Heat exchanger. The heat exchanger comprises atleast one heat exchange tube disposed for heat transfer between two fluids of differential temperatures. One fluid flows through the heat exchange tube and the other fluid flows over the heat exchange tube. The heat exchanger further comprises atleast one tubular turbulator for heat transfer between the two fluids located in contact with the heat exchange tube along the length of the heat exchange tube. The turbulator comprises a flexible wiry helical structure having a plurality of windings of a thermally conducting material wire arranged along the length thereof. The windings have uniform diameter and are held together at close pitch distance with a thermally conducting springy material holding wire running through the helical structure.