Pollution Mechanism And Cleaning Process Optimization Of Heat Exchangers In Aircraft Air-conditioning

Heat exchanger is an important accessory of the aircraft air conditioning systems, the fouling on its cooling surface is a widespread problem in civil aircraft operation. The fouling can decline heat exchanger efficiency rapidly, causing the air conditioning system to malfunction. Severe fouling can even lead to localized corrosion, perforation and fracture on heat exchanger surface, seriously affecting the safety of the equipment.In this paper, the operating condition of the heat exchanger in aircraft air-conditio ning system is analyzed, in order to understand the main source of heat transfer surface fouling. Then the elemental contents of the fouling collected from heat exchanger surfaces are tested. The results showed that the heat exchanger surface fouling mainly come from atmospheric pollutants, including aerosol soluble ions, dust, particulates, suspended solids, soil particles, and organic pollutants.A thin liquid film evaporation experiment is designed to simulate the growth of crystal ization fouling and to study thermal conductivity with the different condition of the heat transfer surfaces. The results display that the catkins increases the adsorption sites fouling nuclei, thus significantly promoting the fouling growth with a compact structure. Residual cleaning agent or oil contamination on the heat transfer surfaces inhabits the fouling growth, and increases the thermal resistance by their selves.Finally, accelerated corrosion experiment is carried out to study the corrosive effect of the simulating fouling layer on aluminum al oys. The results show that halogen elements in the fouling break the passivation of the aluminum surface, thus promote the initiation of the pitting corrosion. The carbon particles in the fouling accelerate the development of corrosion. The studies of the cleaning mechanism demonstrate that cleaning performance is very poor with the ultrasonic power less than 60%. H+ concentration, temperature, and soaking time effective ly improve the cleaning ability of the cleaning agents.