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XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Davide Del Col, Marco Azzolin, Stefano Bortolin, Alberto Cavallini
University of PadovaDepartment of Industrial Engineering
MINICHANNEL DEVICES FOR LOW CHARGE
REFRIGERATING SYSTEMS
XV EUROPEAN CONFERENCE
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Outline
Environmental impact and introduction to minichannel technology
Heat transfer in minichannels
Effect of channel shape
Refrigerant properties and specific charge
Heat exchangers with minimum refrigerant charge
Conclusions
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Environmental impact
The worldwide alert about global warming has led to an increasing interest in new HVAC (heating, ventilation and
air conditioning) technologies with low environmental impact
Effects to be considered:
Indirect EffectEnergy consumption
Direct EffectLeakage of refrigerant
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Why minichannel technology ?
- The refrigerant charge minimization can be considered one of the most important targets for HVAC&R applications to cope with the new environmental challenges.
- Minichannel technology appears to be a very good opportunity to minimize the charge without energy performance loss.
- Instead, minichannel technology can help reducing greenhouse gas emissions by improving component and system energy efficiencies.
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
SQUARE
CIRCULAR
Resarch on minichannels
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Enlarged picture taken with a micro-endoscope
Square cross section minichannel
(1.18 mm side length)
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Condensation HTC: square vs. circular
G = 200 kg/(m2s)
HEAT TRANSFER COEFFICIENT [W/(m2K)]
0
1000
2000
3000
4000
5000
6000
7000
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0VAPOUR QUALITY [/]
HT
C [
W m
-2 K
-1]
0
5
10
15
20
25
30
35
40
45
50
Ts
at-
Tw
all
[K]
G200
G200
G200 t
G200 t
T SAT - T WALL [K]
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Condensation HTC: square vs. circular
0
2000
4000
6000
8000
10000
12000
14000
16000
0.0 0.2 0.4 0.6 0.8 1.0VAPOUR QUALITY [/]
HT
C [W
m-2
K-1
]
G790 SQUARE
G800 CIRCULAR
0
2000
4000
6000
8000
10000
0.0 0.2 0.4 0.6 0.8 1.0VAPOUR QUALITY [/]
HT
C [W
m-2
K-1
]
G400 SQUARE xin=0.92
G400 SQUARE xin=0.68
G400 CIRCULAR
G = 800 kg/(m2s)G = 400 kg/(m2s)
HEA
T TR
ANSF
ER C
OEF
FICI
ENT
[W/(
m2 K
)]
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Condensation: effect of channel shape
G=400 kg m-2 s-1
Modelled liquid-vapour interface in circular and square minichannel with R134a
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
G100 zero-gravity x=0.8
G100 normal gravity x=0.8
G100 zero-gravity x=0.6
G100 normal gravity x=0.6
Liquid-vapour interface during condensation
x = 0.6G = 100 kg m-2s-1
x = 0.8G = 100 kg m-2s-1
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
University of Padova
Tube sheet of minichannel HX
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Condenser internal volume
BPHE
80 plates
8.4 L
MINICHANNEL S&T
2 mm i.d. tubes
2.9 L
Volume reduction = -65%
Charge reduction = -0.8 kg
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Propane charge
Evaporator PHE PHE PHE PHE Condenser PHE MC PHE MC
IHX no no yes yes Measured charge ~3.9 kg ~ 3.1 kg ~ 5.1kg ~ 4.3 kg
Target charge ~ 3.1 kg ~ 2.3 kg ~ 3.5kg ~ 2.7 kg
Piping length not minimized (around 1 kg of R290)~0.5 kg of R290 in the liquid receiver~0.4 kg of R290 in the dehydrating filter
TARGET CHARGE: 0.5m liquid line, no receiver, with filter
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Heat exchanger data
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
ROUHANI NIÑO CISE ZIVI BAROCZY HOMOGEN. EXPERIMENTAL
R2
90
Ch
arg
e R
ed
uct
ion
[kg
]
R 290
LOCKHARTMARTINELLI
CONDENSER CHARGE REDUCTIONMINICHANNEL vs PHE
Comparison between experimental and calculated charge reduction for minichannel condenser vs. PHE
EXP
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Refrigerants properties
Fluid psat [bar] pRED [ - ] ρl [kg m-3] ρv [kg m-3] µl [µPa s] µv [µPa s] λl [W m-1 K-1] GWP
R32 24.783 0.429 893.0 73.3 94.99 13.83 0.115 550
R134a 10.166 0.250 1146.7 50.1 161.45 12.37 0.075 1430
R410A 24.256 0.495 975.33 101.71 95.861 14.882 0.081 2100
R22 15.336 0.307 1128.5 66.193 138.67 13.359 0.077 1810
R1234ze 7.666 0.211 1111.3 40.7 167.00 12.93 0.069 6
R290 13.694 0.322 467.46 30.165 82.844 8.8918 0.087 3
R717 15.554 0.137 579.44 12.034 114.04 10.325 0.443 <1
Properties at TSAT = 40°C
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
0
0,2
0,4
0,6
0,8
Char
ge [k
g]
Cise
Zivi
Baroczy
00,20,40,60,8
11,2
Char
ge [k
g]
Cise
Zivi
Baroczy
Calculated refrigerant charge in minichannels HEXs for different refrigerants (80 kW heat flux at the evaporator, 100 kW at the condenser, 5K subcooling and 5K superheating)
CONDENSERComparison of refrigerant charge
EVAPORATOR
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Specific charge for systems usingHCs and ammonia
Capacity [kW] Refrigerant Specific charge [g/kW]
Cavallini et al. (2010) 100 Propane 25-30
Fernando et al. (2004) 5 Propane 37
Hrnjak and Litch (2008) 13 Ammonia 20
Corberan (2008) 14 Propane 30-40
Park and Jung (2009) 3.8 (H)3.5 (C) R170/R290 157 (H)
142 (C)
(H): Heating(C): Cooling
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Conclusions
- The refrigerant charge reduction in refrigerating systems is a goal to reduce the refrigerants contribution to the greenhouse effect and to reduce atmospheric emissions.- Minichannels are used to reduce the refrigerant charge in the HEs without decreasing performance.- The understanding of dominant mechanisms during boiling and condensation in minichannels is the fundamental basis for the development of accurate design methods.- To evaluate the refrigerant charge in the heat exchangers void fraction correlations must be used.- Systems using minichannels heat exchangers that could work with a specific charge of 30 g/kW with propane have already been developed.
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Thank you for your attention !
davide.delcol@unipd.it
Università degli Studi di PadovaDipartimento di Ingegneria Industriale
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Specific charge: potential charge reduction
Specific charge in the condenser [g/kW]
Specific charge in the evaporator [g/kW]
Ammonia (R717) 13.4 5.38
Propane (R290) 34.4 4.24
Carbon dioxide (R744) 29.8 2.49
R32 44.9 5.34
R134a 124.2 23.16
R410A 65.6 6.51
(Padilla Fuentes Y., Hrnjak P., 2012, Charge reduction potentials of several refrigerants …, Int. Refr. Conf. at Purdue, July 16-19;Padilla Fuentes Y., Hrnjak P., 2012, Experimentally validated microchannel heat exchanger performance …, 10 th IIR G-L Conf. on Natural Refrigerants, Delft.)
XV EUROPEAN CONFERENCE – ITALY THE LATEST TECHNOLOGY IN AIR CONDITIONING AND
REFRIGERATION INDUSTRY - Politecnico di Milano
Heat exchangers data (KTH)
Propane heat pump developed at KTH of StockholmReferences: Fernando et al. (2004)
Heating capacity 4-7.23 kW
Hydraulic diameter 1.42 mm
Number of channels 6
Tube length 651 mm
Baffle plates 31
Refrigerant R290
Evaporator Condenser
Number of tube 30 36
Outer area 0.822 m2 0.985 m2
37 g/kW of R290
Fernando P., Palm B., Lundqvist P., Granryd E., 2004, Propane heat pump with low refrigerant charge: design and laboratory tests, Int. J. of Refrig., 27, 761-773
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