Understanding reduction in the cooling capacity of evaporative cooling systems under low air pressure conditions: A molecular insight

ZJ Tian and YF Liu and YW Chen and C Song and DJ Wang, APPLIED THERMAL ENGINEERING, 280, 128404 (2025).

DOI: 10.1016/j.applthermaleng.2025.128404

The reduction in cooling capacity of evaporative cooling systems remains a major challenge that limits their applications at high altitudes. However, current explanations are often limited to qualitative hypotheses or focused solely on vapor transport perspectives, rather than the liquid-vapor phase transition process itself. In the present study, molecular dynamics (MD) simulations using a droplet are conducted to investigate the underlying mechanisms of this reduction in cooling in evaporative cooling systems. The evaporation behavior of a droplet under air pressures of 1.0, 0.6 and 0.2 bar was studied. The results revealed that interfacial thermal resistance played a critical role in governing heat and mass transfer between the droplet and the surrounding air, especially under varying air densities-a factor often neglected by conventional models. Taking the interfacial resistance at 1.0 bar as the reference, the resistance at 0.6 bar was 5.03 times higher, whereas at 0.2 bar, the resistance was 39.18 times higher. Correspondingly, mass transfer resistance also increased, with values of 3.63 (at 0.6 bar) and 11.51 (at 0.2 bar) times higher than that at 1.0 bar. The combined increase in both interfacial thermal and mass transfer resistances led to a significant reduction in cooling capacity under low-pressure conditions. More specifically, the cooling capacities at 0.6 bar and 0.2 bar were reduced to only 27.42 % and 3.96 % of that observed at 1.0 bar, respectively. These insights provide a mechanistic basis for optimizing evaporative cooling technologies in low-pressure regions, supporting more reliable and efficient thermal management in buildings, power systems, and other engineering applications.

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