Ercan M. Dede

Heat flux cloaking, focusing, and reversal in ultra-thin composites considering conduction-convection effects

Experimental results are presented for heat flux cloaking, focusing, and reversal in ultra-thin anisotropic composites. A two-material system is utilized in the device design, which features an annular region for heat flow control. The effective thermal conductivity layout of the composite is specified through logical combination of the base material constituents. Heat transfer considering conduction-convection is numerically predicted and experimentally verified via infrared thermography. A Biot number analysis reveals the significance of high rates of convection for large-area planar devices, while the experimental results indicate the feasibility of such heat flow control techniques for advanced electronics applications involving natural convection.

Topology Optimization, Additive Layer Manufacturing, and Experimental Testing of an Air-Cooled Heat Sink

Topology optimization of an air-cooled heat sink considering heat conduction plus side-surface convection is presented. The optimization formulation is explained along with multiple design examples. A post-processing procedure is described to synthesize water-tight solid model computer-aided design (CAD) geometry from 3-D point-cloud data extracted from the optimization result. Using this process, a heat sink is optimized for confined jet impingement air cooling. A prototype structure is fabricated out of AlSi12 using additive layer manufacturing (ALM). The heat transfer and fluid flow performance of the optimized heat sink is experimentally evaluated, and the results are compared with benchmark plate and pin-fin heat sink geometries that are conventionally machined out of aluminum and copper. In two separate test cases, the experimental results indicate that the optimized ALM heat sink design has a higher coefficient of performance relative to the benchmark heat sink designs.Copyright

Simultaneous Design Optimization of Permanent Magnet, Coils, and Ferromagnetic Material in Actuators

This paper presents structural topology optimization of an electro/permanent magnet linear actuator. The optimization goal is to maximize the average magnetic force acting on a plunger that travels over a distance of 20 mm. To achieve this goal, the magnetic field sources (i.e., permanent magnet, positive and negative direction coils), and ferromagnetic material of the yoke are simultaneously co-designed using four design variables for each finite element. The magnetic force is calculated using the Maxwell stress tensor method coupled with finite-element analysis. The optimization sensitivity analysis is performed using the adjoint method, and the optimization problem is solved using a sequential linear programming method. To illustrate the utility of the proposed design approach, linear actuators are designed, and the optimal shapes and locations of the yoke permanent magnet, coils, and ferromagnetic part are provided. In addition, the effects of the PM magnetization direction and the current density strength on design results are described.

Multiphysics optimization, synthesis, and application of jet impingement target surfaces

This paper is focused on the synthesis and application of optimized jet impingement target surfaces for electronics device cooling. A multiphysics topology optimization method is reviewed along with two-dimensional results for an optimal local jet impingement heat transfer surface. Multiple surface topologies are utilized as building blocks in the development of a three-dimensional cooling structure having a mini-scale textured surface for jet impingement. The thermal and fluid performance of this structure is compared with that of a benchmark structure using respective multiphysics finite element models comprising a generic electronics package. Conjugate heat transfer and fluid flow results indicate that the optimized jet impingement surface reduces device temperature at the cost of increased pressure drop. The highlighted optimization and synthesis procedure represents a unique approach to the design of complex multiphysics cooling systems.

Heat flow control in thermo-magnetic convective systems using engineered magnetic fields

We present the design of a magnetically controlled convective heat transfer system. The underlying thermo-magnetic instability phenomenon is described, and enhanced convective fluid flow patterns are determined using non-linear programming techniques plus a design sensitivity analysis. Specifically, the magnetic fluid body force is computed by finding the optimal distribution and magnetization direction of a magnetic field source, where the objective is to minimize the maximum temperature of a closed loop heat transfer system. Sizeable fluid recirculation zones are induced by arranging magnetic field generation elements in configurations similar to Halbach arrays. Applications include improved heat flow control for electromechanical systems.

Kilohertz magnetic field focusing in a pair of metallic periodic-ladder structures

Here, we show, analytically and numerically, that in a pair of metallic periodic-ladder structures placed with a central gap, the normally incident magnetic field is focused on a spot of 3 mm (0.6 × 10−5 free space wavelength) full width at half maximum at a 1 mm distance away at 600 kHz. The ladder structures are designed by exploiting the curl of the induced current at each unit cell in the periodic structure. This investigation paves the way for kilohertz magnetic field manipulations.

Experimental Investigation of the Thermal Performance of a Manifold Hierarchical Microchannel Cold Plate

This article is focused on experimental investigation of the single-phase thermal-fluid performance of a manifold microchannel cold plate with integral hierarchical branching channels. The use of a multiphysics topology optimization technique for the development of the studied microchannel structure is briefly reviewed. An experimental test setup is then described followed by measured temperature and pressure results. Specifically, unit thermal resistance and pressure drop values for the hierarchical microchannel jet impingement cold plate are compared with corresponding results for the jet impingement of a flat plate. These experiments confirm that the hierarchical microchannel system provides increased heat transfer with a negligible change in pressure drop when compared with the standard flat plate system.Copyright

Boiling Heat Transfer From an Array of Round Jets With Hybrid Surface Enhancements

The effect of a variety of surface enhancements on the heat transfer achieved with an array of impinging jets is experimentally investigated using the dielectric fluid HFE-7100 at different volumetric flow rates. The performance of a 5 × 5 array of jets, each 0.75 mm in diameter, is compared to that of a single 3.75 mm diameter jet with the same total open orifice area, in single-and two-phase operation. Four different target copper surfaces are evaluated: a baseline smooth flat surface, a flat surface coated with a microporous layer, a surface with macroscale area enhancement (extended square pin–fins), and a hybrid surface on which the pin–fins are coated with the microporous layer; area-averaged heat transfer and pressure drop measurements are reported. The array of jets enhances the single-phase heat transfer coefficients by 1.13–1.29 times and extends the critical heat flux (CHF) on all surfaces compared to the single jet at the same volumetric flow rates. Additionally, the array greatly enhances the heat flux dissipation capability of the hybrid coated pin–fin surface, extending CHF by 1.89–2.33 times compared to the single jet on this surface, with a minimal increase in pressure drop. The jet array coupled with the hybrid enhancement dissipates a maximum heat flux of 205.8 W/cm2 (heat input of 1.33 kW) at a flow rate of 1800 ml/min (corresponding to a jet diameter-based Reynolds number of 7800) with a pressure drop incurred of only 10.9 kPa. Compared to the single jet impinging on the smooth flat surface, the array of jets on the coated pin–fin enhanced surface increased CHF by a factor of over four at all flow rates.

Computational methods for the optimisation and design of electromechanical vehicle systems

The development of advanced electromechanical vehicle systems requires the consideration of multiple physical processes including electromagnetics, fluid flow, heat transfer, and structural mechanics. Accordingly, this paper presents a suite of simulation, optimisation, and design strategies that may be applied to the research and development of modern electric and hybrid-electric vehicles. These computational methods are illustrated through three examples that involve electric motors and electronic systems. Two and three-dimensional topology optimisation studies, parametric geometry sweeps, and multi-scale models are shown to inform unique designs prior to the fabrication and testing of advanced prototypes. It is expected that such computational techniques will have a significant impact on the development of highly efficient future ground transportation systems.

Kilohertz magnetic field focusing and force enhancement using a metallic loop array

We present a device capable of focusing a kilohertz magnetic field and enhancing the associated magnetic force. The device comprises a two-by-two array of electrically conductive metallic loops embedded in a base substrate. Analytical calculations and numerical simulations verify that the induced electrical current in the loop structure influences the magnetic field distribution thus leading to magnetic force enhancement. Experimental measurements of the magnetic force generated by the device operating at one kilohertz are compared with measurements of a control sample without loops. Such devices have logical applications in electromechanical actuators and transducers.