Hsien-Wei Chen

Mechanical and thermal behaviors of nitrogen-doped Zr-Cu-Al-Ag-Ta––An alternative class of thin film metallic glass

Super-plasticity and nano-scale surface roughness make thin film metallic glass (TFMG) a candidate for master mold of micro/nano imprint technique. Meanwhile, better mechanical properties of TFMG undoubtedly expand the life time of master mold. In this study, nitrogen is doped into Zr-based TFMG to exhibit the hardness higher than 10 GPa. Different from elements used to be doped into metallic glass, the role of nitrogen atoms plays in metallic glass is distinct and vital owing to its strong electronegativity. From the correlation of thermal and mechanical behavior, the role and effect of nitrogen in Ta-Zr-Cu-Al-Ag TFMG is discussed and proposed.

Thermal Design Optimization for Strip-Fin Heat Sinks with a Ducted Air Flow

An effective method for performing the thermal optimization of strip-fin heat sinks with a ducted air flow under constraints of pressure drop, mass, and space limitations has been successfully developed. The thermal and hydrodynamic models for strip-fin heat sinks have been developed. The design of experiments approach is performed to explore the relationships between design variables and responses with the minimal number of experimental runs. A statistical method for sensitivity analysis of the design factors, including the size of heat sink footprint, conductivity of sink base, thickness of sink base, stream wise and span wise fin pitch, fin thickness, fin length, fin height, and upstream air velocity, is performed to determine the key factors that are critical to the design; and a response surface methodology is then applied to establish regression models for the thermal resistance and pressure drop in terms of the design factors with an central composite design. Diagnostic analysis of the residuals from the regression model may reveal errors that were not in Gaussian distribution, which is one of the most important assumptions of experimental analysis; in the case of this work, a log-transformation is applied to make the response variance closer to the normal distribution. Furthermore, to screen out the insignificant model terms for the better modeling accuracy, the statistical skill, F-test, is applied. By employing the gradient-based numerical optimization technique, a series of constrained optimal designs have been efficiently performed

Effects of Al and V Additions on Mechanical Response in Thick TiSiCN Nanocomposites Deposited Using Plasma-Enhanced Magnetron Sputtering

Thick TiSiCN and TiAlVSiCN nanocomposite coatings were fabricated by plasma-enhanced magnetron sputtering (PEMS). Characterizations by electron probe microanalyzer (EPMA) and XRD revealed the dependence of films with various precursor flow rates on the constituent composition and structure evolution in coatings. HRTEM images clearly confirmed that a nanocomposite structure existed with grain size below 10 nm. It was believed that nanocrystalline TiCxN1-x-based phases with B1 structure were embedded in an amorphous SiCyNz matrix, and such phase segregation ameliorated the hardness and H/E ratios. In the scratch and ball-on-disc wear tests, the evidence from crack initiation resistance, friction coefficient, and worn surfaces verified that thick nanocomposites exhibited remarkable tribological resistance. Hybrid anti-wear mechanisms on the basis of mechanical property variation, composition distribution, and microstructure evolution were proposed to elucidate the favorable durability of these thick films.

Pressure Drop and Heat Transfer Characteristics for Partially-Confined Heat Sinks in Ducted Flow

The pressure drop and heat transfer characteristics for partially-confined heat sinks with different fin types, including plain-plate fin, pin-fin array and strip-fin array, in ducted flow are investigated. The main focus of the experimental results is on pressure drop and heat transfer characteristics of generalized heat sink in ducted flow with considering the flow top- and side-bypass effects. The parameters controlled in the study are the heating load (Qt ), inlet flow velocity (Ui ), the ratio of heat sink height to duct height (Hs /Hc ), and the ratio of heat sink width to duct width (Ws /Wc ). The ranges of parameters studied are Ui =2~12m/s, Qt =10~30W, Ws /Wc = 0.6~1, and Hs /Hc = 0.5~1. In the present study, an effective friction factor related to the overall pressure drop is defined; and a new experimental correlation for the effective friction factor for generalized heat sinks in ducted flow with top- and side-bypass effects is presented. A satisfactory agreement between the experimental data and the theoretical predictions is achieved with the maximum and average deviations of 17.2% and 9.6%, respectively. As for convective heat transfer performance, the average Nusselt number is not significantly affected by Grashof number; while, it increases significantly with increasing Reynolds number. Furthermore, the thermal performance increases with increasing top or side confinement ratio (Hs /Hc or Ws /Wc ). The best thermal performance occurred at the fully-confined condition, i.e., Hs /Hc =1, Ws /Wc = 1. Based on all the experimental data for three types of partially-confined heat sinks, a generalized correlation of average Nusselt number for partially-confined heat sinks in ducted flow in terms of Re, Hs /Hc and Ws /Wc is presented. The maximum and average deviations of the results obtained by the experimental data from the theoretical prediction are 12.4% and 7.5%, respectively.Copyright

Thermal Optimal Design for Partially-Confined Compact Heat Sinks

An effective method for predicting the optimal thermal performance of partially-confined compact heat sinks under multi-constraints of pressure drop and heat sink mass has been successfully developed. The design variables of PPF compact heat sinks include: heat sink fin and base material, thickness of heat sink base, heat flux, channel top bypass and inlet flow velocity. A total of 108 experimental cases for confined forced convection are designed by the Central Composite Design (CCD) method. According to the results in ANOVA, a sensitivity analysis for the design factors is performed. From the analysis, the effect of inlet flow velocity, which has the contribution percentage of 86.24%, dominates the thermal performance. The accuracies of the quadratic RSM models for both thermal resistance and pressure drop have been verified by comparing the predicted response values to the actual experimental data. The maximum deviations of thermal resistance and pressure drop are 9.41% and 7.20% respectively. The Response Surface Methodology is applied to establish analytical models of the thermal resistance and pressure drop constraints in terms of the key design factors with a CCD experimental design. By employing the Sequential Quadratic Programming technique, a series of constrained optimal designs can be efficiently performed. The numerical optimization results for four cases under different constraints are obtained, and the comparisons between these predicted optimal designs and those measured by the experimental data are made with a satisfactory agreement.Copyright

Real-time animated thermal CAD system for 3-D multilayer structure integrated with compact cold plate

A novel 3-D real-time animated thermal CAD system for electronics multilayer structures having interfacial contact resistances integrated with a compact cold plate has been successfully developed on Microsoft Windows 2000 system. The thermal CAD system is composed of pre-processor subsystem, thermal analyzer, post-processor subsystem and relevant user interfaces and databases. The fundamental design concepts for the developed pre-processor, thermal analyzer, and post-processor are introduced. The developed pre-processor has six options such as the selection of heat sources, multilayer structures, cold-plate core, working fluid, ambient conditions, and current data. The effect of thermal contact resistance between contact solids has been considered in the thermal analyzer. The post-processor can interactively generate real-time color isotherms on the heated surface of 3-D cold-plate model. Furthermore, new multimedia technologies with OpenGL libraries, such as graphical illustrations and real-time 3-D visualization, employed in the present developed CAD system provide a very friendly and interactive interface for users. With the developed thermal CAD system, a practical thermal design case for multilayer structure, which has double-sided discrete heat sources, integrated with a compact double-stack cold plate has been studied. The superiority of the developed CAD system has been demonstrated.