TD-Class-3-Summary

Second Law and Thermodynamic Relations: MSubbu discussed the upcoming topics for the class, focusing on second law of thermodynamics and thermodynamic relations. He explained that the session would cover five questions on the second law, including statements, Carnot engine, entropy calculations, and irreversibility, as well as five questions on thermodynamic relations. MSubbu mentioned that the class would also touch upon questions from Smith and Vanness, Pitzer's thermodynamics book, BG Kyle, GATE-XE, ME. He planned to start with second law aspects, particularly Carnot engine and refrigerators, which he described as the easiest topics.

Carnot Principles and Heat Systems: MSubbu explained the principles of Carnot engines and refrigerators, focusing on the relationship between heat extracted and delivered, and the efficiency of these systems. He emphasized that for Carnot engines and refrigerators, only the temperature levels are needed to calculate efficiency or coefficient of performance, and provided examples of how to use temperature values to find work and useful effects. MSubbu also discussed the concept of heat pumps, explaining their use in cold climates to heat spaces by extracting heat from the ambient environment, and highlighted the differences in useful effects and coefficients of performance between refrigerators and heat pumps.

Entropy Calculations for Heat Transfer: MSubbu explained entropy change calculations for various heat transfer problems, including the mixing of hot and cold waters and the freezing of benzene. He demonstrated how to calculate the entropy change for these processes using the formula dS = dQ/T and showed that the total entropy change is always positive for irreversible heat transfer processes. MSubbu also discussed the concept of reversible processes, where the entropy change of the system plus surroundings is zero, and encouraged students to review a given problem involving heat transfer between two liquid streams for further practice.

Entropy Calculation for Two-Phase Mixture: MSubbu discussed a problem involving the entropy of a two-phase mixture in a tank containing saturated water and steam at 200 degrees Celsius. He explained how to calculate the dryness fraction (quality of vapor) using the given mass of liquid, total volume, and specific volumes of liquid and vapor. The entropy of the mixture can then be determined using the formula S = Sf + x(Sg - Sf), where Sf is the entropy of the saturated liquid, Sg is the entropy of the saturated vapor, and x is the dryness fraction.

Mollier Diagram and Thermodynamic Relations: The discussion focuses on thermodynamic relations and the Mollier diagram. Professor Subbu explains that the Mollier diagram is an enthalpy-entropy chart, often found in steam tables. He states that the slope of the Mollier diagram at constant pressure is represented by the partial derivative of enthalpy with respect to entropy at constant pressure. The professor also mentions that they will be examining five representative problems related to thermodynamic relations, including Maxwell relations and their applications.

Thermodynamic Relations and Diagrams: MSubbu explained how to derive thermodynamic relations using diagrams and variables. He demonstrated how to construct mnemonic diagrams and write equations for different energy variables. MSubbu also discussed the concept of positive and negative quantities and how they relate to the direction of arrows in the diagrams. Finally, he explained how to get Maxwell relations from the mnemonic diagram.

Thermodynamic Principles and Gas Behavior: MSubbu discussed thermodynamic principles, focusing on the properties of gases and phase changes. He explained the behavior of isobars in the vapor region of a Mollier diagram, noting that they have a positive slope and positive curvature. MSubbu also covered the validation of thermodynamic steam table data using Maxwell relations and entropy change calculations. He addressed the conversion of PV diagrams to TS diagrams and the importance of positive slopes in constant pressure and volume processes. The class concluded with a discussion on the unique properties of water, such as its negative slope in the solid-liquid region and the phenomenon of ice floating. MSubbu encouraged students to participate in class discussions and reach out with questions.