pump chambers. In this study, an innovative one-side actuating valveless micropump is proposed and developed to actuate liquid in one direction with high flow rates and pump heads. The three-dimensional, transition numerical models of the micropumps were also employed to predict its performance. It was found that the inlet choking phenomenon was the major reason to make the one-side actuating micropump valve-free, with a flow rate of 0.088 mL/s and a pump head of 45.6 Pa. By adding the secondary chamber, the performance can be improved to 0.989 mL/s and 1291.0 Pa. The maximum pump head in this study was obtained at 1522.5 Pa by using the 0.3-mm-thick secondary diaphragm. In addition, the performance of the micropump can be further improved by adding a nozzle/diffuser element, thus enabling it to achieve the maximum flow rate of 1.133 mL/s at the frequency of 150 Hz. Without additional check valves, the one-side actuating piezoelectric valveless micropump with compact design can perform more accurately and reliably in the applications of biomedical and electronics cooling.

Thermal performance of multiple piezoelectric-magnetic fans

Previous studies introduced novel multiple piezoelectric-magnetic fans (“MPMF”) which can improve its thermal performance effectively with only one piezoelectric actuator. Moreover, the T-shaped fan design also can increase sweep area of fan to drive more air and improve its thermal performance. This study focuses on investigating the effect of fan pitch (P) and gap (G) between fan tip and heat sink. In order to analysis the improvement of thermal resistance, efficiency of MPMF system is defined as the improvement of thermal resistance compared with natural convection in this study. The results show that MPMF can reach the optimal efficiency of MPMF system of 73.53% while aspect ratio of fan pitch (P/L) is 0.23 and the ratio of gap between fan tip and heat sink (G/L) is 0.05. In addition, the cooling ability under different dummy heater power is explored. When dummy heater operates at 90W, the surface temperature of heater can be declined from 187.9°C to 77.3°C. Comparing with the thermal performance of rotary fan (0.25°C/W, 1.8W), thermal resistance of MPMF is 0.62°C/W with the power consumption of 0.15W, 6.7% of the rotary fan.

Municipal Solid Waste Management in Taiwan: From Solid Waste to Sustainable Material Management

Ever since the “Solid Waste Disposal Act” was established in 1974, Taiwan has been developing waste management for nearly four decades. Over the years, the substantial increase in the amount of solid waste and the indiscriminate disposal of waste had caused serious environmental pollution problems. In 1984, the “Municipal Solid Waste (MSW) Disposal Plan” set landfill as the initial goal and incineration as the long-term policy. The “MSW Disposal Plan” was promulgated in 1991, empowering the Government to construct 21 incineration plants to relieve from the burdens of MSW pollution.