Conjugated analysis of heat transfer by natural convection and radiation in a fin array using a semitransparent fluid medium

Despite the significant effects of radiation on heat transfer systems, few studies have sought to verify the importance of this parameter in fins, and only the convective effects are considered. Thus, the objective of this work was to numerically evaluate the heat transfer by natural convection and radiation in an array of horizontal fins, using a transparent (non-participating) and semi-transparent (participating) fluid medium. The governing equations were discretized using the finite volume technique and solved using a CFD code ANSYS CFX. Fin arrays with spacing of 10 and 20 mm and base temperatures of 50, 75, and 100 °C were evaluated. The results showed that the addition of the participant fluid (CO2) promotes a better condition for heat transfer. The model used was validated with literature data and average errors of 4.85% and 6.83% were observed. The CP (pure convection) and CRAIR (convection + radiation with non-participating fluid) cases establish a flow stagnation zone near the base of the heated array, impairing the heat dissipation through the fins. The heat flow values for the CRAIR and CRCO2 (convection + radiation with participant fluid) cases were about 60% higher than those observed for the CP case. It was observed that increasing the spacing between fins resulted in an increase of up to 87% in the number of Nusselt, increasing thermal exchange with the environment. It was also verified that considering the radiation increases the Nusselt number by up to 92%. This effect is even more expressive using a participating fluid (219%).