p-h chart for r134a (si units) · p-h diagram for real vapor compression cycle effect of the gas...
TRANSCRIPT
1
Principles of Refrigeration
MAE 554Professor H. Ezzat Khalifa
Syracuse University
P-h Chart for R134a (SI Units)
2
Psychrometric Chart (ASHRAE)
Psychrometric Processes
Cool Heat
Humidify
Dehumidify
Cool & Dehumidify
Air Conditioning Systems Cool & Dehumidify Air
3
A/C System Psychrometric Processes
Room Condition Line
Coil temperature must be cooler than room dew point (DP) to dehumidify the air Coil Inlet
Room Return Air
Outdoor Air
Room DP
Coil Exit
Reversed Carnot Cycle
s
T
TC
TH
4
0.0
5.0
10.0
15.0
20.0
25.0
30.0
-40.0 -35.0 -30.0 -25.0 -20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0
Cold-Side Temperature - TC, C
CO
P c
20.030.040.050.060.070.0
Carnot Cycle Performance
Sat Cond T, °C
Reversed Carnot Vapor Compression Cycle
s
T
TC
TH
5
Reversed Rankine Vapor Compression Cycle
s
T
TC
TH
Superheat HornIncreased Work
Ideal Practical Vapor Compression Cycle
s
T
TC
TH
Superheat HornIncreased Work
Throttling Lossin Refrigeration
Throttling LossIn Work
6
1
3 2
4
Simple Vapor Compression Cycle
Single-Stage Vapor Compression Cycle
ΔhWΔhE h
P
PE
PC
ΔTSC
ΔhWo
ΔTSH
7
Ideal VCC Performance
0
2
4
6
8
10
-40.0 -30.0 -20.0 -10.0 0.0 10.0
Evap. Sat. Temp., C
CO
P C
0
5
10
15
20
25
Cap
acity
, kW 35.0 COP
50.0 COP
35.0 Q
50.0 Q
Cond. Sat. Temp., ºC
R22Ideal VCC10 CFM
Compressor
Comparison of Ideal VCC with Carnot Cycle
0.5
0.6
0.7
0.8
0.9
1.0
-40.0 -30.0 -20.0 -10.0 0.0 10.0
Evap. Sat. Temp., C
Rel
ativ
e C
OP
0.5
0.6
0.7
0.8
0.9
1.0
35.0
50.0
Cond. Sat. Temp., ºC
8
h
P
PE
PC
PS
PD
11b
1a
2d
1c
3 2
4
P-h Diagram for Real Vapor Compression Cycle
Effect of the Gas Specific Heat Ratio, γ
9
1
23
4
6
7 8
5
Two-Stage VCC with Flash Economizer
ΔhE h
P
PE
PC
ΔTSC
ΔhW1
ΔTSH
1
23
45
6
7
8
ΔhW2
PI
P-h Diagram for 2-Stage VCC with Flash Economizer
10
1
23
45
6
7 8
5
Two-Stage VCC with Subcooler Economizer
ΔhE h
P
PE
PC
ΔTSC
ΔhW1
ΔTSH
1
23
45
6
7
8
ΔhW2
PI
P-h Diagram for 2-Stage VCC with Subcooler
11
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
-40 -30 -20 -10 0 10 20 30 40 50
Intermediate Sat. Temp., C
CO
PC, C
OP C
r
COPC
COPCr
Geometric-MeanIntermediate
Optimum Intermediate Temperature for 2-Stage VCC
0
2
4
6
8
10
-40.0 -30.0 -20.0 -10.0 0.0 10.0
Evap. Sat. Temp., C
CO
PC
35/COP 1
50/COP 1
35/COP 2
50/COP 2
Cond. Sat. Temp., ºC
R22Ideal VCC
Comparison of Two-Stage and Single-Stage VCCs
12
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
1 2 3 4
Number of Stages
Rel
ativ
e C
OP
C a
nd C
apai
ty
Rel. COPRel. Capacity
R22Ideal VCC
Performance of Multi-stage VCCs
14
Cascade System
High-Temperature Refrigerant
Low-Temperature Refrigerant
13
Desirable Characteristics of Refrigerants
• Thermally stable• Safe (toxicity and flammability)• Low cost and widely available• Compatible with materials of construction• High performance
– High latent heat– Low compression superheat– Low throttling losses– High heat transfer properties
• Environmentally benign (ODP and GWP)
Refrigerant Classification
Refrigerants
MixturesPure
Zeotropes Azeotropes
R502
R507
R410A*
R404A*
R407C
Natural CFC HCFC HFC
Ammonia
Propane
R12
R114
R11
R22
R123
R134a
R32
R125
R143a
Iso-Butane
R290-R600a
*Near-Azeotropes
CO2
Used in or considered for Refrigeration
Propane/Iso-Butane
14
Mixture Phase Diagrams
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Mole Fraction, x
Sat.
Tem
pera
ture
Tsat
Liquid Mole-Fraction Vapor Mole-Fraction
P1
P2
Mixture Phase Diagrams
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Mole Fraction, x
Sat.
Tem
pera
ture
Tsat
Liquid Mole-Fraction Vapor Mole-Fraction
P1
P2
Azeotrope
15
NIST Refrigerant Properties
ASHRAE Refrigerant Safety Classification
B3R1140
A3R170, R290, R600a, R1150
High Flammability
B2NH3
A2R32, R142b, R143a, R152a
Low Flammability
B1R123, R764, R21
A1R11, R12, R22, R125, R134a, R407C,
R507, R404A, R410A, R744No Flammability
High ToxicityLow/No Toxicity
Refrigerants marked in Red are ozone depleting substances that are no longer used in new equipment.Refrigerants marked in Green are natural refrigerants that have low GWP,as well as no ODP.
16
Refrigerants: Methane Group
Refrigerants: Ethane Group
17
ODP and GWP for Various Refrigerants
Refrigerant ODP GWP Refrigerant ODP GWP
CFC-11 1.0 1.0 HFC-125 0.0 0.84 CFC-12 1.0 3.05 HFC-134 0.0 0.25 CFC-13 N/A N/A HFC-134a 0.0 0.25 HCFC-22 0.051 0.370 HFC-143a 0.0 1.2 HFC-23 0.0 N/A HFC-152a 0.0 0.029 HFC-32 0.0 0.130 R500 0.78 2.39 CFC-113 0.87 1.300 R502 0.245 5.10 CFC-114 0.74 4.150 R503 N/A N/A HCFC-123 0.016 0.019 R410A 0.0 0.49 HCFC-123a 0.016 0.019 R507 0.0 0.96 HCFC-124 0.018 0.095
ODP (Ozone Depletion Potential), and GWP (Greenhouse Warming Potential) are calculated relative to CFC R11.
Refrigerant Comparison
(1.0) means reference value
Refrigerant CO2 R12 R22 R134a R404A R410A C3H8 NH3
Natural? Yes No No No No No Yes Yes
Flammable? No No No No No No Yes Yes
Toxic? No No No No No No No Yes
Relative Cost 0.1 - (1.0) 4.0 5.0 5.0 0.3 0.2
Volum. Capacity 4.8 0.6 (1.0) 0.7 1.2 1.5 0.9 1.0
Critical Temp.(F) 88 234 205 214 163 158 206 270
P @ 70F (psia) 852 85 136 86 165 216 125 129
ODP 0 1.0 0.05 0 0 0 0 0
GWP (100yr) (1.0) 7100 1500 1300 3750 1730 3 0
18
Refrigerant Pressure-Capacity Relationship
0.0
0.2
0.4
0.6
0.8
1.0
0 100 200 300 400 500Pressure Difference @ ARI [psi]
Volu
met
ric C
apac
ity @
AR
I [To
n/cf
m]
Best FitR123R11R245faR114R600aR12R134aR290R22R407CR717R507R410A
R22
NH3
R404A/R507Propane
R407C
R410A
R134a
R22 & its near neighbors
Comparison of Simple Cycle EER
R22 R134a R290 R407C R507 R410A0.80
0.85
0.90
0.95
1.00
1.05
1.10EER Relative to R22
ARICHEER
19
Relative ARI Capacity [Same Displacement]
0.0
0.5
1.0
1.5
2.0Capacity relative to R22
Relative Compressor Displacement [Same Capacity]
0.0
0.5
1.0
1.5
2.0
2.5
3.0Displacement relative to R22
20
Low Temperature Capacity Comparison
SCT=130F; SH=20F; SC=15F; No LSHX; No Quench
0.1
1.0
-50 -40 -30 -20 -10 0 10 20 30 40 50
Saturated Evaporator Temperature [F]
Cap
acity
Rel
ativ
e to
AR
I
R22R507R134aR410A
Low Temperature EER Comparison
0.1
1.0
-50 -40 -30 -20 -10 0 10 20 30 40 50
Saturated Evaporator Temperature [F]
EER
Rel
ativ
e to
R22
@ A
RI
R22R507R134aR410A
SCT=130F; SH=20F; SC=15F; No LSHX; No Quench
21
Discharge Superheat Comparison
0
50
100
150
200
250
300
-50 -40 -30 -20 -10 0 10 20 30 40 50
Saturated Evaporator Temperature [F]
Dis
char
ge S
uoer
hear
[F]
R22R507R134aR410A
SCT=130F; SH=20F; SC=15F; No LSHX; No Quench
Total Equivalent Warming Impact (TEWI)
Medium Temperature RefrigerationFrom DoE's ORNL Report, 1997
22
Fluid Comparison - R134a vs. R744 (CO2)
Region of Operational Interest
Region of Operational Interest
R744 (CO2)R134a
R134a R744Critical Point 214 F 88 FLow Pressure 10-50 psi 110 - 500 psiHigh Pressure 100-250 psi 750-2000 psi
Other CO2 Properties:High throttling losses Solid CO2 (Dry Ice) at -80F (70 psi)Transcritical Cycle (typical)Much Higher heat transfer potential (2-3x)Temperature ‘glide’ on heat rejection HX
Refrigerant-Lubricant Viscosity
23
Vapor Compressors
Classification of Vapor Compressors
Positive Displacement Machines [PD]: • Reciprocating Piston, Rolling Piston, Scroll, Screw,
Sliding Vane …
Rotodynamic (Turbo) Machines [RD]:• Radial, Mixed-flow Centrifugal; Single and Multi-stage
24
Positive Displacement Vapor Compressors
Compressor Application Range
0.1 1.0 10.0 100.0 1000.0 10000.0
Rotary [HVAC]
Scroll [HVAC]
H Recip [HVAC]
SH Recip [HVAC]
Screw [HVAC]
Centrifugal [HVAC]
ARI Capacity, Tons
25
Positive Displacement Compressors
Piston (Reciprocating)
26
Comparison of P-V Diagrams
Pre
ssur
e
Scroll/Screw (AC & Refrig.)
Volume Displacement
Clearance Volume
Recip. AC
Recip. Refrig.
Up to 60% Up to 60% More CapacityMore Capacity
Piston Compressor Volumetric Efficiency
0.0
0.2
0.4
0.6
0.8
1.0
0 10 20 30 40 50 60
Pressure Ratio
Theo
retic
al V
olum
eter
ic E
ffici
ency
0.0000.0100.0150.0200.0300.0500.0700.100
C
n = 1.15
27
Rolling Piston (Rotary) Compressor Pump
Typical Rolling Piston Compressor
ASHRAE Handbook of Systems and Equipment, 2004
28
Hermetic Scroll Compressor
Scroll Compressor
29
Scroll Compressor Operation
Scroll Operation (DTU)
Typical Scroll Compressor Performance
ASHRAE Handbook of Systems and Equipment, 2004
30
Twin Screw (Lysholm) Compressor
Single Screw Compressor
ASHRAE Handbook of Systems and Equipment, 2004
31
Typical Screw Compressor Performance
ASHRAE Handbook of Systems and Equipment, 2004
Over/Under-compression Loss
0%
20%
40%
60%
80%
100%
0.0 1.0 2.0 3.0 4.0 5.0
Relative Discharge Pressure (Pd/Pd*)
Perc
enta
ge O
ver/
Und
er-c
ompr
essi
on L
oss
3.03.54.05.06.0
VR
Under-compression
32
Screw CompressorsEfficiency Improvement
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0 10 20 30 40 50 60 70 80 90Male Rotor Tip Speed [m/s]
Rel
ativ
e Lo
ss
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Isen
trop
ic E
ffici
ency
Leakage Losses Flow & Viscous Losses
Pump Efficiency
Close leakage gaps & reduce oil injectionClose leakage gaps & reduce oil injection
Sliding Vane Compressor
33
Centrifugal Compressors
Centrifugal Compressor
34
Typical Centrifugal Compressor Impeller
ASHRAE Handbook of Systems and Equipment, 2004
Ns-Ds Diagram for Single-Stage CompressorsFrom O. E. Balje: Turbomachines - A Guide to Design Selection and Theory, Wiley, NY, '81
35
2-Stage Centrifugal Compressor
ASHRAE Handbook of Systems and Equipment, 2004
Polytropic Efficiency
0.830
0.832
0.834
0.836
0.838
0.840
0.842
0.844
0.846
0.848
0.850
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0
Pressure Ratio
Isen
trop
ic E
ffici
ency
ηp = 0.85; γ = 1.1
36
Typical Centrifugal Compressor Performance
ASHRAE Handbook of Systems and Equipment, 2004
IGV Control – Fixed SpeedVariable-Speed Control
Centrifugal Chiller Part-Load Performance
ASHRAE Handbook of Systems and Equipment, 2004
37
Comparison of Chiller Compressors
ASHRAE Handbook of Systems and Equipment, 2004
Expansion Devices
38
Short Restrictor Expansion Device
ASHRAE Handbook of Refrigeration, 2004
Thermostatic Expansion Valve
ASHRAE Handbook of Refrigeration, 2004
39
Constant-Pressure Expansion Valve
ASHRAE Handbook of Refrigeration, 2004
Float-controlled Expansion Valve
ASHRAE Handbook of Refrigeration, 2004
40
Thermally Activated Heat Pump Concept
ASHRAE Handbook of Refrigeration, 2004
Single-Effect LiBr-H2O Absorption Cycle
1
6
4"
7
3
2
4'
5
Solution HX
Condenser
Evaporator Absorber
Generator
Pump
41
Practical Configuration of LiBr-H2O System
ASHRAE Handbook of Refrigeration, 2004
Mixture Phase Diagrams
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Mole Fraction, x
Sat.
Tem
pera
ture
Tsat
Liquid Mole-Fraction Vapor Mole-Fraction
P1
P2
42
Single-Effect LiBr-H2O Cycle Duhring Diagram
T
P
CrystallizationPE
PC
Pure H2O; x=0 x=xsx=xw
TGTC~TATE
1, 7
6 3
2 5
4', 4"
Double-Effect LiBr-H2O Absorption Cycle [1]
3'
1
9
6
10
7'
5
6
2
Condenser
Evaporator Absorber
Generator 1
Pump
7"
Solution HX
3'
8
Pump
Solution HX
Generator 2
4'
4
3
8
4"
43
Double-Effect LiBr-H2O Absorption Cycle [2]
1
10
9"
12
3
2
4'
6'
Condenser
Evaporator Absorber
Generator 1
Pump
4"
3'
54
9'
8' 8
6
Solution HX
Generator 2
Single-Effect LiBr-H2O Cycle Duhring Diagram
T
P
CrystallizationPE
PC
Pure H2O; x=0 x=xsx=xw
TGTC~TATE
1, 8
7 3
2 5
4, 6
44
Pumpless Aqua-Ammonia System
ASHRAE Handbook of Refrigeration, 2004
Bubble Pump
Simple and Regenerative Reversed Brayton Cycle
S
T
2′
3′
6, 1′5
4
3
2
1
45
Regenerative Air Cycle
ConditionedSpace
Exp. Comp.
Recuperator
Gas Cooler
Ambient air
Power
Simple Air Cycle Performance
Ta = 35 ºC; εR = 0.9; η′E = 0.88; η′C = 0.87; δP/P = 0.05; ΔTA = 10 ºC
0.0
0.1
0.2
0.3
0.4
0.5
0.6
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0
Expander Pressure Ratio
CO
P
22.0
12.0
2.0
-8.0
-18.0
-38.0
-58.0
-78.0
-98.0
-118.0
Load Temp.ºC
46
Regenerative Air Cycle Performance
0.0
0.1
0.2
0.3
0.4
0.5
0.6
1.0 2.0 3.0 4.0 5.0 6.0
Expander Pressure Ratio
CO
P
22.0
12.0
2.0
-8.0
-18.0
-38.0
-58.0
-78.0
-98.0
-118.0
Load Temp.ºC
Ta = 35 ºC; εR = 0.9; η′E = 0.88; η′C = 0.87; δP/P = 0.05; ΔTA = 10 ºC
Comparison of Air Liquefaction Cycles
0
2000
4000
6000
8000
10000
12000
Revrsible(Ideal)
Linde Linde + VC Precooler
(-45 C)
Dual-Pressure
Linde
Dual-Pressure
Linde + VCPrecooler
Claude
kJ/k
g Li
quid
Air
47
Rotary Magnetic Refrigerator