Heat Exchanger Library - Overview
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The document provides an overview of a Modelica library for modeling heat exchangers. The library contains geometric models of flat tube heat exchangers that account for segmented, inhomogeneous internal flow and temperature distributions. It allows stacking of multiple heat exchangers and coupling heat exchanger models to external CFD data for the air flow. The library provides default test cases and supports batch simulation workflows for parameter variation and uncertainty analysis.
Heat Exchanger Library - Overview
- 1. An overview HEAT EXCHANGER LIBRARY 1
- 2. • Heat Exchanger Library Key features & capabilities • Model approach and fidelity Heat exchangers Stack example Air side interface • Library contents Package overview AGENDA
- 3. • Modelica library by Modelon • Geometric, segmented heat exchanger models • Several flat tube and louvered fin designs • Inhomogeneous flow and temperature distribution • Heat exchanger stacking • Coupling to CFD data • Prescribed air flow, or driven by pressure gradient – also for inhomogeneous distributions HEAT EXCHANGER LIBRARY
- 4. • Geometric models of flat tube heat exchangers Geometric friction and heat transfer correlations • Air side interface allows heat exchanger stacking • Automatic area fraction calculations on flow segment level • 2D – discretized and lumped flow source and sensor components • Plug-and-play compatible with other Modelon libraries for thermal management KEY FEATURES
- 6. Coolant path discretization: Unique temperature exposed to the wall in each segment. Several segments per pass and multiple layers are accounted for. Example: 2-layered, 3 passes per layer, 4 coolant segments per pass. COOLANT SEGMENTATION
- 7. CHANNEL GEOMETRIES Several geometries are possible. • Free flow area, heat transfer area, etc. calculated automatically • Geometric friction and heat transfer correlations included
- 8. The air flow through each segment assumes uniform flow and temperature. This interface is coupled to the heat exchanger geometry and segmentation, i.e. not suitable as external connector interface when building stacks. AIR SIDE INTERFACE
- 9. 1D-3D COUPLING Distribution Cmin/Cmax NTU = 0 NTU = 5 Interpolated Non-Uniformity Non-Uniformity A0 0.2 0.820 0.818 0.846 A1 0.2 0.859 0.856 0.874 A2 0.2 0.959 0.950 0.958 A3 0.2 0.998 0.991 0.993 A0 0.4 0.815 0.769 0.850 A1 0.4 0.860 0.831 0.900 A2 0.4 0.961 0.948 0.956 A3 0.4 0.998 0.993 0.995 A0 0.6 0.814 0.750 0.821 A1 0.6 0.862 0.810 0.862 A2 0.6 0.962 0.946 0.949 A3 0.6 0.998 0.991 0.991 A0 0.8 0.815 0.811 0.809 A1 0.8 0.864 0.844 0.840 A2 0.8 0.963 0.946 0.938 A3 0.8 0.998 0.989 0.989 A0 1 0.816 0.810 0.808 A1 1 0.866 0.845 0.842 A2 1 0.964 0.971 0.945 A3 1 0.998 0.999 0.998 HXL Simulation Ranganayakulu Paper Non-Uniformity Model compares well with published reference results (analytic FEA)
- 10. Example: Two heat exchangers without common edges. Partly covered by an obstacle causing lower flow rate through a segment. Air flow straigth through the heat exchanger stack is assumed. STACK EXAMPLE (IN LIBRARY) Front view Side view Passes in red
- 11. We introduce the concept of stream tubes. The segment edges are aligned with the component boundaries and depend on component size and position only. For each stream tube, uniform flow rate and pressure drop is assumed. The temperature distribution is independent of the stream tubes. STREAM TUBES Stream tubes Indicated in solid or dotted
- 12. STACK MODEL In the Stacks package, there are different templates and experiment to get a better understanding of how to use the Stack components.
- 13. STACK MODEL The stack can now be built by directly connecting components. The component connectors are independent of the internal component segmentation and includes the flow bypassing the component.
- 14. STACK EXPERIMENT MODEL The air side boundary conditions may be: • Upstream flow and downstream pressure, or • Upstream and downstream pressures per stream tubes • Upstream temperature profile Segmentation is defined on top level, and is automatically propagated to all components The stack is parameterized by the component geometries and positions
- 15. HEAT EXCHANGER There are two subsections to the heat exchangers: • Flat tubes • Plate
- 16. • Cross-flow • Support one phase and two phase • Connected to the surrounding air on the air side HEAT EXCHANGER FLAT TUBE
- 17. FLAT TUBE MODEL External connector: Flow segmented by stream tubes, high resolution temperature profile, full stream field represented (not limited by HX outer edges) Discretized wall Replaceable components
- 18. • Plate with counter flow or concurrent flow • Often uses pressurized media HEAT EXCHANGER PLATE
- 20. Default test cases, to set up your own experiments • Initial values • Steady-state init • Sources • User interaction components TEST BENCHES
- 21. BASIC COMPONENTS
- 22. • MATLAB • Python • Excel BATCHED SIMULATION Experiment settings Parameter modifiers Output of the experiment at the stop time
- 23. BATCHED SIMULATION • Monte Carlo on the HX effectiveness multipliers (uniform distribution between 0.6 & 1) and the flow rate scaling factors (normal distribution with mean 1 and std dev 0.1) • Constant Speed drive cycle at 120 kph with fan off and 50% grill opening (trade-off identified earlier) • Steady-state coolant temperature decreases with increasing HX effectiveness factor. Same trend with the flow rate scaling factor. • Coolant temperature however remains relatively steady over a range of values of both the HX effectiveness and flow rate scaling.