HEAT EXCHANGER

PURPOSE:To contrive to enhance corrosion resistance, by a method wherein the material thickness of an outer periphery part of a flat form tube in a heat exchanger used as a refrigerant evaporator for an automotive cooler or the like is set to be larger on the upstream side of an air flow than that on the downstream side over a predetermined distance. CONSTITUTION:The longitudinal direction of a cross section of the flat form tube is disposed in parallel with the direction of the air flow, and the material thickness t2 of the outer periphery part 6 of the tube 2 is set to be larger on the upstream side of the air flow (c) than that on the downstream side over the predetermined distance l from the upstream side. When a refrigerating cycle is started, a refrigerant is introduced into an evaporator through an inlet-side pipe 3, exchanges heat with air (fed by a blower) through the outside walls of the tube and fins 1 when passing through the tube 2, and cooled air is blown out to the side of the interior of an automobile. When the outside air containing both water and salt components is introduced, water and the salt components are adhered onto the surface of the tube 2 together with dusts or the like, resulting in a corroding environment on the upstream side of the air flow (c). However, since the material thickness of the tube 2 is larger on the upstream side, leakage through the tube does not occur.