In the present work, the design and analysis of a multi-block heat exchanger has been carried out by applying the concept of constructal theory proposed by Bejan. The heat exchanger works on the principle of developing laminar flow in each block carefully designed to avoid fully developed heat transfer coefficient. The additional thermal interaction is provided by the special design allowing heat transfer in ports as well as collecting and distributing channels. Numerical simulations were carried out for different values of heat capacity rate ratios on finned and unfinned constructal heat exchangers and four cross flow heat exchangers (two finned and two unfinned). In all the heat exchangers the heat transfer area is kept the same. To validate the numerical results, experiments were conducted keeping the heat transfer area and boundary conditions same as that of the numerical simulations. The results show that the effectiveness of the constructal heat exchangers, both finned and unfinned, are higher by around 20% compared to that of the conventional cross flow heat exchangers under similar conditions. The experimental result confirms this enhancement and brings out the immense potential of this new type of heat exchanger. (c) 2008 Elsevier Ltd. All rights reserved.