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Chapter 19: Problem 5

Name some irreversible processes that occur in a real engine.

Short Answer

Expert verified
Heat transfer, friction and the combustion process are some irreversible processes that occur in a real engine.

Step by step solution

01

Heat Transfer

The first irreversible process in an engine is the heat transfer that takes place, particularly the heat that is lost to the cooling system and through exhaust. Once energy is lost, it cannot be recovered back into the engine.
02

Friction

Friction inside the engine components is another irreversible process. The engine faces friction while it's running, causing wear and tear on its parts, and that also converts some of the engine's energy into heat energy which is not recoverable back into the useful work.
03

Combustion Process

The combustion process is irreversible. When fuel burns in the engine to release energy for motion, it cannot revert back to its initial state.

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Most popular questions from this chapter

A power plant extracts energy from steam at \(250^{\circ} \mathrm{C}\) and delivers 800 MW of electric power. It discharges waste heat to a river at \(30^{\circ} \mathrm{C} .\) The plant's overall efficiency is \(28 \% .\) (a) How does this efficiency compare with the maximum possible at these temperatures? (b) Find the rate of waste-heat discharge to the river. (c) How many houses, each requiring \(18 \mathrm{kW}\) of heating power, could be heated with the waste heat from this plant?

Use appropriate energy-flow diagrams to analyze the situation in Got It? \(19.2 ;\) that is, show that using a refrigerator to cool the lowtemperature reservoir can't increase the overall efficiency of a Carnot engine when the work input to the refrigerator is included.

A reversible engine contains 0.20 mol of ideal monatomic gas, initially at \(600 \mathrm{K}\) and confined to \(2.0 \mathrm{L} .\) The gas undergoes the following cycle: Isothermal expansion to \(4.0 \mathrm{L}\) \(\cdot\) Isovolumic cooling to \(300 \mathrm{K}\) Isothermal compression to \(2.0 \mathrm{L}\) \(\cdot\) Isovolumic heating to \(600 \mathrm{K}\) (a) Calculate the net heat added during the cycle and the net work done. (b) Determine the engine's efficiency, defined as the ratio of the work done to the heat absorbed during the cycle.

The temperature of \(n\) moles of ideal gas is changed from \(T_{1}\) to \(T_{2}\) at constant volume. Show that the corresponding entropy change is \(\Delta S=n C_{V} \ln \left(T_{2} / T_{1}\right)\).

Refrigerators remain among the greatest consumers of electrical energy in most homes, although mandated efficiency standards have decreased their energy consumption by some \(80 \%\) in the past four decades. In the course of a day, one kitchen refrigerator removes \(30 \mathrm{MJ}\) of energy from its contents, in the process consuming \(10 \mathrm{MJ}\) of electrical energy. The electricity comes from a \(40 \%\) efficient coal-fired power plant. The fuel energy consumed at the power plant to run this refrigerator for the day is a. \(12 \mathrm{MJ}\). b. \(25 \mathrm{MJ}\). c. \(40 \mathrm{MJ}\). d. \(75 \mathrm{MJ}\).
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