refrigeration (kylteknik) - Åbo akademiusers.abo.fi/rzevenho/ref17-oh2.pdf · Åbo akademi univ -...

13.1.2017Åbo 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. 2017

ÅA 424519 Refrigeration / Kylteknik


2.1 The ideal vapour-compression cycle


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

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T

Q

T

QS

T

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:Reversible

:balanceEntropy

in T,s diagram:


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


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


T,s diagram (here for H2O)

isenthalpiclines Pictures: SEHB06

LINES OF CONSTANT ENTHALPY IN THE SATURATION REGION


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.


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


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


R134a data: saturation pressureht

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R134a data: saturation temperature

100°C

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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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.

.

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2.2 Household refrigerators


Household refrigerator /1

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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.


Household refrigerator /2

Picture: T06Picture: ÇB98


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)

13.1.2017Åbo Akademi Univ - Thermal and Flow Engineering - Piispankatu 8, 20500 Turku 18

Picture: HTW08



2.3 Pressure - enthalpy diagrams


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

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32

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QCOP

hh

hh

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The correspondingCarnot cycle

isentropic

alsopossible:

sub-cooling


p,h diagram R-134a

Picture: ÇB98


p,h diagram R-134a

Picture:Ö96


Picture:Ö96

p,h diagram R-717 (NH3)


Picture:Ö96

p,h diagram R-22


p,h diagram R-12

Picture:Ö96


p,h diagram R-744 (CO2)


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



2.4 The real vapour-compression cycle


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


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.


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


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



2.5 Refrigerantsfor vapour-compression refrigerators


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:

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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

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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.

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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.

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Examples ”R-” codes

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



Refrigerant vapour pressure

Vapour pressures of gases and refrigerants

Picture: S90


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


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)

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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)

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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)

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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

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Refrigerant properties

LT = -25 .... -40 °C; MT = -5 .... -25 °C; HT = -5 .... +10 °C13.1.2017Åbo 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)


Picture: HTW08



2.6 Special vapour-compressionrefrigeration systems


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)

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One figure if the samerefrigerant used in both cycles

..

Cascade vapour-compression system


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

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2-stage v-c refrigeration with sub-cooler


Pictures: HTW08


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


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


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


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


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


Picture: HTW08



2.7 Real vapour-compression cycles and p,h diagrams


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


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


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


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


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


Cascade v-c systems /2Cascade systems are commonly used for CO2 →→or natural gas →liquefaction

Pictures: D03

Picture: ÇB98

Linde-Hampsonsystem

Intercooledcompression



2.8 Final remarks


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


”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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See also A11 p. 99


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

.Q2

.

T = T1 T = T2

TT

TTQ

TTQS

T

QS

T

Q

balanceEntropy

QQ

balanceEnergy

gen

gen

.



2.9 Vapour-compression cycleheat pumps


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


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


Heat pumps in Finland(2015 - 2016)

Source / picture: http://www.sulpu.fi (accessed: 13.1.2017)

Heat pumps: to be continued

Total capacity (2015): ~730 000 HPs using~ 5 TWh yeararound buildings


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) 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.html updated and based on “Termodinámica básicay aplicada", Ed. Dossat, Madrid (1992) ISBN 84-237-0810-1

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