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The ability of various arrays of micro pin-fins to reduce maximum temperature of an integrated circuit with a 4 × 3 mm footprint and a 0.5 × 0.5 mm hot spot was investigated numerically. Micro pin-fins having circular, symmetric airfoil and symmetric convex lens cross sections were optimized to handle a background uniform heat flux of 500 W cm−2 and a hot spot uniform heat flux of 2000 W cm−2. A fully three-dimensional conjugate heat transfer analysis was performed and a multi-objective, constrained optimization was carried out to find a design for each pin-fin shape capable of cooling such high heat fluxes. The two simultaneous objectives were to minimize maximum temperature and minimize pumping power, while keeping the maximum temperature below 85 °C. The design variables were the inlet average velocity and shape, size and height of the pin-fins. A response surface was generated for each of the objectives and coupled with a genetic algorithm to arrive at a Pareto frontier of the best trade-off solutions. Stress–deformation analysis incorporating hydrodynamic and thermal loads was performed on the three Pareto optimized configurations. Von-Mises stress for each configuration was found to be significantly below the yield strength of silicon.

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M u lti-o b je c tiv e D es ig n O p tim iz a tio n of B ran ch in g , M u ltiflo o r, C o u n te rflo w M ic ro h e a t E xch an g ersHeat removal capacity, coolant pumping power requirement, and surface temperature nonuniformity are three major challenges facing single-phase flow microchannel com pact heat exchangers. In this paper multi-objective optimization has been performed to increase heat removal capacity, and decrease pumping power and temperature nonuni formity in complex networks of microchannels. Three-dimensional (3D) four-floor config urations of counterflow branching networks of microchannels were optimized to increase heat removal capacity from surrounding silicon substrate (15 x 15 x 2 mm). Each floor has four different branching subnetworks with opposite flow direction with respect to the next one. Each branching subnetwork has four inlets and one outlet. Branching patterns of each o f these subnetworks could be different from the others. Quasi-3D conjugate heat transfer analysis has been performed by developing a software package which uses quasi-ID thermofluid analysis and a 3D steady heat conduction analysis. These two solv ers were coupled through their common boundaries representing surfaces of the cooling microchannels. Using quasi-3D conjugate analysis was found to require one order of magnitude less computing time than a fully 3D conjugate heat transfer analysis while offering comparable accuracy for these types of application. The analysis package is ca pable of generating 3D branching networks with random topologies. Multi-objective opti mization using modeFRONTIER software was performed using response surface approximation and genetic algorithm. Diameters and branching pattern of each subnet work and coolant flow direction on each floor were design variables of multi-objective optimization. Maximizing heat removal capacity, while minimizing coolant pumping power requirement and temperature nonuniformity on the hot surface, were three simul taneous objectives of the optimization. Pareto-optimal solutions demonstrate that thermal loads of up to 500 Wlcm2 can be managed with four-floor microchannel cooling networks. A fully 3D thermofluid analysis was performed for one of the optimal designs to confirm the accuracy of results obtained by the quasi-3D simulation package used in this paper.

Various configurations of aircraft wing tip devices have been investigated by performing 3D aerodynamics analysis. The wing tip device in this study was derived from the wing tips of a soaring bird, featuring three smoothly blended elements. Each multi-winglet configuration was integrated into a complete wing-tail-body aircraft configuration. Geometry of each of the three elements in the multi-winglet was defined using 11 parameters, totaling 33 parameters defining a complete multi-winglet geometry. The current design methodology utilized a second order, 3D geometry generation algorithm based on locally analytical smoothly connected surface patches. This algorithm allows for creation of vastly diverse 3D geometries with minimal number of specified design parameters. A 3D, compressible, turbulent flow, steady state analysis was performed using a Navier-Stokes solver on each configuration to obtain the objective function values. Each configuration was analyzed at a free stream Mach number of 0.25 and at an angle of attack of 11 degrees to mimic the takeoff conditions of a passenger aircraft. Multi-objective optimization was carried out using modeFRONTIER utilizing a radial basis function response surface approximation coupled with a genetic algorithm. Maximizing coefficients of lift and lift-todrag ratio, while minimizing coefficients of drag and the magnitude of the coefficient of moment were the four simultaneous objectives. The multi-winglet concept was shown to have superior performance at subsonic and transonic speeds. Nomenclature Cl= aerodynamic lift coefficient Cd = aerodynamic drag coefficient Cm = pitching moment coefficient Cl / Cd = lift-to-drag ratio L.E.S = leading edge sweep angle T.E.S = trailing edge sweep angle ߬ = relative thickness of the local airfoil ߠf = angle, in degrees, of geometric parameter f ߙ = angle of attack y+ = y -plus distance in turbulent flow calculations

Heat removal capacity, coolant pumping pressure drop and surface temperature non-uniformity are three major challenges facing single-phase flow microchannel compact heat exchangers. In this paper multi-objective optimization has been performed to increase heat removal capacity, and decrease pressure drop and temperature non-uniformity in single-flow microchannels. Three-dimensional (3D) 4-floor branching networks have been applied to increase heat removal capacity of a microchannel from silicon substrate (15×15×2 mm). Each floor has four different branching sub-networks with opposite flow direction with respect to the next one. Each branching network has four inlets and one outlet. However, branching patterns of each of these sub-networks could be different from the others. Conjugate heat transfer analysis has been performed by developing a software package which uses quasi-1D thermo-fluid analysis and a 3D steady heat conduction analysis. These two solvers are coupled through their common boundaries representing surfaces of the cooling microchannels. Using quasi-1D solver significantly decreases computing time and its results are in good agreement with 3D Navier-Stokes equations solver for these types of application. The analysis package is capable of generating 3D branching networks with random topologies. 1341 random cooling networks were simulated using this analysis package. Multi-objective optimization using modeFrontier software was performed using response surface approximation and genetic algorithm. Diameters and branching pattern of each sub-network and coolant flow direction on each floor were design variables of multi-objective optimization. Maximizing heat removal capacity, minimizing pressure drop and temperature non-uniformity on the hot surface were three simultaneous objectives of the optimization. Pareto-optimal solutions demonstrate that thermal loads of up to 500 W/cm2 can be managed with 3D 4-floor microchannel cooling networks.

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