floating head heat exchanger

　　floating head heat exchangerOne end of the tube plate is fixed to the shell, while the other end of the tube plate can freely float inside the shell, as shown in Figure 1. The shell and tube bundle are free from thermal expansion, so when the temperature difference between the two media is large, there is no thermal stress generated between the tube bundle and the shell. The floating head end is designed as a detachable structure, making it easy to insert or remove the tube bundle from the shell (it can also be designed as non detachable), which provides convenience for maintenance and cleaning. But the structure of the heat exchanger is relatively complex, and the floating end small cover cannot know the leakage situation during operation, so special attention should be paid to its sealing during installation.

　　floating head heat exchangerThe structure of the floating head part can be designed in various forms according to different requirements. In addition to considering the free movement of the tube bundle inside the equipment, the convenience of maintenance, installation, and cleaning of the floating head part must also be taken into account. The structure shown in Figure 2 has a floating head that can move freely, but the tube bundle cannot be withdrawn from the shell. The advantage is that under the same shell diameter, there are more tubes arranged and the heat transfer area increases. However, for situations where the outer wall of the heat exchange tube requires frequent cleaning, this structural form is not suitable.

The hook and loop structure shown in Figure 3 must consider the outer diameter Do of the floating head tube plate during design. The outer diameter should be smaller than the inner diameter Di of the shell, and it is generally recommended that the gap b1 between the floating head tube plate and the inner wall of the shell be 3-5 mm. In this way, when the hook ring at the floating head is removed, the tube bundle can be extracted from the shell for maintenance and cleaning. The floating head cover can only be assembled after the tube bundle is installed, so the necessary space for the floating head cover during assembly should be considered in the design.

Hook rings play an important role in ensuring the sealing of the floating head end and preventing leakage between media. With the development of design and manufacturing technology of floating head heat exchangers, as well as the accumulation of long-term usage experience, the structural form of hook rings has also been continuously improved and perfected.
Hook rings are generally of a double open structure, requiring reliable sealing, simple and compact structure, easy manufacturing, and convenient disassembly and assembly.
The commonly used forms of hook loops are shown in Figure 4. Figure 4 (a) shows the A-type hook ring, which was widely used in floating head heat exchangers before the 1950s. The thickness of the hook and loop is determined by strength calculation. Due to the distance between the bottom of the hook ring and the floating head tube plate, the dead angle of the medium in the shell side of the floating head increases, reducing the effective heat transfer area of the tube bundle. Figure 4 (b) shows a B-type hook ring, which is an imported type from abroad. The thickness of the hook ring is determined based on the thickness of the floating head tube plate plus empirical values. Generally, the thickness of B-type hook rings is thinner than that of A-type hook rings. Tighten the double headed bolts of the floating head, type A is longer than type B, and the stability of the bolts is also poor. The inclined slots of the A-type floating head tube plate and hook ring are both 12 °. The B-type structure adopts different inclination angles for the inclined slots of the floating head tube plate and the hook ring. The inclination angle of the tube plate inclined slot is 18 °, while that of the hook ring is 17 °, and the thickness of the hook part is 30mm. The gap between the outer diameter of the tube plate and the inner diameter of the hook ring is controlled at 0.25-0.4mm. In this way, when tightening the bolts, the gap will disappear, allowing the pipe plate to support the hook ring and control the angle of the hook ring, ensuring that the bending deformation of the bolts is within the allowable range and effective sealing.

The structure shown in Figure 5 allows for easy maintenance, installation, and cleaning outside the shell without the need to remove the floating head before installing or extracting the tube bundle. However, the diameter of the shell of this structure is larger than that of the floating head heat exchanger mentioned above. The floating head structure can be made in two forms as shown in Figure 5 (a) and (b).

Figure 6 shows another form of floating head heat exchanger, which is a one-way floating head heat exchanger with a packing box structure at the outlet of the tube side. The structure in Figure 6 (a) should be designed with the outer diameter of the floating end tube plate smaller than the inner diameter of the shell, so that the tube bundle can be extracted from the shell. The outlet pipe connected to the floating head cover should be selected as standard as possible to facilitate installation and manufacturing.