Improve the heat transfer coefficient, mainly from the tube side and shell side heat transfer enhancement factor to consider to improve. Many researchers in this area has a lot of research on, and achieved great results. This paper discusses the heat exchanger tube process heat transfer tubes --- change the shape or the inclusion of inserts in the pipe, introduced the spiral groove tube, striped tube, spiral flat tube, tube inserts, fin , scaling three inner tubes and fin tube and other enhanced heat transfer tube of progress.
1, spiral groove tube
Spiral pipe is a pipe wall with convex and the convex shaped tube, spiral groove on the wall in a phase transition and no phase change heat transfer significantly improved both inside and outside tube heat transfer coefficient, play a bilateral strengthening. Processing based on the surface of fluorescent tubes type spiral groove spirally corrugated tube with a single head and long divided, the main structural parameters are the groove depth e, slots and slot away from the rotation angle p β. United States, Britain, Japan, from 1970 to 1980, the spiral groove tube a lot of research [1]. South China University of Technology, Beijing Polytechnic University and Chongqing University, spiral fluted tube also were tested, and have achieved remarkable results. In addition, the study also showed that more than one head spirally fluted tube long spiral groove tube performance. At present, either from the heat transfer, flow resistance, scaling performance, or from no phase change phase change heat transfer and condensation heat transfer enhancement of spirally corrugated tube heat transfer from theory to practice has reached a high level. Further integration of computer hardware and software development, spiral fluted tube heat transfer simulation on different occasions and simulation, to find a large relational universal and optimized the structure of spiral fluted tube size will be the direction of future research.
2, striped tube
1974 years ago the Soviet Union first proposed stripes and pipes, it is a blank for the ordinary tube, the tube wall by simply rolling out of the groove and the vertical axis, while the formation of the tube around the protruding ring ribs. The strengthening mechanism is: When the tube when the fluid by the lateral rib ring, the axial vortex formed near the wall, increasing the boundary layer of the disturbance, is conducive to heat transfer through the boundary layer. When the vortex is about to disappear, the fluid then flows through to the next transverse ribs, the continuous generation of axial eddy current, and thus maintain a continuous and steady strengthening. Striped tube is mainly used to enhance single-phase fluid tube heat transfer, South China University The study found that, at the same velocity, the stripes and pipe flow resistance than the single head of small spirally fluted tube.
3, spiral flat tube
Switzerland Allares spiral flat tube is first put forward the company, the U.S. company Brown improved a Tube. The unique structure of the tube, the fluid in the spiral flow in the tube to promote turbulence level. Lianglong Hu [3] The experimental study shows that endometrial spiral flat tube heat transfer coefficient is usually a substantial increase than ordinary tubes, the most obvious at low Reynolds number, up to 2 to 3 times; as the Reynolds number, also can increase the heat transfer coefficient is usually more than 50%.
4, the insert
The type of tube insert a lot, there are: Twisted iron, spiral coil, spiral bands, spiral slice, twisted tape and static mixer and so on. Various inserts of the enhanced heat transfer mechanism can be divided into the following four:
(1) the formation of rotating flow;
(2) damage to boundary layer;
(3) Center for replacement fluid and wall have the role of the fluid;
(4) generation of secondary flow. Insert the tube has the advantage of the old equipment to transform the heat exchanger to improve its heat transfer performance. Heat transfer in the same time, to achieve the purpose of removal of dirt. Development of a UK company called Heatex CalGavin the insert, which consists of a set of extensions to the wall of the circular states of body composition, allows the tube side heat transfer efficiency from 2 to 15 times [4]. The company also developed a style called HitranMatrixElements wreath insert, could increase the pressure drop does not greatly improve the heat transfer coefficient under the conditions. Conditions for the liquid, can shell and tube heat exchanger tube heat transfer efficiency by 25 times; for gas conditions, the corresponding values can increase 5 times. In addition, compared with the normal flow rate, which inserts the ability to improve the scaling Tubes 8 to 10 times.
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