International Journal of Heat and Mass Transfer, Vol.116, 1124-1142, 2018
Exergy analysis for unsteady-state heat conduction
Exergy analysis has been used in various fields to quantify the efficiency of various energy transfer processes. So far, most exergy analyses have been performed by assuming steady-state conditions both for a system of focus and its environment. However, steady-state analyses may idealize a problem too much and thereby limit what we can know about the system, since the assumed system is only a snapshot of a certain condition or moment. In particular, a steady-state exergy analysis is not suitable for analyzing problems where the system has a large heat capacity and problems with varying boundary conditions. To understand the exergy transfer and consumption processes in a system whose transient characteristics are critical, an unsteady-state exergy analysis must be conducted.& para;& para;This study presents a methodology for unsteady-state exergy analysis that can be used to study heat conduction problems. Governing equations of entropy and exergy to be parallel to the governing equation of energy are derived in their partial differential forms, and their numerical methods are presented in detail. Based on the proposed methodology, an unsteady-state exergy analysis of a heat conduction problem for a concrete wall is carried out to demonstrate its transient exergy behavior. (C) 2017 Elsevier Ltd. All rights reserved.