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Anti-vibration measures of heat exchanger pipes
Apr 06, 2020

Heat exchanger is a heat transfer equipment for heat transfer when there is a temperature difference between two or more kinds of fluids. It is widely used in the industries of petroleum, chemical industry, energy, metallurgy, refrigeration, medicine, electricity, food, etc., such as liquid phase heating, cooling, evaporation and concentration. There are two main reasons for the vibration of heat exchanger pipe: one is caused by external excitation source. One is fluid flow excitation, and is divided into tube side and shell side excitation vibration. Generally, the vibration amplitude of the flow excitation at the tube side is small and the harm is not serious, which can be neglected. However, when the flow rate is much higher than the normal flow rate, the tube side excitation should be considered. The vibration in the heat exchanger is mainly excited by the medium on the shell side. In addition, as the equipment becomes larger and the shell side velocity is increased as much as possible in order to enhance heat transfer, there are many cases of heat exchanger vibration induced by transverse flow of fluid. The methods to prevent vibration are as follows:

 

1. A longitudinal baffle is added to the heat exchanger to prevent acoustic vibration, so as to reduce the formation of non-axial elastic and mechanical waves, and to change the difference between the acoustic vibration frequency of the gas column and the turbulence chattering frequency. The vibration phenomenon can be reduced by this additional setting. The specific operation method is to add several longitudinal baffles in the shell along the flow direction and place them in the position of the wave belly of the acoustic vibration wave type, in order to change the characteristic length of the transverse dimension in the equipment.

 

2. On the premise of satisfying the heat transfer effect of the heat exchanger, in order to prevent the vibration of the tube bundle, the flow velocity of the fluid should be reduced as far as possible, the Reynolds number should be controlled within a certain range, the frequency of fluid-induced vibration in the shell side should be reduced, and resonance should be prevented. This is an effective and direct method to prevent the vibration of the bundle, but the heat transfer efficiency should be considered.

 

3. Increasing the natural vibration frequency of the pipe can greatly reduce the chance of resonance, and the most effective way is to reduce the span. The natural frequency of the pipe is inversely proportional to the span.

 

4. The most effective method to prevent the occurrence of fluid elastic vibration in the bundle is to increase the rigidity strength of the bundle and increase its natural frequency. For example, the supporting points of the pipe are appropriately increased to shorten the span length of the unsupported pipe, optimize the structure, increase the elastic modulus of the relevant components, increase the moment of inertia of the material, and increase the thickness of the pipe wall and baffle. In the design parameters that determine the inherent characteristics of the tube bundle, the influence of the pipe section radius is greater than the wall thickness, so the effective diameter of the pipe can be increased. It has been proved by practice that the diameter of the baffle tube hole is slightly larger than the outer diameter of the heat exchanger tube 0.25-0.35mm, which can effectively avoid the vibration of the tube bundle. At the same time, the circular corner with a certain radius is inverted to all the pipe holes on the baffle, which can effectively reduce the wear caused by the vibration of the tube bundle.

 

5. In the actual production process, the temperature and pressure often fluctuate frequently due to improper operation, which leads to the fatigue failure of the heat exchange tube bundle due to cyclic load. In order to improve the fatigue limit of the equipment, the startup and shutdown cycle of the equipment can be effectively controlled, and the corresponding detection instruments can be used for online real-time monitoring. Once abnormal conditions are found, the operation can be changed in time. In order to avoid the excessive fluctuation of the fluid in the tube bundle, the excessive change of the fluid flow velocity and the direct erosion of the heat exchanger tube bundle by the liquid flow medium, it can be taken to set up the impingement plate or the guide tube or the diverter at the fluid inlet of the heat exchanger tube bundle.

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