Holtec heat exchangers are engineered to meet the unique demands of nuclear applications such as cyclic loadings and high flow rates. Holtec International’s research and development effort has yielded many technology advances in the field of heat transfer apparatus. Two inventions, the “Non-Segmental Baffles” and “Precision Formed Stakes” have become staples in the industry. Holtec’s anti-vibration tubestakes prevent collisions between adjacent tubes in bundles susceptible to flow-induced vibrations. The non-segmental baffle is a Holtec innovation that protects tube bundles subjected to high volume shellside flows and prevents failure from flow induced vibration.
Non-Segmental Baffles
The Non-Segmental Baffle provides an ideal solution for non-condensable accumulation and resultant corrosion problems in condensers. The Non-Segmental Baffle is a tube support device providing isotropic support to the tube against lateral vibration and permits axial flow of the shellside fluid. Holtec’s non-segmental baffles are a lattice structure of integrally welded stainless steel strips, installed as a replacement or supplement to the standard drilled plate baffles to eliminate tube vibration without affecting the required thermal hydraulic characteristics of the equipment. Non-Segmental baffles are used by Holtec in a variety of heat exchange equipment since 1987.
Anti-Vibration Stake (AVS)
As its name implies, the Anti-Vibration Stake (AVS) is used to protect tubes in tubular heat exchangers from vibrating vigorously inside the shell-side space from fluid flow. Fluid-elastic whirling and turbulent buffeting are among the many mechanisms that cause the tube spans to vibrate excessively. Invariably, the underlying reason is a low fundamental frequency mode of the tube span. The frequency of a tube span is inversely proportional to its length. In a manufactured heat exchanger where cross baffles can not be added, the anti-vibration stakes (AVS) provide an effective means to reduce the unsupported tube span and thus increase its natural frequency. Addition of the AVS would add to increased shell-side pressure loss which should be considered by the heat exchanger designer.
The AVS has been most widely used in the retrofit and refurbishment of existing tube bundles. If a tube bundle vibrates, the AVS is a sure solution so long as the bundle is physically accessible.
The AVS is essentially a precision formed strip such that it can be inserted between the tube rows with modest force thus serving as a lateral point support to the tube. Experience indicates that a properly engineered AVS will not cause local wear of the tubes or lose its effectiveness over time.
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