Supersonic condensation CO2 heat pump for enhanced low-temperature heating of electric vehicles

Motivated by the low-temperature heating demand of electric vehicles, a transcritical CO 2 heat pump integrated with a supersonic condensation and deposition chamber (SCDC) is investigated as a potential approach to reduce Joule-Thomson throttling loss and improve heating performance under cold climate conditions. However, the coupled behaviors of supersonic expansion, non-equilibrium condensation, droplet slip, and radial migration of high-pressure CO 2 in the SCDC have not yet been clarified. A novel Euler-Lagrange condensation model considering droplet nucleation, growth inside SCDC was built. Meanwhile, the experimental platform was established to investigate the phase-change behavior of CO 2 and the heating performance of SCDC system. The simulated axial pressure distribution and COP under the experimental validation conditions show good agreement with the experimental measurements. It reveals that increasing the swirl number to 0.38 raises the maximum swirl strength to 1.45, thereby enhancing droplet radial migration and wall deposition. As the inlet pressure increases from 4.0 to 6.0 MPa, the heterogeneous droplet diameter at the SCDC outlet decreases from 5.73 to 5.32 μm, and the homogeneous droplet diameter increases from 0.058 to 0.090 μm. Compared with the conventional heat pump, the supersonic condensation heat pump (SCHP) still maintains stable operation at −17.0 °C when p in = 4.0 MPa where JT-based heat pump (JTHP) fails. Under an ambient temperature of 3.15 °C, SCHP maintains COP range of 2.52 to 1.94 as the discharge pressure increases, which is higher than the corresponding 2.40 to 1.87 of the JTHP.