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.
