Thermal Regression Analysis

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3. Modeling and Numerical Simulation Method Experimental methods have been used to find which design of a radiator or HEX is economic and efficient. However, because of the high cost and the complexity of experiments, a numerical method is adopted in the present work to analyze the performance of HEXs. The physical model of the HEX has to be simplified and certain assumptions have to be set up. Meanwhile the governing equations and corresponding boundary conditions are introduced for the simulation model. On the other hand, the grid independence is carried out to ensure the accuracy and validity of the numerical models. At the end, several important parameters are defined for the analysis of thermal performance and pressure loss in HEXs. 3.1 …show more content…

The finite volume method (FVM) is adopted to convert the governing equations to algebraic equations, so that they can be solved numerically. The Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm is used to couple pressure and velocity. A second-order upwind scheme is used for the space discretization of the momentum, energy and turbulence equations in the simulations. 41 The convergence criterion for continuity, momentum, k and Ɛ equations is below 10-3 .However, for the energy convergence needs to satisfy also the energy balance between the air zone and the water zone under the countercurrent flow condition. Thus, the convergence criterion for energy is below 10-8. The mesh generation is carried out by the preprocessor-software ICEM. There are two major techniques in the mesh generation. One is the blocking technique (mostly for Hexa Meshing, as shown in Fig. 3.4). Another one is the auto meshing technique. The HEX region occupies most of cells (60 ~ 70 % of the whole computational domain). Fig. 3.4. Meshing for the computations: (a) 2-D cross-sectional …show more content…

The results of the grid study for different HEXs are shown in Tables 3.3 and 3.4. It is found that the relative deviation of the pressure drops among the three sets of the grid system is less than 2.2 % in the graphite foam corrugated fin. Furthermore, the relative deviation of the heat transfer coefficients between the three sets of grid system is less than 3 % in the graphite foam corrugated fin. Thus, in order to save computational time and keep the accuracy of the simulation, the Case 2 mesh system is chosen for the graphite foam corrugated fin. The same method was adopted to check the grid independence of other configurations of fins. At the end, the Case 2 grid system is chosen for all the fins. Table 3.4. Grid independence study based on h (frontal velocity is 14 m/s). Case 1 Case 2 Case 3 h Grid H Grid h Grid h deviation (W/m2•K) (W/m2•K) (W/m2•K) (%) Pin-finned (63- 431.24 (93- 400.52 (113- 402.60 0.5 - 7.1 (G) 79-19) 79-19) 79-19) Corrugated (49- 259.26 (75- 263.40 (75- 267.04 1.4 - 3 (G) 81-11) 81-11) 81-19) Stagger (G) (99- 450.10 (99- 454.46 (121- 461.49 1.5 - 2.5 83-11) 83-17) 83-17) Wavy (139- 1077.6 (139- 1088.2 (150- 1100 1.1 - 2 corrugated 100- 100- 100- (G) 15) 21) 21) Wavy

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