Electrohydrodynamic driven airflows for microelectronics thermal management

• Main Author: Ramadhan, Abdulmajeed A.
• Other Authors: Thompson, Harvey ; Summers, Jonathan ; Kapur, Nik
• Published: University of Leeds 2018
• Subjects: 621
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.752571

The increasing demand for effective and compact thermal solutions for the next generation of thin and high-power density consumer electronics is challenging the capability of miniature mechanical systems to meet the required cooling performance. Due to their attractive and unique advantages with no moving parts, design flexibility, small-scale structure, low height profile, silent operation, and effective flow generation, electrohydrodynamic (EHD) air movers are well positioned to become a key emerging cooling technology as alternative to conventional rotary fans. In its general objective, this thesis aims to investigate the benefits and highlight the features of EHD air movers as a thermal management cooling solution in advanced and small-scale microelectronics, supporting all previous efforts in this direction. Due to the strong influence of the geometric parameters of EHD devices on the corona discharge process and the resulting EHD flow, numerical modelling represents a powerful tool to design and optimize EHD devices, especially of complex and small-scale structures, where the capability of experimental investigations is limited or challenging. This study presents an accurate and validated numerical method to solve the coupled equations of electrostatics, charge transport and fluid flow for the two-dimensional (2D) modelling of EHD airflow induced through a wire-to-plane/grid channel configuration, and is the first to develop a three-dimensional model (3D) that couples the EHD flows with conjugate heat transfer modelling. Based on thermal management requirements and from a design perspective, a comprehensive investigation and analysis into the influence of geometric parameters on the efficiency of EHD wire-to-grid blowers is performed and optimal configurations are proposed for a range of heights from 9 to 15 mm. Results reveal that using fine emitter wires is more efficient than thicker ones, and the grounded electrode locations affect significantly the electric field distribution and the blower efficiency. It is also found that using the grid as a further collector increases the blower performance, with higher flow production, lower operating voltage and reduced blower size. Further numerical developments are devoted to optimize the configuration of miniature wire-to-plane EHD blowers for heights up to 10 mm, which is the most preferred geometry for integration in the cooling systems of thin electronic applications. For ranges of fixed operating power and voltage, the efficient optimized electrode gaps are predicted and defined by simple expressions. The influence of channel sidewall on the EHD flow rate and velocity profile are investigated and the results show that the 2D modelling is valid to effectively predict flow rates produced by wide and short EHD blowers compared to that obtained by 3D simulations. A combined EHD air blower that enables a reduction in the level of applied voltage and a control of flow production is developed. Performance comparisons against commercial rotary blowers demonstrate that the optimized miniature EHD blowers are more competitive for cooling miniaturized and extended heated surfaces based on blower size, flow rate with uniform velocity profile, and power consumption. A novel design of an EHD system integrated with compact heat sinks is presented as a thermal management cooling solution for advanced and thin consumer applications. Results of a parametric study demonstrate that the EHD system offers flexible structure design with the ability to reduce the height and increase the width as required, providing a unique feature to be installed in low-profile laptops. Moreover, compared to traditional cooling systems used in the current standard low power laptops, the proposed EHD system offers promising cooling performance with higher thermal design power (TDP), reduced thermal solution volume and lower height profile.