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    turbulence pulsating is proximal or equal to natural fre-
    quency of tube, fierce vibration will take place.
     
    2.4. Fluid-Elastic Whirling
     
    This is characterized by tubes vibrating in an orbital or
    “whirling” manner, once sufficient energy is available
    for resonance to occur. This motion is produced when
    the shell side flows across the tubes causes both lift and
    drag movement of tubes at their natural frequencies. It
    can lead to a “runaway” condition if the energy supplied
    to tubes cannot be absorbed by the system damping and,
    thereby, lead to failure of tubes due to flow-induced vi-
    bration. Such a failure is likely to occur if the cross flow
    velocity is greater than a critical velocity.
     
    2.5. Acoustic Resonance
     
    Acoustic resonance occurs only on the condition that
    shell-side fluid is gas. When gas flows across tube bun-
    dle, acoustic standing waves, which is perpendicular to
    both tubes and flow direction, may come into being and
    be reflected repeatedly by inner wall of heat exchanger.
    Meanwhile, as gas flows across tube bundle, Karman’s
    vortex street comes into being behind tubes. And when
    frequency of vortex street accords with the frequency of
    acoustic standing waves, the couple will come and all the
    kinetic energy of flow media will be transmuted to acous-
    tic pressure waves, thereby vibration and strong noise will
    appear in heat exchanger.
     
    3. Problem Definition & Objective
     
    Flow-induced vibration analysis of a shell and tube heat  
    exchanger is an integral element of its thermal design. A
    proper design is one that is absolutely safe against failure
    of tubes due to flow induced vibration. Most sophisti-
    cated thermal design software packages carry out vibra-
    tion analysis as a routine ingredient of thermal design.
    This is essential since it is during thermal design that the
    geometry of a heat exchanger is finalized and it is this
    same geometry, along with flow, physical and property
    parameters, determines whether the given heat exchanger
    is safe against failure of tubes due to flow-induced vibra-
    tions. Flow-induced vibration is a very complex subject
    and involves the interplay of several parameters, many of
    which are not very well established. Although many cases
    of failure of tubes due to flow-induced vibration has been
    reported in the past several years, and an understanding of
    the factors responsible for these failures leave much to be
    desired. The literature depicts several interesting studies
    on specific facets of the vibration problem; however, very
    few investigations have considered the specific problems
    associated with shell and tube heat exchangers.  
    Hence in order to provide a simple solution to above
    stated problem, in this work Flow-induced Vibration
    Analysis of a STHE is performed to optimize the design
    Parameter. It is found that the FVA of STHE helps in
    achieving optimization in design of STHE by prevention
    of tube failure caused due to flow induced vibration. 5. Flow-Induced Vibration Analysis [FVA]
     
    Table 2  shows the Flow-Induced Vibration Analysis
    Results of STHE by using HTRI software.
     
    6. Results & Discussion
     
    From Figure 2, it is observed that the bundle shell acous-
    tic frequency decreases from  inlet to exit, hence the na-
    ture of the plot is parabolic. Acoustic resonance is due to
    gas column oscillation and is excited by phased vortex
    shedding. The oscillation creates an acoustic vibration of
    a standing wave type. The generated sound wave will not
    affect the tube bundle unless the acoustic resonant fre-
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