water and steam exergy exergy by heat transfer exergy in ...lab.fs.uni-lj.si/kes/erasmus/exergy...
TRANSCRIPT
Laboratorij za termoenergetiko
Energy management
Water and steam
Exergy
Exergy by heat transfer
Exergy in the case steam turbine expansion
Properties of water and steam
Energy Management 2
Properties of water and steam- density
Energy Management 3
water
Moist steam
Superheated steam
Properties of water and steam - volume
Energy Management 4
water
Moist steam
Saturated steam
Properties of water and steam - entalphy
Energy Management 5
water
Moist steam
Superheated steam
Properties of water and steam – Molliere diagram h-s
Energy Management 6
Properties of water and steam - table
Energy Management 7
tlak
specifični volumen
specifična entalpija
specifična entropijatemperatura
sprememba
agregatnega
stanja
voda
para
Properties of water and steam - table
Energy Management 8
tlak nasičenja
specifični volumen
specifična entalpija
specifična entropija
vrela voda nasičena para
v = v' + x(v" - v')
h = h' + x(h" - h')
s = s' + x(s" - s')
suhost pare:
x =mpara
mpara + mvoda
Exergy
Exergy is the convertible part of energy and can be described in several ways
it is the energy that can be completely converted into any other form of energyat given surroundings conditions
it is the largest quantity of work that can be produces in a technical devicefrom working media with given starting parameters
it is the smallest required quantity of work to raise working media fromsurroundings conditions to any other condition provided that heat is broughtinto the process only from the environment
Exergy depends on surroundings conditions which limits the 'usability' of enerycarried by working media. If working media is in balance with the surroundingsno energy can be extracted from it without using additional source of energy.
Anergy is the part of energy that cannot be converted into any other form ofenergy including exergy. Internal energy of the environment is pure anergy.
Energy Management 9
Exergy
Energy Management 10
Exergy
Energy Management 11
Specific exergy of working media
Energy Management 12
ideal(reversible)
process:
• internal energy of the working media, U1
• volume work for inserting the work media into the system, p1 V1
• internal energy of the working media, Uamb
• volume work to eject the work media from the system, pamb Vamb
• heat dissipated,Qout = Tamb(S1 - Samb)
• acquired workWt = Wt,max
U1 + p1 V1 = Uok + pamb Vamb + Qod + Wt,max
Wt,max = H1 – Hamb – Tamb(S1 – Samb)
wt,max = e = h – hamb – Tok(s – samb)
Examples of defining properties of water and steam
Using the tables of water and water vapor properties, determine the volume of 2.5 kg of water/steam that has
• a temperature of 60 ° C and a pressure of 1 bar
• temperature 150 ° C and pressure 1 bar
• temperature 150 ° C and pressure 20 bar
Determine the state of 4 kg of water/steam at 160 ° C and
• pressure 10 bar
• volume 0.8 m3
• specific enthalpy of 2780 kJ/kg
Energy Management 13
Examples of determining the properties of water and steam
Linear interpolation
Energy Management 14
pnpn
pp yy
xx
xxyy
primer parameter 1 parameter 2 iskano
1 p = 20 bar T = 180 °C v =
2 p = 5 bar T = 306 °C h =
3 p = 8 bar h = 3000 kJ/kg T =
4 T = 50 °C s = 6,75 kJ/kgK h =
5 p = 1,9 bar T = 120 °C s =
6 p = 7 bar x = 0,813 v =
7 p = 105,3 bar v = 0,02 m3/kg T =
Examples of determining the properties of water and steam
Linear interpolation
Energy Management 15
pnpn
pp yy
xx
xxyy
primer parameter 1 parameter 2 iskano
1 p = 20 bar T = 180 °C v = 0,001127 m3/kg
2 p = 5 bar T = 306 °C h = 3077 kJ/kg
3 p = 8 bar h = 3000 kJ/kg T = 273,1 °C
4 T = 50 °C s = 6,75 kJ/kgK h = 2163,15 kJ/kg
5 p = 1,9 bar T = 120 °C s = 7,1517 kJ/kgK
6 p = 7 bar x = 0,813 v = 0,2220 m3/kg
7 p = 105,3 bar v = 0,02 m3/kg T = 341,0 °C
The exergy losses in the case of heat transfer
In case of a water-water heat exchanger find the loss of exergy flow and analize dependenceof transferred exergy flow and required heat transfer area on inlet temperature of the colderwater. The warm water enters with 90 °C and exits with 60 °C while mass flow rate is17 kg/s. Mass flow rate of the cold water is 12,8 kg/s and its inlet and outlet temperaturesare 30 °C and 70 °C, respectively.
Energy Management 16
The exergy losses in the case of heat transfer
Energy Management 17
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
10 20 30 40 50
rela
tivn
a p
ovr
šin
a p
ren
osn
ika,
rela
tivn
a iz
gub
a e
kse
rgije
vstopna temperatura hladne snovi / °C
površina izguba eksergije
Exergy loss in a heat exchanger - mixer
For the case of of mixer heat exchanger shown in the figure calculate the global entropy (systemand surroundings) if ambient temperature is 20 °C. Calculate lost exergy due to mixing of bothflows?
Energy Management 18
Energy and exergy flows in the turbine
team is entering a turbine with a pressure of 110 bar and a temperature of 530 °C andexpands to a pressure of 0,06 bar. Steam flow rate is 15 kg/s. Surrounding conditions are1 bar and 25 °C. Calculate
- turbine power
- inlet and outlet exergy flows and
- energy and exergy balance
for an ideal turbine with thermal efficiency 1 as well as a real turbine where outlet steamdryness is 0,84. Verify the validity of Gouy-Stodola theorem.
Energy Management 19
Reduction cooling station
Energy Management 20
For the system shown in the figure find missing parameters as well as energy and exergyflows for two operating regimes:a) all steam from the boiler is directed throgh the turbineb) parameters of superheated steam are reduced in reducing and cooling stationConstruct a Rant chart for both regimes. Surrounding conditions are 1 bar and 20 °C.
Reduction cooling station
Energy Management 21
reducirno-hladilna postaja turbina