1. Thermoelectric energy harvesting system for a bearing node of a power microturbine
Using intelligent materials and structures to develop and implement the concept of the innovative bearing system in power microturbine rotors
Energy harvesting for bearing nodes, microturbine setups, rotating machinery
Project Description
The scope of the project activities focuses on elaborating the comprehensive design plan for the rotor support of power microturbines. The special attention will be driven to the devices that operate in low boiling medium environment (Chlorofluorocarbon, HFE 7100, SES 36, ethanol, silicon oil). To meet the demands of harsh operating conditions the bearing system in such machines base on the foil bearings.
Throughout the project duration the basic research on materials has been conducted in order to knowingly select among the state-of-the-art materials. To perform the experiments on the selected samples the test rigs and experimental setups have been designed and created both for steady and start-stop test cycles. The tests were planned so that to follow the VAMAS directives for new construction materials.
The materials selected for tests (wear, friction coefficients, concentrated and distributed contact characteristics) were:
Copper based alloys (CuSn10, CuSiMn1, CuZr5, CuCr5, CuSn6, CuMn5, NiCu25, CuNi25, CuAl5, CuAl7) the physical, mechanical, thermal and micro-structural properties have been tested,
- Surface modified Inconel (ion implantation, glow discharge nitriding, sputtering, vapor deposition),
Copper matrix copmosites doped with ceramic phase (alumina, graphite),
- Matrix composites of nickel and copper-doped phase ceramic (alumina),
Design Methodology
Apart from the classical approach to the design of thermoelectric energy harvesting devices it was assumed that the structure of the harvester may influence the heat reservoirs it is attached to f. ex. by introducing the insulating partitions. As the integration of the thermoelectric generating module is planned at the design stage of the device it can lead to the higher power level recovered via this harvesting technique.
The equivalent model of the bearing node may be by simplification represented via resistive mesh in order to perform the sensitivity analysis, optimization task or to choose the design scenarios. As the adopted methodology gives a versatile possibilities it is already possible at the early stage of development to assess the power density characteristics of the harvester.
CuAl5
CuAl7
CuSn10
Results
The multiphysics simulations as well as the adopted analytical and thermal network equivalent models proved their accuracy. The experimental results show good consistency with the numerical predictions. By proper choice of the model structure it is possible to simulate the whole system including the generator unit, power management unit and the connected circuitry as well as heat conduction and heat spreading mechanisms.
CuSi3Mn1
CuNi25
NiCu25
Figure: Materials for bumb and top foil
Bottom: Wear test results
Figure: Top: Test aparatus for wear tests
The results of the project are applicable for such industry branches like distributed energetics, engineering and aviation. The most attention is driven toward the cogeneration capabilities of microturbines in household CHP plants. The low boiling agent that can be used to power the turbine's blades as well as to lubricate the foil bearings is a perfect medium to be used with natural gas furnaces. The final effects of the project include the full design path for the foil bearings of 3rd generation, elaboration of the manufacturing processes and tools (micro welder, forming tools etc.). 1 2 3 1 2 3
Figure: Experimental vs numerical comparison showing good level of consistency
The harvester is able to power the devices while they are working continuously or in burst mode (intervals of active and sleep modes) that would be of preferred type for monitoring nodes in SHM (Structural Health Monitoring), MCM (Machine Condition Maintanance) or CBM (Condition Based Maintanance) applications. 5 4
5) The assembly of the foil bearing prototype
3) 4) Bump foil just after forming process
Figure: 1) 2) Experimental setup for high speed testing equipped with bearing housing having thermoelectric capabilities
Figure: Sensitivity analysis results; Heat sink resistance vs power level; Insulating partition resistance vs power level
For more information refer to the project official website:
Figure: Harvested power level vs measurement cycle duration for both continuous and burst mode