The Maisotsenko cycle (M-Cycle) has emerged as a promising indirect evaporative cooling technology capable of achieving high cooling effectiveness with significantly lower energy consumption than conventional vapor-compression systems. Although previous studies have investigated the thermal performance of M-Cycle heat and mass exchangers, the influence of airflow velocity on the coupled heat transfer, mass transfer, and energy characteristics of the system has not been systematically quantified. In the present study, a two-dimensional steady-state analytical model was developed to investigate the effect of inlet air velocity on the thermodynamic and hydrodynamic performance of an M-Cycle-based indirect evaporative cooler. The model incorporates coupled heat and mass transfer, evaporation, airflow dynamics, and pressure losses within the dry and wet channels of the heat and mass exchanger. Simulations were performed over an air velocity range of 0–20 m/s, and key performance indicators including outlet air temperature, relative humidity, cooling capacity, convective heat transfer coefficient, fan power consumption, coefficient of performance (COP), energy efficiency ratio (EER), and seasonal energy efficiency ratio (SEER) were evaluated. The results demonstrate that airflow velocity exerts a strong nonlinear influence on system performance. At low velocities, longer residence times enhance evaporative cooling and reduce the outlet air temperature to approximately 22.3 °C; however, the outlet air approaches saturation conditions. Increasing the velocity improves convective heat transfer but simultaneously reduces residence time and increases pressure losses. An optimum operating condition was identified at approximately 7 m/s, corresponding to a cooling capacity of 17,642 Btu/hr (5.12 kW), an outlet temperature of 22.27 °C, a relative humidity of 71%, and a fan power consumption of 125.8 W. Under these conditions, the system achieved maximum energy performance with COP, EER, and SEER values of 38.21, 130.42 Btu/hr·W, and 144.91 Btu/hr·W, respectively. Further increases in velocity resulted in reduced evaporative effectiveness and rapidly increasing fan energy consumption, leading to lower overall efficiency. The findings identify the optimal airflow regime for M-Cycle operation and provide design guidance for improving the performance and energy efficiency of indirect evaporative cooling systems.
Bakhtiari et al. (Mon,) studied this question.