| Summary: | The air conditioning heat exchangers of the Airbus A320 are plate wavy fin type. Operational aircraft such as the A320 suffer from failure in commercial service owing to operational fouling and the aim of the research was to investigate the causes of large commercial aircraft air conditioning system failures, attributed to overheating. The aim of the thesis is to research the problems relating to the failure of the Environmental Control System (ECS), and to publish data and findings. The ECS plate fin heat exchangers (PFHE) of live aircraft were examined during hanger maintenance, and later the fouling was analysed and the sources were identified. A series of experiments were designed to replicate an aircraft ECS PFHE operation, similar to that fitted to the A320 using two types of wavy fins (fine and coarse). The novelty of the research was to design a series of experiments that reproduce the aircraft PFHE operations, which included the fouling of the wavy fins. Compressed air was used to replicate the outside 'ram' air cooling flow, · and hot bleed engine air flow was replicated by two electrical heating mats. A new method was used to produce the experimental fouling material which replicated the real world situation. The effects of fouling on fins were observed in terms of heat transfer, pressure drop and fouling analysis. Pressure drop experimental results appeared to be generally consistent yet lower than literature correlations of Hesselgreaves (2001) and Kays and London (1984). The additional fouling supply introduced to the compressed air flow was less than 2% of the total mass flow. Analysis of fouling materials deposited on the fins using scanning mobility particle sizing (SMPS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques indicated that fouling samples from live aircraft were very similar to those used in the experiments. The experimental film heat transfer coefficients for the empty channel and the two types of fins were calculated using the analytical solution, initially clean and later fouled. It was expected that the higher number of fins would result in a higher heat transfer performance, yet the experimental results and some predictions indicated this was not the case. The predictions of the film heat transfer coefficients based on the correlations demonstrated that some of the results vary significantly when compared to the experimental coefficients. It was noted that at times, the temperature distribution of the apparatus walls were not symmetrical, resulting in transverse heat conduction.
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