## 3 Results and Discussion  
### Numerical Simulations Results  
Figure 6a,b depict the numerical simulation of the temperature and velocity distribution of the CLRDL with the ALFHS and CUFHS mounted devices. This figure confirms that natural or free convection is caused by density differences because of the buoyancy induced by the velocity flow pattern. Comparing Figure 6a,b reveals that hot air rises faster in the ALFHS. Heat sink circulation concentrates the air flow centrally at the inside top of the test box; the air then diffuses along the surface below the top cover of the test box. Due to the buoyancy force, the top area and the area around the testing downlight had a high temperature; areas close to the plywood wall and in the lower position had a lower temperature. For the CUFHS, in Figure 6b, the air flow based on the heat sink circulation is similar to that of the ALFHS, except for a difference in the hot air flow behavior. Figure 6b indicates that the CUFHS provides an enlarged hot air diffusion region around the testing downlight. The different heat dissipation orientations and affected areas for heat transfer and convection of the designed ALFHS and CUFHS are displayed. Figure 4: Two photos of heat sinks; (**a**) ALFHS and (**b**) CUFHS. Figure 5: Photo of the experimental setup for the ALFHS or the CUFHS mounted to the CLRDL after INST. The flow velocity of the ALFHS was 0.14 m/s. The velocity of the CUFHS was 0.01 m/s lower than that of the ALFHS. The velocity of the CUFHS was slower than that of the ALFHS. This resulted in hot air rising at low speeds. Nevertheless, because the porous medium of the CUFHS had a large area-to-volume ratio, the contribution of heat dissipation was greater along all of the porous medium surfaces. The results show that the LED \(T_{\mathrm{sp}}\) values of the CLRDL with the ALFHS and CUFHS were 91.7 and 91.8 \({}^{\circ}\)C.  
Figure 7 presents the temperature field and fluid flow velocity field. The color slice shows the temperature field distribution. The arrow volume shows the fluid flow velocity field. The left color legend for temperature field from dark blue to dark red denotes low to high temperature. Next to the temperature legend is the color legend for arrow volume; the arrow volume color indicates the velocity field, with dark blue to dark red denoting low to high fluid velocity, respectively. The arrow indicates  
Figure 6: Illustration for the numerical simulation results of the CLRDL after INST (**a**) with mounted ALFHS; and (**b**) with mounted CUFHS. the fluid flow direction from minimum to maximum velocity in each velocity field. A consistent connection between the temperature distribution and velocity field was indicated in the numerical simulation, with the phenomenon of higher ambient temperature being accompanied by a higher velocity in the test box (Figure 7). As shown in Figure 8a1, at points \(T_{1}\) and \(T_{2}\), the area temperature was greater than 65 \({}^{\circ}\)C (\(T_{2}\)), with the highest temperature in the center area (\(T_{1}\)). Figure 8b1 indicates the same position for the CUFHS. The temperature was much lower than is shown in Figure 8a1. As mentioned, because the porous media of the CUFHS had a large area-to-volume ratio, and larger heat-exchanger surface  
Figure 7: Simulation results of temperature and fluid flow velocity fields (view of yz plane) after INST. (**a**) with mounted ALFHS; and (**b**) with mounted CUFHS. area, the contribution of heat dissipation was greater along all of the porous surfaces. Therefore, the temperature distribution shown in Figure 8b1 at equivalent positions was lower than Figure 8a1. In Figure 8a2, the most marked temperature of the ALFHS is 91.8 \({}^{\circ}\)C (\(T_{\rm sp}\)); however, the temperature of the point near the wall of the test box (\(T_{3}\)) was much lower than the \(T_{\rm sp}\). Figure 8b2 shows the same position for the CUFHS: the \(T_{\rm sp}\) was 91.7 \({}^{\circ}\)C and T\({}_{3}\) was similar to that shown in Figure 8a2 for the ALFHS.