Second Law of Thermodynamics Explained: Entropy, Heat Engines, Refrigerators and Heat Pumps
Graphical Abstract Introduction The First Law of Thermodynamics tells us that energy is conserved. However, it does not explain why some energy transformations are possible while others are not. For example: Why does heat naturally flow from hot objects to cold objects? Why can't a refrigerator cool a room without consuming power? Why can no engine convert all heat into work? The answers are provided by the Second Law of Thermodynamics. The Second Law introduces the concept of entropy and establishes the direction of natural processes. Learning Outcomes After studying this article, students will be able to: ✓ Understand the limitations of energy conversion. ✓ State the Second Law of Thermodynamics. ✓ Explain Kelvin-Planck and Clausius statements. ✓ Describe heat engines, refrigerators, and heat pumps. ✓ Understand reversible and irreversible processes. ✓ Define entropy and entropy generation. ✓ Apply Second Law concepts to engineering systems. Why Do We Need the Second Law? Consi...