Po Ting Lin

Parametric Modeling and Optimization of Chemical Vapor Deposition Process

This paper focuses on the parametric modeling and optimization of the Chemical Vapor Deposition (CVD) process for the deposition of thin films of silicon from silane in a vertical impinging CVD reactor. The parametric modeling using Radial Basis Function (RBF) for various functions which are related to the deposition rate and uniformity of the thin films are studied. These models are compared and validated with additional sampling data. Based on the parametric models, different optimization formulations for maximizing the deposition rate and the working areas of thin film are performed.Copyright

Conjugate thermal transport in the channel of an extruder for non-newtonian fluids

Abstract A two-dimensional conjugate heat transfer model has been developed for non-Newtonian materials being processed in a single screw extruder. Employing finite difference numerical methods, the governing equations for the fluid and solid regions are salved separately and an iterative numerical procedure is used for matching these solutions at the boundaries of the different regions, such as the barrel, screw and fluid domains. The flow and thermal fields in the screw channel for the non-Newtonian fluid and the thermal fields in the barrel and the screw are obtained. It is found that heat conduction in the screw and in the barrel, particularly that in the latter, has a significant effect on the flow and on the thermal transport. The dependence of the process characteristics on the material properties, thermal boundary conditions, and on the dimensions of the extruder is determined, indicating the need to consider conjugate transport effects for a realistic and accurate modeling of the process. These effects must also be included in the design and control of the extruder system in order to obtain optimal heat transfer and desired product quality.

Designs of Multiple Microchannel Heat Transfer Systems

In this paper, two different configurations of multiple microchannel heat sinks with fluid flow are investigated for electronic cooling: straight and U-shaped channel designs. Numerical models are utilized to study the multiphysics behavior in the microchannels and validated by comparisons with experimental results. Three responses, including thermal resistance, pressure drop, and maximum temperature, are parametrically modeled with respect to various variables such as dimensions of the channels, total number of channels, and flow rate. Multi-objective optimization problems, which minimize the thermal resistance and the pressure drop simultaneously, are formulated and studied. Physical constraints in terms of channel height, maximum temperature, and pressure are further investigated. The Pareto frontiers are studied and the trade-off behavior between the thermal resistance and the pressure drop are discussed.Copyright

NUMERICAL APPROACH TO MODEL HEAT TRANSFER IN POLYMER MELTS FLOWING IN CONSTRICTED CHANNELS

A numerical approach is developed to study the thermal transport in polymer melts flowing through narrow channels with contraction. Attention is focused on the flow and heat transfer of practical polymer melts used in plastic industries, such as low-density polyethylene (LDPE), which cannot be regarded as Newtonian in their behavior. The rheological model used in this study is based on a power law variation of viscosity with shear rate, along with temperature and pressure dependent viscosity. The flow and heat transfer, which are strongly coupled through the temperature dependence of the viscosity, are solved by using a finite volume method with a nonuniform staggered grid system. The results are presented for axisymmetric tubes, which characterize the nozzle for an injection molding machine or the die in plastic extrusion. The effect of heat generation by viscous dissipation is included. The effects of varying the channel contraction ratio and other dimensions, as well as of the mass flow rate, are explo...

Design and Optimization of Multiple Microchannel Heat Transfer Systems

In this paper, two different configurations of multiple microchannel heat sinks, with fluid flow, are investigated for heat removal: straight and U-shaped channel designs. Numerical models are utilized to study the multiphysics behavior in the microchannels and these are validated by comparisons with experimental results. The main focus of this work is on the design and optimization of these systems and to outline the methodology that may be used for other similar thermal systems. Three responses, including thermal resistance, pressure drop, and maximum temperature, are parametrically modeled with respect to various design variables and operating conditions such as dimensions of the channels, total number of channels, and flow rate. Multi-objective optimization problems, which minimize the thermal resistance and the pressure drop simultaneously, are formulated and studied. Physical constraints in terms of channel height, maximum temperature, and pressure are further investigated. The Pareto frontiers are studied and the trade-off behavior between the thermal resistance and the pressure drop are discussed. Characteristic results are presented and discussed. [DOI: 10.1115/1.4024706]

A Hybrid Reliability Approach for Reliability-Based Design Optimization

Reliability-based Design Optimization problems have been solved by two well-known methods: Reliability Index Approach (RIA) and Performance Measure Approach (PMA). RIA generates first-order approximate probabilistic constraints using the measures of reliability indices. For infeasible design points, the traditional RIA method suffers from inaccurate evaluation of the reliability index. To overcome this problem, the Modified Reliability Index Approach (MRIA) has been proposed. The MRIA provides the accurate solution of the reliability index but also inherits some inefficiency characteristics from the Most Probable Failure Point (MPFP) search when nonlinear constraints are involved. In this paper, the benchmark examples have been utilized to examine the efficiency and stability of both PMA and MRIA. In our study, we found that the MRIA is capable of obtaining the correct optimal solutions regardless of the locations of design points but the PMA is much efficient in the inverse reliability analysis. To take advantages of the strengths of both methods, a Hybrid Reliability Approach (HRA) is proposed. The HRA uses a selection factor that can determine which method to use during optimization iterations. Numerical examples from the proposed method are presented and compared with the MRIA and the PMA.Copyright

Bounded Target Cascading in Hierarchical Design Optimization

Analytical Target Cascading method has been widely developed to solve hierarchical design optimization problems. In the Analytical Target Cascading method, a weighted-sum formulation has been commonly used to coordinate the inconsistency between design points and assigned targets in each level while minimizing the cost function. However, the choice of the weighting coefficients is very problem dependent and improper selections of the weights will lead to incorrect solutions. To avoid the problems associated with the weights, single objective functions in the hierarchical design optimization are formulated by a new Bounded Target Cascading method. Instead of point targets assigned for design variables in the Analytical Target Cascading method, bounded targets are introduced in the new method. The target bounds are obtained from the optimal solutions in each level while the response bounds are updated back to the system level. If the common variables exist, they are coordinated based on their sensitivities with respect to design variables. Finally, comparisons of the results from the proposed method and the weighted-sum Analytical Target Cascading are presented and discussed.Copyright

Reliability-based optimisation of chemical vapour deposition process

In this paper, the process of Chemical Vapour Deposition (CVD) in a vertical impinging reactor is simulated and optimised using the reliability-based performance measure approach for the deposition of a thin film of silicon from silane. The key focus is on the rate of deposition and on the quality of the thin film produced. Proper control of the governing transport processes results in large area film thickness and composition uniformity. The effect of important design parameters and operating conditions are studied using numerical simulations. Response surfaces are generated for deposition rate and uniformity of the deposited film using compromise response surface method for the range of design variables considered. The resulting response surfaces are used to optimise the CVD system by considering the uncertainty in the design variables.

Design and Optimization of Multiple Microchannel Heat Transfer Systems Based on Multiple Prioritized Preferences

Multiple microchannel heat transfer systems have been developed for the urge of rapid and effective cooling of the electronic devices, which have become smaller and more powerful but also produced more heat. Two different types of single-phase liquid cooling, including the straight and U-shaped microchannel heat sinks, have been utilized to reduce the temperature of the electronic chips. The cooling performances however depend on the preferences of different factors such as the thermal resistances, the pressure drops, and the heat flows at the solid-fluid interfaces. Lower thermal resistance represents higher temperature reduction; lower pressure drop means lower usage of the pumping power; and higher heat flows indicates more effective cooling between the heat spreader and the liquid. In this paper, an optimization strategy based on the prioritized performances has been developed to find the optimal design variables for multiple objectives: minimal thermal resistances, minimal pressure drops and maximal heat flows. The fuzzy and correlated preferences are modeled by the Gaussian membership functions with respect to different levels of the objective function values. The overall performances are formulated based on the prioritized preferences and maximized on the Pareto-optimal solution set to find the solutions for various preference conditions. Two case studies have been discussed. The first case considered the prioritized preferences based on uni-objective function values while the second one focused on the preferences of the thermal resistances and the efficiency measures, correlatively evaluated by the flow rates, pressure drops, and heat flows.Copyright

Reliability-based design optimization of electrothermal microactuators using Hybrid Reliability Approach

This paper focuses on the design optimization of the applications of electrothermal polysilicon microactuators with the considerations of uncertainties from mathematical models and random variables. The deflections and actuation forces in the micro-cantilevers are modeled based on experiment results; furthermore, the non-negligible errors due to extrapolations are estimated numerically. The response models are utilized to formulate Reliability-Based Design Optimization problems. The Hybrid Reliability Approach is utilized to accurately and efficiently solve the probabilistic problems by adaptively selecting the reliability analyses from the accurate Modified Reliability Index Approach and the efficient Performance Measure Approach. Lastly, three different micro-actuators are designed and optimized with various levels of bound conditions.