Kuo-Hsiang Chien

Investigations of the Thermal Spreading Effects of Rectangular Conduction Plates and Vapor Chamber

This study examines the spreading ability of rectangular plates numerically, analytically, and experimentally. The effect of aspect ratio, defined as an equivalent radius of a heater divided by that of a spreader plate, is investigated. The numerical results show a very good agreement with the analytical solutions. From the calculated results, the spreading resistance of the conduction plates with a small aspect ratio is higher than the one-dimensional conduction resistance. Calculated results also show that the spreading ability of a metal plate would be affected slightly by the external convective heat-transfer coefficient when the ratio of the longitudinal heat convection to the lateral heat spreading is less than 0.1. In addition to the numerical analysis, experimental comparisons between copper∕aluminum plates and a vapor chamber having the same thickness have been conducted. The experimental results show that the thermal resistance of the metal plates is independent of input power whereas that of the vapor chamber shows a noticeable drop with increased power. For the influence of concentrated heat source, the surface temperature distributions for the metal plates become concentrated with a reduced aspect ratio. However, the variations of the aspect ratio and the input power would yield minor effects to the surface temperature distribution of the vapor chamber. As compared with the conduction plates, the vapor chamber would offer a lower temperature rise and a more uniform temperature distribution. Thus, the vapor chamber provides a better choice as a heat spreader for concentrated heat sources.

Determination of Optimized Rectangular Spreader Thickness for Lower Thermal Spreading Resistance

This study presents an approximation for determining an optimized thickness of a concentric heated rectangular plate and derives an analytical solution for spreading resistance of a spreader having orthotropic conductivities. The solution for the orthotropic plate is obtained by separation of variables, and the optimized thickness is determined by taking the derivative of the thermal resistance with respect to the spreader thickness. According to the calculated results, an enhanced in-plane spreading effect can reduce the spreading resistance. The spreading resistance dominates the overall resistance of thin plates, whereas the one-dimensional conduction resistance becomes important for thick plates. However, the predicted optimized thickness from the approximation shows a disparity from the analytical results, while the aspect ratio between a spreader and heat source is less than 0.2. Even so, the thermal resistance corresponding to the predicted thickness is still in good agreement with the analytical solution. The proposed approximation will be useful for practical thermal design of heat sinks by predetermining the spreader thickness.

A Numerical Study of the Nozzle/Diffuser Micro-Pump

This study numerically investigated the performance of micro Nozzle/diffuser pump subject to the influence of frequency, opening angle, and amplitude. It is found that the net flowrate of a micro-pump increased with pumping frequency and opening angle. However, a level off phenomenon of the net flowrate vs. amplitude is seen at an amplitude nearby 150-200 µm and at an opening angle above 10 degree. This phenomenon is associated with two factors that compensate with each other. One is the free jet flow from the outlet that overturns and blocks the flow from the inlet. The other is the reduction of the strength of the jet flow at a larger amplitude owing to effective increase of cross sectional area.

Thermal Management of a Notebook Computer

In this study, simulations are made to resolve a 100 W heat dissipating capacity of a portable PC in (with a CPU IHS size of 31 mm × 31 mm). The problem is investigated via a commercially available software (Icepak version 4.1). The present design incorporates heat pipe to convey heat from the hot spot towards the heat sinks. The heat sinks are optimized subject to heat loads and their locations. The calculated results of a double heat sinks design show a 30 °C less temperature when compared to a single heat sink module. This is because double heat sinks design provides much more uniform temperature and eliminates the edge effect. Moreover, the effect of fin pitches is also examined in this study. It is found that the best performance is at a fin thickness of 0.2 mm and at a fin pitch of 2.4 mm. Depending on the optimal parameters of the thermal module, the chip temperature can be reduced to approximately 75 °C.© 2005 ASME