Wave fins

Wave fins which are disposed inside a heat exchanger housing of a heat exchanger in order to cause a turbulent flow of fluid through direct contact with the fluid. The wave fins include a plurality of hills, a plurality of valleys and a plurality of sidewalls. The hills and valleys are connected to each other via the plurality of sidewalls. The sidewalls partition fluid passages between the hills and the valleys through which fluid passes. The hills, the valleys and the sidewalls form main waveforms that extend in a longitudinal direction so as to be waved in a first radius of curvature. One or more bent portions are formed on intermediate portions of the main waveforms, the bent portions being connected to remaining portions of the main waveforms so as to be bent at a second radius of curvature.