(SEM III) THEORY EXAMINATION 2021-22 THERMODYNAMICS

This is the B.Tech Semester III theory examination paper for Thermodynamics (KME301).
The exam carries 100 marks and thoroughly evaluates a student’s understanding of basic laws of thermodynamics, pure substances, gas power cycles, refrigeration cycles, psychrometry, entropy, energy equations, and real-life thermodynamic applications.

The paper is divided into three structured sections – A, B, and C, covering conceptual questions, numerical problems, derivations, and cycle analysis.

SECTION A – Short Answer Questions (20 Marks)

This section contains 10 compulsory questions of 2 marks each.
It tests fundamental thermodynamics concepts such as:

Microscopic vs macroscopic point of view

Quasi-static process

Second-law efficiency & impossibility of PMM-II

High-grade vs low-grade energy

Joule–Thomson coefficient and inversion curve

Triple point & critical point of pure substances

Refrigeration effect & improving it

Dryness fraction & ways to improve it

Improving C.O.P. of vapour compression cycle

Available vs unavailable energy

These questions check basic conceptual clarity.

SECTION B – Medium-Length Numerical & Descriptive Questions (30 Marks)

Students must attempt any three out of five questions.
Topics include:

Nozzle Flow Problem

Finding exit velocity using the steady flow energy equation and mass flow rate using inlet conditions.

Combined Heat Pump & Heat Engine System

Solving energy interaction:

Heat extracted & delivered

Heat engine driving a machine

Carnot cycle efficiency relations

First & Second T–dS equations

Derivation and relation between heat capacities CpC_pCp​ and CvC_vCv​.

Phase Change Definitions using P–V–T Diagram

Triple point, critical point, saturation state, subcooled & superheated state.

Bell-Coleman Refrigeration Cycle (Air-Cycle Refrigerator)

Given:

Compression (PV^1.4 = const)

Expansion (PV^1.2 = const)
Students must calculate:

Work done per kg of air

COP of the refrigeration plant

This section checks theory + applied numericals.

SECTION C – Long Numerical / Advanced Thermodynamics Problems (50 Marks)

There are five main questions (Q3–Q7) each with two parts, and students must attempt one from each.

Q3 – Internal Energy Equation / Psychrometry

(a) Internal energy equation u=3.56pv+84u = 3.56pv + 84u=3.56pv+84 with a polytropic process PV1.2=constPV^{1.2} = \text{const}PV1.2=const:

Students must compute:

Heat transfer QQQ

Change in internal energy ΔU\Delta UΔU

Work transfer WWW
for two different processes.

(b) Psychrometric problem (Air at 22°C DBT, 30% RH):

Calculate:

Vapour pressure

Humidity ratio

Vapour density

Enthalpy

Q4 – Rankine Cycle / Heat Capacity Relation

(a) Rankine cycle with steam expanding from 20 bar & 360°C to 0.08 bar:

Find:

Net work

Cycle efficiency

Percentage reduction when turbine/pump efficiency = 80%

(b) Prove:

Cp−Cv=−T(∂V∂T)p2(∂P∂V)TC_p - C_v = -T\left(\frac{\partial V}{\partial T}\right)_p^2 \left(\frac{\partial P}{\partial V}\right)_TCp​−Cv​=−T(∂T∂V​)p2​(∂V∂P​)T​ 

Q5 – Clapeyron Equation / Refrigeration (R-12)

(a) Clapeyron & Clausius–Clapeyron equations

Their importance during phase change.

(b) Vapour compression cycle using R-12:

Find COP (i) without subcooling (ii) with 5°C subcooling.

Q6 – Absorption System / Entropy Problems

(a) Lithium–bromide water absorption system

Diagram + working + applications.

(b) Entropy changes for heating water under:

Single-reservoir heating

Two-stage heating

Method with almost zero entropy generation

Q7 – Thermodynamic Cycles / Second Law Equivalence

(a) Thermodynamic cycle with:

Isochoric heat addition

Adiabatic expansion

Isobaric compression

Prepare energy balance sheet and net energy change.

(b) Show equivalence of Kelvin–Planck and Clausius statements of second law.