System design of aircraft air conditioning system (3^nd Report: Study on the icing analysis for the high-pressure water separation)

Abstract

The purpose of this paper is to develop an analytical model of frost/ice formation on the heat exchanger (condenser) of high-pressure water separation used in the air conditioning system of commercial jet aircraft. The high-pressure water separation is based on the heat exchange between the upstream and downstream sides of the same air flow with pressure difference. That is, relatively high-pressure and warmer air upstream of a condenser with high humidity is cooled by relatively low-pressure and cooler air discharged from a turbine downstream of the condenser; condensed water in the high-pressure side is removed by a water separator while in the low-pressure side the super-cooled water mist is produced by adiabatic expansion process in the turbine. In the both sides, when the heat-exchange fins are below the freezing temperature of the humid air, frost/ice formation occur, although their physical mechanism are utterly different. In this study, a phase-change model taking the features of a cross-flow heat exchanger into account is newly proposed. In particular, attention is focused on the increase of the pressure drop in the lower pressure side due to frost/ice formation. The validity of the analytical model is checked by the comparison with the experiment.