Teach Second Law of Thermodynamics via Analysis of Flow through Packed Beds and Consolidated Porous Media

• Main Author: Rajinder Pal
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: Fluids
• Subjects: undergraduate education; applications of fluids; fluid mechanics; packed bed; porous media; non-equilibrium thermodynamics; entropy generation; pressure loss; Ergun equation; Forchheimer equation
• Online Access: https://www.mdpi.com/2311-5521/4/3/116

The second law of thermodynamics is indispensable in engineering applications. It allows us to determine if a given process is feasible or not, and if the given process is feasible, how efficient or inefficient is the process. Thus, the second law plays a key role in the design and operation of engineering processes, such as steam power plants and refrigeration processes. Nevertheless students often find the second law and its applications most difficult to comprehend. The second law revolves around the concepts of entropy and entropy generation. The feasibility of a process and its efficiency are directly related to entropy generation in the process. As entropy generation occurs in all flow processes due to friction in fluids, fluid mechanics can be used as a tool to teach the second law of thermodynamics and related concepts to students. In this article, flow through packed beds and consolidated porous media is analyzed in terms of entropy generation. The link between entropy generation and mechanical energy dissipation is established in such flows in terms of the directly measurable quantities such as pressure drop. Equations are developed to predict the entropy generation rates in terms of superficial fluid velocity, porous medium characteristics, and fluid properties. The predictions of the proposed equations are presented and discussed. Factors affecting the rate of entropy generation in flow through packed beds and consolidated porous media are identified and explained.