Characterizing transformation and degradation
Scientific articles that generalize the fundamentals of our technology
Abstract
Entropy generation, formulated by combining the first and second laws of thermodynamics with an appropriate thermodynamic potential, emerges as the difference between a phenomenological entropy function and a reversible entropy function. The phenomenological entropy function is evaluated over an irreversible path through thermodynamic state space via real-time measurements of thermodynamic states. The reversible entropy function is calculated along an ideal reversible path through the same state space. Entropy generation models for various classes of systems—thermal, externally loaded, internally reactive, open and closed—are developed via selection of suitable thermodynamic potentials. Here we simplify thermodynamic principles to specify convenient and consistently accurate system governing equations and characterization models. The formulations introduce a new and universal Phenomenological Entropy Generation (PEG) theorem. The systems and methods presented—and demonstrated on frictional wear, grease degradation, battery charging and discharging, metal fatigue and pump flow—can be used for design, analysis, and support of diagnostic monitoring and optimization.
Abstract
Modern concepts in irreversible thermodynamics are applied to system transformation and degradation analyses. Phenomenological entropy generation (PEG) theorem is combined with the Degradation-Entropy Generation (DEG) theorem for instantaneous multi-disciplinary, multi-scale, multi-component system characterization. A transformation-PEG theorem and space materialize with system and process defining elements and dimensions. The near-100% accurate, consistent results and features in recent publications demonstrating and applying the new TPEG methods to frictional wear, grease aging, electrochemical power system cycling—including lithium-ion battery thermal runaway—metal fatigue loading and pump flow are collated herein, demonstrating the practicality of the new and universal PEG theorem and the predictive power of models that combine and utilize both theorems. The methodology is useful for design, analysis, prognostics, diagnostics, maintenance and optimization.
Abstract
The adverse effect of heat and high temperatures on our bodies and everything around us is evident. But quantifying the degradation impact of heat is nontrivial and intractable. In this article, thermodynamic free energy is used to elucidate the significance of energy dissipation-induced temperature rise on the performance, reliability and durability of all systems, biological and physical. Transformation and degradation are distinguished. The mechanism of temperature rise impact on a system’s microstructure is characterized by the microstructurothermal (MST) energy/entropy. In this article, the MST entropy is quantified for various system types, showing a significant contribution to system performance and durability. During exercise, temperature rise alone induced an average of 204% increase in cardiovascular strain in elite cyclists, with active physiological work restorative. Lithium-ion batteries undergoing active cycling showed an MST entropy contribution of 40% of overall capacity fade. Mechanically sheared lubricant grease experienced thermal degradation of <1% of overall degradation, partly due to the transformation measure used. The benefits of active, often forced, cooling on systems and materials are shown. This article is recommended to engineers, designers, medical doctors and other system analysts for use in dissipation/degradation characterization and minimization.