Baffle rod and baffle plate heat exchanger

https://bbs.hcbbs.com/thread-1021961-1-1.html There are relevant discussions on the forum, and experts have provided detailed explanations, so I won’t repeat them here! Additionally, it is recommended to search for keywords related to the problems you need to solve first in the future, to improve learning efficiency!

Since the development of the baffle rod heat exchanger in the 1980s, it has been widely used in the petrochemical industry. SINOPEC Luoyang Research Institute prepared standard atlas for it at the end of the 1980s, and tens of thousands of such units must have been put into actual use.

The disadvantages of baffle rods are: 1. High processing difficulty； 2. It causes induced vibrations, leading to damage to the heat exchanger. The baffle rods cause the fluid to flow across the tube bundle; while this enhances heat transfer, it also induces vibrations in the fluid. The damage caused by these induced vibrations to the heat exchanger manifests itself in the following ways: 1) The tubes collide with each other, and when the vibration amplitude of the tubes is high enough to cause them to collide frequently, this leads to wear and thinning of the tube walls, eventually resulting in their destruction ； 2) The tubes continuously collide with the walls of the baffle rods due to vibration, resulting in tube rupture ； 3) The connection between the vibrating tube and the tube sheet is subjected to high stresses, which over time causes damage to the expansion joints and welds due to these stresses, leading to leaks at the joints ； 4) The tube suffers from stress fatigue due to repeated bending caused by vibration, and prolonged continuous vibration can lead to the tube breaking ； 5) Vibration-induced stress fluctuations can cause microdefects in the pipe to grow until cracks occur. For counterflow rod tube heat exchangers, measures to reduce the amplitude of induced vibrations include: 1) reducing the flow velocity across the tube bundle ； 2) Increase the natural frequency of the heat transfer element, such as by increasing the wall thickness of the tube or reducing its span. Obviously, these two measures are contradictory, because to reduce the span of the tubes, it is necessary to increase the number of baffle rods, and an increase in the number of baffle rods in turn leads to an increase in the flow velocity within the transverse tube bundle. At this point, to reduce the flow velocity, the only option is to increase the diameter of the heat exchanger shell; this not only increases the volume of the heat exchanger but also, as the flow velocity decreases, the heat transfer coefficient drops. 3. The presence of flow dead zones and leakage currents results in an actual heat transfer efficiency that is much lower than the theoretical value ； The existence of flow dead zones and leakage flow are another major issue in baffle rod heat exchangers. Due to the fact that the leakage flow through the gaps between the shells and that through the gaps in the baffle rods flow longitudinally, whereas the main flow flows transversely, their contribution to heat exchange is very low. In addition, there is a flow dead zone between the baffle rods and the cylinder; when the flow velocity is low, this reduces the effective heat transfer area involved in heat exchange by 25% to 30%. These are all the reasons for the low heat transfer coefficient of shell-and-tube heat exchangers. In addition, the low flow velocity on the shell side and the presence of dead zones can also lead to dirt deposition, scaling, and corrosion. In addition, the shell-side flow velocity is also controlled to prevent induced vibration. 4. High flow resistance on the shell side: As the fluid repeatedly passes sideways across the tube bundle and continuously changes direction, this results in high flow resistance on the shell side. When designing baffled heat exchangers, this resistance on the shell side often becomes a key factor that influences the selection of the equipment, and it also increases the pumping power required on the shell side. 5. Prone to scaling. 6. When used as a cold oil cooler, the Reynolds number in the shell side of the counterflow rod heat exchanger is relatively low.

The baffle rod heat exchanger was developed and applied in the last century by Phillips Petroleum in the United States to avoid the vibration-induced damage problems associated with baffle plate heat exchangers. In China, Sinopec also carried out development and industrial application in the early 1980s; at the same time, it expanded its efforts to develop and apply baffle rod condensers. After successful industrial trials, these technologies were quickly put into widespread use, and by the early 1990s, a series of standard diagrams had been established. The relationship between the baffle rod in Building 4# and heat exchangers with baffle plates needs to be understood in the opposite way to be basically correct.