Improved cooling system for USQ's small scale icing wind tunnel

Turbofan engine icing is a relatively new mode of icing attributed to solid phase ice accretion inside the engines. This occurs during flights at high altitudes through convective regions, where tiny ice crystals are ingested and make contact with the engine’s warm internal surfaces. The University of Southern Queensland has a small scale icing wind tunnel dedicated to studying aspects of thermal and particle conditions characteristic of ice accretion initiation in turbofan engines. This dissertation aimed to improve the operation of the facility’s refrigeration system by investigating the feasibility of implementing a steady flow work extraction device to super cool pressurised air via expansion processes. A DEPRAG rotary vane air motor was sourced to conduct the bulk of testing on, using K type thermocouples to measure a maximum temperature drop of 20.7oC. After this preliminary testing, the air motor was disassembled to assist in development of a theoretical system model using equations based on geometry and fluid mechanics; tuned using recorded data as a reference. This went to show that the expansion process of air over short periods followed a roughly isentropic relationship. Further work was done to determine whether this relationship held over longer periods of expansion. Secondary testing was conducted after redesigning the cylinder rotor housing to maximise temperature drop. Results from this test provided only minor improvement, producing a maximum temperature drop of 21.2oC. The relative size of the cylinder bore, and the speed of the motor are believed to have nullified the adaptations made to initiate the expansion phase earlier (i.e. when the working chamber had a smaller initial volume). It is posed that this resulted in the vanes reforming working chambers at a similar position to what they did in the original motor. A customised rotary vane air motor was designed to overcome these issues in design and operation by being larger and slightly slower. Unfortunately time constraints prevented this from advancing into fabrication and testing phases. The findings from this project suggest that small commercial air motors are not capable of conditioning air cold enough to be a feasible alternative to the current cooling system. It also suggests that small motors are difficult to modify when aiming to increase their maximum temperature drops. In the case of the DEPRAG air motor, its high speed and small cylinder bore are believed to interfere with the amount of expansion experienced by affecting vane (or working chamber) engagement. Larger temperature drops may be possible using larger sized rotary vane air motors, such as the customised rotary vane air motor designed in this project. However a key assumption in this is that the isentropic behaviour of expanding air observed in the DEPRAG air motor carries over to larger motors, and there is no easy way to confirm this without additional testing on such an air motor