Évaluation des paramètres influençant le temps d'endurance d'un fluide antigivre sous précipitations de neige /

Abstract

Snow and ice accumulation can change the shape of critical aeroplane surfaces, while on the tarmac or waiting for take-off, such as wings, flight control surfaces and leading edges. This can lead to a loss of aerodynamic performance during take-off, which may at times prove to be dangerous. De-icing and anti-icing protection methods have been developed to avoid such accidents during take-off. Anti-icing and de-icing fluids applied to an aeroplane's critical surfaces while waiting for take-off are among the most used techniques used to prevent snow accumulation or to make it melt.Glycol based fluids are characterised by their protection time, commonly called endurance time, which is determined based on an evaluation carried out in an environmental test chamber, according to standard APR5485. Endurance time is measured by exposing an anti-icing fluid covered plate to a snowfall below 0°C.The purpose of this thesis is to understand the behaviour of the anti-icing fluid during snow endurance tests, to determine the parameters influencing the failure of the fluid and to determine the mechanism of fluid failure.The experimental setup defined in the standard was modified to simplify the phenomena under study. The experimental setup used during the tests carried out in LIMA'S 9m environmental test chamber consisted of a flat, 50cm long and 30cm wide aluminum plate and an aluminum snow box equipped with an acetal cylinder. The cylinder contains hemispherical holes allowing the snowflakes to fall in groups with two intensities, 10 and 25 g/dm 2 /h. The plate is parallel to the ground, surrounded by insulated walls allowing the snow to accumulate and preventing the fluid from escaping. A heating element under the plate maintains its temperature at the value defined by the standard and two thermocouples located at the plate/heating element interface measures and controls the temperature. Another thermocouple is used to measure the temperature of the fluid during the experiment. The temperature control in the climate chamber is automated to maintain the temperature at the required levels of-5°C, -10°C, -14°C, and -25°C. The assembly is linked to a controller that maintains the plate temperature at the desired level by controlling its power supply. The controller and the assembly are linked to a computer, which automatically records the air, plate and fluid temperatures, the precipitation intensity and the weight of the snow precipitated during the test, as well as the power consumption. Experimental runs were performed using a generic fluid containing propylene glycol. 400 ml of fluid was poured on the plate during each run, forming a 2.7 mm thick layer.Results have shown that the air temperature remains constant with small, regular fluctuations throughout the run for all conditions. For runs at temperatures higher than -25°C, the plate temperature is at approximately the desired temperature at the beginning of the test and decreases rapidly to a minimum value. The lowering of the temperature is compensated for by an...