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The purpose of this study is to develop an analytical model of cross-flow heat exchangers with offset strip fins which are usually equipped in the aircraft air conditioning system (so called the environmental control system, ECS). The ECS mainly consists of four cross-flow heat exchanges, i.e., a primary heat exchanger, a secondary heat exchanger, a reheater and a condenser. Because of the special requirements of the design for the aircraft, the primary and secondary heat exchangers are set adjoiningly; the reheater and the condenser are also set adjoingly. Therefore, in both the pairs, the effect of the temperature profile of the upstream component (the secondary heat exchanger or the reheater) on those of the downstream component (the primary heat exchanger or the condenser) should be taken into account for precise prediction of the system. To this end, a core element model was newly proposed in this study. In addition to the effect of temperature profile, phase changes (condensation and evaporation) of water included in the humid air simultaneously occur except for the primary heat exchanger. Regarding these phenomena, the method of sensible heat fraction (SHF) to convert the latent heat into the equivalent sensible heat was introduced, and the global and local SHF models were examined by comparison with the experiments. The prediction by these models were found to agree well with the actual performance of the ECS operations.

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.

The purpose of this study is to clarify the effect of a component for high-pressure water separation, which is included in the air conditioning system of the general commercial aircrafts, on the air-cycle operation (reverse Brayton cycle); the high-pressure water separation consists of water separator and two heat exchangers called reheater and condenser, respectively. This paper briefly describes the typical system configuration of the air-cycle refrigeration progressed with evolutions in turbofan engine. Since nowadays, 4-Wheel air-cycle has been a trend on the aircraft air conditioning system, this paper theoretically shows its advantage on the basis of the thermodynamic cycle study. In the following chapters, an analysis was conducted on the interaction between a reheater and a condenser when each heat transfer performance changes from the baseline operating point. Also, the comparative study was made on the system performances by the 3-wheel and 4-wheel air-cycle. In addition, this paper describes how the heat transfer performance is designed for the reheater and the condenser under the system requirements for the entire air conditioning system.