2 nd International Conference on Sustainable Energy and Resource Use in Food Chains Numerical modelling and performance maps of a printed circuit heat exchanger for use as recuperator in supercritical CO 2 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 RCUK Centre for Sustainable Energy Use in Food Chains
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains Presentation outline • Overview on sCO 2 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 M. Marchionni 2
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains Why sCO 2 ? Low High Compactness environmental efficiency impact RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 3
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains sCO 2 power cycles +7% efficiency if coupled with an ORC or other cascade systems +7% RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 4
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains sCO 2 power cycles for WHR High sCO 2 thermal stability Reduced footprint and costs Reduced water consumptions RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 5
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains Heat exchangers in sCO 2 systems • Harsh operating conditions • High temperature gradients Printed Circuit Heat Exchanger (PCHE) • Intense thermal duties • Key components RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 6
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains 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 RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 7
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains 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 M. Marchionni 8
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains Simulation setup Geometrical features and materials of the test case • Geometrical features of the PCHE Wetted parameter [mm] 5.14 elementary unit are defined Hydraulic diameter [mm] 1.22 Cross-sectional area [mm 2 ] 1.57 • Identical boundary conditions are set Length [mm] 272.00 Plate thickness [mm] 1.63 • Channel surface roughness neglected Surface roughness Neglected Material Stainless steel 316L • Material thermophysical properties as function of its temperature Simulation setups Boundary conditions Cold side Hot side • Reduced computational effort Mass flux [kg/(sm 2 )] 509.3 Inlet temperature [°C] 100 400 • NIST Refprop dll for the calculation of Outlet pressure [bar] 150 75 the CO 2 thermophysical properties 1D 3D Spatial discretization [mm] 6.8 <0.05 Computational time 5 seconds 1 day RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 9 9
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains 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 RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 10
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains 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 [mm 2 ] 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 RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 11
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains Calibration results 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 72.9 800 210 300 Pressure drop [kPa] 180 Temperature [°C] 700 Heat load [kW] 240 150 600 180 120 500 120 90 60 60 400 0 1 2 3 4 5 0 1 2 3 4 5 0 1 2 3 4 5 Case Case Case The highest error of 5.7% is shown for the pressure drop on the cold side in the 4 th off-design case RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 12
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains 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 RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 13
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains 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 sCO 2 mass flow rate, the hot side inlet temperature and the cold side inlet pressure have a beneficial effect on the overall heat transfer coefficient RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 14
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains 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 RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 15
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains 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 overall pressure drop RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 16
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains 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 sCO 2 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 RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 17
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains Future work waste heat recovery station • Integration of the PCHE model developed in the sCO 2 power unit dynamic model generator compressor turbine RECUPERATOR • Experimental validation of the modelling approach through the test rig currently under construction at Brunel University London gas cooler RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 18
2 nd International Conference on Sustainable Energy and Resource Use in Food Chains Acknowledgements This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 680599 RCUK Centre for Sustainable Energy Use in Food Chains M. Marchionni 19
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