Verification of the heat transfer and friction factor of the AR=2 smooth channel without baffle is performed by comparing with the previous values under a similar operating condition as shown in Fig. 2a and b, respectively. The current numerical smooth channel result is found to be in excellent agreement with exact solution values obtained from the open literature [21] for both the Nusselt number and the friction factor, less than±0.25% deviation. The exact solutions of the Nusselt number and the friction factor for laminar flows over AR=2 smooth channels with constant wall temperature are as follows [21]: