Thermodynamics Important Questions for R20 JNTU Students
Introduction
Thermodynamics is the heart of mechanical engineering. It explains how energy is transformed from one form to another — the science behind engines, turbines, boilers, and refrigerators.
For B.Tech mechanical students, this subject not only appears in semester exams but also plays a big role in GATE, IES, and job interviews.
This Mechworlz guide includes unit-wise key theory questions and numerical problem areas to help you revise effectively and score high.
Unit 1: Basic Concepts & First Law of Thermodynamics
Key Theory Questions
Define system, surroundings, and boundary.
Explain open, closed, and isolated systems with examples.
What is a thermodynamic property?
Differentiate between intensive and extensive properties.
Define state, process, and cycle.
What is the difference between heat and work?
Explain the concept of energy interactions.
What is the Zeroth Law of Thermodynamics?
State and explain the First Law of Thermodynamics.
What are quasi-static and non-quasi-static processes?
Explain the concept of internal energy, enthalpy, and flow work.
Write short notes on specific heat at constant volume and pressure.
Explain the concept of steady-flow energy equation (SFEE).
What are the assumptions made in SFEE?
Derive SFEE for a nozzle and turbine.
Numerical Focus Areas
Energy balance using First Law.
Work and heat transfer for isothermal, isobaric, adiabatic, and polytropic processes.
Closed vs open systems energy conversion.
Application of SFEE to compressor, boiler, and turbine systems.
P–V diagrams and area interpretation problems.
Unit 2: Second Law of Thermodynamics & Entropy
Key Theory Questions
State the Kelvin-Planck and Clausius statements.
Define heat engine, refrigerator, and heat pump.
Explain the concept of COP and efficiency.
Derive the efficiency of a Carnot engine.
What is entropy? Give its physical meaning.
Explain reversible and irreversible processes with examples.
What is Clausius inequality?
Define available energy and unavailable energy.
What are perpetual motion machines (PMM I & II)?
State Kelvin-Planck statement limitations.
What is heat reservoir and sink?
Explain entropy generation in irreversible processes.
How does entropy help determine process direction?
Numerical Focus Areas
Carnot cycle efficiency and COP problems.
Entropy change during heating/cooling.
Work and heat transfer using T–S diagrams.
Problems on heat engines and refrigerators.
Reversible vs irreversible heat transfer examples.
Unit 3: Properties of Pure Substances & Steam Tables
Key Theory Questions
Define pure substance.
Explain phase change and p–v–T surface.
What is dryness fraction?
Explain saturated, wet, and superheated steam.
Define latent heat of vaporization.
What is critical point and triple point?
How do you use steam tables?
What is the Mollier chart (h–s chart) and its use?
What is a throttling process?
Explain Rankine cycle steam properties.
Differentiate between boiler efficiency and thermal efficiency.
Explain superheating and its effect on performance.
Numerical Focus Areas
Determine enthalpy, entropy, and dryness fraction using steam tables.
Calculate mass of steam formed during expansion.
Find internal energy of a given state.
Throttling calorimeter and separating calorimeter problems.
Change of phase calculations on p–v and T–s diagrams.
Unit 4: Thermodynamic Cycles
Key Theory Questions
Explain the Otto cycle and derive efficiency.
Explain the Diesel cycle and Dual cycle.
Compare the efficiencies of Otto, Diesel, and Dual cycles.
Explain the Rankine cycle and its components.
What is Regenerative Feed Heating?
Explain Reheat and Economizer functions.
Define mean effective pressure (MEP).
What factors affect cycle efficiency?
Explain Brayton cycle for gas turbines.
What is a Closed and Open cycle?
What is cut-off ratio and compression ratio?
Define isentropic efficiency for turbine and compressor.
Explain p–v and T–s diagrams for various cycles.
Numerical Focus Areas
Efficiency of Otto, Diesel, and Dual cycles.
Work done, MEP, and power output.
Rankine cycle performance with pump and turbine work.
Effect of reheat and regeneration on efficiency.
Compressor and turbine isentropic efficiency problems.
Unit 5: Gas Mixtures & Psychrometry
Key Theory Questions
Define Dalton’s Law of Partial Pressures.
What is a gas mixture?
Derive gas constant of a mixture.
Define specific humidity, relative humidity, and dew point.
Explain psychrometric chart and its uses.
What is adiabatic saturation?
Explain cooling and dehumidification processes.
What are sensible heating and cooling?
Explain the working of a simple air conditioning system.
What is enthalpy of moist air?
Explain wet-bulb temperature and dry-bulb temperature.
Numerical Focus Areas
Humidity ratio, dew point, and relative humidity calculations.
Use of psychrometric equations for cooling and heating.
Problems on mixing of air streams.
Air-conditioning load and heat balance numericals.
Extra Exam-Oriented Short Questions
Define the term “control volume.”
What is meant by “thermal equilibrium”?
What is the relation between Cp and Cv for ideal gases?
What is a polytropic process? Give examples.
What is the difference between reversible and irreversible heat transfer?
Define heat transfer modes (conduction, convection, radiation).
What is Joule’s experiment related to thermodynamics?
What is isentropic expansion?
What is the Clausius–Clapeyron equation used for?
Define mechanical efficiency of an engine.
Numerical and Problem-Oriented Questions
A gas expands from 1 bar to 5 bar following PV¹·² = constant. Find the work done.
Calculate the change in internal energy when 200 kJ of work is done by a gas and 50 kJ of heat is rejected.
An engine works on the Otto cycle with a compression ratio of 8. Calculate its air-standard efficiency.
Find the efficiency of a Carnot engine operating between 400 K and 300 K.
Determine the entropy change when 1 kg of steam condenses at 100°C.
Calculate the power developed by a turbine handling steam with given inlet and outlet enthalpies.
Derive expressions for work and heat transfer for an isothermal process.
A gas undergoes an adiabatic compression from 100 kPa, 0.5 m³ to 600 kPa. Find the final volume and work done.
A refrigerator works between 300 K and 250 K. Determine its COP and work required for 1000 kJ of heat removal.
For a Rankine cycle, calculate the efficiency given inlet and outlet conditions of steam.
Tips for JNTU R20 Students
Focus on conceptual clarity of the First and Second Laws.
Practice derivations and cycle diagrams regularly.
Attempt previous year university questions for better understanding.
Revise formulas daily and practice numerical problems topic-wise.
Conclusion
Thermodynamics becomes simple when you connect concepts with applications and practice numericals regularly. These unit-wise questions will help you cover both theory and problem-solving areas for university, GATE, and job interviews.
Keep learning with Mechworlz — your trusted guide to make Mechanical Engineering simple, smart, and career-ready.
