4.5. Post-processing

Post-processing is the final stage of the CFD simulation, aiming to display the temperature and velocity fields, as well as the streamlines in the simulation domain. This stage is useful in the intermediate phases of the simulation, allowing its calibration based on the experimental data; at the end of the simulation, the final temperature and velocity fields and the streamlines are presented in a graphical form.

Figures 28–30 present the temperature fields in the three vertical planes taken into account (see Figure 23); the results show that, for the lower shelves, the temperature is with at least 4�C higher than the one required (5�C, according to ISO 23954-2:2005), which means that this area is not adequate for the storage of refrigerated goods.

Figure 31 presents the velocity field profile in the middle plane, at the exit of the horizontal grill (GPA).

Figure 32 presents the velocity field in the vertical right plane and also in the horizontal plane, in the vicinity of the base air grill (GRA). In the horizontal plane, air velocity was comprised Food Chilling Methods and CFD Analysis of a Refrigeration Cabinet as a Case Study http://dx.doi.org/10.5772/intechopen.69136 67

Figure 28. Temperature field in the left plane of the cabinet, at the end of the 6 min simulation [C].

4.4. Processing

66 Refrigeration

approximately 12 h.

lower than 10�<sup>6</sup>

grill (GPA).

4.5. Post-processing

.

Table 3. Linear relaxation factors.

presented in a graphical form.

is not adequate for the storage of refrigerated goods.

maximum number of iterations for one step was 10.

In the processing stage, the time step was set at 0.2 s, the number of steps was 1800, and the

The simulation was performed on a Pentium IV, DualCore 6400, 2.4 GHz system with 4 GB RAM; for 6 min of simulation and a total number of 18,000 iterations, the computing time was

In order to prevent the equation coefficients from changing too quickly, the change in dependent variables from one iteration to another was slowed by "relaxing" them. Thus, the linear relaxation method was used for the control of the CFD simulation in order to maintain its stability; Table 3 presents the values of the relaxation factors for the different physical parameters.

Property Variable Relaxation factor, α

Pressure p 0.3 Density ρ 0.5 Lift force F 0.5 Momentum ν<sup>i</sup> 0.8 Turbulent kinetic energy k 0.6 Dissipation rate of the turbulent kinetic energy ε 0.6 Turbulent viscosity μ<sup>t</sup> 0.8 Energy E 0.7

In this CFD simulation, the convergence criterion was selected so that the residues remained

Post-processing is the final stage of the CFD simulation, aiming to display the temperature and velocity fields, as well as the streamlines in the simulation domain. This stage is useful in the intermediate phases of the simulation, allowing its calibration based on the experimental data; at the end of the simulation, the final temperature and velocity fields and the streamlines are

Figures 28–30 present the temperature fields in the three vertical planes taken into account (see Figure 23); the results show that, for the lower shelves, the temperature is with at least 4�C higher than the one required (5�C, according to ISO 23954-2:2005), which means that this area

Figure 31 presents the velocity field profile in the middle plane, at the exit of the horizontal

Figure 32 presents the velocity field in the vertical right plane and also in the horizontal plane, in the vicinity of the base air grill (GRA). In the horizontal plane, air velocity was comprised

Figure 29. Temperature field in the middle plane of the cabinet, at the end of the 6 min simulation [C].

between 0.4 and 0.6 m/s; these values were significantly lower than the average value of 1.7 m/s, which was considered as a boundary condition for GRA, showing the non-uniformity of the air curtain in this area.

Figure 30. Temperature field in the right plane of the cabinet, at the end of the 6 min simulation [C].

The streamlines presented in Figure 33 complete the picture of the air curtain in terms of air velocity, while Figures 34 and 35 display the streamlines in terms of air temperature; the results can be summarized as follows:

Figure 31. Velocity field profile at GPA, in the middle plane, at the end of the simulation.

Food Chilling Methods and CFD Analysis of a Refrigeration Cabinet as a Case Study http://dx.doi.org/10.5772/intechopen.69136 69

Figure 32. Velocity field profile in the vicinity of GRA and in the vertical right plane.

Figure 33. Streamlines for air velocity [m/s].

The streamlines presented in Figure 33 complete the picture of the air curtain in terms of air velocity, while Figures 34 and 35 display the streamlines in terms of air temperature; the

Figure 30. Temperature field in the right plane of the cabinet, at the end of the 6 min simulation [C].

Figure 31. Velocity field profile at GPA, in the middle plane, at the end of the simulation.

results can be summarized as follows:

68 Refrigeration


Figure 34. Streamlines for air temperature, front view [C].

Figure 35. Streamlines for air temperature, rear view [C].
