Forced air cooling with rotary fans is the most popular cooling solution for electronic products. However, increasing heat generation in microelectronics, and the demand for ever smaller portable devices, has resulted in heat fluxes and form-factors that push the limits of conventional rotary fan-based air cooling technology. Electrohydrodynamic (EHD) ionic wind pumps offer an attractive alternative to fans. In this technique, applying a voltage to a sharp electrode ionizes nearby air molecules, which are then propelled by the electric field transferring momentum to neutral air molecules, generating bulk airflow and cooling. The fundamental principles of this technology have been investigated theoretically and experimentally. However, few real world applications have been produced to date due to technical challenges such as device miniaturization, high voltage generation, electromagnetic interference (EMI), and reliability. This paper discusses the successful integration of an EHD cooling system into a laptop computer. The stock rotary fans in the laptop cooling system were removed and directly replaced with EHD blowers. Airflow and thermal performance measurements, both at the device and system level are presented.

Electrohydrodynamic (EHD) cooled laptop

Ion wind generation and the application to cooling

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.

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 (EHD) 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. The airflow, so called ";corona wind";, 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 enhancement. The EFA investigated in this study consists of a microfabricated AFM-cantilever corona electrode using combination of deep reactive ion etching (DRIE) and reactive ion etching (RIE), and a flat collecting electrode that doubles as the thermal exchange surface. The fabrication and testing results of a microfabricated EFA are presented in paper. Free and EFA-enhanced forced convection heat transfers are both reported by measuring the heating power difference of the collecting electrode under constant surface temperature.

Heat Transfer Enhancement Measurement for Microfabricated Electrostatic Fluid Accelerators

As the demand for advanced microelectronic devices of small form factor and high power density has increased, the capability of the miniaturized mechanical solutions for effective cooling has become critical. Electrohydrodynamic (EHD) air blowers have great potential as alternative cooling solutions over the traditional mechanical systems to meet the thermal management requirements with flexible design and considerable flow production for effective heat removal. In this paper, a numerical analysis and optimization of wire-to-plane EHD air blowers are performed based on 2-D developed models validated against previous data. For a range of blower heights from 2 to 10 mm, the location and length of the collecting plane located at the blower walls apart from the emitter wire electrode are investigated and optimized based on pumping efficiency using the ranges of fixed operating powers and voltages. Simple relations for each optimization method are presented to determine the optimal blower configuration. Results of flow rate and static pressure obtained by each optimized blower show good agreement with those predicted by EHD scaling laws previously presented.

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Numerical Analysis and Optimization of Miniature Electrohydrodynamic Air Blowers

Existing thermal management methods for electronics do not meet 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 (EHD) ionic wind pumps, have the potential of becoming a critical element of electronic thermal management solutions. In our previous experiment, a proof-of-concept meso-scale microfabricated silicon EFA device was demonstrated for enhanced forced convection cooling, enabling a maximum surface temperature reduction of 25°C over an actively heated substrate. In order to further investigate its feasibility for cooling in electronics and enable further device optimization for cooling purposes, it is essential to analyze key characteristics of microfabricated silicon EFA devices. The EFA devices investigated in this study consist of a microfabricated silicon cantilever corona electrode, and a wide and flat collector electrode. Experimental setups include one for current vs. voltage (IV) measurement and one for the longevity test. IV measurements were conducted for cantilever structures with lengths of 5 mm and 8 mm for electrode separation distances of 5, 4, 3, and 2 mm. The tested devices include uncoated and TiW-coated silicon cantilever structures. In the longevity tests, only uncoated silicon cantilever structures were tested and an electrode separation distance of 5 mm was used.Copyright © 2007 by ASME

C. Sticht

Papers

Heat Transfer Enhancement Measurement for Microfabricated Electrostatic Fluid Accelerators

Characterization of Microfabricated Cantilever-to-Plane Electrostatic Fluid Accelerators for Cooling in Electronics