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Optimization of Transcritical R744
Gas Coolers with MicroGroove
Smaller Diameter Copper Tubes
Heat Transfer Technologies
Content:
• Gas cooler design considerations
• Gas cooler design examples 1-3
• Copper alloys for use in CO2 systems
• Gas cooler case study
• Applications
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
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
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
• 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
Gas Cooler design example 1
Source: LU-VE Group
Gas Cooler design example 2
Source: LU-VE Group
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
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
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
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
Gas cooler with 5 mm
MicroGroove tubes
technology (Chillventa 2018)
Gas Cooler Case study
Source: LU-VE Group
Plus Supermarket
Gorinchem, Netherlands
Case Study, ATMO Europe 2018
Livio Perrotta, LU-VE Group
Gas Cooler applications
Source: LU-VE Group
Plus Supermarket
Gorinchem, Netherlands
Gas Cooler applications
Source: LU-VE Group
Plus Supermarket
Gorinchem, Netherlands
CO2
CO2
Gas Cooler applications
Source: LU-VE Group
Small diameter copper tubes gas cooler
Conclusions
• Reduce refrigerant charge
• Reduce weight and cost
• Improve efficiency
For additional info visit www.microgroove.net
Optimisation of transcritical R744 gas coolers with Microgroove smaller diameter copper tubes

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Optimisation of transcritical R744 gas coolers with Microgroove smaller diameter copper tubes

  • 1.
  • 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