EPRI: Spray-Freezing of Phase-Change Materials for Decoupled Condensation and Heat Rejection in Next Generation Air-Cooled Power Plants

1357918蒸汽驱动发电厂的sunthermal管理系统约占美国淡水总取水量的40%。由于全球淡水资源的不断减少，这些系统的持续运行带来了重大的工程挑战。因此，该项目旨在开发变革性的“干式冷却”技术，彻底消除现代发电厂冷却蒸汽冷凝器的用水。这将实现使用气冷喷雾冷冻相变材料（PCM）。在蒸汽方面，无论环境空气条件如何，浆液浴中的固体PCM颗粒都会将蒸汽冷凝温度固定在恒定的低值。在空气侧，与目前的风冷冷凝器（ACCs）相比，毫米大小的PCM液滴的喷雾冷冻将显著增加表面积和传热系数。这种方法解耦了冷凝和散热过程，显著降低了蒸汽冷凝温度、压降和系统尺寸。此外，提出的喷雾冷冻储能概念还将为其他高负荷制冷和供暖应用（包括建筑暖通空调和数据中心）提供高容量、快速充放电的储能解决方案。德雷塞尔大学（Drexel University）、先进冷却技术公司（ACT）和WorleyParsons （WP）之间的合作将有助于弥合基础研究与商业化颠覆性技术开发之间的差距。研究生和本科生都将受益于ACT和WP的研究合作和实习机会。该项目利用相变材料（pcm）的喷雾冻结来解耦新型风冷冷凝器的蒸汽冷凝和散热。喷雾冷冻技术广泛应用于食品工业，因为在高表面体积比的液滴中可以实现快速冷却速率。在提出的系统中，热量从冷凝器蒸汽传递到由悬浮在液化PCM中的固体PCM颗粒组成的浆液浴。然后将液态PCM从浴槽中抽出并喷射到冷却塔中，在那里热量被排出到周围的空气中。PCM液滴在对流冷却时凝固，并回落到PCM浆液浴中完成循环。这个整合的大学-工业团队将结合相变材料、复杂流体、两相流和风冷热交换器方面的专家，研究基本的科学原理，并克服实现和最终实施这种新型喷雾冷冻冷凝器概念的技术挑战。校企合作的具体任务是：(i)开发具有高导热性和最佳喷雾/喷射特性的新型PCMs；（ii）研究喷嘴的设计和操作对液滴喷射和冻结的影响；描述PCM浆料在一排排蒸汽管上同时熔化和流动的特征；（iv）设计、制造和表征实验室规模的组件和亚规模的概念验证喷雾冷冻冷凝器系统。这些任务将通过集成的研究方法来实现，包括先进的建模和直接实验表征pcm的热流体特性，复杂的流体流动和对流传热。

1357918SunThermal management systems for steam-driven electric power plants account for approximately 40% of total fresh water withdrawals in the US. Due to dwindling access to fresh water resources worldwide, continued operation of these systems poses a significant engineering challenge. As such, this project aims to develop transformative "dry-cooling" technologies completely eliminating the use of water for cooling steam condensers in modern electric power plants. This will be achieved using air-cooled spray-freezing of phase-change materials (PCM). On the steam side, solid PCM particles in a slurry bath will anchor the steam condensation temperature to a constant, low value regardless of ambient air conditions. On the air side, spray freezing of millimeter-sized PCM droplets will dramatically increase surface area, as well as heat transfer coefficient, as compared to current air-cooled condensers (ACCs). This approach decouples the condensation and heat rejection processes, significantly reducing steam condensation temperature, pressure drop, and system size. Additionally, the proposed spray-freezing thermal energy storage concept will also provide high capacity, fast charging/discharging storage solutions for other high-load cooling and heating applications, including building HVAC and data centers. The collaboration between Drexel University, Advanced Cooling Technologies (ACT), and WorleyParsons (WP), will help to bridge the gap between fundamental research and disruptive technology developments for commercialization. Both graduate and undergraduate students will benefit from research co-ops and internship opportunities at ACT and WP. This project leverages the spray-freezing of phase-change materials (PCMs) to decouple steam condensation and heat rejection in the development of novel air-cooled condensers. Spray freezing techniques are widely used in the food industry, due to the fast cooling rates achievable in high surface-to-volume ratio droplets. In the proposed system, heat is transferred from the condenser steam to a slurry bath comprised of solid PCM particles suspended in liquefied PCM. The liquid PCM is then drawn from the bath and sprayed into a cooling tower, where the heat is rejected to the ambient air. The PCM droplets solidify as they are convectively cooled, and fall back to the PCM slurry bath completing the cycle. The integrated university-industry team will combine experts in phase change materials, complex fluids, two-phase flow, and air-cooled heat exchangers to investigate both fundamental scientific principles as well as overcome technical challenges in the realization and eventual implementation of this novel spray-freezing condenser concept. The specific tasks of the university-industry collaboration are to:(i) Develop novel PCMs with high thermal conductivity and optimal spray/jetting characteristics;(ii) Investigate the effects of nozzle design and operation on spraying and freezing of droplets;(iii) Characterize the simultaneous melting and flowing of PCM slurries over banks of steam tubes;(iv) Design, fabricate, and characterize lab-scale components and sub-scale proof-of-concept spray-freezing condenser systems.These tasks will be achieved through an integrated research methodology including advanced modeling and direct experimental characterizations of thermofluidic properties of PCMs, complex fluid flows, and convective heat transfer.