The perfect heat exchanger should meet the following basic requirements when designing or selecting:
(1) Reasonably achieve the specified process conditions;
(2) The structure is safe and reliable;
(3) Easy to manufacture, install, operate and maintain;
(4) Economically reasonable.
The one end tube plate of the floating head heat exchanger is fixed to the casing, and the tube plate at the other end can float freely in the casing, and the casing and the tube bundle are free to expand, so when the temperature difference between the two media is large, the tube bundle and No temperature difference stress is generated between the housings. The floating end is designed as a detachable structure so that the tube bundle can be easily inserted or withdrawn from the housing. (Also designed to be unremovable). This provides convenience for inspection and cleaning. However, the structure of the heat exchanger is complicated, and the floating end small cover cannot know the leakage during operation. Therefore, pay special attention to the seal when installing.
The structure of the floating head portion of the floating head heat exchanger can be designed in various forms according to different requirements. In addition to the necessity of free movement of the tube bundle within the device, it is also necessary to consider the convenience of inspection, installation and cleaning of the floating head portion.
The outer diameter Do of the floating tube sheet must be considered in the design. The outer diameter should be smaller than the inner diameter Di of the casing. Generally, the gap between the floating head tube plate and the inner wall of the casing is recommended to be b1=3~5 mm. Thus, when the hook of the floating head is removed, the tube bundle can be withdrawn from the housing. It is convenient for inspection and cleaning. The floating head cover can only be assembled after the tube bundle is installed, so the necessary space for ensuring the floating head cover during assembly should be considered in the design.
The hook ring plays an important role in ensuring the sealing of the floating end and preventing the leakage between the media. With the development of the design and manufacturing technology of the steamed-head heat exchanger and the accumulation of experience in the long-term use, the structural form of the hook and loop has also been improved and improved.
The hooks are generally split-type structures, requiring reliable sealing, simple and compact structure, and convenient for manufacturing and disassembly.
With its high reliability and wide adaptability, the floating head heat exchanger has accumulated rich experience in long-term use. Despite the challenges of new heat exchangers that have emerged in recent years, they have in turn contributed to their own development. Therefore, it has so far been dominated in various heat exchangers.
The tube forms the heat transfer surface of the heat exchanger, and the size and shape of the tube have a large effect on heat transfer. When a small diameter pipe is used, the heat exchange area per unit volume of the heat exchanger is larger, the equipment is relatively compact, the metal consumption per unit heat transfer area is small, and the heat transfer coefficient is also high. However, it is troublesome to manufacture, and the pipe is easy to scale and difficult to clean. Large diameter tubes are used for viscous or dirty fluids, and small diameter tubes are used for cleaner fluids.
The choice of pipe material should be based on the pressure, temperature and corrosivity of the media.
The arrangement of the tubes of the heat exchanger on the tubesheet not only considers the compactness of the equipment, but also the properties of the fluid, the structural design and the manufacturing and manufacturing aspects. There are four standard arrangements for the tube on the tubesheet: an equilateral triangle and a regular triangle arrangement for cleaning the shell-side media without mechanical cleaning. The square and the corner square arrangement can make the small bridge between the tubes form a straight channel, which is easy to be cleaned by machinery, and is generally used in the case where the tube bundle can be taken out between the tubes for cleaning.
In addition, for multi-tube heat exchangers, a combined arrangement method is often used, which generally adopts a triangular arrangement in each process, and a square arrangement is often used between the processes, so that the position of the partition plate is conveniently arranged.
When the heat exchanger has a large diameter and a large number of tubes, the heat exchange tubes must be arranged as much as possible in the arcuate space around the tube bundle. This not only effectively increases the heat transfer area, but also prevents short-circuiting of the shell-side fluid in the arcuate region to adversely affect heat transfer.
The choice of the center distance of the heat exchange tubes on the tube plate should take into account the compactness of the structure, the heat transfer effect, and the strength of the tube sheet and the space required to clean the outer surface of the tube. In addition to this, the method of fixing the tube on the tube sheet is also considered. If the spacing is too small, when the welding connection is used, the welds of the adjacent two tubes are too close, and the quality of the weld is not easily protected by heat; if the expansion is used, the pressing force may cause excessive deformation of the tube sheet and loss. The bond between the tube and the tube sheet. The center distance of the heat transfer tubes generally used is not less than 1.25 times the outer diameter of the tubes.
When the heat exchanger requires more heat exchange area and the pipe cannot be made too long, the diameter of the casing must be increased to arrange more pipes. In order to increase the tube flow rate and increase the heat transfer effect, the tube bundle must be split so that the fluid flows through the tube bundles in sequence.
In order to make the heat exchanger into a multi-tube process, a certain number of partitions can be respectively arranged in the pipe box at one end or both ends.