Abstract
Resulting from Moore’s law in semiconductor technology, the progresses such as shrinking feature size, increasing transistor density, lead to higher chip power dissipations and heat fluxes. Consequently, new and novel cooling techniques are of interest. Two-phase heat transfer involving the evaporation of a liquid in a hot region and the condensation of the resulting vapor in a cooler region can provide large heat fluxes needed for microelectronic packages to operate at acceptable temperature levels. Spray cooling, which involves the boiling of a working fluid on a heated surface, is an example of efficient heat transfer scheme that exploit the benefits of two-phase heat transfer. The latest studies have focused on spray cooling on micro-structured silicon surfaces and the employment of nano-textured surfaces to accomplish enhanced boiling heat transfer. The droplets can be shortened thickness and attained on the nanotextured surface by the surface tension gradient of surface porosities. As such, small droplets can be transported at high rates to quickly remove dissipated heat from the surface. This study proposes the hydrodynamic characteristics of droplet impingement on heated surfaces and compares the effect of surface temperature when using water on a plane and nanotextured surface. Various surface temperatures, including single-phase (non-boiling) and two-phase (boiling) conditions, are included. Droplet impact velocity, transient spreading diameter and rebounding temperature are measured. Results show that the nanotextured surface enhances the heat transfer for evaporative cooling at lower surface temperatures, which is indicated by a shorter evaporation time. And the comparison of bending CNTs and vertical CNTs, the bending CNTs is more hydrophilic than the vertical one. Results also show that on the angle of inclination of the nanostructures can increased the droplet spread area and reducing the film thickness, enhancing the effect of the vertical thermal conductivity and the potential of the lateral liquid transport. A comparison of the various height CNTs, results show the rebounding temperature of the 8.1μm-tall CNTs can attain to 244.5℃ and the critical heat flux is 110 W/cm2, the mean heat transfer coefficient of the higher nanotextured surface was approximately 170% higher than of the plane surface. A comparison of the various height CNTs, results show the rebounding temperature of the 8.1μm-tall CNTs can attain to 244.5℃ and the critical heat flux is 110 W/cm2, the mean heat transfer coefficient of the higher nanotextured surface was approximately 170% higher than of the plane surface. Comparison of various curvature CNTs in the same height, The rebounding temperature of the slope of 2.56 CNTs can reach 238.7 ℃, while there are 108 W/cm2 performance on the critical heat flux. Prove the performance of CNT length and curvature can enhance the spray cooling ability.