Flow induced vibration

Bellows can vibrate, both from internal fluid flow and externally imposed mechanical vibrations. Internal flow liner sleeves prevent flow-induced resonance, which produces bellows fatigue failure in minutes at high flow velocities. Mechanically induced resonant vibration is avoided by a bellows with a natural frequency far away from the forcing frequency, if known. Multiple-ply bellows are less susceptible to vibration failure because of the damping effect of interply friction. 

Flow-induced tube vibration occurs at critical fluid velocities through tube banks, and is to be avoided because of the severe damage that can result. Methods to predict and correct vibration problems may be found in Eisinger Trans. ASME J. Pressure Vessel Tech., 102, 138-145 [May 1980]) and Chen J. Sound Vibration, 93, 439-455 [1984]). 

This aspect is not included here, but is related to optical flow diagnostics. It is based again on the principle of the optical Doppler effect. Multifunctional equipment is available for noncontact measurements of flow-induced vibration on surfaces of structural elements, for acoustic measurements, and for calibration of accelerometers and vibration transducers. 

The maximum unsupported tube spans in Table 10-6 do not consider potential flow-induced vibration problems. Refer to Section 6 for vibration criteria. 

Chenoweth, J. W. and J. Taborek, Flow-Induced Tube Vibration Data Banks for Shell-and-Tube Heat Exchangers, Heat Transfer Eng,Y. 2, Oct.-Dec. (1980) p. 28. 

Similar considerations apply to the selection of pressure drops where there is freedom of choice, although a full economic analysis is justified only in the case of very expensive units. For liquids, typical values in optimised units are 35 kN/m2 where the viscosity is less than 1 mN s/m2 and 50-70 kN/m2 where the viscosity is 1-10 mN /m2 for gases, 0.4-0.8 kN/m2 for high vacuum operation, 50 per cent of the system pressure at 100- 200 kN/m2, and 0 per cent of the system pressure above 1000 kN/m2. Whatever pressure drop is used, it is important that erosion and flow-induced tube vibration caused by high velocity fluids are avoided. 

When a high-pressure drop is utilised, care must be taken to ensure that the resulting high fluid velocity does not cause erosion or flow-induced tube vibration. 

ESDU 87019 (1987) Flow induced vibration in tube bundles with particular reference to shell and tube heat... 

Yan Y, Thorpe RB, Pandit AB (1988) Cavitation noise and its suppression by air in orifice flow. In Proceedings of the International Symposium on Flow Induced Vibration and Noise, Chicago, ASME, pp 25 10... 

The underlying mode of action, involving as it does the flow induced vibration of a steel blade, immediately suggests the problem of erosion by particulate matter - the sand blasting effect. Despite this apparent drawback a whistle has been used in this Scott Bader process over several years without blade replacement. 

If the oscillation of motion of fluid with respect to an electrode is imposed upon a stationary system and the perturbation is not small with respect to the steady-state then new effects can appear. For example, the flow induced by the motion can have both an oscillating and a steady component (the latter due to the interaction between viscous and inertial effects in the boundary layer) and the oscillating part may have components which are harmonics of the imposed oscillation. In some cases the stationary component of the induced flow can, indeed, dominate the oscillating component. These effects are particularly seen for vibrating electrodes. 

Blevins—Flow-Induced Vibration, Van Nostrand-Reinhold. 

Standard pipe sizes will be used for the inlet and outlet nozzles. It is important to avoid flow restrictions at the inlet and outlet nozzles to prevent excessive pressure drop and flow-induced vibration of the tubes. As well as omitting some tube rows (see Section 12.5.4), the baffle spacing is usually increased in the nozzle zone, to increase the flow area. For vapours and gases, where the inlet velocities will be high, the nozzle may be flared, or special designs used, to reduce the inlet velocities Figure 12.17a and b. The extended... 

Moretti, P. M. (1973) Am. Inst. Chem. Eng. 74th National Meeting, New Orleans, March 14th. A critical review of the literature on flow-induced vibrations in heat exchangers. 

In Solids, heal conduction is due to two effects the lattice vibrational waves induced by the vibrational motions of the molecules po.sitioned at relatively fixed positions in a periodic manner called a lattice, and the energy transported via the free flow of electrons in the solid (Fig. 1—28). The Ihermal conductivity of a solid is obtained by adding the lattice and electronic components. The relatively high thermal conductivities of pure metals arc primarily due to the electronic component. The lattice component of thermal conductivity strongly depends on the way the molecules are arranged. For example, diamond, which is a liighly ordered crystalline solid, has the highest known thermal conductivity at room temperature. 

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