Numerical Simulation of Mixing Unit Performance of Civil Aircraft Environmental Control System

The mixing unit of civil aircraft environmental control system is the supplier of cabin air, which undertakes the mixing function of fresh air and recirculated air, as well as the distribution function of the air flow into each cabin zone. The performance of the mixing unit determines the thermal comfort of the crews and passengers. In order to predict the mixing unit performance under various operating conditions, the numerical simulation method is applied in this paper. Three parameters are applied for evaluating the mixing unit performance, including the temperature variance of mixing unit outlets, the surface uniformity of outlet temperature and the pressure drop. Four typical operating conditions of mixing unit are studied, including cooling mode with double PACKs, cooling mode with single PACK, heating mode with double PACKs and heating mode with single PACK. The simulation results show that, the outlet temperature variance and maximum temperature difference of the mixing unit under cooling mode with double PACKs are 62.4% and 35.6% lower than those under the cooling mode with single PACK.