**3. Description of the Geometry of the Repeating Element of the Exchanger**

Figure 1 presents a 3D view and geometry of analysed PFTHE. Directions of air and water flow are shown. Figure 1b illustrates a repetitive fragment of air between one fin pitch in PFTHE (grey colour). In this case, fin pitch equals 3 mm. However, the distance between surfaces of the adjacent plate fins is 2.84 mm. This is because the fin thickness is 0.14 mm. In the same picture, we can observe yellow colours in front and behind the PFTHE. Those fragments are free zones of air for the correct performance of CFD simulation. Each zone is 5 mm in length (Figure 1b). The diameter of the tubes is 12mm. Air Inlet in CFX software is set as a constant temperature: 20 ◦C. Air outlet is set as an opening condition with checking mass average temperature in the outlet cross section of air. The rest of the boundary conditions of the CFX software are shown in Figure 2a.

(**a**) (**b**)

**Figure 1.** (**a**) The analysed PFTHE: 3D view; (**b**) Repetitive fragment of the PFTHE with run-up zone using in ANSYS-CFX 2020 R2: geometry, mm.

**Figure 2.** Repetitive fragment of the PFTHE with run-up zone using in ANSYS-CFX 2020 R2: (**a**) boundary conditions; (**b**) finite element mesh.
