Twisted tube is a kind of enhanced heat transfer tubes that firstly presented by Swedish Alards Company, and then improved by the USA’ Koch Heat Transfer Company, LP.
Fig. Structure of twisted tube Fig. Twisted tube with carbon steel, stainless steel, copper
Structure and manufacture of twisted tube
The structure feature of twisted tube is that every cross section is an oval, when when assembled into heat exchangers they exchanger 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.
Enhanced heat transfer principles of twisted tube
The unique structure of twisted tube can make the flow in tube pass and shell pass in the spiral motion at the same time, by this way it enhanced the turbulent intensity. The heat transfer coefficient of the twisted tube is 40% higher than the normal one, but the pressure drop is almost the same.
Advantages of heat transfer with twisted tube
Fig. Stereogram of the twisted tube (Stainless steel) Fig.Stereogram of the twisted tube (Carbon steel) Fig. Stereogram of the twisted tube (Cooper)
Seamless steel twisted tubes used for producing heat exchangers are complete ones without joints. Common materials used in steel tubes shows in bellow chart。
Specification of twisted tube
Fig. Basic dimension parameter figure of twisted tube
Note: The above table is the basic parameter of standard twisted tube. Twisted tube can be manufactured as the St and L, if there are special requirements.
Application of the Twisted tube
As twisted tube has been fast developed and improved in recent years, it is much more reliable and effective, which can almost be used in all kinds of shell and tube heat exchangers. More than 1000 twisted tube heat exchangers have been used since 1984, which can be used in gas-gas, liquid-liquid and liquid-gas heat transfer process, including chemistry, petroleum, food, papermaking, electric power, metallurgy, mining, and urban heating industries.