A heat exchanger is a heat transfer device that transfers heat between two or more fluids when there is a temperature difference. It is widely used in industries such as petroleum, chemical, energy, metallurgy, refrigeration, pharmaceuticals, power, and food for liquid-phase heating, cooling, evaporation, and concentration. There are two main causes of vibration in heat exchanger tubes: one is external excitation sources, and the other is fluid flow-induced vibration, which can be further divided into tube-side and shell-side vibrations. Generally, tube-side flow-induced vibrations have small amplitudes and are not very harmful, so they can be ignored. However, tube-side vibrations only need to be considered when the flow velocity is much higher than normal. Vibrations within the heat exchanger are mainly caused by the shell-side medium. Even at normal flow velocities, shell-side flow can cause significant vibrations, posing the greatest risk to the heat exchanger. Furthermore, with the increasing size of equipment and the pursuit of higher shell-side flow velocities to enhance heat transfer, instances of heat exchanger vibrations induced by lateral fluid flow are becoming increasingly common. Therefore, methods to prevent vibration include:
1. Adding longitudinal baffles to the heat exchanger prevents acoustic vibration, thereby reducing the formation of non-axially transmitted elastic and mechanical waves and altering the differences between the acoustic vibration frequency and turbulent chattering frequency of the air column. This additional arrangement reduces the occurrence of vibration phenomena. Specifically, several longitudinal baffles are added to the shell along the flow direction, positioned at the antinodes of the acoustic vibration wave pattern, to change the characteristic length of the transverse dimension of the equipment.
2. To prevent tube bundle vibration while ensuring heat transfer efficiency, the fluid flow velocity should be reduced as much as possible to keep the Reynolds number within a certain range, thereby lowering the frequency of shell-side fluid-induced vibration and preventing resonance. This is a relatively effective and direct method to prevent tube bundle vibration, but heat transfer efficiency must also be considered, and a balance must be struck between the two.
3. Increasing the natural frequency of the tube can greatly reduce the chance of resonance. The most effective way is to reduce the span. The natural frequency of the tube is inversely proportional to the span. If the span is halved, the natural frequency will increase by about three times.
4. The most effective way to prevent fluid elastic vibration in tube bundles is to increase their rigidity and natural frequency. This can be achieved by appropriately increasing the number of support points on the tubes, shortening the unsupported span, optimizing the structure, increasing the elastic modulus of relevant components, increasing the moment of inertia of the material, and increasing the thickness of the tube walls and baffles. Among the various design parameters that determine the inherent characteristics of the tube bundle, the influence of the tube cross-sectional radius is greater than that of the wall thickness; therefore, the effective diameter of the tubes can be increased. Practical experience has shown that a baffle orifice diameter slightly larger than the outer diameter of the heat exchange tubes by 0.25–0.35 mm can effectively prevent tube bundle vibration. Simultaneously, rounding all orifices on the baffles with a certain radius can effectively reduce wear caused by tube bundle vibration.
5. In actual production processes, frequent fluctuations in temperature and pressure due to improper operation often lead to cyclic loads and fatigue failure of the heat exchanger tube bundle. To improve the fatigue limit of the equipment, the start-up and shutdown cycles of the equipment can be effectively controlled, and appropriate testing instruments can be used for online real-time monitoring. Once an abnormality is detected, the operating conditions can be changed in a timely manner. To avoid excessive pulsation and velocity changes in the fluid within the tube bundle, and to prevent the liquid medium from directly scouring the heat exchanger tube bundle, measures such as installing anti-scouring plates, guide tubes, or flow dividers at the fluid inlet of the heat exchanger tube bundle can be taken.
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