Thermodynamics Quiz - Otto and Diesel Cycles

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Questions and Answers

What is a thermodynamic system characterized by?

Being an isolated section of the universe

A collection of dynamic processes occurring simultaneously

Only containing gases or vapors

A quantity of matter enclosed by a boundary (correct)

What can the boundary of a thermodynamic system be described as?

Real or imaginary (correct)

Only rigid and fixed

Nonexistent in closed systems

Always a physical barrier

In thermodynamic contexts, which of the following is considered part of the surroundings?

Any energy flowing across the boundary (correct)

The fixed structures forming the boundary

The system itself

The matter inside the system

What type of system specifically allows energy in the form of heat or work to cross its boundaries?

Open system (D) Signup and view all the answers

Which example best represents the concept of a working fluid in a thermodynamic system?

The water circulating in a hydraulic system (C) Signup and view all the answers

What is the compression ratio of the air-standard Otto cycle mentioned?

8:1 (D) Signup and view all the answers

In an air-standard diesel cycle, what is the cut-off ratio given for the engine with a compression ratio of 20?

3 (C) Signup and view all the answers

What is the maximum temperature reached in the Otto cycle with a maximum temperature of 1560℃?

1560℃ (D) Signup and view all the answers

For the given diesel engine cycle with a heat addition of 2800 kJ/kg, what is the expected nett work output?

1485.3 kJ/kg (A) Signup and view all the answers

What is the thermal efficiency of the diesel cycle with a compression ratio of 16:1?

0.53 (B) Signup and view all the answers

In the Otto cycle described, what is the clearance volume as a percentage of the swept volume?

12% (A) Signup and view all the answers

What is the nett cycle work output for the air-standard Otto cycle with intake pressure of 1 bar?

188.97 kJ/kg (C) Signup and view all the answers

What is the heat supplied in kJ/kg for the air-standard Otto cycle described with a stroke of 10 cc?

313.26 kJ/kg (B) Signup and view all the answers

What process occurs from state 3 to state 4 in a gas power cycle?

Isentropic expansion (D) Signup and view all the answers

What is the formula for calculating the thermal efficiency of the Diesel cycle?

$\eta = 1 - \frac{Q_r}{Q_s}$ (B) Signup and view all the answers

How is the thermal efficiency affected by the cut-off ratio, $\beta$?

It decreases as $\beta$ increases. (C) Signup and view all the answers

What describes the Dual Combustion Cycle?

Heat is added in two parts, with one at constant volume. (D) Signup and view all the answers

In the equation for thermal efficiency, what does $r_v$ represent?

Compression ratio (D) Signup and view all the answers

What factor does not affect the thermal efficiency of the Diesel cycle?

Specific heat at constant volume ($C_v$) (A) Signup and view all the answers

During which process is heat rejected in the gas power cycle?

Constant volume heat rejection (B) Signup and view all the answers

Which relationship correctly represents the thermal efficiency formula involving cut-off ratio $\beta$ and specific heat ratio $\gamma$?

$\eta = 1 - \frac{\beta \gamma - 1}{\gamma(\beta - 1)r_v}$ (C) Signup and view all the answers

What is the change in entropy for a perfect gas during a reversible process?

It is equal to the heat added divided by the average temperature. (A) Signup and view all the answers

In a constant volume process, what is the relationship between heat (Q) and internal energy (U)?

Q equals the change in internal energy. (B) Signup and view all the answers

For a constant volume process with a perfect gas, which of the following factors influences the change in entropy?

Initial and final temperatures. (A) Signup and view all the answers

What happens to the change in entropy if the temperature remains constant during a process?

It becomes zero. (D) Signup and view all the answers

What does the expression $dS = \frac{Q}{T}$ represent in thermodynamics?

Change in entropy. (B) Signup and view all the answers

In a constant volume process, which variable is directly affected by the change in temperature?

Entropic change. (A) Signup and view all the answers

According to the first law of thermodynamics, which equation applies for a constant volume process?

Q = ΔU. (D) Signup and view all the answers

In the context of thermodynamics, what does the letter 'm' signify in the formula used for change of entropy?

Mass of the substance. (C) Signup and view all the answers

In the T-S diagram for a constant volume process, what does the slope represent?

Rate of entropy change. (B) Signup and view all the answers

What can be inferred about a perfect gas going through a reversible process in terms of entropy?

Entropy can only increase. (D) Signup and view all the answers

What is the process that occurs during the isentropic expansion in the turbine?

The fluid expands without heat exchange (A) Signup and view all the answers

What is the thermal efficiency formula for the Carnot cycle as derived from the temperatures?

$1 - \frac{T_2}{T_1}$ (D) Signup and view all the answers

During which process is isothermal heat rejection in the condenser performed?

Process 2 to 3 (C) Signup and view all the answers

What is one limitation of the Carnot vapour cycle in steam power plants?

A large feed pump is needed to compress wet steam (A) Signup and view all the answers

What is the role of the feed pump in the Carnot cycle?

To raise the pressure of the working fluid (C) Signup and view all the answers

Which of the following statements regarding thermal efficiency is accurate for a Carnot cycle?

Its efficiency cannot exceed that defined by temperature limits (D) Signup and view all the answers

What occurs during the isentropic compression process in the feed pump?

The fluid is compressed without heat exchange (D) Signup and view all the answers

Which process corresponds to the heat supply in the boiler during the Carnot cycle?

Process 4 to 1 (B) Signup and view all the answers

What does the work ratio in a steam power cycle represent?

The relationship between work output and work input (C) Signup and view all the answers

Which of the following equations represents the thermal efficiency of the Rankine cycle without considering feed pump work?

$\eta = \frac{(h1 - h4)}{(h1 - h2)}$ (D) Signup and view all the answers

What is approximate relationship between enthalpies in a Rankine cycle when feed pump work is neglected?

$h4 \approx h3$ (D) Signup and view all the answers

Specific steam consumption is defined as the mass of steam required to produce how much work?

1 kWh of work (A) Signup and view all the answers

Which statement correctly describes the normal assumption about the feed pump work in steam power cycles?

Feed pump work is often negligible compared to turbine work (D) Signup and view all the answers

The formula for calculating the work done in a steam cycle is based on which of the following terms?

Enthalpy changes across the turbine and pump (B) Signup and view all the answers

If the enthalpy at state 4 ($h4$) approaches the enthalpy at state 3 ($h3$), what impact does this have on thermal efficiency?

It increases thermal efficiency (C) Signup and view all the answers

In the context of power cycles, what is typically true about the enthalpies measured?

They fluctuate based on temperature and pressure variations (A) Signup and view all the answers

Which parameter is crucial for determining the specific steam consumption (S.S.C.)?

Power output in watts (C) Signup and view all the answers

What happens to the thermal efficiency if the turbine work decreases significantly?

Thermal efficiency decreases (B) Signup and view all the answers

Study Notes

Module Overview

This module, Thermofluids II (ME2401), is a second-year course continuing from Thermofluids I.
It covers thermodynamics of power cycles (gas and steam), air compressors, and fluid mechanics.
The aim is to provide students with fundamental knowledge in these areas.

The module includes various topics, with page numbers for reference.
Topics cover a review of Basic Thermodynamics, the Second Law of Thermodynamics, Gas Power Cycles, Steam Power Cycles, Air Compressors, and Fluid Mechanics.

Teaching Plan

The module's topics are broken down into weekly lecture and tutorial/laboratory sessions.
The lecture schedule includes topics like Review of Basic Thermofluids, The Second Law of Thermodynamics, Gas Power Cycles, Steam Power Cycles, Air Compressors and Fluid Mechanics.
It also includes scheduled breaks in the semester.

Assessment

The assessment comprises various components: Mid Term Test, Pre-Tutorial Assignment, Laboratory, and Semestral Exam.
Weightages for each component differ.
Specific formats for each component are indicated (e.g., term test, tutorial assignments, lab reports, semester exam).

Topic 1: Review of Basic Thermofluids

A thermodynamic system is a quantity of matter enclosed by a boundary for investigation.
Surroundings are the space outside the system boundary.
Types of systems: closed system (matter does not cross the boundary), open system (matter crosses the boundary).
Sign conventions: Heat supplied (+ve), Heat rejected (-ve), Work input (-ve), Work output (+ve)
Thermodynamic properties: pressure, volume, temperature, internal energy, enthalpy. Specific quantities are intensive properties (independent of mass) like specific volume, specific internal energy etc.
First Law of Thermodynamics: Energy is conserved; the change in a system's internal energy equals the heat added minus the work done. This principle applies to both closed (non-flow) and open (steady-flow) systems, as presented by the Non Flow Energy Equation (NFEE) and the Steady Flow Energy Equation (SFEE) respectively.
Perfect Gas Laws: The Ideal Gas Equations of State and non-flow processes, expressed in equations and using p-V diagrams. This section also includes tables of formulae for perfect and steam gases in the various states of constant pressure, constant volume, contstant temperature and adiabatic stages.
Steam Properties: Properties of water(liquid and gas or steam) explained through diagram, including saturated water, saturated steam (x=0),wet steam (0<x<1), dry saturated steam (x=1) and superheated steam. Equations for interpolation where properties are not given are detailed within the pages of this topic.

Topic 2: The Second Law of Thermodynamics

The second law deals with the direction of energy transfer.
Implications of the second law include Kelvin-Planck and Clausius statements.
Reversible and irreversible processes are defined, with a focus on criteria for reversibility.
The concept of entropy is crucial to understand; changes in entropy, both for gases in various processes (constant pressure, volume, temperature, adiabatic) and steam in similar processes are defined, demonstrated and explained.

Topic 3: Gas Power Cycles

The module discusses different gas power cycles, particularly Carnot, Otto, Diesel, and Dual Combustion cycles.
Assumptions, processes, and applications of each cycle are described and illustrated in both p-V and T-s diagrams.
Limitations of each cycle are also stated.

Topic 4: Steam Power Cycles

This topic outlines different steam power cycles (Carnot, Rankine, Rankine with superheat, Rankine with reheat).
Components, parameters, and limitations of each cycle are covered, with emphasis on calculated works and parameters in T-s diagrams
Advantages of superheat and reheat cycles are further explained.
Equations used to calculate work ratio, thermal efficiency, specific steam consumption, power developed, and turbine isentropic efficiency across different stages are detailed in each cycle

Topic 5: Air Compressors

This topic focuses on the function and operation of reciprocating piston compressors.
Types of compressors are briefly mentioned.
Theoretical cycle diagrams and calculation methods for relevant performance parameters are explained.
Important considerations for minimum work conditions are discussed, along with volumetric efficiency and indicated power calculations.

Topic 6: Fluid Mechanics

The fundamental concepts of fluid mechanics, relating to conservation of momentum, are presented.
Applications specific for enclosed and open flows across various scenarios like flat plates, curved plates, and nozzles are described using Newton's second law of motion, as well as Bernoulli's principle.
Assumptions and equations needed to determine the relevant forces are covered, and there are several examples in this topic.

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Description

Test your knowledge on thermodynamic systems, specifically focusing on the Otto and diesel cycles. This quiz covers concepts such as compression ratios, working fluids, and thermal efficiency. Perfect for students studying thermodynamics at an advanced level.