Presentazione del Prof. Claudio Zilio (Università di Padova) al XVI Convegno Europeo il 12 giugno 2015 - 1a sessione

1. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Heat transfer of low GWP
refrigerant mixtures as possible
alternatives to R404A
Claudio Zilio
Dept. Management and Engineering – University of Padova

2. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
Presentation outline
• R404A (R507) replacement candidate refrigerants: general
considerations
•Numerical analysis of a finned coil condenser and an
evaporator in a drop-in scenario
•Conclusions

3. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
Replacing R404A with mixtures
R404A: R125 / R143a / R134a (44/52/4)
R143a: GWP = 3800; A2; NBP 225.91 K
R32: GWP = 650; A2L; NBP 221.50 K
Adding other fluids to “tune” the thermodynamic property of the mixture:
HFC (R134a, R152a)
HC (butane, propane, isopentane)
HFO (R1234yf, R1234ze(E))

4. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
Replacing R404A with mixtures
R404A: R125/R143a/R134a (44/52/4); GWP = 3943; A1
R438A: R32/125 /134a /600/601a (8.5/45/44.2/1.7/0.6): GWP = 706; A1
R452A: R32/125 /1234yf (11/59/39); GWP = 2141; A1
R511A: R290/E170 (95/5); GWP = 3; A3

5. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
Main properties
Temp.
glide
Vapor
Phase
Press.
Reduc.
press.
[ - ]
Liquid
Phase
Density
Vapor
Phase
Density
Latent
Heat
Liquid Ph.
Therm.
Cond.
Liquid
Phase
Viscosity
Vol.
cooling
capacity
[K] [bar] [kg/m3
] [kg/m3
] [kJ/kg] [mW/m K] [µPa s] [kJ m-3
]
R404A 0.5 6.003 0.161 1150.0 30.5 165.8 73.1 179.4 5052
R452A 3.9 5.361 0.135 1239.8 28.1 162.9 77.6 192.3 4582
R438A 5.3 4.455 0.104 1248.1 21.9 181.2 86.0 219.4 3971
R511A 0 4.742 0.116 535.1 10.4 375.2 107.0 126.4 3889
Temp.
glide
Vapor
Phase
Pressure
Liquid
Phase
Density
Vapor
Phase
Density
Liquid Ph.
Therm.
Cond.
Liquid
Phase
Viscosity
[K] [bar] [kg/m3
] [kg/m3
] [mW/m K] [µPa s]
R404A 0.3 18.146 964.7 101.6 58.0 102.6
R452A 3.3 16.843 1050.6 94.4 61.5 111.9
R438A 4.1 14.758 1074.5 75.6 68.0 129.0
R511A 0 13.722 473.3 30.3 87.8 83.5
Relevant thermodynamic and thermophysical properties at 0°C (dew
temperature)
Relevant thermodynamic and thermophysical properties at 40°C (dew temperature)

6. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
Main characteristics of the finned coil
Characteristics Evaporator Condenser
Longitudinal tube spacing [mm] 19 19
Transverse tube spacing [mm] 25 25
Tube length [mm] 1150 800
Inside tube diameter [mm] 9.2 7.8
Number of rows [mm] 6 6
Number of tubes per row [mm] 12 16
Number of refrigerant circuits 6 3
Fin spacing [mm] 4 2.1
Fin type corrugated louver
AIR
REFRIG.
“Prevailing” counter-flow
arrangement

7. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Air Conditioning and Refrigeration
Conference
Finned coil modeling
1
2
3
4
…
N
1
1+N
1+2N
…
1+RN
…
1
2
3
4
…
N
1
1+N
1+2N
…
1+RN
…
AirAir
Number of tube
discretization elements
Number of tube
discretization elements
CO2CO2
Number of tubes
per rank
Number of tubes
per rank
Number of ranksNumber of ranks
R32
Condenser Evaporator
Refrig. HTC Casson et al. (2002)
Silver, Bell & Ghaly correction
Wojtan et al. (2005)
Thome (1989) correction
Refrig. pressure drop Cavallini et al. (2002) Friedel (1979)
Refrigerant void fraction Rouhani and Axelsson (1970) Rouhani and Axelsson (1970)
U-bend pressure drop Equivalent length = 30D Equivalent length = 30D
Air-side HTC Proprietary data-base Proprietary data-base

8. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
R404A operating conditions (simulation input)
Condensate Sub-cooling [K] 3.0
Average condensation temperature (dew-
bubble)
[°C] 40.0
Dew condensation temperature [°C] 40.2
Air inlet condenser (dry bulb) [°C] 32.0
Condenser air volumetric flow rate [m3
h-1
] 3450
Vapor Superheat [K] 3
Dew evaporation temperature (evap. outlet) [°C] -7.0
Air inlet evaporator (dry/wet bulb) [°C] 4/2.9
Evaporator air volumetric flow rate [m3
h-1
] 2720
Evaporator
Condenser

9. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
Condeser simulation results
Refrigerant
Power
[W]
Dew temp.
[°C]
R404A 8315 40.2
R452A 9196 41.7
R438A 9176 42.1
R511A 8532 40.0
Condenser performance (40 °C
average condensation temperature, 3 K
subcooling)
0
1000
2000
3000
4000
5000
6000
7000
0 50 100 150 200
Refr.HTC[Wm-2K-1]
Node [ - ]
R452A R404A
Refrigerant local heat transfer coefficient

10. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
30
35
40
45
50
0 50 100 150 200
Temperature[°C]
Node [ - ]
Refr. Temp. Air temp.
30
35
40
45
50
0 50 100 150 200
Temperature[°C]
Node [ - ]
Refr. Temp. Air temp.
Temperature profiles in the condenser
R404A R452A

11. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
Evaporator performance under fixed cooling
capacity
Refrigerant
Average
temperature*
[°C]
R404A -7.1
R452A -7.2
R438A -7.6
R511A -8.0
Reference for R404A: -7.1 °C average evaporation temperature, 3 K
superheating. Cooling capacity 7700 W
0
1000
2000
3000
4000
5000
0 50 100
Refr.HTC[Wm-2K-1]
Node [ - ]
R452A R404A R511A R438A
* Average temperature calculated
between the saturation temperature at
the evaporator inlet and outlet
Refrigerant local heat transfer coefficient

12. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
-10
-5
0
5
10
0 50 100
Temperature[°C]
Node [ - ]
Refr. Temp. Air temp.
-10
-5
0
5
10
0 50 100
Temperature[°C]
Node [ - ]
Refr. Temp. Air temp.
Temperature profiles in the evaporator
R404A R452A

13. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
Conclusions
The analysis carried out in “prevailing” counter-flow arranged
finned coil condenser and evaporator showed that:
R438A , R452A, R511A can be considered viable solutions from
the point of view of condenser performance.
R438A and R511A results seem to indicate that a re-design
(circuitry modification or overall heat transfer area increase) to
achieve the same heat transfer performance of R404A.

14. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Dept. Management and Engineering – University of Padova
Thank you!
claudio.zilio@unipd.it