Numerical modelling and performance maps of a printed circuit heat - - PowerPoint PPT Presentation

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

RCUK Centre for Sustainable Energy Use in Food Chains

Numerical modelling and performance maps of a printed circuit heat exchanger for use as recuperator in supercritical CO2 power cycles

Matteo Marchionni*, Lei Chai, Giuseppe Bianchi, Savvas A.Tassou

Brunel University London, Uxbridge UB8 3PH, United Kingdom

Paphos, Cyprus 17-19 October 2018

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Presentation outline

• Overview on sCO2 heat to power systems
• 3D CFD model
• 1D CFD approach
• 1D/3D results comparison
• 630 kW PCHE calibration
• PCHE performance maps
• Conclusions and future work

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

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Why sCO2?

Compactness Low environmental impact High efficiency

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sCO2 power cycles

+7%

+7% efficiency if coupled with an ORC or other cascade systems

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sCO2 power cycles for WHR

High sCO2 thermal stability Reduced footprint and costs Reduced water consumptions

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2nd International Conference on Sustainable Energy and Resource Use in Food Chains

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Heat exchangers in sCO2 systems

• Harsh operating conditions
• High temperature gradients
• Intense thermal duties
• Key components

Printed Circuit Heat Exchanger (PCHE)

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3D CFD model

• 3D CFD model of a PCHE elementary heat

transfer unit developed in ANSYS FLUENT

• Periodic and symmetry boundary conditions
• standard k-ε turbulence model
• SIMPLEC algorithm to couple the pressure

and velocity field

• Buoyancy and entrance effect are

considered

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2nd International Conference on Sustainable Energy and Resource Use in Food Chains

• M. Marchionni

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1D modelling procedure

• The channel are discretized along

the flow direction

• Geometrical features of the

channel cross-section are set

• Dittus-Boelter heat transfer

correlation

• Colebrook equation

RCUK Centre for Sustainable Energy Use in Food Chains

2nd International Conference on Sustainable Energy and Resource Use in Food Chains

• M. Marchionni

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Simulation setup

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• Geometrical features of the PCHE

elementary unit are defined

• Identical boundary conditions are set
• Channel surface roughness neglected
• Material thermophysical properties as

function of its temperature

• Reduced computational effort
• NIST Refprop dll for the calculation of

the CO2 thermophysical properties

Geometrical features and materials of the test case

Wetted parameter [mm] 5.14 Hydraulic diameter [mm] 1.22 Cross-sectional area [mm2] 1.57 Length [mm] 272.00 Plate thickness [mm] 1.63 Surface roughness Neglected Material Stainless steel 316L

Simulation setups

Boundary conditions Cold side Hot side Mass flux [kg/(sm2)] 509.3 Inlet temperature [°C] 100 400 Outlet pressure [bar] 150 75 1D 3D Spatial discretization [mm] 6.8 <0.05 Computational time 5 seconds 1 day

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2nd International Conference on Sustainable Energy and Resource Use in Food Chains

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1D/3D comparison

• Temperatures and pressures in several sections of the cold and hot channel match
• The heat transfer coefficient predictions of the two models present an offset, which is mainly due to the

different calculation procedures adopted

• The 1D modelling approach cannot predict the thermal entrance effect in the PCHE channels

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2nd International Conference on Sustainable Energy and Resource Use in Food Chains

• M. Marchionni

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1D model calibration of a 630 kW PCHE

630 kW PCHE characteristics

Channel geometry

Wetted parameter [mm] 5.14 Hydraulic diameter [mm] 1.22 Cross-sectional area [mm2] 1.57 Length [mm] 1012 Type Straight

PCHE properties

Material Stainless steel 316L Channel surface roughness Neglected Channel discretization length [mm] 25.3 Number of channels per row 54 Number of rows 42

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2nd International Conference on Sustainable Energy and Resource Use in Food Chains

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Calibration results

12 Design (1) Off-design #1 (2) Off-design #2 (3) Off-design #3 (4) Off-design #4 (5)

mass flow rate [kg/s] 2.06 1.57 2.09 2.09 2.62 cs temp in [°C] 72.9 72.9 875 62.0 72.9

60 90 120 150 180 210 1 2 3 4 5

Pressure drop [kPa] Case

60 120 180 240 300 1 2 3 4 5

Temperature [°C] Case

400 500 600 700 800 1 2 3 4 5

Heat load [kW] Case

The highest error of 5.7% is shown for the pressure drop on the cold side in the 4th off-design case

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Performance maps

1.57 kg/s (75% of the design case) 2.06 kg/s (design point) 2.62 kg/s (125% of the design case)

• A reduction of the cold side inlet pressure increments the thermal power exchanged by the PCHE
• The thermal power exchanged rises accordingly to the hot side inlet temperature

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Overall heat transfer coefficient

1.57 kg/s (75% of the design case) 2.06 kg/s (design point) 2.62 kg/s (125% of the design case)

• The increase of the sCO2 mass flow rate, the hot side inlet temperature and the cold side inlet pressure

have a beneficial effect on the overall heat transfer coefficient

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Effectiveness

1.57 kg/s (75% of the design case) 2.06 kg/s (design point) 2.62 kg/s (125% of the design case)

• An increased mass flow rate and inlet pressure of the cold side negatively affect the effectiveness of the

PCHE

• A rise of the effectiveness can be observed when the inlet temperature of the hot side is incremented

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2nd International Conference on Sustainable Energy and Resource Use in Food Chains

• M. Marchionni

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Pressure drops

1.57 kg/s (75% of the design case) 2.06 kg/s (design point) 2.62 kg/s (125% of the design case)

• An increment of the hot side inlet temperature and the working fluid mass flow rate cause higher pressure

losses across the heat exchanger

• On the contrary, an increase of the cold side inlet pressure is beneficial for the reduction of the PCHE
• verall pressure drop

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2nd International Conference on Sustainable Energy and Resource Use in Food Chains

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Conclusions

• A 1D modelling procedure has been herein presented, the approach validated by

means of a 3D CFD model of a PCHE heat transfer elementary unit

• A 630 kW PCHE, which will be used in the sCO2 test rig at BUL, has been modelled
• Performance maps of the heat exchanger have been reported as a function of the

working fluid mass flow rate, the hot side inlet temperature and the cold side inlet pressure

• The results shown that several trade-off must be considered when selecting the

main cycle thermodynamic parameters

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Future work

• Integration of the PCHE model developed in the

sCO2 power unit dynamic model

• Experimental validation of the modelling approach

through the test rig currently under construction at Brunel University London RECUPERATOR

waste heat recovery station compressor turbine gas cooler generator

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Acknowledgements

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This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 680599