Lesson 7.1: Basic Concepts (System, Properties, Processes, Cycles)

Thermodynamics is the study of energy, work, and heat transfer in systems. GATE and PSU exams often test fundamental definitions, laws, and thermodynamic cycles.

🔹 1. Introduction

• Definition: Thermodynamics studies energy transformation and its effect on matter.

• Applications: Steam turbines, internal combustion engines, refrigeration, HVAC, power plants

• Key Concepts: System, surroundings, boundary, state, property, process, cycle

🔹 2. System & Surroundings

• System: Part of the universe under study

  • Types:

    1. Open System (Control Volume): Mass and energy can cross boundary (e.g., turbine, pump)

    2. Closed System (Control Mass): Only energy can cross, mass constant (e.g., piston-cylinder)

    3. Isolated System: Neither mass nor energy crosses boundary

• Surroundings: Everything outside the system

• Boundary: Separates system from surroundings

🔹 3. Properties

• Definition: Characteristics used to describe a system

• Examples: Pressure (P), Temperature (T), Volume (V), Internal Energy (U), Enthalpy (H)

• Types:

  • Intensive: Independent of mass (P, T)

  • Extensive: Dependent on mass (V, U)

🔹 4. Processes

• Definition: Transformation of a system from one state to another

• Types of Processes:

  1. Isothermal: Temperature constant → ΔU = 0, Q = W

  2. Adiabatic: No heat transfer → Q = 0, ΔU = -W

  3. Isobaric: Pressure constant → W = PΔV

  4. Isochoric: Volume constant → W = 0

• Reversible vs Irreversible:

  • Reversible: Ideal, no entropy generation

  • Irreversible: Real processes, entropy increases

🔹 5. Thermodynamic Cycles

• Definition: A series of processes that return the system to its initial state

• Common Cycles:

  1. Carnot Cycle: Ideal, maximum efficiency

  2. Otto Cycle: Spark ignition engine

  3. Diesel Cycle: Compression ignition engine

  4. Rankine Cycle: Steam power plants

  5. Brayton Cycle: Gas turbines

• Cycle Efficiency:

η=WnetQin\eta = \frac{W_\text{net}}{Q_\text{in}}η=Qin​Wnet​​

🔹 6. Solved Examples (PYQ Style)

1. Identify system type for piston-cylinder and turbine

2. Calculate work done in isothermal expansion

3. Determine efficiency of ideal Carnot cycle

🔹 7. Practice Exercises

1. Classify systems: open, closed, isolated

2. Identify properties as intensive or extensive

3. Solve problems for work and heat in different processes

4. Analyze simple thermodynamic cycles and calculate efficiency

🔹 8. Summary

• System & Surroundings: Basis of thermodynamic study

• Properties: Intensive and extensive

• Processes: Isothermal, adiabatic, isobaric, isochoric

• Cycles: Carnot, Otto, Diesel, Rankine, Brayton

• Applications: Engines, power plants, refrigeration, HVAC