Entropy 26(9), 791 (2024)
Exergy Flow as a Unifying Physical Quantity in Applying Dissipative Lagrangian Fluid Mechanics to Integrated Energy Systems
Ke Xu1,2, Yan Qi1, Changlong Sun3, Dengxin Ai1, Jiaojiao Wang3,4, Wenxue He3,4, Fan Yang3,4 and Hechen Ren3,4,5,*
1 Electric Power Research Institute of State Grid, Tianjin Electric Power Company, Tianjin 300010, China
2 State Grid Smart Internet of Vehicle Co., Ltd., Beijing 100052, China
3 Center for Joint Quantum Studies, Department of Physics, Tianjin University, Tianjin 300350, China
4 Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Department of Physics, Tianjin University, Tianjin 300350, China
5 Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207, China
* ren@tju.edu.cn
Abstract
Highly integrated energy systems are on the rise due to increasing global demand. To capture the underlying physics of such interdisciplinary systems, we need a modern framework that unifies all forms of energy. Here, we apply modified Lagrangian mechanics to the description of multienergy systems. Based on the minimum entropy production principle, we revisit fluid mechanics in the presence of both mechanical and thermal dissipations and propose using exergy flow as the unifying Lagrangian across different forms of energy. We illustrate our theoretical framework by modeling a one-dimensional system with coupled electricity and heat. We map the exergy loss rate in real space and obtain the total exergy changes. Under steady-state conditions, our theory agrees with the traditional formula but incorporates more physical considerations such as viscous dissipation. The integral form of our theory also allows us to go beyond steady-state calculations and visualize the local, time-dependent exergy flow density everywhere in the system. Expandable to a wide range of applications, our theoretical framework provides the basis for developing versatile models in integrated energy systems.
