Kwang-Yong Kim

Shape Optimization of Micro-Channel Heat Sink for Micro-Electronic Cooling

A numerical investigation of 3D fluid flow and heat transfer in a rectangular micro-channel has been carried out using water as a cooling fluid in a silicon substrate. Navier-Stokes and energy equations for laminar flow and conjugate heat transfer are solved using a finite volume solver. Solutions are first carefully validated with available analytical and experimental results; the shape of the micro-channel is then optimized using surrogate methods. Ratios of the width of the micro-channel to the depth and the width of the fin to the depth are selected as design variables. Design points are selected through a four-level full factorial design. A single objective function thermal resistance, formulated using pumping power as a constraint, is optimized. Mass flow rate is adjusted by the constant pumping power constraint. Response surface approximation, kriging, and radial basis neural network methods are applied to construct surrogates and the optimum point is searched by sequential quadratic programming.

Multi-objective optimization of a centrifugal compressor impeller through evolutionary algorithms

Abstract This paper presents the design optimization of a centrifugal compressor impeller with a hybrid multi-objective evolutionary algorithm. Reynolds-averaged Navier—Stokes (RANS) equations are solved with the shear stress transport turbulence model as a turbulence closure model. Flow analysis is performed on a hexahedral grid through a finite-volume solver. Two objectives, viz., the isentropic efficiency and the total pressure ratio (PR), are selected with four design variables that define the impeller hub and shroud contours in meridian terms for optimizing the system. The validation of numerical results was performed through experimental data for the total PR and the isentropic efficiency. Objective-function values are numerically evaluated through the RANS analysis at design points that are selected through the Latin hypercube sampling method. A fast and elitist non-dominated sorting genetic algorithm (NSGA-II) with an ε-constraint strategy for local search coupled with a surrogate model is used for multi-objective optimization. The surrogate model, the radial basis neural network, is trained on discrete numerical solutions by the execution of leave-one-out cross-validation for the dataset. The trade-off between the two objectives has been ascertained and discussed in the light of Pareto-optimal solutions. The optimization results show that the isentropic efficiency and the total PR are enhanced at both design and off-design conditions through multi-objective optimization.

Multiobjective Optimization of a Grooved Micro-Channel Heat Sink

The shape optimization of a micro-channel heat sink with a grooved structure has been performed using a multiobjective evolutionary algorithm. The thermal-resistance and pumping-power characteristics of the micro-channel heat sink have been investigated numerically. For optimization, four design variables, i.e., the ratios of the groove depth to the micro-channel height, the groove pitch to the micro-channel height, the groove diameter to pitch, and the micro-channel width to height are selected. The thermal resistance and the pumping power are the objective functions. The Navier-Stokes and energy equations for laminar flow and conjugate heat transfer are solved using a finite-volume solver. In comparison with a smooth micro-channel, a decrease in the thermal resistance and an increase in the Nusselt number are obtained in a grooved micro-channel at the expense of pumping power. The thermal resistance in a grooved micro-channel is lower than that in a smooth micro-channel for a fixed pumping power. The ratio of the groove pitch to micro-channel height is found to be the most Pareto-sensitive (sensitive along the Pareto-optimal front), whereas the ratio of the micro-channel width to height is found to be the least Pareto-sensitive variable.

Multiobjective Optimization of a Microchannel Heat Sink Using Evolutionary Algorithm

A multiobjective performance optimization of microchannel heat sink is carried out numerically applying surrogate analysis and evolutionary algorithm. Design variables related to microchannel width, depth, and fin width are selected, and two objective functions, thermal resistance and pumping power, are employed. With the help of finite volume solver, Navier-Stokes analyses are performed at the design sites obtained from full factorial design of sampling methods. Using the numerically evaluated objective function values, polynomial response surface is constructed for each objective functions, and multiobjective optimization is performed to obtain global Pareto optimal solutions. Analysis of optimum solutions is simplified by carrying out trade-off with design variables and objective functions. Objective functions exhibit changing sensitivity to design variables along the Pareto optimal front.

Thermal Optimization of a Microchannel Heat Sink With Trapezoidal Cross Section

A microchannel heat sink shape optimization has been performed using response surface approximation. Three design variables related to microchannel width, depth, and fin width are selected for optimization, and thermal resistance has been taken as objective function. Design points are chosen through a three-level fractional factorial design of sampling methods. Navier‐Stokes and energy equations for steady, incompressible, and laminar flow and conjugate heat transfer are solved at these design points using a finite volume solver. Solutions are carefully validated with the analytical and experimental results and the values of objective function are calculated at the specified design points. Using the numerically evaluated objective-function values, a polynomial response surface model is constructed and the optimum point is searched by sequential quadratic programming. The process of shape optimization greatly improves the thermal performance of the microchannel heat sink by decreasing thermal resistance of about 12% of the reference shape. Sensitivity of objective function to design variables has been studied to utilize the substrate material efficiently. DOI: 10.1115/1.3103931

Optimization of a Hybrid Double-Side Jet Impingement Cooling System for High-Power Light Emitting Diodes

Optimization of a hybrid double-side jet impingement cooling system for high-power light emitting diodes (LEDs) was performed using a hybrid multi-objective evolutionary approach and three-dimensional numerical analysis for steady incompressible laminar flow and conjugate heat transfer using Navier‐Stokes equations. For optimization, two design variables, i.e., ratios of the diameter of jet holes and the distance from the exit of upper impinging hole to chips to thickness of substrate were chosen out of the various geometric parameters affecting the performance of the cooling system. To evaluate cooling performance and pressure loss of the system, two objective functions, viz., the ratio of the maximum temperature to average temperature on the chips and pressure coefficient, were selected. Surrogate modeling of the objective functions was performed using response surface approximation. The Pareto-optimal solutions were obtained using a multi-objective evolutionary algorithm, and performances of three representative Paretooptimal designs were discussed compared to a reference design. In the optimal designs, higher level of uniform cooling was generally achieved with higher pressure coefficient. The Pareto-sensitivity analysis between the objective function and design variable was also performed. [DOI: 10.1115/1.4026536]

Parametric performance evaluation of a hydraulic centrifugal pump

Parametric study of a hydraulic centrifugal pump with backward curved blades has been performed numerically using three-dimensional Reynolds-averaged Navier-Stokes equations. The shear stress transport turbulence model was used for analysis of turbulence. The finite volume method and an unstructured grid system were used for the numerical solution. The optimal grid system in the computational domain was selected through a grid dependency test. Tested parameters were related to the geometry of the impeller and volute: seven variables defining the hub and shroud contours and the blades angle of impeller, and two variables defining the inlet width and expansion angle of volute. The effects of these parameters on the hydrodynamic performance of the centrifugal pump have been investigated. It was found that the centrifugal water pump with the twisted blades has the enhancing efficiency compared to the straight blades pump.