The structure feature of twisted tube is that every cross section is an oval, when assembled into heat exchangers they can be mixed bundles (that is, the mix of twisted tubes and bare tubes), and also can be a pure twisted tube bundle.

The manufacturing process of twisted tube includes:"partial pressure" and "distortion". The tube’s cross section is nearly an ellipse, of which the ratio of long axis and short axis is designed according to the flow velocity in tubes passes and shell passes of heat transfer tubes. When the flow rate in tube pass is low, the ratio of the long axis and short axis shall be increased, or the flow surface shall be reduced in order to increase the flow rate.