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

Drexel University, Philadelphia PA

Investigators

Abstract

1357918 Sun Thermal 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.