are evenly spaced along the face of the charge gas plate 42 a b the raised contoured ridges 62 a c define multiple charge gas channels 50 a d the charge gas channels 50 a d are substantially sinusoidal in the preferred embodiment the shape of the charge gas channels 50 a d are determined by the shape of the raised contoured ridges 62 a c similarly each of the exhaust plates 44 a b include raised contoured ridges 66 a c the raised contoured ridges 66 a c are also substantially sinusoidal in order to reduce the pressure drop in the flow of the exhaust gas it is particularly important in the exhaust gas plates 44 a b to have substantially sinusoidal raised contoured ridges 66 a c and therefore substantially sinusoidal contoured exhaust gas channels 56 a d such that the exhaust gas flowing along the exhaust gas plates does not encounter sharp cornered regions where it is likely that the exhaust gas which contains some particulate would deposit that particulate on the surface of the exhaust plate such particulate deposition results in fouling and increased pressure loss of the exhaust gas and therefore decreases the mechanical and thermal efficiency of the heat exchanger the gases follow the directions indicated by their respective arrows exhaust gas plates 42 a b and exhaust gas plates 44 a b are preferably constructed of stainless steel or any other suitable material having good thermal transfer characteristics and corrosion resistance referring now to fig4 an enlarged view of the heat exchanger 20 is shown with the charge gas plates.