Title Page
Contents
Abstract 11
Chapter 1. Introduction 13
Chapter 2. Mathematical modeling 20
2.1. Mass conservation 20
2.2. Momentum conservation 21
2.3. Reaction kinetics 23
2.4. Energy equations 24
Chapter 3. Design of CFD domain 26
3.1. Geometry and mesh generation 26
3.1.1. Multi-tubular reactor 26
3.1.2. A simplified single tube reactor with cooling jacket 30
3.2. Model parameters 31
3.3. Solution strategy 33
Chapter 4. Simulation results 37
4.1. Mesh independent test and model validation results 38
4.2. Parametric studies via multi-tubular reactor 42
4.2.1. Effect of thermal conditions 43
4.2.2. Effect of temperature 49
4.2.3. Effect of gas velocity 52
4.3. Cooling effects of different molten salts and tube diameters on the reactor performance 54
4.3.1. Effect of different molten salts with varying sodium nitrate concentrations on cooling performance 54
4.3.2. Effect of different mixtures of other nitrate salts on cooling performance 57
4.3.3. Economic considerations of salts 62
4.3.4. Effects of different diameters 64
Chapter 5. Software development 67
5.1. Software implementation 67
5.1.1. Software structure 67
5.1.2. User interface specifications 67
5.1.3. ANN model development for data prediction 69
5.1.4. Genetic algorithm (GA) for process variables optimization 73
5.2. Case studies for software validation 74
5.2.1. Case 1: NOx reduction 76
5.2.2. Case 2: Reactor performance optimization 78
5.2.3. Case 3: Removal of herbicide (diuron) from wastewater 80
5.2.4. Case 4: Contaminant (pyrene) removal from soil 81
5.2.5. Case 5: High free-fatty-acids (FFA) removal during biodiesel production 83
Chapter 6. Conclusion 86
References 91
Table 1. Kinetic parameters of reaction rates for butadiene and carbon dioxide production. 24
Table 2. Geometric dimensions of the multi-tubular reactor. 27
Table 3. Process conditions and model parameters. 32
Table 4. Computational boundary conditions. 34
Table 5. Numerical discretization schemes. 35
Table 6. Thermophysical properties of novel salts with respect to different sodium nitrate concentrations. 55
Table 7. Coefficients of density and viscosity correlations. 58
Table 8. Physical properties of six molten nitrate salts. 59
Table 9. Economic evaluation of different molten salts (A: LiNaKCsCaNO₃, B: LiNaKCsNO₃, C: LiNaKNO₃, D: NaKCaNO₃, E:... 63
Table 10. Parameters used in the optimization ANN model. 72
Table 11. Parameters used in a default configuration of GA. 74
Table 12. Summary of five case studies employed for the software validation. 74
Table 13. Comparison between optimal-process input variables obtained from Shin et al. [36] and this work. 78
Table 14. Comparison between optimal process variables resulting in maximum pyrene removal realized by [55] and in this work. 83
Figure 1. 3D multi-tubular reactor model. 27
Figure 2. Generated multi-tubular reactor mesh for the CFD simulation. 29
Figure 3. Geometry and mesh generated for the CFD simulation: (a) a geometry of 3D tubular reactor. (b) Generated mesh... 31
Figure 4. Summary of the CFD solution strategy. 34
Figure 5. Mesh independent test results of the mesh A, B, and C: (a) mole fraction of butene; (b) mole fraction of butadiene; (c)... 39
Figure 6. CFD model validation results: (a) mole fractions. (b) adiabatic temperature profiles. 41
Figure 7. Mole fractions distribution and mole fraction contour plot under isothermal conditions: (a) mole fraction distributions of... 44
Figure 8. Mole fractions distribution and mole fraction contour plot under non-isothermal conditions: (a) mole fraction... 45
Figure 9. Mole fractions distribution and mole fraction contour plot under adiabatic conditions: (a) mole fraction distributions of... 47
Figure 10. Temperature contour and profiles of a multi-tubular reactor under different thermal conditions: (a) temperature... 48
Figure 11. Mole fractions distribution along the reactor length at the temperature range between 610 K and 670 K: (a) butene;... 50
Figure 12. Mole fractions and reactor performance profiles as a function of temperature: (a) mole fractions; (b) conversion, yield,... 51
Figure 13. Mole fractions distribution along the reactor length at the temperature range between 3.25 m/s and 35.31 m/s: (a)... 53
Figure 14. Mole fractions and reactor performance profiles as a function of gas velocity: (a) mole fractions; (b) conversion, yield,... 54
Figure 15. Temperature and concentration profiles with seven different NaNO₃ and KNO₃ concentrations at their melting... 56
Figure 16. Temperature and concentration profiles with six different molten nitrate mixtures at melting temperatures: (a)... 60
Figure 17. Temperature and concentration profiles with six different molten nitrate mixtures at 633 K: (a) temperature; (b)... 62
Figure 18. Temperature and concentration profiles with seven different diameters: (a) temperature; (b) butadiene mole fraction;... 66
Figure 19. GUI specifications. (a) Menu bar; (b) case setup and prediction; (c) analysis and plot; (d) process variable optimization... 69
Figure 20. Developed framework for ANN architecture optimization using GA. 71
Figure 21. Results of an optimized ANN model plotted using the software package. (a) A correlation matrix; (b) a regression plot... 77
Figure 22. Regression analysis and comparison of predicted results against the simulation results of [38]. (a) A regression... 79
Figure 23. 3D surface plots of the diuron removal efficiency values predicted by the current software with respect to various... 81
Figure 24. Plots generated by the current software for the prediction results according to the experimental data obtained... 82
Figure 25. Comparison between software predicted values, experimental data, and ANN predicted result of. 85