Transforming pool boiling into a pumpless self-sustained flow boiling system for efficient cooling at high heat fluxes

当前电子产品小型化的趋势引入了更高的热产生率，同时大大减少了散热的表面积。池沸相变冷却是一种很有吸引力的冷却方法。流动沸腾效率更高，但需要一个泵，这使得它更复杂。该项目提出了一个创新的概念，将池沸腾转变为一个自我持续的无泵流沸腾系统，并显著提高了冷却性能。它利用一个锥形的间隙，其中一个气泡在增加流动面积的优先方向上膨胀，并在加热器表面上产生一个自我持续的流动。所提出的工作将提供对基础物理的透彻理解，并使不同流体的优化设计能够显着改善散热。它将为本科生和研究生提供教育机会，同时为少数民族和女性学生创建一个新的推广活动“TinkerEngLab”，提供实践经验。他们将参加以贫困地区中学生为对象的“超越9.8”活动。该项目的目标是发展对流体流动和传热机制的基本理解，这些机制驱动气泡在锥形间隙中生长和膨胀时的自我持续流动。这将通过以下几个方面来完成：1)分析工作，以建立气泡生长过程中的传热、压力恢复和锥形微间隙中的压降之间的联系；2)数值工作，以深入了解气泡生长和瞬时压力场；3)实验工作，以验证和实际数据。将获得气泡下微层形成的基本信息以及气泡生长各阶段壁面压力分布。挤压气泡的数值模拟将利用实验室开发的先进代码来预测动态条件下锥形微间隙中的压力场，并将通过使用微机电传感器和高速可视化的压力映射进行实验验证。数值研究的结果将被纳入发展一个流动动力学和传热的理论气泡挤压模型。这些知识和模型将为开发不同工况下不同流体的高效冷却系统提供设计理论。这项工作预计将引入一种范式转变，因为池沸腾将不再受到液体停滞池的限制，而是将融入流动，从而在不需要泵的情况下实现前所未有的冷却性能。它的主要应用包括电子冷却，但这项工作也将为工业和商业应用开辟新的途径。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Current trend of electronics miniaturization introduces higher heat generation rates while substantially reducing surface area for heat dissipation. Phase change cooling with pool boiling is an attractive cooling method. Flow boiling is more efficient but requires a pump, which makes it more complex. This project presents an innovative concept that transforms pool boiling into a self-sustained pumpless flow boiling system and dramatically improves cooling performance. It utilizes a tapered gap in which a bubble expands in a preferential direction of increasing flow area and creates a self-sustained flow over the heater surface. The proposed work will provide thorough understanding of the underlying physics and enable optimal designs with different fluids for dramatically improving heat dissipation. It will offer educational opportunities to undergraduate and graduate students, while creating a new outreach activity "TinkerEngLab" with hands-on experience to minority and women students. The team will participate in an outreach activity called Beyond 9.8 for middle school students from underprivileged schools.The goal of the project is to develop a fundamental understanding of the fluid flow and heat transfer mechanisms that drive the self-sustained flow as a bubble grows and expands in a tapered gap. It will be accomplished through – 1) analytical work to establish the link between heat transfer around a growing bubble, pressure recovery and pressure drop in the tapered microgap, 2) numerical work to provide insight into bubble growth and instantaneous pressure field, and 3) experimental work for validation and practical data. Fundamental information on microlayer formation under a bubble and pressure distribution at the wall at various stages of bubble growth will be obtained. The numerical simulation of squeezing bubble will utilize advanced code developed in the lab to predict pressure field in the tapered microgap under dynamic conditions, and these will be experimentally validated by pressure mapping using micro-electromechanical sensors and high-speed visualization. The findings from the numerical study will be incorporated in developing a theoretical bubble squeezing model for flow dynamics and heat transfer. The knowledge and the model will provide design theories for developing highly efficient cooling systems with different fluids under different operating conditions. The work is expected to introduce a paradigm shift as pool boiling will no longer be limited by a stagnant pool of liquid, but will incorporate flow for achieving unprecedented cooling performance without requiring a pump. Its main application includes electronics cooling, but the work will open up new avenues in industrial and commercial applications as well.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.