Superposition method to investigate the thermal performance of heat sink with embedded heat pipes

This article utilizes the thermal performance experiment with superposition method to investigate the thermal performance of heat sinks with one and two pairs of embedded heat pipes. A heat sink with embedded heat pipes transfers the total heat capacity from the heat source to both the base plate and heat pipes, and then disperses heat into the surrounding air via the forced convection. The heat capacity carried by embedded heat pipes can be found using the thermal resistance analytical approach stated in this article. The results show that two and four heat pipes embedded in the base plate carry 36% and 48% of the total dissipated heat respectively; in addition, when the total heating power of the heat sink with two embedded heat pipes is 140 W, the total thermal resistance reaches its minimum value of 0.27 °C/W, while for the heat sink with four embedded heat pipes, when the total heating power is between 40 W and 240 W, the total thermal resistance is 0.24 °C/W, meaning that the thermal performance is better than that of heat sink with two embedded heat pipes.     

Development of 30 Watt high-power LEDs vapor chamber-based plate

This study utilizes experimental analysis with window program VCTM V1.0 to investigate the thermal performance of the vapor chamber and apply to 30 Watt high-power LEDs. The thermal experiment method is derived a novel empirical formula for the effective thermal conductivity of the vapor chamber and calculated its thermal performance. Results show that the maximum effective thermal conductivity is 870 W/m °C from the novel empirical formula, and comparing it with the experimental value, the calculating error is no more than ±5%. And the LED vapor chamber-based plate works out hot-spot problem of 30 Watt high-power LEDs, successfully.     

Thermal module design and analysis of a 230 W LED illumination lamp under three incline angles

This study investigates on the thermal performance of the 230 W LED projection lamp cooling module in the natural convection and modifies fin parameters including fin spacing, height and thickness and LED base plates materials to achieve optimal heat dissipation and performance through experimental and simulation analysis. Results show that the best values of cooling module are 1.1 mm aluminum fin thickness, 7.5 mm pitch, and 31 mm height and can effectively reduce the LED junction temperature under 75 °C at 90° incline angle. The impact of the incline angle of the LED vapor chamber-based plate to the thermal performance of the present cooling module should be assessed before such a structure of vapor chamber cooling system is used to cool high power LED system. And the experimental results are in good agreement with the theoretical results, whose calculating error is not more than ±10%. A novel comparative process of 230 W LED projection light is developed.     

3-D numerical and experimental models for flat and embedded heat pipes applied in high-end VGA card cooling system

The present study utilizes the three-dimension numerical and experimental methods to investigate the optimum thermal performance of a flat heat pipe-thermal module application in high-end VGA card cooling system, and compares that with a traditional copper metal based plate embedded three 6 mm diameter heat pipe-thermal module under three dissimilar inclination angles of 0°, 90° and 180°. The optimization for the thermal modules researches into various fin material, thickness and gap. Results show that the flat heat pipe-thermal module has the best thermal performance at high power GPU of 180 W and inclination angle of 180°. Simulation results show in good agreement with experimental results within 5%. Therefore, the thermal performance of a flat heat pipe-thermal module can be accurately simulated and analyzed by employed the manner introduced in this paper and is able to cope with the higher heat flux GPU over 62.5 W/cm² in the future.     

Air cooling for a large-scale motor

This article experimentally and numerically investigates the thermal performance of a large-scale motor with a capacity of 2350 kW. The large-scale motor consists of a centrifugal fan, two axial fans, a shaft, a stator, a rotor and a heat exchanger with 637 cooling tubes. The test rigs are set up to measure the performance of the fans and the temperature distributions of the motor. The models of the fan and motor have been implemented in a Fluent software package to predict the flow and temperature fields inside the motor. The calculated results show good agreement with the measured data. In order to improve the motor thermal performance, several methods have been adopted, which are aiming to enhance the fan performance by changing the geometry, to redesign a new heat exchanger with guide vanes, and to optimize the distance between the axial fans. The modified design can decrease the temperature rise by 6 °C in both the stator and rotor.     

Analysis of thermal conductivity in HI-LEDs lighting materials

The present study devised a measurement system to estimate the thermal conductivity of electronic product materials, especially in HILEDs lighting materials, exhibiting distinct thermal characteristics by conducting thermal performance experiments and theoretical analyses. First, steady-state conduction analysis with thermal resistance method was investigated on three composite material substrates of unknown heat conduction coefficients through a substrate material named Bakelite of low thermal conductivity revealing stable quality. Second, one-dimension semi-infinite transient conduction analysis was utilized to investigate metal materials with high thermal conductivities. Results showed that the Bakelite experimental module was verified for 62.5 % of the original wattages, which closest to the thermal conductivity 0.233 W/m-K of the Bakelite. And these composite materials M1, M2 and M3 composed of polymer and epoxy were 1.311, 0.844 and 2.403 W/m-K, respectively. The thermal performance experiments were investigated and the results have proved the correctness of the theoretical model. According to the experimental results, calculating the temperature value of the metal materials comprising cotton insulation and the transient analysis, this study determined the temperature error to be less 20 %. Consequently, a transient measurement system and method for metal materials with high heat conduction coefficients was established. Finally, the results of this work are the useful thermal conductivity method to facilitate rapid analysis in the future.

     

Frequency Shift of Carbon-Nanotube-Based Mass Sensor Using Nonlocal Elasticity Theory

The frequency equation of carbon-nanotube-based cantilever sensor with an attached mass is derived analytically using nonlocal elasticity theory. According to the equation, the relationship between the frequency shift of the sensor and the attached mass can be obtained. When the nonlocal effect is not taken into account, the variation of frequency shift with the attached mass on the sensor is compared with the previous study. According to this study, the result shows that the frequency shift of the sensor increases with increasing the attached mass. When the attached mass is small compared with that of the sensor, the nonlocal effect is obvious and increasing nonlocal parameter decreases the frequency shift of the sensor. In addition, when the location of the attached mass is closer to the free end, the frequency shift is more significant and that makes the sensor reveal more sensitive. When the attached mass is small, a high sensitivity is obtained.     

Analyzing the pressure-difference phenomenon between the condensing and boiling sections in a heat pipe cooling system

The heat pipe cooling system in this study consists of a flat evaporator, a condenser, and rising and falling tubes with water as working fluid. The working fluid has different water levels inside the two components. This is due to the vapor pressure deficits of the evaporation section and condenser section. This paper utilizes condensing and boiling pressure-difference theory and measures the temperature of the condenser wall to develop a theoretic model for the water level deficit inside the thermal module. Results indicate that the working fluid infiltrates the condenser and indirectly verifies the phenomenon leading to the different water levels inside the cooling system. Moreover, the water level height difference theory presented in this study may reduce the length of the condenser by 3.14 cm.     

A non-fluorine mold release agent for Ni stamp in nanoimprint process

This study presents a novel material as an anti-adhesive layer between Ni mold stamps and polymethyl methacrylate (PMMA) substrate in nanoimprint process. A polybenzoxazine ((6,6’-bis(2,3-dihydro-3-methyl-4H-1,3-benzoxazinyl))) molecule self-assembled monolayer (PBO-SAM) considering as anti-adhesive coating agent demonstrates that non-fluorine-containing compounds can be improve the nanoimprint process in Ni/PMMA substrates. In this work, the nanostructure-based Ni stamps and the imprinted PMMA mold are performed by electron-beam lithograph (EBL) and our homemade nanoimprint equipment, respectively. To control the forming of fabricated nanopatterns, the simulation can be analyzed their effect of temperature distributions on the deformation of PBO-SAM/PMMA substrate during hot embossing lithography (HEL) process. Herein the diameter of pillar patterns is 200 nm with and 400 nm pitch on Ni stamp surface. Based on the hydrophobic PBO-SAM surface in this conforming condition, the results of Ni mold stamps infer over 90% improvement in controlling quality and quantity.     

Thermal investigations on LED vapor chamber-based plates

This study utilizes a thermal-performance experiment with the illumination-analysis method to discuss the thermal performance of three kinds of LED based plates comparing the experiments, theories, and simulation thermal resistances. The results show that the thermal performance of the LED vapor chamber-based plate is better than that of the LED copper-based plate with an input power above 5 W. And the experimental thermal resistance values of LED copper- and vapor chamber-based plate are 0.41 °C/W and 0.38 °C/W at 6 W respectively. And the illumination of 6 Watt LED vapor chamber-based plate is 5% larger than the 6 Watt LED aluminum-based plate. Thus, the LED vapor chamber-based plate has the best thermal performance above 5 W.