Thermal Management with Supercritical Carbon Dioxide under Extreme Applications

<p>A unique challenge in thermal system design is minimizing the power required to operate cooling systems while maintaining effective heat removal. Traditional cooling systems utilize single-phase fluids where the heat transfer mechanisms are well understood. To meet a variety of cooling demands, a range of technologies are available, including microchannel forced convection, jet impingement, porous media, nanofluids, pin fin arrays, and film cooling, each offering distinct advantages and limitations. While the performance of single- or two-phase cooling systems are generally predictable, in extreme thermal environments, new cooling solutions are needed to improve overall system efficiency and reliability.</p> <p>Supercritical fluids, particularly supercritical carbon dioxide (sCO2), have received significant attention for various applications due to their unique thermodynamic properties near the critical point. By using sCO2 as a working fluid, systems can be more compact, achieve higher heat transfer coefficients, and have a reduced environmental impact while maintaining lower pumping power requirements compared to single-phase systems. Effective utilization of supercritical fluids requires a thorough understanding of how these properties change the effect on the heat transfer coefficient and the pumping power.</p> <p>Two unique applications were examined: heat transfer to sCO2 under high heat-flux conditions and gas-coolers operating near the critical point for use within heat pump water heaters. Under high heat flux, it was determined that despite a Richardson number of < 1.0·10−4, gravity should still be simulated, especially at low mass fluxes where heat transfer deterioration can occur. It was also observed that even under high mass fluxes, the pressure drop is still relatively low at only 3.2% of the operating pressure. On the other hand, when sCO2 is utilized within a gas-cooler, increasing the relative roughness on the CO2 side of the heat exchanger can increase the effectiveness of the heat exchanger. However, it should be noted that this is only the case if the CO2 has the lower heat capacitance within the heat exchanger. If water (or another cooling fluid) has a lower heat capacitance, increasing the relative roughness only increases pressure drop and pumping power requirements.</p>

Name thesis:degree_name

Doctor of Philosophy in Aerospace Engineering

Level thesis:degree_level

Dissertation - Open Access

Discipline thesis:degree_discipline

Aerospace Engineering

Year

2025

Author dc:creator

• Hardy, Devon

• high heat flux
• sCO2
• supercritical fluids
• gas-cooler
• Star CCM
• CFD
• analytical
• thermal management
• pseudo-boiling
• Aerodynamics and Fluid Mechanics
• Energy Systems
• Heat Transfer, Combustion
• Nuclear Engineering
• Propulsion and Power

Repository record dc:identifier

https://commons.erau.edu/edt/935

OAI identifier oai:identifier

oai:commons.erau.edu:edt-1977