Igor Krichtafovitch

Design and optimization of electrostatic fluid accelerators

Electrostatic air propulsion is a promising technology with such potential applications as energy-efficient ventilation, air sterilization, cooling of electronics, and dehumidification. The challenges of existing designs include the need to increase air speed, backpressure, energy efficiency, and heat exchange capability. The ultimate goal of this direction of research is to create multi-channel energy efficient ionic pumps. In the described project, a single cell analysis is conducted in this study as a building block of future designs. This paper presents the numerical simulation and experimental results of electrostatic fluid accelerators. This study was conducted for the purpose of optimizing device characteristics through the control of the electric field distribution. Simulations were performed for multiple collector electrode voltage distributions. A method to quantify the change in pump performance between different voltage distributions is presented. The influence of space charge on pump performance is also discussed. A significant improvement of air velocity generated by optimized electrostatic fluid accelerators has been achieved using the proposed approach.

CFD analysis of electrostatic fluid accelerators for forced convection cooling

Classic thermal management solutions for microelectronics are becoming inadequate and there is an increasing need for fundamentally new approaches. Electrohydrodynamic ionic wind pumps, also known as electrostatic fluid accelerators (EFA), have the potential for becoming a critical element in electronics thermal management solutions. As the EFA field continues to evolve, developing new EFA-based technologies will require accurate models that can help predict pump performance metrics, such as air velocity profile, back pressure, and cooling effectiveness. Many previous modeling efforts only account for electrostatic interactions. For truly accurate modeling, however, it is important to include effects of fluid dynamics and space charge diffusion in charge transport. The modeling problem becomes especially challenging for the design and optimization of EFA devices with greater complexity and smaller dimensions. This paper presents a coupled physics finite element model (FEM) using a complete EFA charge transport model including charge diffusion and fluid dynamic effects. A cantilever EFA structure is modeled and analyzed for forced convection cooling. Numerical modeling predicts maximum air velocities of approximately 4 m/s and a maximum convection heat transfer coefficient of 280 W/(m2K) for the cantilever EFA structure investigated. Preliminary experimental results for a microfabricated cantilever EFA device for forced convection cooling are also discussed.

Heat-Transfer-Enhancement Measurement for Microfabricated Electrostatic Fluid Accelerators

Air cooling, because of its simplicity, remains as the most popular cooling solution for microelectronics in the consumer market. However, the trend of increasing heat generation in microelectronics and the demand for compact devices result in heat fluxes approaching the limit of conventional rotary-fan air-cooling technology. Electrostatic fluid accelerators (EFAs), also known as electrohydrodynamic ionic wind pumps, have the potential of becoming a critical element of electronic thermal-management solutions. In this technique, application of voltage to a sharp electrode ionizes air molecules, which are propelled by the electric field, transferring part of their energy to neutral air molecules, thus creating airflow and cooling effects. The airflow, so-called ldquocorona wind,rdquo can be used discretely for hot-spot cooling or integrated into a compact thermal-exchange surface to decrease the fluid boundary layer and increase heat transfer. The EFA investigated in this paper consists of a microfabricated atomic force microscopy (AFM)-cantilever corona electrode and a flat collecting electrode that doubles as the thermal-exchange surface. The fabrication results, as well as electrical and thermal performance characterization of microfabricated EFAs, are presented in this paper. Air-gap separation distances of 2, 3, 4, and 5 mm between the corona electrode and the thermal-exchange surface were examined under constant surface-to-ambient-temperature difference of approximately 38.3degC.

Coupled-Physics Modeling of Electrostatic Fluid Accelerators for Forced Convection Cooling

Classic thermal management solutions are becoming inadequate and there is an increasing need for fundamentally new approaches. Electrohydrodynamic ionic wind pumps, also known as electrostatic fluid accelerators (EFA), have the potential for becoming a critical element in electronics thermal management solutions. As the EFA field continues to evolve, developing new EFA-based technologies will require accurate models that can help predict pump performance metrics, such as air velocity profile, back pressure, and cooling efficiency. Many previous modeling efforts only account for electrostatic interactions. For truly accurate modeling, however, it is important to include effects of fluid dynamics and space charge diffusion. The modeling problem becomes especially challenging for the design and optimization of EFA devices with greater complexity and smaller dimensions. This paper presents a coupled-physics finite element model (FEM) that accounts for space charge generation from a corona discharge, as well as space charge diffusion and fluid dynamic effects in EFAs. A cantilever EFA structure is modeled and analyzed for forced convection cooling. Numerical modeling predicts maximum air velocities of approximately 7 m/s and a maximum convection heat transfer coefficient of 282 W/(m 2 K) for the cantilever EFA structure investigated. Preliminary experimental results for a microfabriacted cantilever EFA device for forced convection cooling are also discussed.

Miniaturization of Electrostatic Fluid Accelerators

Existing thermal-management methods for electronics do not meet the technology needs and remain a major bottleneck in the evolution of computing, sensing, and information technology. The decreasing size of microelectronic components and the resulting increasing thermal output density require novel cooling solutions. Electrostatic fluid accelerators (EFAs), also known as electrohydrodynamic ionic wind pumps, have the potential of becoming a critical element of electronic thermal-management solutions. In order to take full advantage of EFA-based thermal management, it is essential to miniaturize EFA technology. This paper demonstrates the successful operation of a mesoscale microfabricated silicon EFA. Several cantilever structures fabricated in bulk silicon with radii of tip curvature ranging from 0.5 to 25 mum are used as the corona electrode. The device was fabricated using the combination of deep reactive ion etching (DRIE) and reactive ion etch (RIE) microfabrication processes. Forced convection cooling is demonstrated using infrared imaging, showing a 25degC surface temperature reduction over an actively heated substrate. The fabrication and test results of a mesoscale microfabricated EFA are presented in this paper.

Numerical simulation and optimization of electrostatic air pumps

Electrostatic air propulsion is a promising technology with such potential applications as energy-efficient ventilation, cooling of electronics, and dehumidification. The challenges of existing designs include the need to increase air speed, backpressure, energy efficiency, heat exchange capability, and longevity. This paper presents the numerical simulation results of an electrostatic air pump for the purpose of optimizing device characteristics through control of the inner pump electric field profile. A sharp-edge-to-parallel-plane electrode geometry with unipolar positive corona is chosen to generate linear electric field distribution and minimize energy loss. Simulations were performed for multiple collector electrode voltage distributions. A method to quantify the change in pump performance between different voltage distributions is presented. The influence of space charge on pump performance is also discussed. The ultimate goal is to create multi-channel energy efficient ionic pumps, however, single cell analysis is conducted in this study as a building block of future designs.

CFD analysis of electrostatic fluid accelerators for forced convection cooling [erratum] [Dec 08 1745-1753]

In the above titled paper (ibid., vol. 15, no. 6, pp. 1745-1753, Dec 08), there were misprints in the symbols of equation (1) to (7). These have already been corrected in the electronic version of IEEE Xplore. The correct equations are presented here.