Abstract: A fin satisfies 0°<?2<tan?1[(L±?)/{(S1?D1)/2?L/tan?1}], where S1 is a distance between an upstream end and a downstream end of a first inclined portion, D1 is a distance between an upstream end and a downstream end of a flat portion, ?1 is an angle between a reference plane and the first inclined portion in the flow direction, ?2 is an angle between the reference plane and the second inclined portion in the flow direction, ? is a distance between the reference plane and the flat portion, and L is a distance between the reference planes of the fins adjacent to each other. ?2 gradually decreases as a measurement direction of the angle is shifted from the row direction to the air flow direction and is minimum when the measurement direction is orientated in the air flow direction.

Abstract: A fin satisfies 0°<?2<tan?1[(L±?)/{(S1?D1)/2?L/tan ?1}], where S1 is a distance between an upstream end and a downstream end of a first inclined portion, D1 is a distance between an upstream end and a downstream end of a flat portion, ?1 is an angle between a reference plane and the first inclined portion in the flow direction, ?2 is an angle between the reference plane and the second inclined portion in the flow direction, ? is a distance between the reference plane and the flat portion, and L is a distance between the reference planes of the fins adjacent to each other. ?2 gradually decreases as a measurement direction of the angle is shifted from the row direction to the air flow direction and is minimum when the measurement direction is orientated in the air flow direction.