thermo

Question 1

what is the rankine cycle?

Answer 1

its a reversible steam power plant cycle (no losses due to irreversibility)

Question 2

how do you work out specific volume?

Answer 2

v=1/p

Question 3

what is internal energy?

Answer 3

internal energy gives the amount of energy bound up within a substance due to its temperature and pressure

Question 4

what is enthalpy?

Answer 4

its similar to internal energy which represents energy bound up within the system due to its temperature and pressure and capacity for doing work

Question 5

adiabatic meaning?

Answer 5

there is no heat transfer

Question 6

isentropic requirements?

Answer 6

it needs the process to be adiabatic and reversible (as perefect as possible) (Δs = 0)
∆𝑠=𝑠2−𝑠1=0

Question 7

what are the propertis of extesive systems?

Answer 7

its total valuie depends upon the extent of the system (how many kilograms) i.e volume, internal energy, enthalpy and entropy

Question 8

what are the properties of intensive systems?

Answer 8

its value is independent of the extent of the system, i.e pressure and volume

Question 9

what is the first law of thermodynamics?

Answer 9

the law describes what must apply to a cyclic process = a process that returns exactly to start point. Q = ΔU + W

Question 10

displacement equations?

Answer 10

constant volume dv=0 W12 1 => pdv=-px
∫
2
constant pressure dp=0 W12 1 => pdv=-p(v2-v1)
∫
2

Question 11

what is reversibility?

Answer 11

W=∫pdV
for it to be reversible the system must be in a state of equilibrum (pressure constant throughout the system)
change of state is called (state of quasiequilibrium)
for many processes Teq < < Tprocess

Question 12

what is irreversibility?

Answer 12

most procces are not perfect and are said to be irreversible. W=∫pdV

Question 13

what is work transfer in a cyclic process?

Answer 13

check phone for answer

Question 14

steady flow energy equation?

Answer 14

h1+ (v1^2/2)+gz1+(Q/m)-(W/m) = h2+(v2^2/2)+gz2
(h=enthalpy in this case)

Question 15

turbine and compresser equation?

Answer 15

in this case heat transfer (Q)=0 and difference in potential (gz)=0 z1=z2
W/m=(h1-h2)+(v1^2-v2^2)/2

Question 16

boiler and heater equation?

Answer 16

in this case work (W)=0 and difference in potential (gz)=0
z1=z2
Q/m=(h2-h1)+(v2^2-v1^2)/2

Question 17

nozzle equation?

Answer 17

in this case work (W), heat transfer (Q) and difference in potential (gz) are normally negligible (=0)
(h1-h2)=(v1^2-v2^2)/2 (frequently v1 < < v2)
v2^2=2(h1-h2)

Question 18

1st law but open system equation?

Answer 18

h=u+pv

Question 19

pure substance properties?

Answer 19

pure substance is matter of a single chemical composition, e.g water. if the whole system contains only water then it is not important if it is in the ice, water or steam phase, its still considered pure

Question 20

what is the rankine cycle efficiency?

Answer 20

it should be <40% (if its above that its probaly wrong)
n=net work out/heat in => Wt-Wp/Qb
but Wp < < < Wt so Wt/Qb

Question 21

calculations for rankine cycle?

Answer 21

W/m is negligible, so Δh is negligible > > Hin = Hout
n=Wt/Qb=> −ΔhT/ΔhB=> h3-h4/h3-h2

Question 22

turbine (adiabatic) equations?

Answer 22

n=work out for actual turbine/work out for perfect turbine=>
ΔHactual/ΔHperfect = h1-h2/h1-h2s (see phone for diagram)

Question 23

compressors (adiabatic) equations?

Answer 23

n=work out for actual compressor/work out for perfect compressor
ΔHactual/ΔHperfect = h2-h1/hs2-h1

Question 24

ideal gas equations?

Answer 24

pv=Rt and (p1 v1)/T1 = (p2 v2)/T2

Question 25

univerval gas constant?

Answer 25

pV = mRT
(Po Vo)/To=MR=> R=8.3143 kj/kgmol.K

Question 26

definitions of specific heat?

Answer 26

@constant pressure
Cp=(dh/dT)p The relationship between enthalpy and temperature for a process occurring at constant pressure. Cp may not be constant

@constant volume
Cv=(du/dT)v The relationship between internal energy and temperature for a process occurring at constant volume, Cv may not be constant

Question 27

definitions of specific heat for a prefect gas?

Answer 27

for perfect gas vlaues Cp abd Cv are constant
h2-h1=Cp(T2-T1) u2-u1=Cv(T2-T1) 𝛾=Cp/Cv

Question 28

useful equations for Cp and Cv?

Answer 28

h = u + pv (for any pure substance)
h = u + RT (for an ideal gas)
dh = du + RdT (differentiate)

Question 29

for a semi perfect gas or perfect gas?

Answer 29

dh = CpdT and du = CvdT
CpdT = CvdT + RdT
Cp = Cv + R
R = Cp - Cv

Question 30

Constant volume process

Answer 30

using 1st law Q = Δu + W
V is constant, so dV = 0, pdV = 0, W=0
and Q = Δu = CvΔT
for process 1-2: Q = Cv(T2-T1)
since V is constant, p1/T1=p2/T2
Q=CvT1(T2-1)/T1 = CvT1 (p2-1)/p1

Question 31

constant pressure process

Answer 31

using 1st law Q = Δu + W
for a reversible process 1-2
Q = h2-h1 = Cp(T2-T1)

Question 32

constant temperature process

Answer 32

using 1st law Q = Δu + W
W = p1v1 ln(v2/v1)
since T1 = T2 = T and p2v2 + p1v1 =RT
W = p1v1 ln(v2/v1) = RT ln (v2/v1) = RT ln(p1/p2)
since ΔT = 0, Δu = 0 and 1st law gives Q=W

Question 33

What is the 2nd law of thermodynamics?

Answer 33

Delta S= 0 =>100%