(SEM III) THEORY EXAMINATION 2023-24 THERMODYNAMICS

This question paper is designed to evaluate a student’s understanding of the fundamental principles, laws, and applications of thermodynamics, which form the basis of mechanical engineering. The exam is divided into three structured sections — A, B, and C, each testing different cognitive levels such as conceptual clarity, analytical ability, application skills, and problem-solving strength. Students are required to attempt all sections, and wherever necessary, they are free to assume suitable data to complete the numerical solutions.

SECTION A — Short Conceptual Questions (14 Marks)

Section A contains seven very short but concept-heavy questions, each carrying 2 marks, and designed to test the student’s foundation in thermodynamics. These questions focus on definitions, basic laws, conceptual differences, and fundamental thermodynamic properties. Students are expected to write precise and meaningful explanations.

Topics covered in this section include:

The basic thermodynamic system elements such as system, surroundings, boundaries, and universe, which lay the groundwork for analyzing energy interactions.

The Zeroth Law of Thermodynamics, which establishes the principle of temperature measurement and forms the basis of thermometers.

Key differences between work and heat, helping students understand modes of energy transfer.

Concepts like Perpetual Motion Machine of the First Kind (PMM-I), which violates the First Law and is physically impossible.

The distinction between reversible and irreversible processes, which is essential for understanding entropy generation.

Terms such as available and unavailable energy, important for studying energy quality and thermodynamic efficiency.

The Triple Point, which uniquely defines the temperature and pressure where all three phases of a substance coexist in equilibrium.

This section ensures that students demonstrate a strong conceptual foundation before moving to advanced applications.

SECTION B — Analytical and Descriptive Questions (21 Marks)

Section B requires students to attempt any three questions, each worth 7 marks, covering deeper theoretical explanations, derivations, and numerical problem-solving. This section examines the student’s ability to:

Apply thermodynamic laws

Perform mathematical derivations

Analyze relationships between variables

Solve real-life engineering problems

The questions in this section revolve around:

Thermometric Properties and Temperature Measurement

Students may be asked to solve temperature-based problems using given thermometric relations, reinforcing their understanding of temperature scales and calibration methods.

First Law of Thermodynamics for Closed Systems

A detailed derivation of heat–work relationships in adiabatic processes strengthens the student’s ability to apply the First Law to engineering situations like compressors or expansion cylinders.

Entropy Changes in Adiabatic Processes

Learners must demonstrate how entropy behaves in reversible and irreversible adiabatic processes, showing their ability to connect thermodynamic laws with practical scenarios.

Material Properties—Expansion and Compressibility

This includes derivations for volume expansion coefficient, isothermal compressibility, and adiabatic compressibility, explaining how substances react under temperature and pressure variations.

Measurement of Dryness Fraction

Students learn practical steam quality measurement methods (such as throttling calorimeter, separating calorimeter, and combined calorimeter) and their industrial importance.

This section emphasizes clarity of thought, systematic derivations, and the ability to connect theory with numerical evaluation.

SECTION C — Long Answer / Application-Based Problems (21 Marks)

Section C requires students to attempt one question from each part, with each question carrying 7 marks. This section focuses on in-depth understanding, multi-step problem solving, and application of thermodynamic laws in real engineering systems.

Macroscopic and Microscopic Views of Thermodynamics

Students may explain how thermodynamics is studied from two perspectives — one dealing with bulk properties, and the other dealing with molecular behavior. The concept of continuum is also included to justify why engineers treat substances as continuous matter rather than discrete particles.

Nozzle Flow Calculations

Students apply the steady-flow energy equation to analyze how steam velocity changes during flow through an insulated nozzle, compute enthalpy changes, and understand energy conversion from enthalpy to kinetic energy.

Reversible Adiabatic Processes & Constant-Pressure Heating

Numerical problems test the understanding of reversible adiabatic expansion using the relation PV^γ = constant, followed by additional heating processes to determine the total work done.

Steady Flow Energy Equation (SFEE)

Learners must derive SFEE and apply it to real-life devices like throttling valves and pumps. This tests whether the student can interpret enthalpy changes, work interactions, and energy flow in engineering components.

Second Law of Thermodynamics Applications

Students may explain Kelvin–Planck and Clausius statements and show mathematically that both express the same impossibility principle — making it an important conceptual question.

Properties of Water/Steam & Rankine Cycle

This part includes topics such as dryness fraction, subcooled liquid, superheated steam, and enthalpy calculations. Students may also derive the efficiency of the Rankine cycle, which forms the basis of steam power plants.

Helmholtz & Gibbs Free Energy

Detailed explanations of these thermodynamic potentials help students understand energy available for work in different conditions and how these functions predict system behavior.

Additional Questions Added (as requested):

To enhance the paper and improve coverage, here are 2 extra questions that can be added to any section:

Additional Question 1 (Section B)

Explain the concept of thermodynamic equilibrium. Discuss the conditions required for a system to remain in thermal, mechanical, and chemical equilibrium.

Additional Question 2 (Section C)

Derive the relation between enthalpy, internal energy, pressure, and volume (h = u + pv). Explain its physical significance in flow processes.

Final Summary

This thermodynamics paper thoroughly evaluates the student’s understanding of basic concepts, laws, thermodynamic properties, energy interactions, and engineering applications. The structure ensures that students not only memorize definitions but also apply thermodynamic principles to real-world engineering systems such as nozzles, throttling devices, pumps, refrigeration units, and steam power cycles.