Thermodynamics Quiz: Laws and Applications

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Questions and Answers

What does the first law of thermodynamics state for a closed system?

Net work delivered equals the net heat lost to the surroundings.

Net heat gained equals the total internal energy change.

Net work done is independent of heat exchanges.

Net work delivered equals the net heat gained from the surroundings. (correct)

Which cycle is associated with steam power plants?

Rankine cycle (correct)

Brayton cycle

Otto cycle

Reversed Carnot cycle

In analyzing refrigeration cycles, what is crucial for performance calculations?

Time-energy graphs

Pressure-enthalpy charts (correct)

Velocity-pressure charts

Temperature-entropy diagrams

What is a key characteristic of irreversibilities in thermodynamic systems?

They lead to energy loss in the cycle. Signup and view all the answers

What does optimization in thermodynamic systems aim to achieve?

Balance subsystem performance for optimal total system efficiency. Signup and view all the answers

What does phase equilibrium in ideal binary mixtures describe?

The coexistence of different phases at certain conditions. Signup and view all the answers

Which of the following best describes a combined cycle gas turbine power plant?

It combines steam and gas cycles for increased efficiency. Signup and view all the answers

What role does the equilibrium constant play in analyzing chemical reactions?

It indicates whether a reaction will occur spontaneously. Signup and view all the answers

What characterizes a reversible process?

The system and surroundings remain unchanged. Signup and view all the answers

Why is it important for a reversible process to occur slowly?

To prevent unnecessary kinetic energy from being imparted to the system. Signup and view all the answers

What happens when two bodies of different temperatures are brought together?

Heat flows from hotter to cooler body, making the process irreversible. Signup and view all the answers

What condition must be met for heat transfer between two bodies to be considered reversible?

The temperature difference must be zero or infinitesimally small. Signup and view all the answers

What occurs during a reversible process in terms of energy?

Energy can be recovered completely without loss. Signup and view all the answers

Which of the following statements about heat transfer is true?

Heat flow is directed from hot to cold in irreversible processes. Signup and view all the answers

What does the Clausius inequality reveal about the work done on surroundings in a system?

It must be zero or negative. Signup and view all the answers

Which of the following best describes a process that cannot be reversed?

It involves mechanical friction that dissipates energy. Signup and view all the answers

In a situation where TA = TB, what is the state of heat flow?

Heat flow will be zero, indicating reversibility. Signup and view all the answers

For a reversible engine, what can be said about the integral of dQ/T over a complete cycle?

It equals zero. Signup and view all the answers

What happens to the Clausius inequality if a reversible cycle is reversed?

It contradicts the original inequality. Signup and view all the answers

What conclusion can be drawn from the statement that I (dQ/T)rev = 0 for a reversible cycle?

No net energy transfer occurs. Signup and view all the answers

Which of the following statements about the inequalities for reversible cycles is true?

Only one inequality holds true at a time. Signup and view all the answers

What does the equation Q − W = △U represent in a closed system?

The relationship between heat added and internal energy change Signup and view all the answers

In the context of an open system, what does the term pv represent in the steady flow energy equation?

Flow work done on the system Signup and view all the answers

What is indicated by the term ṁ in the steady flow energy equation?

Mass flow rate into the system Signup and view all the answers

How can the first law of thermodynamics be expressed for a process from state 1 to state 2?

Q − W = U2 − U1 Signup and view all the answers

What does the equation dQ − dW = dU signify in thermodynamics?

Net energy change in a system is equal to heat minus work Signup and view all the answers

In the specific form of the steady flow energy equation, what does the term 1/2c^2 represent?

Kinetic energy per unit mass Signup and view all the answers

What is the relationship between Q̇ and Ẇs in the steady flow energy equation?

Q̇ compensates for losses due to Ẇs Signup and view all the answers

What is the significance of the term g z in the steady flow energy equation?

It accounts for gravitational potential energy Signup and view all the answers

What is the fundamental statement of the second law taken in these notes?

Clausius' Statement Signup and view all the answers

According to Clausius' statement, what is required for heat to flow from a cooler body to a hotter body?

Work done on the system Signup and view all the answers

Which of the following is NOT a consequence of the second law of thermodynamics?

Entropy of the universe decreases Signup and view all the answers

What does Clausius’ statement imply about cyclic processes?

They require external work to transfer heat from cold to hot. Signup and view all the answers

What is the saturation temperature at 1 bar as given in the example?

$99.63^{ ext{o}} C$ Signup and view all the answers

What is the entropy change when transitioning from saturated liquid to saturated vapor at constant pressure or temperature called?

Entropy of vaporization Signup and view all the answers

What does Planck’s statement indicate about heat extraction from a reservoir?

It cannot occur without additional energy input. Signup and view all the answers

Which of the following best describes the relationship between heat and work according to Clausius?

Heat cannot flow without work being done. Signup and view all the answers

Given the state of the turbine, what is the initial entropy value at 500°C and 100 bar?

$6.5994 ext{ kJ kg}^{-1} ext{ K}^{-1}$ Signup and view all the answers

Why is Clausius’ statement important in thermodynamics?

It provides a framework for understanding entropy. Signup and view all the answers

What is the dryness fraction ($x_2$) of the steam when it exhausts at 20°C?

0.8 Signup and view all the answers

What does the second law of thermodynamics imply about the direction of natural processes?

They will always reach thermal equilibrium. Signup and view all the answers

Which of the following is true about the turbine's entropy change?

The overall entropy change of the universe is positive. Signup and view all the answers

What does an adiabatic steam turbine imply about heat exchange with the surroundings?

It does not exchange heat with the surroundings. Signup and view all the answers

How is the overall entropy change of the system calculated?

It is the sum of the entropy of the surroundings and system. Signup and view all the answers

Which statement about the turbine's irreversible behavior is accurate?

The turbine is irreversible because the total entropy of the universe is positive. Signup and view all the answers

Study Notes

Engineering Science - Second Year - Second Law of Thermodynamics

Course title: Engineering Science
Year: Second Year
Topic: Second Law of Thermodynamics
Term: Michaelmas 2024
Lecturer: Dr Tobias Hermann
Notes developed by: P.D. McFadden
Last edit: Dr Tobias Hermann - September 2024

Introduction

First Law already covered in previous year.
Focuses on conservation of energy in terms of heat and work.
Second Law introduces limitations of converting all heat into useful work.
Explains the concept of reversibility.
Explores the new concept of entropy.

Books

Rogers, G.F.C. and Mayhew, Y.R., Engineering Thermodynamics Work And Heat Transfer 4th edition (Longman) - Most comprehensive.

Syllabus

Thermodynamics (10 lectures)
Introduction to Second Law.
Second Law, Corollaries, Reversible Processes.
Thermodynamic Temperature Scale and Entropy.
Second Law Cycles: Steam and Gas Turbine Cycles.
Heat Exchanger Analysis, Refrigeration Systems
Thermodynamic Equilibrium.
Gibbs Energy.
Clausius-Clapeyron equation.
Equilibrium in Ideal Binary Mixtures.
Chemical Reaction Equilibrium and Equilibrium constants.

Learning Outcomes

Understanding of Second Law of Thermodynamics and its corollaries.
Understanding the Carnot Cycle and the equivalence of thermodynamic and ideal gas temperature scales.
Ability to analyse heat engines and reversed heat engines. (irreversible, reversible).
Deriving entropy and calculating entropy changes in fluids.
Familiarity with the general thermodynamic relations and their applications .
Analyzing systems with irreversibilities.
Understanding of operation of Turbo-jet engines.
Understanding the Rankine Cycle.
Appreciating the methods for enhancing steam cycle efficiency.

Acknowledgements

Notes largely compiled by the late Dr. Peter McFadden.
Credit given to other faculty members (Dr. Nick Hankins, Dr. Colin Wood, Prof. Peter Ireland, Prof. Richard Stone, and Dr. Peter Whalley) for their contributions.
Contact information for feedback provided.

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Description

Test your understanding of thermodynamics with this quiz, which covers key concepts such as the first law of thermodynamics, refrigeration cycles, and phase equilibrium. Explore the characteristics of reversible processes and the implications of heat transfer in different systems. Perfect for students studying thermal sciences or engineering!