Chapter 8

Question 1

common device for the direct conversion of chemical (molecular) energy into electrical energy, without the intermediate generation of heat

Answer 1

Electrochemical cell, battery

Question 2

reactants are supplied continuously to the electrodes

Answer 2

fuel cell

Question 3

high temperatures are attained by conversion of the chemical energy of a fuel directly into internal energy within the work-producing device

Answer 3

internal-combustion engine

Question 4

The operation as represented is reversible, consisting of two isothermal steps connected by two adiabatic steps.

Answer 4

Carnot cycle

Question 5

In Steam powerplant, Step 1-2 is

Answer 5

isothermal vaporization taking place in a boiler at temperature TH, wherein heat is transferred to saturated-liquid water at rate QH, producing saturated vapor

Question 6

In Steam powerplant, Step 2-3 is

Answer 6

is reversible adiabatic expansion of saturated vapor in a turbine producing a two-phase mixture
of saturated liquid and vapor at TC. This isentropic expansion is represented by a vertical line

Question 7

In Steam powerplant, Step 3-4 is

Answer 7

is an isothermal partial-condensation process at lower temperature TC, wherein
heat is transferred to the surroundings at rate QC

Question 8

In Steam powerplant, Step 4-1 is

Answer 8

is an isentropic compression in a
pump. Represented by a vertical line, it takes the cycle back to its origin, producing saturated liquid water at point 1

Question 9

The power produced by the turbine W turbine is much _________ the power requirement of the pump Wpump

Answer 9

greater than

Question 10

The net power output is equal to the difference between the ______ input in the boiler and the ________ rejection in the condenser.

Answer 10

rate of heat

Question 11

efficiencies of practical
heat engines are lowered by

Answer 11

Irreversibilities

Question 12

are increased when the average temperature at which heat is absorbed in the boiler is increased and when the average temperature at which heat is rejected in the condenser is decreased

Answer 12

Efficiencies

Question 13

an alternative cycle is taken as the standard, at least for fossil-fuel-burning power plant.

Answer 13

Rankine cycle

Question 14

operate on a cycle that departs from the Rankine cycle due to
irreversibilities of the expansion and compression steps.

Answer 14

Power plants

Question 15

serves to transfer heat from a burning fuel (or from a nuclear reactor or even a solar-thermal heat source) to the cycle

Answer 15

The boiler

Question 16

transfers heat from the cycle to the
surroundings

Answer 16

the condenser

Question 17

increased when the pressure and hence the vaporization temperature in the boiler is raised

Answer 17

Thermal efficiency of a steam power cycle

Question 18

True or False: high boiler pressures and temperatures favor low efficiencies

Answer 18

False, favor high efficiencies

Question 19

in practice power plants seldom operate at pressures much above ______ or temperatures much above _______

Answer 19

10,000 kPa, 600°C

Question 20

increases as pressure and hence temperature in the condenser is reduced

Answer 20

Thermal efficiency of power plants

Question 21

must be higher than the temperature of the cooling medium, usually water, and this is controlled by local conditions of climate and geography

Answer 21

condensation temperatures

Question 22

True or false: Power plants universally operate with condenser pressures as low as practical

Answer 22

True

Question 23

In a steam power plant, the _____ is an inert medium to which heat is transferred from an external source

Answer 23

Steam

Question 24

It is therefore characterized by large heat-transfer surfaces:

Answer 24

(1) for the absorption of heat by the steam at a high temperature in the boiler, and
(2) for the rejection of heat from the steam at a relatively low temperature in the condenser.

Question 25

In an internal combustion engine, a fuel is ___________

Answer 25

burned within the engine itself

Question 26

In an internal combustion engine, the combustion products serve as ___________

Answer 26

the working medium

Question 27

________ steadily into an internal combustion engine, and combustion products flow steadily out of it

Answer 27

fuel and air

Question 28

no __________ undergoes a cyclic process, as does steam in a steam power plant.

Answer 28

working medium

Question 29

The most common internal-combustion engine, because of its use in automobiles

Answer 29

Otto Engine

Question 30

The Otto engine's cycle consists of how many strokes and starts with what stroke?

Answer 30

4 strokes, intake stroke at P=k

Question 31

During the second stroke of the an Otto engine, all valves are ______, and the fuel/air mixture is ________

Answer 31

closed, compressed

Question 32

In an otto engine, after the mixture is compressed the mixture is then ignited, by a firing of a spark plug, and combustion occurs so rapidly that the ________ remains nearly constant while the ________ rises along line segment.

Answer 32

Volume, pressure

Question 33

During the otto engine's third stroke, _______ is produced

Answer 33

Work

Question 34

The effect of increasing the compression ratio

Answer 34

to increase the efficiency of the engine, that is, to increase the work produced per unit quantity of fuel

Question 35

It consists of two adiabatic and two constant-volume steps, which comprise a heat-engine cycle for which the working fluid is air in its ideal-gas state with constant heat capacity

Answer 35

air-standard Otto cycle

Question 36

the __________ cannot be increased arbitrarily but is limited by pre-ignition of the fuel

Answer 36

compression ratio

Question 37

For sufficiently high compression ratios, the temperature rise due to ________ will ignite the fuel before the _________ stroke is complete.

Answer 37

compression

Question 38

Compression ratios in automobile engines are usually not much above _______

Answer 38

10

Question 39

The fundamental difference between the Otto cycle and the Diesel cycle is that in the Diesel cycle the_______ at the end of compression is sufficiently high that combustion is initiated _________

Answer 39

temperature, spontaneously

Question 40

higher compression ratio that carries the compression step to a higher pressure results to

Answer 40

higher temperature

Question 41

For the same compression ratio, the Otto engine has a _______ efficiency than the Diesel engine.

Answer 41

higher

Question 42

The _______ and ______ engines exemplify direct use of the energy of high-temperature, high-pressure gases acting on a piston within a cylinder; no heat transfer with an external source is required.

Answer 42

Otto, diesel

Question 43

________ are more efficient than reciprocating engines

Answer 43

turbines

Question 44

The gas turbine is driven by ________ from a combustion chamber

Answer 44

high-temperature gases

Question 45

The entering air is _________ to a pressure of several bars before combustion.

Answer 45

compressed (supercharged)

Question 46

The higher the temperature of the combustion gases entering the turbine, the ___________ of the unit

Answer 46

higher the efficiency

Question 47

The idealization of the gas-turbine engine is called the __________

Answer 47

Brayton cycle

Question 48

The entire power plant, consisting of a compression device and a combustion chamber, as well as a nozzle, is known as a ________.

Answer 48

jet engine

Question 49

Because the kinetic energy of the exhaust gases is directly available for propelling the engine and its attachments, jet engines are most commonly used to _______

Answer 49

power aircraft

Question 50

The axial-flow compressor completes the job of compression, and then fuel is injected and burned in the __________

Answer 50

combustion chamber

Question 51

Hot combustion-product gases first pass through a turbine where expansion provides just enough power to drive the _________

Answer 51

compressor

Question 52

If the compression and expansion processes are ______ and _______, the turbojet engine follows the Brayton cycle

Answer 52

adiabatic, reversible

Question 53

A rocket engine differs from a jet engine in that the _________

Answer 53

oxidizing agent is carried with the engine

Question 54

Instead of depending on the surrounding air to support combustion, the rocket is

Answer 54

self-contained

Question 55

In rockets burning liquid fuels, the oxidizing agent is pumped from tanks into the _________

Answer 55

combustion chamber

Question 56

The combustion takes place at a constant _______ and produces _________ product gases that are expanded in a nozzle

Answer 56

high pressure, high-temperature

Question 57

In rockets burning solid fuels, the _____ and ________ are contained together in a solid matrix and stored at the forward end of the combustion chamber

Answer 57

fuel, oxidizer

Question 58

Combustion and expansion are much the same as in a jet engine but a solid-fuel rocket requires no ___________, and in a liquid-fuel rocket the ________ is small because the fuel and oxidizer are pumped as liquids.

Answer 58

compression work