University of Twente Student Theses
Thermal Degradation of Grease
Dokter, Jorn (2024) Thermal Degradation of Grease.
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| Abstract: | The thermal degradation of lubricating grease is investigated using a temperature-only thermodynamic model. This model is derived from first principles in accordance with existing models to include heat storage, heat transfer and evaporation mechanisms via their respective entropies. As grease churning in a bearing experiences high amounts of thermal degradation, the thermodynamic model is utilised to characterise the thermal entropy generation. These entropies are then used to define a novel three-phase approach to characterise churning behaviour. These three phases are: the initiation phase, continuation phase and termination phase. The churning measure ϕ is introduced and applied to experimental data, where it was found to be able to quantitatively characterise peak- and plateau-type churning behaviour. The same temperature-only model is applied to greases thermally aged for 10, 20 and 30 days at 130◦C in a nitrogen atmosphere. The greases tested are Li/M (lithium soap/mineral base oil), Li/SS (lithium soap/semi-synthetic base oil) and PU/E (polyurea/synthetic ester base oil). Critical rheological, thermo-physical and mechanical properties are measured on fresh and aged grease samples: bleed capacity measure, heat capacity, storage modulus, thermal strain coefficient and yield stress. The Degradation-Entropy Generation methods are applied to find degradation coefficients that characterise the thermal degradation with an accuracy of R2 > 0.99. The impacts of all three active thermal mechanisms on the degradation of greases are investigated and quantified. All three mechanisms are shown critical for accurately modelling thermal degradation. The tested greases are ranked in thermal degradation resistance using their degradation coefficients. |
| Item Type: | Essay (Master) |
| Faculty: | ET: Engineering Technology |
| Subject: | 52 mechanical engineering |
| Programme: | Mechanical Engineering MSc (60439) |
| Link to this item: | https://purl.utwente.nl/essays/98637 |
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