1a sessione

1. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Heat Exchanger Optimisation
using Zeotropic Refrigerant R-
455A
Claudio Zilio
Dept. Management and Engineering – University of Padova
Nacer Achaichia
Honeywell, Gaston Geenslaan,14 Heverlee B3001, Belgium
Giacomo Villi
Alfa Laval S.p.A., Via delle Albere, 5 – 36045, Vicenza

2. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Presentation outline
• R404A (R507) replacement candidate refrigerants: general
considerations
•Numerical analysis of a finned coil condenser in a drop-in
scenario with R455A
•Conclusions

3. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Replacing R404A with mixtures
R143a: GWP = 4800; A2; NBP 225.91 K
R125: GWP = 3170; A1; NBP 225.06 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))
Carbon dioxide
R404A: R125/R143a/R134a (44/52/4); GWP = 3943; A1

4. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Replacing R404A with mixtures: R455A
R404A: R125/R143a/R134a (44/52/4); GWP = 3943; A1
R455A: R744/R32/R1234yf (3/21.5/75.5); GWP = 146; A2L
17.3 bar
Tavg: 40 °C Tdew: 44.85 °C
Tbubble: 35.15 °C

5. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
-10
0
10
20
30
100(PR455A-
PR404A)/PR404A
p rl rv cpl hlv ll ml
Relevant thermodynamic and thermophysical properties at 40°C (average
saturation temperature; i.e. R404A @ 1822 kPa; R455A @ 1730 kPa)
28% larger latent heat of condensation for R455A i.e. lower refrigerant mass flow
rate under fixed heat duty hypothesis

6. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
0
1
2
3
4
5
6
0 500 1000
HTC(Wm-2K-1)
Mass flux (kg m-2 s-1)
R404A R455A
Effect of mass flux on the condensation heat transfer coefficient (HTC) at
vapour quality 0.5 and average saturation temperature 40°C.
Cavallini et al. 2009 model + Silver, Bell and Ghaly correction for R455A
Comparing R404A and R455A heat transfer coefficients
7.7 mm ID
tube

7. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Penalty factor PF for 7.7 mm ID tube, 40 °C average saturation temperature, x=0.5.
1
10
100
400 500 600 700 800
PF(K2)
Mass flux (kg m-2 s-1)
R404A R455A
Cavallini et al. Penalty factor approach

8. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Main characteristics of the finned coil
“Prevailing” counter-flow
arrangement
Refrigerant
Air
Characteristics
Longitudinal tube spacing [mm] 21.6
Transverse tube spacing [mm] 25
Tube length [mm] 1140
Inside tube diameter (fin tip) [mm] 7.7
Number of rows [-] 4
Number of tubes per row [-] 48
Number of refrigerant circuits [-] 4-48
Fin spacing [mm] 2.1
Type of fins louvered
Tube inner surface microfin

9. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Air Conditioning and
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
Refrig. HTC Cavallini et al. (2009)
Silver, Bell & Ghaly correction
Refrig. pressure drop Cavallini et al. (2000)
U-bend pressure drop Equivalent length = 30 D
Air-side HTC Proprietary data-base

10. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
R404A operating conditions (simulation input)
Condenser
Condensate / Superheating [K] 0.0
Average condensation temperature
(dew-bubble)
[°C] 40.0
Dew condensation temperature [°C] 40.2
Air inlet condenser (dry bulb) [°C] 25.0
Condenser air face velocity [m s-1] 2.0

11. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Condenser simulation results: effects of number
of circuits in parallel
R404A condenser performance (40 °C average condensation temperature, 0 K
subcooling, 0 K superheating)
0
10
20
30
40
50
0 20 40
Heatflowrate(kW)
Number of circuits in parallel
R404A avg. sat temp. 40°C

12. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Condenser simulation results: effects of number
of circuits in parallel
R455A condenser performance (0 K subcooling, 0 K superheating): changing
average saturation temperature in order to have heat duty equal to R404A
37.0
37.5
38.0
38.5
39.0
39.5
40.0
0
10
20
30
40
50
0 20 40
Avg.sat.tempR455A(°C)
Heatflowrate(kW)
Number of circuits in parallel
R404A avg. sat temp. 40°C

13. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Condenser simulation results: 16 circuits in
parallel
R404A and R455A same heat duty, 0 K subcooling and superheating
Local temperature profiles
0
10
20
30
40
50
0 50 100 150 200 250
Temperature(°C)
Node (-)
Air
R455A
R404A

14. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Condenser simulation results
As a consequence, average (dew-bubble) saturation temperature of R455A, at the
same heat duty, is lower than R404A one.
0
10
20
30
40
50
0 50 100 150 200 250
Temperature(°C)
Node (-)
Air
R455A
R404A

15. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Condenser simulation results: 16 circuits in
parallel
R404A and R455A same heat duty, 0 K subcooling and superheating
Local temperature profiles
0
10
20
30
40
50
0 50 100 150 200 250
Temperature(°C)
Node (-)
R404A
Air

16. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Condenser simulation results: 16 circuits in
parallel
R404A and R455A same heat duty, 0 K subcooling and superheating
Local temperature profiles
0
10
20
30
40
50
0 50 100 150 200 250
Temperature(°C)
Node (-)
R455A
Air

17. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Condenser simulation results: superheating effect
Condenser performance (16 circuits in
parallel)
0 K subcooling, 0 K vap. Superheating,
compression isoentropic efficiency 0.65
Average evaporation temperature
-35°C.
Fixed heat duty: 48.7 kW
R404A: 40.0 °C average
condensation temperature @ p=1822
kPa)
R455A: 36.3 °C average
condensation temperature @ p=1581
kPa)
Local temperature profiles
0
20
40
60
80
0 50 100 150 200 250
Temperature(°C) Node (-)
R404A
R455A
Air

18. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Condenser simulation results: superheating effect
Condenser performance (16 circuits in
parallel)
0 K subcooling, 0 K vap. Superheating,
compression isoentropic efficiency 0.65
Average evaporation temperature
-35°C.
Fixed heat duty: 48.7 kW
R404A: 40.0 °C average
condensation temperature @ p=1822
kPa)
R455A: 36.3 °C average
condensation temperature @ p=1581
kPa)
Local temperature profiles
0
20
40
60
80
0 50 100 150 200 250
Temperature(°C) Node (-)
R404A
Air

19. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Condenser simulation results: superheating
Local temperature profiles
0
20
40
60
80
0 50 100 150 200 250
Temperature(°C) Node (-)
Condenser performance (16 circuits in
parallel)
0 K subcooling, 0 K vap. Superheating,
compression isoentropic efficiency 0.65
Average evaporation temperature -
35°C.
Fixed heat duty: 48.7 kW
R404A: 40.0 °C average
condensation temperature @ p=1822
kPa)
R455A: 36.3 °C average
condensation temperature @ p=1581
kPa)
Air
R455A

20. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Conclusions
In this paper R455A and R404A heat transfer performance is
compared thermodynamically, by means of the Penalty Factor
approach and then with reference to a commercially available
finned coil condenser simulated by means of a detailed 3-D
simulation code.
The analysis showed that R455A can be a viable option from the
point of view of the condenser performance when considering a
drop-in scenario of R404A.
However, attention should be paid in the design of a quasi-
counterflow design of the finned coil circuits, in order to avoid
performance penalizations as a consequence of the R455A
temperature glide.

21. Latest Technology in Refrigeration and Air Conditioning - XVII European Conference Milano, 9 - 10 June 2017
Thank you!
claudio.zilio@unipd.it