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Multifunctional AC-unit
Effsys project H26 Chen Yang, EGI Department, KTH Per Lundqvist, EGI Department, KTH Peter Platell, RANOTOR AB Marc Graaf, VISTEON GMBH
Background
• The number of automobiles are increasing rapidly • Internal combustion engines (ICE) waste a large part of the supplied energy • A more environmental friendly and more efficient propulsion and air conditioning system is therefore needed 2020-04-30 2
This idea:
A bottoming cycle system that utilize the waste heat from car engine coolant and exhaust gas combined with • A supercritical AC system • Carbon dioxide as a working fluid • By cooled exhaust gas recirculation (EGR) NO X emissions are suppressed 2020-04-30 3
Design Concepts
• CO 2 -AC system in summer that work in reversed mode as a transcritical power cycle in winter • CO 2 -AC system in summer and CO 2 Brayton power system all the year • CO 2 –AC system and CO 2 combined cycle Brayton • Auxiliary power unit (APU) 2020-04-30 4
Design Procedure
• Total design is performed in three steps – Basic cycle analysis and concept selection – Compact gas heat exchangers design – Compressor and expander selection and economic evaluation • EES is used for simulation and calculation 2020-04-30 5
First Stage
Basic cycle analysis
Basic Cycle Model
Cycle number Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 Cycle 6
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Cycle description CO2 Transcritical refrigeration cycle CO2 Transcritical power cycle, which preset gas heater pressure to 130 bar and expansion inlet temperature to 130
℃
CO2 Transcritical power cycle, which preset the gas heater pressure up to 300 bar CO2 Brayton cycle, with pressure range from 130bar to 300 bar CO2 Brayton cycle with reheating CO2 Combine cycle, which combine the Transcritical refrigeration cycle and Brayton Cycle
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No 1 - CO 2 Refrigeration Cycle
• Transcritical cycle • Evaporation pressure 40 bar • Evaporation temperature 5 ℃ • Condensing pressure 130 bar • Condensing temperature 130 ℃ • Condenser outlet temperature 40 2.566
℃ • The system COP is 2020-04-30 8
No 2 - CO 2 Transcritical Power Cycle
• Transcritical cycle • Condensing pressure 60 bar • Gas cooler CO 2 inlet temperature 62.38
℃ • Gas cooler CO 2 outlet temperature 21.98
℃ • Pressure in gas heater 130 bar • Gas heater CO 2 inlet temperature 33.12 ℃ • Gas heater CO 2 outlet temperature 130 ℃ • The system thermal efficiency is 0.1276
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No 3 - CO 2 APU Cycle
• Transcritical cycle • Condensing pressure 60 bar • Gas cooler CO 2 inlet temperature 62.38
℃ • Gas cooler CO 2 outlet temperature 21.98
℃ • Pressure in gas heater300 bar • Gas heater CO 2 inlet temperature 64.82 ℃ • Gas heater CO 2 outlet temperature 210 ℃ • The system thermal efficiency is 0.2366 2020-04-30 10
No 4 - CO 2 Brayton Cycle
• Brayton cycle • Condensing pressure130 bar • Gas cooler CO 2 inlet temperature 208.9
℃ • Gas cooler CO 2 outlet temperature 130 ℃ • Pressure in gas heater300 bar • Gas heater CO 2 inlet temperature 210.2 ℃ • Gas heater CO 2 outlet temperature 300 ℃ • The system thermal efficiency is 0.1632
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No 5 - CO 2 Brayton cycle with reheating
• Pressure in gas heater300 bar • Gas heater CO 2 inlet temperature 210.2 ℃ • Gas heater CO 2 outlet temperature 300 ℃ • Reheating pressure 160 bar • CO 2 temperature after reheating 300 • Pressure in gas cooler 130 bar • The system thermal efficiency is 0.1139
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No 6 - CO 2 Combined cycle
• Pressure in gas heater 300 bar • Gas heater CO 2 inlet temperature: 210.2 ℃ • Gas heater CO 2 outlet temperature: 300 ℃ • Pressure in gas cooler 130 bar • Gas cooler CO 2 inlet temperature 208.9
℃ • Gas cooler CO 2 outlet temperature 40 ℃ • Evaporation pressure 40 bar • Evaporation temperature 5 ℃ • The system COP is 2.566
• Thermal efficiency is 0.1632 2020-04-30 13
Results Analysis and Discussion
• Theoretical values are promising but must be verified experimentally • Low thermal efficiencies can be justified due to the fact that we use waste heat • Reheat cannot raise the efficiency of this CO 2 Brayton cycle 2020-04-30
2 5 . 0 0 % 2 0 . 0 0 % 1 5 . 0 0 % 1 0 . 0 0 % 5 . 0 0 %
0.00%
C O 2
CO2 transcritical power cycle
t r a n s c r i t i c a l
CO2 transcritical power cycle-apu
p o w e r c y c l e
CO2 Brayton cycle CO2 Brayton cycle with reheating 14
Second Stage
Heat exchanger design
Mainly focus on three types of heat exchangers : – Evaporator for compartment room — exchanger between CO air 2 heat and compartment – HRHX — heat exchanger between CO 2 and exhaust gas – Gas cooler — CO 2 heat exchanger between and ambient air 2020-04-30 16
Heat Exchanger Design Basic
• A compact counter flow heat exchanger with laminar flow at the airside is chosen. • The laminar flow technology gives the possibility for good heat transfer with low pressure drop and a high area per volume ratio. •Nusselt number is “ constant ” •k is constant
h
Nu
k d
•The lower d (hydraulic diameter), the higher h (heat transfer coefficient) 17 2020-04-30
Ranotor compact heat exchanger
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Calculation model
Three inlets Counter flow Air pass three pipes at the same time 2020-04-30 19
Calculation Window and Results
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A-C Cycle Calculation window
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Shape Figure
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Brayton Cycle Calculation window
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Shape Figure
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APU Cycle Calculation window
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Shape Figure
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Combine Cycle Calculation Window
EES 27
Shape Figure
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Results Analysis and Discussion
• Ranotor’s heat exchanger has a quite low pressure drop at the airside • Low pressure drop leads to low fan power, which means: – Reduce the consumption of electricity ― gasoline – Provide a more quite, comfortable driving environment • Unique shape of Ranotor’s heat exchanger provides more flexibilities for installation 2020-04-30 29
General Discussion and Further Research Suggestion
General discussion and Further research suggestion
• More work on optimum pressure and temperature selection • Influence of various operating parameters (off design) on efficiency • Integration of suction gas HX in cycle(s) • Prototype testing of components and cycle(s) 2020-04-30 31