The cold (water) side includes large S-shaped fins in its flow channels. The calculation model of the cold side is presented in Fig. 5. The model size is 90.78 12.37 1.35 (mm), which is almost 0.42% of the whole heat exchanger volume. Regarding boundary conditions, the periodic condition was applied to both side walls.The bottom plane is the symmetrical plane. Furthermore, the top wall temperature was 2 C higher than the fluid inlet temperature all the way along the channel. The inlet temperatures were 278.15 K and 358.15 K, to simulate a part near the inlet and outlet of the heat exchanger. The flow rate was 6.04 1041.75 103 kg/s.