25.10.2018Åbo Akademi Univ - Thermal and Flow Engineering - Piispankatu 8, 20500 Turku 1/72
2. Vapour-compression refrigerationprocesses
Ron ZevenhovenÅbo Akademi University
Thermal and Flow Engineering Laboratory / Värme- och strömningstekniktel. (02 215)3223 ; [email protected]
Refrigeration (Kylteknik) course # 424519.0 E v. 2018
ÅA 424519 Refrigeration / Kylteknik
25.10.2018Åbo Akademi Univ - Thermal and Flow Engineering - Piispankatu 8, 20500 Turku 2/72
2.1 The ideal vapour-compression cycle
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Reversed Carnot cycle /1
Condensation / evaporation of a fluid can be done at almost anytemperature/pressure combination, unlike freezing / melting, and involves greater heat effects (ΔHvaporisation >> ΔHmelting) for example: water
The Carnot power cycle can be executed in reverse within the saturation dome of a refrigerant fluid
Picture: ÇB98
liquid-vapoursaturation
dome
1-2 and 3-4: reversible and isothermal (~ heat)2-3 and 4-1:Isentropic (~ work)
maximum thermalefficiencyηth = 1 – QH/QL
if reversibleηth = 1-TH/TL
H
L
H
L
H
H
L
L
H
Hgen
L
L
T
T
Q
Q
T
Q
T
Q
T
QS
T
Q
:Reversible
:balanceEntropy
in T,s diagram:
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Reversed Carnot cycle /2
The (reversed) Carnot cycle is the most efficient cycle operating between two temperature levels. But:
process 2-3 involves compression of a two-phase mixture,and
process 4-1 involves expansion of ”wet” refrigerant
Picture: ÇB98
liquid-vapoursaturation
dome
1-2 and 3-4: reversible and isothermal
2-3 and 4-1:isentropic
maximum thermalefficiencyηth = 1 – QH/QL
if reversible ηth = 1-TH/TL
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Ideal vapour-compression cycle /1
Operating the Carnot cycleoutside the saturation region → no isothermalconditions, for heat absorption and rejection
Expansion step (3-4) can be simplified by using a throttling valve (or a capillary tube)
This results in a process with 3 reversible steps, and 1 irreversible step
Picture: ÇB98
QH = 2∫3 Tds
QL = 4∫1 Tds
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T,s diagram (here for H2O)
isenthalpiclines Pictures: SEHB06
LINES OF CONSTANT ENTHALPY IN THE SATURATION REGION
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Ideal vapour-compression cycle /2
Step 4-1: boiling ofrefrigerant at low p and T
Step 1-2: compressionof saturated vapour to high p and T
Step 2-3: high pressuresuperheated gas is cooled to saturatedliquid at high T, high p
Step 3-4: expansion to low p, also T down (due to someevaporation)
Note: sub-cooling a bit beyond (3) reducesthe risk of ”flashing” in the evaporator
Picture: ÇB98
For each step:(Qin - Qout) + (Win -Wout) + mrefr· (hin-hout) = 0.
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Pressure levelsA freezer at -18°C in
a room at 21°COperation pressures for
evaporator and condensor are the vapour pressures for Tcold and Thot for the refrigerantReversible if cold
reservoir Tlow = Tcold , hot reservoir Thigh = Thot
For R-134a, psat = 1.44 atm @ -18°C, 5.84 atm @ +21°C
0°F = -18°C 70°F = 21°C 250°F = 121°C
Picture: T06
R-134a
Reversible: Trefrigerant = Treservoir
Thigh = 21°C, Tlow = -18°CCOPR = 1 / (Thigh/Tlow -1) = 6.6
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Example: ideal vapour-compression cycle /1
A vapour-compression refrigerationcycle uses refrigerant R-134a at pressure levels p1 = 1.4 bar and p2 = 8 bar, respectively, with massflow ṁ = 0.05 kg/s.
Calculate: – The rate of heat removal QL and
compressor power input Win
– The rate of heat rejection QH and the COPR of the refrigerator
Answer: data for R-134a gives Tlow = -18.8°C, Thigh= 31.3°C,
for (1) h1 = hg = 236.0 kJ/kg; s1 = sg = 0.932 kJ/(kg.K); for (2) s2 = s1 gives h2 = 272.1 kJ/kg, for (3) h3 = hf = 93.42 kJ/kg, s3 = 0.346 kJ/(kg.K); for (4) h3 ≈ h4,
Source & picture: ÇB98
25.10.2018Åbo Akademi Univ - Thermal and Flow Engineering - Piispankatu 8, 20500 Turku 10/72
R134a data: saturation pressureht
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R134a data: saturation temperature
100°C
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25.10.2018Åbo Akademi Univ - Thermal and Flow Engineering - Piispankatu 8, 20500 Turku 12/72
R134a data: superheated vapourht
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1.6 MPa
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Example: ideal vapour-compression cycle /2
Answer (cont.):
QL = m· (h1-h4) = 7.13 kW
Win = m· (h2-h1) = 1.80 kW
QH = QL + Win = 8.93 kW
COPR = QL / Win = 3.96 = (h1-h4)/(h2-h1)
Source & picture: ÇB98
Comment:Replacing the throttling valve (3→4) by an isentropic turbine (3→4s) gives, with h4s = 86.92 kJ/kg a turbine power output of 0.34 kW, reducing the net power input Win to 1.46 kW.The removal of heat from the refrigerated space QL increases from 7.13 kW to m· (h1 – h4s) = 7.46 kW. COPR increases from 3.96 to 5.11, an increase of 29%.
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ÅA 424519 Refrigeration / Kylteknik
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2.2 Household refrigerators
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Household refrigerator /1
Pic
ture
& te
xt: h
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Four Main Components: Compressor, which increases the
pressure of the refrigerant vapour, pushing it through the system, and increasing the vapour's temperature above that of the surrounding kitchen.
Condenser, usually behind the refrigerator, where the refrigerant vapour condenses to a liquid.
Expansion valve, which causes a sudden drop in refrigerant pressure, causing it to boil; also called a "metering" valve, since it passes only as much liquid as can be completely vaporised in the evaporator.
evaporator, where the latent heat of refrigerant vaporisation is absorbed from the cold box.
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Household refrigerator /2
Picture: T06Picture: ÇB98
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Irreversible heat transferA freezer at -18°C in
a room at 21°CHeat transfer TO the refrigerant in evaporatorand FROM the refrigerantin condensor requires a temperature difference
ΔT, say, ΔT = 10°C →Tcold = -28°C (psat = 0.93 bar), Thot = + 31°C (psat = 7.93 bar) for the refrigerant
Picture: T06
R-134a
Irreversible, real: Trefrigerant ≠ Treservoir ; if ΔT =10°C→ Tcold = -28°C, Thot = +31°CCOPR = 1 / (Thot/Tcold -1) = 4.2
Thot
Tcold
Tcold 1°C ↑ or Thot 1°C ↓gives COP ↑ by 2-4 %
Tsurr
Thot
Tcold
Tcold space
COPR,rev
= 6.6
0°F = -18°C 70°F = 21°C 250°F = 121°C
Temperature rise (”lift”) for heat transfer (here: air cooling)
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Picture: HTW08
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2.3 Pressure - enthalpy diagrams
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Pressure, enthalpy diagramsIn a p, h diagram
1. the vapour-compressionrefrigeration cycle gives straight lines for 3 of the 4 steps, and
2. the heat transferred (QH, QL) is proportional to the length of the lines
Picture: ÇB98
case ideal the for
p @ hh and p @ hh 3f31g1
12
32
12
41
hh
hh
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QCOP
hh
hh
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in
HHP
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The correspondingCarnot cycle
isentropic
alsopossible:
sub-cooling
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p,h diagram R-134a
Picture: ÇB98
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p,h diagram R-134a
Picture:Ö96
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Picture:Ö96
p,h diagram R-717 (NH3)
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Picture:Ö96
p,h diagram R-22
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p,h diagram R-12
Picture:Ö96
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p,h diagram R-744 (CO2)
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p,h diagram R-407c ÅA VST heat pump
A zeotropic blend of difluoromethane (R-32), pentafluoroethane (R-125), and 1,1,1,2-tetrafluoroethane (R-134a)
Note slopinglines forboiling /condensation
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2.4 The real vapour-compression cycle
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Real vapour-compression cycle /1
In a real refrigeratorquite a fewirreversibilitiesreduce the efficiency:– Fluid friction
(gives heat )– Heat exhange
with the surroundings
The real process differs a bit from the ideal process: To ensure complete vaporisation, the refrigerant is slightly
overheated at the evaporator inlet (8)
A (long) line between evaporator and compressor gives fluid friction and heat exchange with surroundings (8→1)
Picture: ÇB98
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Real vapour-compression cycle /2
More differencescompared to the ideal process:
The compression is not isentropic:∆s > 0 (1→2) or∆s < 0 (1→2’)
by cooling, decreasing the
volume ! Picture: ÇB98
There will be some pressure drop between compressor and condensor, in the condensor, between condensor and throttling device (2/2’→4→5) and in the evaporator
The saturated liquid will be sub-cooled before going to the throttling device, located near the evaporator.
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Example: real vapour-compression cycle /1
A vapour-compression refrigerationcycle uses refrigerant R-134a with mass flow ṁ = 0.05 kg/s.
Vapour enters the compressor at -10°C, 1.4 bar and leaves it at 50°C, 8 bar.
The vapour enters the condenser at 7.2 bar and is cooled to 26°C.
The throttling valve reduces the pressure to 1.5 bar.
Calculate:– The heat removal QL and the
compressor power Win
– The adiabatic (isentropic) efficiencyof the compressor
– The COPR value
Picture: ÇB98
• Neglect the heat tranfer and pressure drops in connecting lines
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Example: real vapour-compression cycle /2
At p1,T1: h1 = 243.4 kJ/kg At p2,T2: h2 = 284.4 kJ/kg At p3,T3: h3 ≈ hf = 85.75 kJ/kg h4 ≈ h3
QL = ṁ· (h1-h4) = 7.88 kW Win = ṁ· (h2-h1) = 2.05 kW Adiabatic eff. of compressor
ηc = (h2s – h1)/(h2-h1)p2s = 8 bar, s2s = s1, h2s = 281.1 kJ/kggives ηc = 0.919
Finally, COPR = QL/Win = 7.88 kW / 2.05 kW = 3.84
Picture: ÇB98
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2.5 Refrigerantsfor vapour-compression refrigerators
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Refrigerants, freezing mixtures In a refrigeration process, energy is converted into
transferred heat, using a heat carrier. The heat carrier medium will take up the heat at a low
temperature (and pressure) and gives it off at highertemperature (and pressure) at another location
A refrigerant (sv: köldmedie, kylmedel) participates in the process by a phase transition and/or pressure changes. It can also be electricity !
A cooling or freezing mixture(sv: köldblandning) can carry or store heat, which can involve a phase transition, but little or no pressure changes. Coolant for an engine:
not a refrigerant..... Pic
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: http
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Refrigerants for vapour-compression (v-c) systems /1
Tcritical > Tprocess, maximum and Tmelt < Tprocess, minimum
Reasonable pressure levels psat at Tboil and Tcondens
Large Δhvaporisation/condensation (”latent heat”) per unit volume Safe handling, non-toxic, no smell Low cost Chemically stable Should not be problematic
– when contacting water, oil, air– when contacting metals, rubber or
other polymers– at high temperatures (non-flammable !)– for the environment: ozone layer depletion, the enhanced greenhouse
effect
Pic
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: ww
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25.10.2018Åbo Akademi Univ - Thermal and Flow Engineering - Piispankatu 8, 20500 Turku 36/72
Refrigerants for v-c systems /2 Most important: the temperature levels of the cold and hot
spaces with which the refrigerant exchanges heat Temperatures at the
condensor ranges from -20°C (cold winter air) to +85°C (heat pumps)
At the lowest temperature the refrigerant should have enoughpressure to allow for 1) transport to the evaporator (and compressor), 2) proper operation of the throttling device and 3) avoid air leakage into the system → in practice a bit > 1 bar
At the highest temperature the pressure should not be so high that expensive pressure vessels and tubing elements are needed → in practice below 20 bar, preferably.
Pic
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: http
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: http
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Refrigerants for v-c systems /3 R-codes Used / found in refrigeration systems (see also D03, TW00):
– CFCs (chloro fluoro carbons), HCFCs (hydro chloro fluoro carbons), HFCs (hydro fluoro carbons) mostly CFCs: R-11 in water chillers in building air conditioning, R-12 in domestic refrigerators, in automotive air conditioning, R-22 in air conditioning, in industrial refrigeration, R-134a replaces R-12, R-502 (R-115 / R-22 mix) in supermarket refrigeration
– Ammonia primarily in food refrigeration; other inorganics (R-7xx)– Hydrocarbons (C3, C2, C2
= ...) (R-6xx)– (Non-)Azeotropic mixtures R-4xx and R-5xx, respectively– Inorganics R-7yy, yy = molar mass (g/mol): NH3 R-717,
CO2 R-744 making a return; used in aircraft– Air also used in aircraft; and also: Water
Not used any longer: ethyl ether, MeCl, SO2
Halogenated hydrocarbon R-code: rightmost digit = no. of F, 10-digit = 1+no. of H, 100-digit = -1+no. of C, 1000-digit = no. of double bonds, ”a” indicates isomer unbalance, the rest is Cl, ”B” = no. of Br.
Pic
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Examples ”R-” codes for refrigerants
R-11 F=1, H+1 = 1, C-1 = 0, rest is Cl
CFCl3
R-134a: F = 4, H = 2, C = 2, a: assymmetric
C2H2F4 CF3-CFH2
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Refrigerant vapour pressure
Vapour pressures of gases and refrigerants
Picture: S90
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Some refrigerant data
* for pressure = 1 bar ** azeotrope
Gas Refrigerant T boil °C * Gas Refrigerant T boil °C *
(C2H5)2O R-610 +35 CCl3F R-11 +24
SO2 R-764 -10 CCl2F2 R-12 -30
CH3Cl R-40 -24 CHClF2 R-22 -41
CH2Cl2 R-30 +40 C2Cl3F3 R-113 +48
NH3 R-717 -34 C2Cl2F4 R-114 +4
CO2 R-744 -78 C2ClF5 R-115 -38
CH4 R-50 -162 CF3CH2F R-134a -26
C2H6 R-170 - 89 CHClF2 + C2ClF5 ** R-502 -46
i-C4H10 R-600a -12hydrocarbon
mix HC-12a -33
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Refrigerants for v-c systems /4Boiling temperatures for 1 bar and 20 bar
Ammonia: -33°C and +50°C R12: -30°C and +70°C R11: +25°C and +140°C R114: +5°C and +120°C R134a: -26°C and + 68°C
Heat of vaporisation and density at 0°C: Ammonia: 1260 kJ/kg, 3.45 kg/m3 → 4350 kJ/m3
R22: 207 kJ/kg, 21.23 kg/m3 → 4400 kJ/m3
(volumetric heat of vaporisation)
Pic
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: http
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Greenhouse gases (GHGs) Greenhouse gases (GHGs), most importantly carbon
dioxide (CO2), methane (CH4) and nitrous oxide (N2O) trap the outgoing solar radiation that is emitted by the earth’s surface, which leads to global warming
Note that water causes ⅔ of the greenhouseeffect; the changing amounts of other GHGs cause an enhanced greenhouse effect
Other GHGs and their global warming potential (GWP, CO2 = 1 by definition) – CH4 (~22), N2O (~300) – HFCs (hydro fluoro carbons) (140-11700)– PFCs (per fluoro carbons) (7400)– SF6 (23900)
Pic
ture
: http
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Source: ZK01
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ODS substances do not have a direct global warming effect but influence the formation/ destruction of tropospheric/ stratospheric ozone
Most important: CO, NOx, non-methane VOCs (volatile organic compounds)
Class I ODS (Ozone Depleting Potential, ODP 0.1….10)– Carbon tetrachloride, methyl chloroform, halons CnFxClyBrz
– CFCs are replaced by non-ODS (but GHG!) compounds: HFCs, PFCs, SF6
Class II ODS (ODP << 1) – HCFCs (hydrogenated
chloro fluoro carbons)
ODP = (definition) 1 for CFC-11 (R-11)
Ozone depleting substances (ODS)
Pic
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: http
://w
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Source: ZK01
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Refigerant use in Finland Most important: CFCs R11, R12; HFC R134a
(R-22 belongs to HCFC group) Finnish decision 1990: use of CFC forbidden except
in special cases EU legislation: production and import/expert of
CFCs forbidden as of 1995, as a well as putting CFC containing products on the market
HCFC use (mainly R-22) is phased out Alternatives should be found for HFCs also (mainly
R-134a and R- 400-types): Kigali agreement Oct. 2016 e.g. https://www.theguardian.com/environment/2016/oct/15/kigali-deal-hfcs-climate-change
CFCs, HCFCs and HFCs are hazardous wastes Special regulations as to the handling of CFC-
containing coolers, freezers, and isolation materials (R-11 in poly urethane foam !)
In the future, more use of iso-butane (R-600a), propane, propene, CO2 and ammonia
End-of-liferefrigeratorhandling at Ekokem
Pic
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Sources: Ö96, D03, SKL06/12
Refrigerant properties
LT = -25 .... -40 °C; MT = -5 .... -25 °C; HT = -5 .... +10 °C25.10.2018Åbo Akademi Univ - Thermal and Flow Engineering - Piispankatu 8, 20500 Turku 45
Table: HTW08
Refrigerant selection and COP(compared to R22; air conditioning with evaporator at T = 5°C)
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Picture: HTW08
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2.6 Special vapour-compressionrefrigeration systems
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Two cycles, a bottoming cycle and a topping cycle are connected via a heat exchanger
For the heat exchanger without heat losses or kinetic / potential energy effects, and mass streams mA, mB :
Picture: ÇB98 In industry, efficiency
may be more importantthan simplicity
Sometimes the temperature range is too wide for a singlev-c cycle→ use a cascade cycle(with several refrigerants)
)hh(m)hh(m
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One figure if the samerefrigerant used in both cycles
..
Cascade vapour-compression system
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Example: 2-stage vapour-compression system Consider the system in the Figure:
a cascade v-c refrigerator operating between 1.4 and 8 bar with R-134a as refrigerant. The heat exchangeroperates at 3.2 bar for both streams. (In practice p and T are a bit higher in the bottom cycle.) Mass stream mA = 0.05 kg/s. Calculate– mass stream mB, – the heat stream QL taken from the
refrigerated space– compressor power Win
– the COPR for the process
Picture: ÇB98
4.46kW 1.60
kW 7.13COP
kW 1.60WWW kW; 7.13Q
kg/s; 0.039
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.
2-stage v-c refrigeration with sub-cooler
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Pictures: HTW08
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2-stage compression refrigeration In a cascade
system using one refrigerant, a mixing chamber (flash chamber) can be used instead of a heat exchanger
Referred to as multistage compression refrigeration systems
Saturated vapour from the flash chamber is fed to the high pressuire compressor, saturated liquid is fed to the low pressure expansion valve
Picture: ÇB98
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Example: 2-stage compression refrigeration /1 Consider the system in the Figure:
a cascade c-v refrigeratoroperating between 1.4 and 8 bar with R-134a as refrigerant. The refrigerant leaves the condenser as saturated liquid and is throttled to a flash chamber at 3.2 bar. The vapour product is mixed with the refrigerant leaving the lowpressure condenser.
Assuming that both compressorsare isentropic and that the refrigerant leaves the evaporatoras saturated vapour: (continues)
Picture: ÇB98
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Example: 2-stage compression refrigeration /2
Calculate The mass fraction, x, (”quality”)
of the refrigerant that is evaporated when throttled to the flash chamber
The amount of heat that is removed from the refrigeratedspace and the compressor work per unit mass refrigerant flowingthrough the condenser, qL and w, and
The COPR for the system;
using the given T,s plot
Picture: ÇB98
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Example: 2-stage compression refrigeration /3 The mass fraction, x, of refrigerant
evaporated as it is throttled to the flash chamber equals x6 = (h6-hf)/ (hg-hf) =(h6-h7)/(h3-h7) = 0.205
The amount of heat removed from the refrigerated space per unit mass equals qL = QL / m = (1-x6)· (h1-h8) = 145.3 kJ/kg
Enthalpy h9 follows from h9 = x6· h3 +(1-x6)· h2 = 251.9 kJ/kg
With s9 = 0.929 kJ/(kg· K) = s4 (at 8 bar) it follows from the data tables for R-134a that h4 = 271.1 kJ/kg
Compressor work win = (1-x6)· (h2-h1)+(h4-h9) = 31.8 kJ/kg COPR = qL/win = 145.3 / 31.8 = 4.56 Picture: ÇB98
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Refrigeration at more than one temperature (as in an ordinary household refrigerator + freezer) can be accomplished with one compressor by throttling in two steps
Using one throttle valve and one cold temperature would give ice in the refrigerator section.
Multi-purpose refrigeration with a single compressor Picture: ÇB98
Trans-critical CO2 cycle
Evaporation at -10°C, ~26 bar, gas cooling at +120 40°C, at ~100 bar
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Picture: HTW08
ÅA 424519 Refrigeration / Kylteknik
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2.7 Real vapour-compression cycles and p,h diagrams
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Real v-c refrigeration process A real vapour-
compression refrigeration process in a p, h diagram:– 1s = throttle valve in– 2s = throttle valve out– 2i = evaporator in– 2u = evaporator out– 2k = compressor in– 1k = compressor out– 1i = condenser in– 1u = condenser out
Picture: Ö96
Includes pressure drop over connection lines 2u-2k and 1k-1i; heat exchange with surroundings and in the compressor
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A commercial v-c refrigerator
Using a water-cooled condensor and a heat exchanger Temperature, pressure and heat of vaporisation can be optimised
Picture: D03
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Heat exchange between evaporator outlet and condensor outlet can improve the COPR value.
Superheating by increased compressor pressure gives no improved efficiency but only results in larger condensor equipment
Subcooling also ensures 100% liquid to the throttling valve and gives either more heat extracted from the refrigerated space, or a smaller required refrigerant mass flow
Less attractive if the suction line to the compressor is long, especially when using ammonia as refrigerant
Picture: D03
Vapour-compression refrigerationprocess with superheat / subcooling
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Two-stage compression refrigeration
Especially suitable for wide temperature ranges while still using onerefrigerant at acceptable vapour pressures (a one-stage +10°C/-30°C unit can reach -65°C with two stages or -100°C with three)
With minimum and maximum pressures p1 and p2 it can be shown that the optimum intermediate pressure level pm = √(p1· p2)
Disadvantages are lower efficiency, higher power input, increasedtemperature of refrigerant vapor from first compressor
Picture: Ö96
com
pres
sor
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Cascade v-c systems /1 A two-stage
cascade uses two different refrigerants and heat exchange
Allows for a lower temperature than with a single-stage system
Typically -150°C can be reached
Compressor work decreases → COP improves
Picture: D03
Condenser B of system I is cooled by evaporator C of system 2
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Cascade v-c systems /2Cascade systems are commonly used for CO2 →→or natural gas →liquefaction
Pictures: D03
Picture: ÇB98
Linde-Hampsonsystem
Intercooledcompression
ÅA 424519 Refrigeration / Kylteknik
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2.8 Final remarks
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Defrosting, purging air Defrosting is
necessary from time to time to remove ice (from air humidity)
An effective method is to use hot refrigerant gas from compressor; otherwise warm air, water or electricity can be used
Air leaking into the system lowers the efficiency (usually being immiscible with the refrigerant it acts as an insulator at heat transfer surfaces, making the condensor ”smaller”)
Manual or automatic purging methods can remove this air
Picture: D03
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”Tons of refrigeration” For refrigerators used for producing ice, one way to
express the capacity is as ”tons of refrigeration” 1 ”ton of refrigeration” = heat needed to freeze 1 short
ton (= 2000 lbm = 907kg) water at 0°C to ice at 0°C in 24 hours
1 ”ton of refrigeration” = 211 kJ/min = 200 BTU/min= 3.52 kW heat removal from the refrigerated space
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Heat exchanger irreversibilities (vS91)
A simple steady-state heat transfer process; heat is transported from medium 1 to medium 2 by conduction through a material that separates them.
Temperature T1 > T2
Thermodynamic analysis
This shows that Sgen is large for large temperaturedifferences (T1-T2) and lowtemperatures T1 and T2
Q1
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ÅA 424519 Refrigeration / Kylteknik
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2.9 Vapour-compression cycleheat pumps
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Heat pumps using v-c cycle
A heat pump vapour-compression system with reversing valve for summer / cooling (a) or winter / heating operation (b)
Pictures: KJ05
NOTE: COPHP =COPR +1
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Heat pumps in Finland(2013/2014)
Source / picture: http://www.sulpu.fi (accessed: 3.11.2014)
Total capacity(2013/2014): 600 000 HPs using4 TWh yeararound buildings
GSHP = ground-source HP
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Heat pumps in Finland(end of 2017)
Source / picture: http://www.sulpu.fi (accessed: 25.10.2018)
Heat pumps: to be continued
Total capacity (2017): ~ 850 000 HPs using~ 6 TWh yeararound buildings
pcs
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Sources #2 A11: R. C. Arora ”Refrigeration and air conditioning”, 2nd. Ed. PHI Learning
Private Limited , New Delhi (2011) CB98: Y.A. Çengel, M.A. Boles “Thermodynamics. An Engineering Approach”, McGraw-Hill (1998) D03: İ. Dinçer “Refrigeration systems and applications” Wiley (2003)
HTW08: G.F. Hundy, A.R. Trott, T.C. Welsh “Refrigeration and air conditioning 4th ed. Butterworth-Heinemann (2008)
KJ05: D. Kaminski, M. Jensen ”Introduction to Thermal and Fluids Engineering”, Wiley (2005) SEHB06: P.S. Schmidt, O. Ezekoye, J. R Howell, D. Baker “Thermodynamics: An Integrated
Learning System” (Text + Web) Wiley (2006) S90: A.L. Stolk ”Koudetechniek A1”, Delft University of Technology (1990) SKL06/12: Suomen Kylmäliikkeiden Liitto (2006, 2012) http://www.skll.fi/ T06: S.R. Turns ”Thermal – Fluid Sciences”, Cambridge Univ. Press (2006) TW00: A.R. Trott, T.C. Welsh ”Refrigeration and Air-Conditioning” 3rd Ed.
Butterworths-Heineman (2000) ZK01: R. Zevenhoven, P. Kilpinen ”Control of pollutants in flue
gases and fuel gases” Picaset (Espoo), 2001 (Chapter 9) http://users.abo.fi/rzevenho/gasbook.html Ö96: G. Öhman ”Kylteknik”, Åbo Akademi University (1996) See also: Martinez, I. ”Lectures on Thermodynamics” – lecture 18 (English or Spanish)
http://webserver.dmt.upm.es/~isidoro/bk3/index.htmlupdated and based on “Termodinámica básica y aplicada", Ed. Dossat, Madrid (1992) ISBN 84-237-0810-1
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