With the rapid adoption of new energy vehicles (NEVs), effective thermal
management has become a crucial factor for enhancing performance, safety, and
efficiency. This study investigates the steady-state and dynamic characteristics
of a secondary loop CO₂ (R744) thermal management system designed for electric
vehicles. The secondary loop system presents several benefits, such as improved
safety through reduced refrigerant leakage and enhanced integration capabilities
with existing vehicle subsystems. However, these advantages often come at the
cost of decreased thermodynamic efficiency compared to direct systems.
Experimental evaluations were conducted to understand the effects of varying
coolant flow rates, discharge pressure, and dynamic startup behaviors. Results
indicate that while the indirect system generally shows a lower coefficient of
performance (COP) than direct systems, optimization of key parameters like
coolant flow rate and discharge pressure can significantly enhance performance.
Specifically, optimizing the coolant flow rate resulted in a COP increase of up
to 92.6% under certain conditions, while proper management of discharge pressure
improved the heating capacity and system efficiency. Additionally, dynamic
analysis of startup behaviors revealed the importance of effectively managing
refrigerant distribution to achieve stable system operation and minimize energy
losses. These findings provide valuable insights into the engineering
feasibility and potential improvements of secondary loop systems. By focusing on
the optimization of flow rate, pressure management, and startup control, this
study supports the development of more sustainable and energy-efficient
solutions for the thermal management of NEVs, ultimately contributing to the
wider adoption of environmentally friendly transportation technologies.