Yoram Shabtay, Microgroove International Copper Association & Heat Transfer Technologies

2. Optimization of Transcritical R744
Gas Coolers with MicroGroove
Smaller Diameter Copper Tubes
Heat Transfer Technologies

3. Content:
• Gas cooler design considerations
• Gas cooler design examples 1-3
• Copper alloys for use in CO2 systems
• Gas cooler case study
• Applications

4. Gas Cooler design considerations
Tube wall thickness and yield strength needs to
accommodate maximum operating pressures.
• 45 – 60 – 85 bar for unit coolers
• 130 bar for gas coolers.
Source: LU-VE Group

5. Standard design: 45 bar MAX
CO2 gas cooler: 120 bar MAX
• Withstands high pressure without
special copper alloy or very large
tube wall thickness.
• Low viscosity of CO2 allows for
smaller tubes with long circuits,
allowing for optimal pressure
drops.
• Smaller tubes reduce internal
volume and refrigerant charge,
allowing for compact coils.
Tube Pattern:
20 mm x 17,32 mm
Using 5 mm OD tube
Gas Cooler design considerations
Source: LU-VE Group

6. Two approaches to gas cooler design:
A. Modify pressure range of existing (HFC) condensers to
accommodate higher pressure (e.g., change tube thickness)
B. Optimize design capitalizing on the peculiar properties of CO2
• Smaller tubes (e.g., 5 mm OD)
• Compact geometry
• Spray system Adiabatic system
Gas Cooler design considerations
Source: LU-VE Group

7. • High operating pressure: 130 bar
• Low CO2 outlet temperature
• Air outlet temperature can be
increased due to the large ΔT (counter
flow). This means lower air flow,
energy consumption, noise level.
• Redesign circuits and number of
supply inlets due to the difference in
viscosity of CO2 compared to HFC
fluids.
Gas Cooler design considerations
Source: LU-VE Group

8. Gas Cooler design example 1
Source: LU-VE Group

9. Gas Cooler design example 2
Source: LU-VE Group

10. CO2 Gas Cooler Unit 5 mm tube 5/16 inch Tube
Percent
Drop
Capacity BTU/h (kilowatt) 43,000 (12.6) 43,000 (12.6)
Design Pressure PSIA (MPa) 1005 (68.4) 1005 (68.4)
Coil Size
inch x inch
(cm x cm)
18 x 37
(46 x 94)
18 x 37
(46 x 94)
Rows 4 4
Fin Density fins / inch 15 12.5
Tube Pattern
inch x inch
(mm x mm)
0.75 x 0.45
(19 x 11.4)
1.00 x 0.625
(25 x 15.9)
Tube Material copper Copper
Tube OD Inch (mm) 0.197 (5.0) 0.3125 (7.94)
Tube Wall Inch (mm) 0.040 (1.0) 0.049 (1.25)
Tube Weight Pounds (kg) 24.5 (11.1) 37.7 (17.1) 35%
Fin Material aluminum aluminum
Fin Thickness Inches (mm) 0.0039 (0.10) 0.0045 (0.114)
Fin Weight Pounds (kg) 7.5 (3.4) 9.5 (4.3) 21%
Total Internal
Volume
liter 1.2 2.2 45%
Source: Super Radiator Coils
Gas Cooler design example 3

11. Copper alloys for CO2 systems
UNS Alloy C19400
Min. 97.0% Cu; 2.1 to 2.6% Fe
• Good thermal conductivity due to high copper content
• Increased strength and temperature stability
• UTS min @ 60 ksi versus Std. Copper @ 36 ksi
• Corrosion resistance slightly improved
• Commonly used in transmission lines from cooler-to-
rack and rack-to-cooler
• Reduce tube wall thickness in gas coolers
For more Information: 2019 ATMO America
Presentation by Yoram Shabtay

12. Gas Cooler Case study
R404A CO2 CO2
Number of fans 3 3 1
Front coil area, m2 5.28 5.28 2.56
Number of rows 3 3 6
Number of inlets 66 (std) 22 21
Fan positioning induced-draft
induced-
draft
forced-
draft
Cooler outlet temperature,
at equal power (air at 25°C)
40 °C
(condensation)
25.3 °C
(ΔT = 0.3)
28.8 °C
(ΔT = 3.8)
Or: (relative) thermal rating
cooler outlet temp. = 30 °C
100
(ΔT = 3K)
158
(ΔT = 3K)
96.0
(ΔT = 3K)
R404A condenser, 170kW capacity with initial ΔT of 15 K,
Compared to CO2 gas coolers of the same power range
Source: LU-VE Group

13. Gas Cooler Case study
This achievement was made possible because of the design strategy
adopted by LU-VE, consisting of the utilization of high performance heat
transfer surfaces and of miniaturized geometries (small diameter tubes)
even for large heat exchangers.
COOP WETTINGEN - Zurig - Switzerland Gas cooler
Source: LU-VE Group

14. Gas cooler with 5 mm
MicroGroove tubes
technology (Chillventa 2018)
Gas Cooler Case study
Source: LU-VE Group

15. Plus Supermarket
Gorinchem, Netherlands
Case Study, ATMO Europe 2018
Livio Perrotta, LU-VE Group
Gas Cooler applications
Source: LU-VE Group

16. Plus Supermarket
Gorinchem, Netherlands
Gas Cooler applications
Source: LU-VE Group

17. Plus Supermarket
Gorinchem, Netherlands
CO2
CO2
Gas Cooler applications
Source: LU-VE Group

18. Small diameter copper tubes gas cooler
Conclusions
• Reduce refrigerant charge
• Reduce weight and cost
• Improve efficiency
For additional info visit www.microgroove.net