EVAPORATOR

PROBLEM TO BE SOLVED: To improve an evaporator so as to increase the heat transfer coefficient of the circumferential average sufficiently, by forming the bottom part of an evaporating tube line to be recessed toward the center side of the evaporating tube line from the cylindrical surface having the extended cylindrical inner peripheral surface which constitutes the inner side of the evaporating tube line except for this bottom part. SOLUTION: An evaporator is equipped with an evaporating tube line 12 in which a refrigerant flows. The bottom part of this evaporating tube line 12 is substantially formed to be recessed toward the center side of the evaporating tube line 12 from the cylindrical surface having the extended cylindrical inner peripheral surface which constitutes the inner periphery of the evaporating tube line except for this bottom part. The bottom part of the evaporating tube line 12 is flattened. Since the bottom of the evaporating tube line 12 is flattened, the wet interface angle of the refrigerant 22 of the liquid phase containing dissolved refrigerating machine oil becomes large. Especially, the contact area of the liquid phase part and the tube wall becomes large in a separate stream, and the heat transfer coefficient of the circumferential average improves. If R410A, which is a refrigerant mixture of difluoromethane and pentafluoroethane, is used as the refrigerant, pressure loss is reduced.