HEAT EXCHANGER

PROBLEM TO BE SOLVED: To secure the sufficient rigidity of a casing of a heat exchanger while thinning and lightening the same. SOLUTION: An evaporator 23 performs the heat exchanging between an exhaust gas flowing in exhaust gas channels 50, 55, 56 formed inside the casing 31, and the water flowing the inside of heat conductive pipes 61, 67, 70 mounted in the exhaust gas channels 50, 55, 56. By brazing the spiral heat conductive pipe 61 along an inner face of the cylindrical casing 31, the casing 31 and the heat conductive pipe 61 are reinforced by each other to improve the rigidity, whereby the casing 31 can be thinned and lightened. Further by making the exhaust gas channel 50 at a downstream side where the exhaust gas of the comparatively low temperature flows, and the heat conductive pipe 61 at the upstream side where the water of the comparatively low temperature flows, function as heat insulating layers, the escape of the heat from the casing 31 can be effectively prevented. COPYRIGHT: (C)2003,JPO