Thermodynamics

Question 1

what is thermodynamics

Answer 1

the study of heat, work, and temperature and their relation to energy with matter

Question 2

define heat transfer

Answer 2

how energy is transferred when there is a temperature difference

Question 3

3 types of heat transfer

Answer 3

conduction, convection, and radiation

Question 4

equation for heat transfer

Answer 4

Ein − Eout =∆𝑈=mcv∆T

Question 5

define conduction

Answer 5

transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles

Question 6

what does k represent in the equation for conductivity

Answer 6

thermal conductivity f the material, which is a measure of the ability of a material to conduct heat

Question 7

rate of heat conduction through a plane layer equation

Answer 7

Q.con = -kA (∆T/∆x)

Question 8

define convection

Answer 8

mode of energy transfer between a solid surface and the adjacent liquid of gas that is in motion, and it involves the combined effects of conduction and fluid motion

Question 9

faster the fluid motion, the ______ the convection heat transfer

Answer 9

greater

Question 10

when there is no bulk fluid in motion, heat transfer between solid surface and adjacent fluid is by pure ________

Answer 10

conduction

Question 11

what is the name for this: fluid is forced to flow over the surface by external means such as fan, pump, or the wind

Answer 11

forced convection

Question 12

what is the name for this: fluid motion is caused by buoyancy forces that are induced by density differences due to the variation of temperature in the fluid

Answer 12

natural convection

Question 13

define radiation

Answer 13

energy emitted by matter in the form of electromagnetic waves (or photons) as a result of changes in the electronic configuration of the atoms or molecules

Question 14

does radiation require the presence of an intervening medium

Answer 14

no

Question 15

heat transfer at the ______ ____ ______ and suffers no attenuation in a vacuum.

Answer 15

speed of light

Question 16

in an isolated system, can mass and/or energy cross the system boundary

Answer 16

no, the amount of matter and energy in the system is fixed

Question 17

in an closed system, can mass and/or energy cross the system boundary

Answer 17

mass cannot pass the system boundary, but the system may exchange heat, receive/exert forces. matter is fixed - control mass

Question 18

in an open system, can mass and/or energy cross the system boundary

Answer 18

mass, heat, and work can cross the system boundary. - control volume

Question 19

define state

Answer 19

the condition of the system as described by the systems thermodynamic properties

Question 20

define reference state

Answer 20

In thermodynamics, we are only
concerned with the changes of energy in the system, not
the energy values at the particular states. Therefore, we
can choose any state as the and assign zero value to the
internal energy or enthalpy of a substance at that state.

Question 21

define steady state

Answer 21

the system properties are not changing
as function of time

Question 22

define process

Answer 22

a path between two states. Adiabatic,
isothermal, isobaric process are of particular interest

Question 23

define equilibrium

Answer 23

when the system is unchanging in
terms of thermal, mechanical, phase, and chemical
characteristics

Question 24

define extensive properties

Answer 24

depends on the extent/amount of material in the system; these are properties that are additive

Question 25

define intensive properties

Answer 25

do not depend on the extent/amount of material in the system; these are properties that are not additive

Question 26

is viscosity an intensive or extensive property

Answer 26

intensive

Question 27

is enthalpy an intensive or extensive property

Answer 27

extensive

Question 28

is color an intensive or extensive property

Answer 28

intensive

Question 29

is temperature intensive or extensive property

Answer 29

intensive

Question 30

is internal energy intensive or extensive property

Answer 30

extensive

Question 31

define fuel

Answer 31

any material that can be burned to release thermal energy, most familiar fuels are composed of mainly hydrogen and carbon - hydrocarbon

Question 32

define combustion

Answer 32

a chemical reaction during which a fuel is oxidized and large quantity of energy is released

Question 33

what two things do you need to start combustion

Answer 33

1: fuel into contact with oxygen 2: above the fuels ignition temperature

Question 34

define complete combustion

Answer 34

all the carbon in the fuel burns to CO2, all the hydrogen burns to H2O etc

Question 35

basic definition of energy

Answer 35

the ability to do work

Question 36

Work is done when a ______ acts over some distance or displacement. this can also be expressed as a _______ acting over some change in volume

Answer 36

force pressure

Question 37

is work transfer a system property

Answer 37

no

Question 38

work transfer depends on the ________ _______

Answer 38

process path

Question 39

what is the first law of thermodynmics

Answer 39

conservation of energy, energy can not be destroyed or created, it can only be converted

Question 40

heat is defined as the form of energy, which can only be transferred when two systems have a _________ difference

Answer 40

temperature

Question 41

Q>0: heat transfer _____ the system

Answer 41

into

Question 42

Q<0: heat transfer _____ of the system

Answer 42

out

Question 43

W>0:

Answer 43

system is doing the work

Question 44

W<0:

Answer 44

work is done on the system

Question 45

what is the second law of thermodynamics

Answer 45

Entropy, in an isolated system, can never be reduced, it always increases, or, at best, remains unchanged

Question 46

is entropy a thermodynamic property or a state function

Answer 46

both! entropy being a thermodynamic property makes it state function

Question 47

is entropy an extensive or intensive property

Answer 47

extensive

Question 48

entropy GENERATION can be used to quantity the _____________ of a process

Answer 48

irreversibility

Question 49

No process is possible whose sole result is the transfer of _____ from a body of lower temperature to a body of higher temperature.

Answer 49

heat

Question 50

does the first law describe the balance of energy or the direction of a process

Answer 50

balance of energy

Question 51

does the second law describe the balance of energy or the direction of a process

Answer 51

direction of process

Question 52

does water have higher entropy when it exists as a liquid or vapor

Answer 52

vapor

Question 53

how to calculate the net work out of the system

Answer 53

Wnet,out = Qin - Qout (kj)

Question 54

thermal efficiency equation

Answer 54

nth = network output/ total heat input = Wnet,out/ Qin

Question 55

what is the most efficient heat engine, theoretically

Answer 55

Carnot engine

Question 56

equation for Carnot engine

Answer 56

nth = 1 - TL / TH

Question 57

what are the 4 components of a steam power plant

Answer 57

pump, boiler, turbine, condenser

Question 58

what component is considered as Qin of the steam power plant

Answer 58

the boiler

Question 59

what component is considered as Qout of the steam power plant

Answer 59

condenser

Question 60

what component is considered as Wout of the steam power plant

Answer 60

turbine

Question 61

heat engines transform a ______form of energy, into a ______ form

Answer 61

degraded noble

Question 62

what are the two noble forms of energy

Answer 62

electrical or mechanical

Question 63

why is efficiency always less than 1

Answer 63

we have to reject part of the input heat

Question 64

why is the carnot engine the most efficient heat engine

Answer 64

the entropy at the output is equal to that ar the input

Question 65

what two diagrams do we use for a heat engine

Answer 65

p-v and T-s

Question 66

what do you call it when entropy is constant

Answer 66

isentropic process

Question 67

for a carnot engine, what should the temperature be in

Answer 67

kelvin

Question 68

define voltaic cells

Answer 68

devices that convert chemical energy directly into electricity

Question 69

examples of voltaic cells

Answer 69

flashlight battery, automobile battery, fuel cells

Question 70

describe how a voltaic cell works

Answer 70

provides a flow of electrons through redox reaction in an external circuit, where useful work can be done. To harness this energy, the reaction is split into two separate half reactions: the oxidation and reduction reactions, and they are put into two different containers with a wire to drive the electrons from one side to the other

Question 71

describe these two types of voltaic cells: expendable and reusable

Answer 71

expendable: not worth preserving after its first discharge reusable: can be rechargeable or refuellable

Question 72

describe rechargeable

Answer 72

activity is restored by electric charging current, such as car batteries

Question 73

describe refuellable

Answer 73

deliver a sustained output because their consumables, fuel, and oxidant are replenished - fuel cell

Question 74

consider fuel cell as a battery that has a continuous supply of _____ and _____

Answer 74

fuel and oxidant

Question 75

do fuel cells run down or need recharge

Answer 75

no, that's how they differ from batteries

Question 76

describe a fuel cell

Answer 76

require a continuous source of fuel, such as hydrogen, natural gas, propane, and biogas, and oxygen (usually from air) to sustain the chemical reaction. They continuously produce electricity and heat as long as fuel is supplied.

Question 77

describe a battery

Answer 77

the chemical energy usually comes from substances that are already present in the battery. Rechargeable batteries consist of reversible cell reactions that allow them to regain their cell potential, through the work done by passing currents of electricity.

Question 78

a negative electrode, catalyst causes the fuel to undergo oxidation reactions that generate ions and electrons

Answer 78

anode

Question 79

a positive electrode, another catalyst causes ions, electrons, and oxygen to react, forming water and possibly other products

Answer 79

cathode

Question 80

in addition t electricity, fuel cells produce ______ _______, ______, and depending on fuel source, very small amounts of _____ _____ and other emissions

Answer 80

water vapor, heat, nitrogen

Question 81

allow ions, often positively charged hydrogen ions (protons) to move between the two sides of the fuel cell

Answer 81

electrolyte

Question 82

what is the general energy efficiency of a fuel cell

Answer 82

40-60%

Question 83

how can a fuel cell efficiency reach 85%

Answer 83

if waste heat is captured in a cogeneration scheme

Question 84

Fuel cells can operate at __________ efficiencies than combustion engines

Answer 84

higher

Question 85

fuel cells can convert the __________ energy in the fuel directly to _________ energy without requiring an intermediate degradation into _____

Answer 85

chemical electrical heat

Question 86

Fuel cells have ______ or _____ emissions compared to combustion engines. Hydrogen fuel cells emit only water, addressing critical climate challenges as there are no __________ _________ emissions.

Answer 86

lower or zero carbon dioxide

Question 87

Fuel cell: There also are no air pollutants that create ______ and cause health problems at the point of operation.

Answer 87

smog

Question 88

Fuel cells are ________ during operation as they have few moving parts

Answer 88

quieter

Question 89

Fuel cells: Expansion is easy because of __________ construction

Answer 89

modular

Question 90

Fuel cells: It can use __________ heat for ambient heating, or high temperature exhaust gases for co-generation

Answer 90

rejected

Question 91

_____ ______ has fast response to __________ changes and good overload characteristics

Answer 91

fuel cell demand

Question 92

why fuel cells

Answer 92

-higher efficiencies, lower or zero emissions, no air pollutants, quieter, modular, fast response

Question 93

The _________ the temperature, the larger the _______ the cell can deliver, but tend to reduce _________ of components.

Answer 93

higher current lifetime

Question 94

Most early fuel cells used _______ electrolytes which can leak, require liquid _____ and ___________ management, and may be corrosive. Modern cells tend to use _______ electrolytes.

Answer 94

liquid level and concentration solid

Question 95

Simplest fuel is hydrogen, which is difficult to _______. Higher _________ fuel cells can use CO as fuel. Methanol is used in portable _________ equipment.

Answer 95

store temperature electronic

Question 96

Electrolytes can be _________, ______, molten carbonates, or ceramic.

Answer 96

alkaline, acid

Question 97

Electrolytes can be alkaline, acid, ______ _________, or ________.

Answer 97

molten, carbonates, ceramic

Question 98

Hydrogen fuel cells - uses hydrogen to produce ________ and _______ with only _____ and _______ as byproducts

Answer 98

electricity and water water and heat

Question 99

What does the catalysts at the anode do for a hydrogen fuel cell

Answer 99

separates hydrogen mcl into protons and electrons, which take different paths to the cathode

Question 100

what happens at the cathode of the hydrogen fuel cell

Answer 100

The protons migrate through the electrolyte to the cathode, where they unite with oxygen and the electrons to produce water and heat

Question 101

The electrons go through an ______ _______, creating a flow of electrons

Answer 101

external circuit

Question 102

what are the two applications of fuel cells

Answer 102

stationary power plants and fuel cell electric vehicles(FCEVs)

Question 103

what is the central capacity of stationary power plants. What is the dispersed capacity of stationary power plants. what is the on-site electrical generators wattage

Answer 103

central utility-operated power plants of large capacity (up to 1 GW) * dispersed utility-operated power plants (tens of MW) * on-site electrical generators (some 10–100 kW).

Question 104

What are the pros of FCEVs

Answer 104

fast refueling time in just a few minutes more efficient than combustion engines, and zero carbon emissions

Question 105

what are the cons of FCEVs

Answer 105

more expensive than battery EV, require expensive hydrogen fuel stations, fuel is expensive and may come from carbon-intensive sources, safety concerns

Question 106

what are the 5 main components of a hydrogen fuel cell system vehicle

Answer 106

hydrogen tanks, air intake, fuel cell system, battery, electric motor