Application of a Thermodynamic Concept for the Analysis of Structural Degradation of Soap Thickened Lubricating Greases

Kuhn, Erik

doi:10.3390/lubricants6010007

Cited by 9 publications

(2 citation statements)

References 9 publications

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“…charge.-The Carnot limitation, which governs the availability of a system's energy for work, was expressed by Burghardt 62 for a heat source as Energy added = Available energy + U navailable energy. [41] Equation 39 describes C, which can be decomposed into a phenomenological component C phen that establishes the battery's actual path, and a reversible component C rev that establishes its ideal path. The phenomenological charge transfer C phen can be correlated directly with phenomenological entropy terms (first two right-hand side terms) in Equation 36as…”

Section: Phenomenological Charge Measured Charge and Reversiblementioning

confidence: 99%

“…Using a logarithmic fatigue limit model, they reported a correlation coefficient over 0.95. Kuhn [38][39][40][41][42] demonstrated, with experimental verification, grease characterization using thermodynamic energy and, more recently, entropy. Experimental works by Bryant et al [43][44][45][46] correlated solid interfacial frictional wear with entropy flow out of a tribo-control volume, leading to the formulation of the Degradation-Entropy Generation DEG theorem.…”

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confidence: 93%

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Thermodynamics of Lead-Acid Battery Degradation: Application of the Degradation-Entropy Generation Methodology

Osara

Bryant

2019

J. Electrochem. Soc.

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This article details a lead-acid battery degradation model based on irreversible thermodynamics, which is then verified experimentally using commonly measured operational parameters. The model combines thermodynamic first principles with the Degradation-Entropy Generation theorem, to relate instantaneous and cyclic capacity fade (loss of useful charge-holding capacity) in the lead-acid battery to the entropy generated via the underlying dissipative physical processes responsible for battery degradation. Equations relating capacity fade to battery cycling are also formulated and verified. To show robustness of the approach, nonlinear data from uncontrolled and severely abusive battery cycling-including overdischarge-was measured and used to verify formulations. A near 100% agreement between the thermodynamic battery model and measurements is achieved. The model also gives rise to new material and design parameters to characterize all lead-acid batteries.

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Section: Phenomenological Charge Measured Charge and Reversiblementioning

confidence: 99%

mentioning

confidence: 93%

Thermodynamics of Lead-Acid Battery Degradation: Application of the Degradation-Entropy Generation Methodology

Osara

Bryant

2019

J. Electrochem. Soc.

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Experimental Study on the Expended Energy on Structural Degradation of Lubricating Greases

2022

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One of the keystones of tribological studies is the energetical approach to the lubrication process. In the particular case of lubricating greases, part of the lubrication process's energy dissipates due to a shear-induced structural rearrangement of the 3D network of the thickening agent dispersed in the base oil. This fact confers them a particular consistency, mechanical stability, rheological and tribological behaviour. In this research work, we investigate the mechanical structural degradation induced by shear stress applied in rheological tests (rotational and oscillation mode) and the influence of thickener (type and composition) and base oil on both the degradation process and the expended mechanical energies. For this purpose, lithium, calcium and polyurea-based greases of NLGI grade 2 were used. These greases have been manufactured with a different base oil (mineral, synthetic and vegetable oils) and kinematic viscosity of 48 or 240 mm2/s. Some biogenic greases were also included in this research. The optical microscopy analysis revealed thickener particles-based agglomerates with different shapes and sizes that reduced notably, if not almost completely destroyed, after stress. Due to the thickener particles-based agglomerates distribution, significant differences in the shear-induced frictional energy inside the bulk grease during the shear process were detected. The size of agglomerates depended on both the thickener content and the base oil viscosity and not the type of base oil.

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An approach of the internal friction-dependent temperature changes for conventional and pure biogenic lubricating greases

Ahme,

Kuhn,

Delgado

2023

Friction

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This work investigated the temperature changes inside the bulk of lubricating greases under controlled high-shear stress conditions (250–500 s−1). For this purpose, a newly developed temperature-measuring cell called Calidus was successfully tested. The temperature changes (ΔT) have been related to the greases’ components (thickener, base oil-type, and composition) and the structural degradation of the lubricating greases. Furthermore, a theoretical approach was proposed for calculating the internal temperature change of lubricating greases during shear stress. All greases showed an internal temperature profile characterised by a sudden rise in ΔT within the first 4 h from starting the test and subsequent ΔT decay until it reaches the steady state value. Furthermore, it was found that greases C1 and C5, formulated with lithium and calcium soap, respectively, with different soap content (16.1 wt% and 9.7 wt%, respectively), but the same base castor oil, showed the highest value of the maximum ΔT, c.a. 3.2 K, and the most drastic drop of ΔT. These greases showed both the highest specific densities and heat capacities. In addition, they showed the lowest ratio of expended energies (Rtee), which means more structural degradation in the stressed grease. On the contrary, the grease C3, with 13 wt% of Li-soap but the lowest base oil’s viscosity, showed the lowest maximum ΔT and the temperature profile was characterised by a moderate variation of ΔT along the test. The biogenic grease B3 developed a low-temperature change in the group of pure bio-genic greases close to grease C3.

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Application of a Thermodynamic Concept for the Analysis of Structural Degradation of Soap Thickened Lubricating Greases

Cited by 9 publications

References 9 publications

Thermodynamics of Lead-Acid Battery Degradation: Application of the Degradation-Entropy Generation Methodology

Thermodynamics of Lead-Acid Battery Degradation: Application of the Degradation-Entropy Generation Methodology

Experimental Study on the Expended Energy on Structural Degradation of Lubricating Greases

An approach of the internal friction-dependent temperature changes for conventional and pure biogenic lubricating greases

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