# Thermal Analysis of Radiation Heat Transfer of Improved Fractal Solar Collectors
## 3 Results and Discussions
A zero internal emissivity indicates that the dish does not emit any heat from the inside, while a zero diffuse fraction indicates that the surface does not scatter the incoming light at all but reflects it all regularly. These features allow the parabolic dish to direct the light precisely towards the focal point. In addition, the direct visible and direct infrared (IR) values are also entered as zero within the absorptivity topic. A zero direct visible absorptivity indicates that the dish does not absorb any incoming light in the visible light spectrum but completely reflects it. However, in real conditions, the high \"direct IR\" absorptivity means that the collector can capture the infrared energy from the sun and convert it into heat. This indicates that the dish can use some of the radiation to heat itself, but this effect is neglected in the simulations. As a result, these idealized assumptions allow us to analyze the maximum potential performance of the system, although the performance in real conditions deviates slightly from the ideal case. Figure 8: Time-dependent distribution of temperature at outlet water. Figure 7: Details of the mesh structure: (**a**) the air domain, (**b**) the solar collector and parabolic dish region, (**c**) the inlet region, and (**d**) the outlet region. The hydrodynamic performance of the fractal collector system is given in Figure 9. Figure 9 shows the entire modeled domain. When the flow velocity dynamics experienced around the system and the dish are examined in detail in Figure 9, it is seen that the fluid velocity varies between 0 m/s and 0.73 m/s. This wide velocity range reflects the complex flow dynamics in the system. In the inner parts of the fractal collector, especially in the lower and middle fractals, the blue and light blue colors, where the velocity is generally low, are observed between 0 and 0.20 m/s. These low velocity regions increase heat transfer by allowing the water to absorb heat for a longer period of time. Higher velocities are observed at the outer edges of the fractal structure and especially at the upper parts, in green and yellow colors, between 0.33 and 0.53 m/s. These high-velocity regions indicate that the heated water moves rapidly upwards, which confirms the principle of natural convection. At the bottom of the system, at the entry point, yellow and orange colors are between 0.46 and 0.66 m/s, and relatively high velocities are observed. This situation shows that cold water enters the system rapidly. Similarly, high velocities are observed at the top, in other words, at the exit point, which means that the heated water is effectively removed from the system. Complex flow patterns and vortices are observed around the fractal structure, especially in the lower and middle toroidals. This turbulent flow contributes to the efficiency of the system by increasing heat transfer. The high velocity values observed in orange and red colors between 0.59 and 0.73 m/s in the regions close to the inner surface of the parabolic dish and the air currents created by the dish are understood to affect the overall heat transfer performance of the system. As a result, the numerical velocity distribution analysis shows that the fractal collector system operates effectively from a hydrodynamic point of view. The low-velocity regions optimize the heat transfer, while the high-velocity regions provide efficient transport of heated water. In addition, the observed turbulence and vortices further increase the heat transfer and contribute to the overall efficiency of the system. Figure 9: Path line velocity at the middle plane (**a**) general view and (**b**) enlarged view on the fractal collector. Figure 10 shows the temperature distribution in the collector system consisting of a parabolic dish and three toroidal fractals as a result of the numerical analysis. The red region (around 350 K) seen on the parabolic dish surface indicates the area where the sun rays are concentrated.