Electrical machines for aerospace applications often operate close to the allowable thermal limits due to high power density requirements. The power density of electrical machines is generally dependent on the machine and thermal management design. At flight level, a reduced pressure exists which in turn results in more challenging thermal management. Aerospace electric machine manufacturers are often limited with respect to the implemented cooling mechanisms. That is, natural convection systems are the norm, as fan cooled and fluid cooled machines may suffer from reliability issues. The original contribution of this work, is the design, testing, and implementation of an alternative forced cooling convective system (FCCS) based on piezoelectric fans. This thesis commences by an investigation of the capabilities of MotorCAD (a sophisticated analytical lumped thermal package) and how it can be utilised in a fully integrated way to optimise (for a maximum power density and an overall minimum motor mass) both the electromagnetic and thermal aspects of a typical traditional horizontally-mounted permanent magnet synchronous machine (PMSM) operating at flight level. The resultant analytical temperature values were then compared to actual experimental temperature data. Piezoelectric fans are then investigated as a potential, fault tolerant FCCS that may enhance the overall cooling of a motor. These fans could be implemented in the aerospace industry as they do not suffer from the same reliability issues as traditional FFCS’s. Detailed thermal results indicating the effective piezoelectric fan cooling range together with the overall cooling effectiveness over a traditional vertical straight-finned heat sink (unit – cell) , operating under different operating conditions are also presented. Furthermore, the fin/fan geometry that minimises the thermal resistance whilst minimising the overall cooling mass is presented. Particle Image Velocimetry (PIV) techniques were implemented to further understand the flow fields generated by an oscillating piezoelectric fan. Common parameters governing the fluid flow (vibration amplitude, separation distance, fin spacing and fan orientation) were investigated and the results are herewith presented. Designs of a supporting structure for the proposed FCCS implementation are drawn up and analysed through FEA. A prototype structure was built and its durability tested. Furthermore, the reliability (fault tolerance) of the suggested FCCS was evaluated. The feasibility of implementing this innovative cooling technique was further investigated by performing a study on the weight saving potential of the FCCS over traditional natural convective fins, and the FCCS geometry that minimises the thermal resistance whilst minimising the overall mass is selected. Furthermore, a prototype FCCS was built and tested.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:559624 |
| Date | January 2012 |
| Creators | Gilson, Gareth M. |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/12568/ |
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