Vapour

Question 1

Define systems and surroundings

Answer 1

• Surroundings are the whole universe
• The system is part of the universe which contains a definite quantity of matter and is confined within some closed surfaces

Question 2

Define Controll volume

Answer 2

space into which, or from which, a substance flows

Question 3

Define an intensive property

Answer 3

does not depend on mass

Question 4

Define an extensive property

Answer 4

depend on mass of system

Question 5

Define a thermodynamic property

Answer 5

• qualities that serve to describe a system.

- have a unique value when a system is in a particular state and do not depend on the previous state

Question 6

Define a thermo dynamic system

Answer 6

quaintly if mater contained within some closed surface

Question 7

Define a phase

Answer 7

quantity of matter that has the same chemical composition throughout

Question 8

Define a state

Answer 8

condition as described by giving values to its properties at particular instants

Question 9

What is a process?

Answer 9

path of successive states through which a system passes

Question 10

How do you work out the change in property?

Answer 10

integral of d phi between phi 2 and phi 1 = phi 2 - phi 1

Question 11

What is the quality of a liquid-vapour system

Answer 11

ratio of mass of saturated vapour to total mass in the system

Question 12

What is the equation for quality

Answer 12

x = mg / m

Question 13

What does first law state?

Answer 13

during any cycle that a system undergoes, the cyclic integral of the heat quals to the cyclic integral of the work

Question 14

Draw a TV graph and state its regions

Answer 14

• R4
• superheated
• quality
• compressibility

Question 15

What is the alternative form of first law?

Answer 15

Q(1-2) = E2 - E1 + W(1-2)
dE = delta Q - delta W

Question 16

What does the total heat transfer equal?

Answer 16

Q = u2- u1 +m(v2^2 - v1^2)/2 + mg (z2-z1) + w2

Question 17

What does enthalpy equal for steam?

Answer 17

h = (1-x)hf + xhg

Question 18

What does enthalpy equal for other gases?

Answer 18

h = cpT

Question 19

What does the volume of steam equal?

Answer 19

V = m (xvc + (1-x)vf)

Question 20

For constant volume and specific heat, what does the change in internal energy equal?

Answer 20

u2 - u1 = integral of Cv dt between T2 nd T 1

Question 21

For constant pressure and specific heat, what does the change in enthalpy equal?

Answer 21

h2 - h1 = integral of cp dt between T2 nd T 1

Question 22

From first law what does h1 equal?

Answer 22

H1 = H2

Question 23

What does the heat transfer out equal?

Answer 23

Q out = hin - hout

Question 24

What are the relations for a isobaric process?

Answer 24

P1 = P2 = V1/T1 = V2/T2
Q = mCv(T2 - T1)

Question 25

What are the relations for an isothermal process?

Answer 25

T1 = T2 = P1 V1 = P2 V2 Q = mCp(T2 - T1) Q - W = delta U

Question 26

What are the relations for an adiabatic process?

Answer 26

P1V1 ^ y = P2V2 ^ y change in U = (P2V2 - P1V1)/(1 - k) T2/T1 = (V1/V2)^k-1 T2/T1 = (P2/P1) ^k-1/k

Question 27

What is an adiabatic process?

Answer 27

occurs without transfer of heat or matter

Question 28

What are the relations for a poly tropic process?

Answer 28

P1V1^n = P2V2^n

Question 29

What does the mass flow rate equal?

Answer 29

row 1 A 1 V 1 = m1 = m2 for a steady state

Question 30

What are pumps?

Answer 30

- devices that transfer energy to a gas flowing through them - increase pressure

Question 31

What are compressors and blowers?

Answer 31

- transfer energy to a gas flowing through them | - increase pressure

Question 32

What are turbines?

Answer 32

- work is down by a fluid on a set of rotating blades | - pressure decreases

Question 33

What is a nozzle?

Answer 33

-increase velocity for a flowing fluid by decreasing pressure

Question 34

What is a diffuser?

Answer 34

-increase pressure by decreasing velocity

Question 35

What is the equation for net work on a compressor/turbine/pump?

Answer 35

W = m (h2 - h1)

Question 36

What is a heat exchanger?

Answer 36

devices that transfer heat from hotter body to colder body or to surroundings

Question 37

What are the features of heat exchangers?

Answer 37

- velocity doesn't change - pressure drop is small - protenial energy change is negligible - no work occurs

Question 38

What is the heat transfer equation for heat exchangers?

Answer 38

Q = m (h2 - h1)

Question 39

What does the second law state?

Answer 39

Processes proceed in certain directions

Question 40

What is a heat engine?

Answer 40

device that operates in a thermodynamic cycle and does a certain amount of net positive work through the transfer of heat from a high temperature body to a low temperature body

Question 41

What is a heat pump?

Answer 41

device that operates in a cycle that requires work and that accomplishes the transfer of heat from a low T body to a high T body

Question 42

What is the thermal efficiency of a heat engine?

Answer 42

n = W/Qh = 1 - Ql/Qh

Question 43

What is the efficiency of a heat pump?

Answer 43

B = Ql/ W = Ql/(Qh-Ql)

Question 44

What is the kelvin - plank statement?

Answer 44

It is impossible to construct a heat engine that operates in a cycle that receives a given amount of heat and does an equal amount of work

Question 45

What is clausis statement?

Answer 45

It is impossible to construct a refrigerator that operates without input of work. This implies that coefficient of performance b is less than infinity

Question 46

What is a reversible process?

Answer 46

a process that once having occurred can reverse and in doing so leave in changes in either system of surroundings

Question 47

Why is a carnot cycle the most efficient?

Answer 47

every process is reversible

Question 48

What are the four stages in a carnot cycle?

Answer 48

1) revisable isothermal expansion 2) reversible adiabatic expansion 3) reversible isothermal compression 4) reversible adiabatic compassion

Question 49

For all revisable heat engines what is Q equal to?

Answer 49

integral of delta Q/ T = 0

Question 50

For all irreversible heat engines what is Q equal to?

Answer 50

integral of delt Q/T less than 0

Question 51

What is entropy?

Answer 51

unavailability of a system's thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system.

Question 52

What is the change in entropy?

Answer 52

s2 - s1 = integral of delta Q / T

Question 53

In a saturated region, what is the entropy?

Answer 53

s = sf + xsfg

Question 54

What is the change in entropy of ideal gasses?

Answer 54

s2 - s1 = cv ln(T2/T1) + k ln(v2/v1)

Question 55

What does T ds equal?

Answer 55

T ds = dH - Vdp | = du + Pdv

Question 56

What is the efficiency of a turbine?

Answer 56

Wa/Ws

Question 57

What is the efficiency of a compressor?

Answer 57

Ws/Wa

Question 58

What are the 4 processes in a ranking cycle?

Answer 58

1-2 isentropic compression (pump) 2-3 constant pressure heat addition (boiler) 3-4 isentropic Expansion (turbine 4-1 contrant pressure heat extraction

Question 59

What is the efficiency of a rankine cycle?

Answer 59

n = Wt/Qb

Question 60

How can you improve a rankine cycle?

Answer 60

- increase output pressure P2 or boiler outlet temp T3 - increase boiler pressure while maintain T mad and min P - however this does lead to low quality of steam and the droplets cause damage to turbines

Question 61

What is the rankine reheat cycle

Answer 61

- steam passing through turbine is reheated which raises T to state 5 - steam then passes through low P section of the turbine and enters condenser at state 6 - this then reduces moisture in the turbine

Question 62

What is the coefficient of performance for the vapour refrigeration cycle

Answer 62

COP = B = Q in / W in

Question 63

Why isn't an actual vapour refrigeration cycle ideal

Answer 63

- pressure drops due to friction in pipes - heat transfer through pipes - pressure drops and heat transfer in condenser - fictional effects