# Aerodynamic Drag Study of the Heat Exchange Equipment with Different Fin Geometries
## 5 Results and Discussion
The orientation of the fins with flow from a larger diameter to a smaller one is more aerodynamic than the opposite orientation. In our opinion, this is explained by the fact that the flow that hits the ribs is well dissected by it, and the subsequent decrease in diameter contributes to the reduction in turbulence and flow distribution, which positively affects the drag coefficient. On the basis of numerous simulations, an array of data was obtained and, based on them, a graphical dependence of the Reynolds number on the drag coefficient was constructed, which is presented in Figure 8.  
Analyzing the obtained arrays of values, the following can be noted: the lowest value of the drag coefficient is observed when the fins are oriented in flow from a larger diameter to a smaller one (Figure 8, red curve 2). The values of the drag coefficient significantly depend  
Figure 8: Dependence of the resistance coefficient \(C_{X}\) of special fins on the Reynolds number Re: 1—longitudinal flow around the fins from the side of the smaller diameter; 2—longitudinal flow around the fins on the side of the larger diameter; 3—transverse flow around the fins. on the flow regime. In the laminar flow regime (Re < 2300), the average value of \(C_{X}\) = 1.04, in the transitional flow regime (2300 < Re < 10,000), \(C_{X}\) = 0.74, and in the turbulent regime (Re > 10,000), \(C_{X}\) = 0.22. This case is characterized by a significant decrease in the drag coefficient during the transition from the laminar to the turbulent flow regime; the minimum is observed at the flow speed in the range between 2 and 3 m/s, which corresponds to the range between number Re = 9668 and 14,503, while for the transition from the transitional to the turbulent movement regime, the value is in the range between \(C_{X}\) = 0.18 and 0.14. A further increase in speed leads to a smooth, slight increase in the drag coefficient. This variant of fin orientation can be attributed to a well-streamlined body in which flow separation occurs weakly, which affects small values of the drag coefficient. A different situation is observed with the orientation of the fins in the flow from a smaller diameter to a larger one (Figure 8, green curve 1). In the laminar mode (Re < 2300), the average value of \(C_{X}\) = 1.74, in the transitional mode (2300 < Re < 10,000), \(C_{X}\) = 1.68, and in the turbulent mode (Re > 10,000), \(C_{X}\) = 0.96. Characteristic for this case of rib orientation are higher values of the drag coefficient than in the previous version, over the entire speed range, although it has a noticeable tendency to decrease with increasing Reynolds numbers. This variant of the orientation of the fins can be attributed to a poorly streamlined body, in which the separation of the flow occurs more pronounced, which affects the higher values of the resistance coefficient. With the orientation of the fins with transverse flow, the maximum values of the drag coefficient are achieved in the entire range of Reynolds numbers (Figure 8, purple curve 3). In the laminar mode (Re < 2300), the average value of the aerodynamic resistance coefficient is \(C_{X}\) = 1.74, in the transitional mode (2300 < Re < 10,000), \(C_{X}\) = 1.68, and in the turbulent mode (Re > 10,000), \(C_{X}\) = 0.96. Characteristic of this variant of orientation is a slight change in drag coefficients in different modes of fluid movement. Therefore, for this range of studies, the value of the coefficient can be considered averaged for these modes of movement--\(C_{X}\) = 1.96. This variant of finning can be attributed to bodies with a blunt frontal part, which strongly divides the flow into a zone of high and low pressure, which causes a high coefficient of frontal resistance. For nozzles with eight ribs in their study, [PERSON] obtained the value of the coefficient of aerodynamic drag in CFD modeling--\(C_{X}\) = 1.14 at a speed of 10.03 m/s [29].