A new enhanced surface for forced-air convection heat transfer effective in the range of Reynolds numbers lower than 3000 was invented. This technique is called "breathing effect". The surface has many perforations and is bent to form a trapezoidal shape. A heat exchanger constructed with these surfaces has enlargement and contraction parts alternately along the flow passages. The mechanism of the heat transfer enhancement is due to the secondary flow induced by the suction and injection through the perforations, and to the frequent boundary layer interruption at each contraction part. The invented process of the breathing effect and its applications are presented in order to spread the practical application of the breathing effect.