Squeeze films

Equation 3-40 is the expression for the squeeze film behavior of a rotating shaft under a dynamically fluctuating load. In the time interval 

Booth and Hirst [10] examined the squeeze film problem for two rigid circular parallel plates of radius separated by an oil film of thickness fi (h fi ) see Fig. 3-5. Starting with the Navier-Stokes equations in cylindrical coordinates, they obtained the relations 

These equations can be simplified and solved the original publication can be consulted for details. For an isoviscous liquid the integrated solution yields the Stefan equation  

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When normal hydrodynamic and squeeze-film action gives inadequate load support, the fluid may be pressurized externally before being introduced into the bearing film in the manner of Figure 2b and c. Such a procedure is common for starting and slow speeds with heavy machines, or with low viscosity fluids. 

This chapter discusses the most popular features and controls that are critical to turboexpander operations. Among those discussed are magnetic bearings, squeeze film dampers, radial fit bolts, valve arrangements for FCC expanders, FCC expander load shedding technology, and surge detection and avoidance. 

Squeeze film dampers have long been used to combat rotor dynamic and stability problems that conventional bearings cannot solve on turbomachinery rotor systems. The use of squeeze film dampers in problem process machinery has tainted it as a treat-the-symptom solution, and many users shy away from using squeeze film dampers for this reason. Also, their limited use is explained by the difficulty in accurately predicting performance, particularly with o-ring supported dampers. 

Source F. Y. Zeidan, Application of Squeeze Film Dampers," Turbomachinery International, September/October 1995. 

Certain facets of squeeze film dampers should be thoroughly understood to properly select the specific design required for a given application. Highlighting the theory of squeeze film dampers is helpful in dlls regard. 

The following describes some of the commonly used squeeze film dampers and introduces one of the more novel damper designs, which clearly has application in turboexpanders. Examples of the optimization process required in the design and selection of squeeze film dampers and their applications to solve stability and critical speed problems are also demonstrated. 

Squeeze Film Dampers without a Centering Spring... 

Figure 6-22. Squeeze film damper without a centering spring.

Figure 6-23. Schematic cf an c-ring suppcrted squeeze film damper.

These layouts are configured as shown in Figure 6-25. The cantilevered support ribs, along with die sector diey are supporting at bodi ends, form a centering spring element. The small gap between die sector and die outer ring forms die squeeze film damper clearance... 

Figure 6-25. Schematic of an integral centering flexure pivot spring squeeze film damper.

In process equipment, squeeze film dampers are primarily used to improve rotordynamic stability. They are commonly used as a last... 

Figure 6-26. Schematic of a split integral squeeze film damper.

The use of a squeeze film damper in series with the tilting pad bearings introduces flexibility and damping to the bearing support. The... 

The squeeze film damper in series with a fluid film bearing also provides a means for improving the synehronous response, an advantage rarely used with proeess type equipment. The tight vibration restrietions with the latest API speeifieations, and the even more restrietive speeifieations dietated by users, makes the squeeze film damper an attraetive and praetieal alternative to more eostly and time... 

SELF- aENCRATeO SQUEEZE FILM FLUID PRESSURE DISTRIBUTION... 

Figure 13-7. Modes of fluid-film lubrioation (a) hydrodynamio, (b) hydrostatio, (o) squeeze film, (d) hybrid.

G., Squeeze Film Lubrication of a Short Porous Journal Bear- [38]... 

Lin, J. R., Squeeze Film Characteristics Between a Sphere and [40] a Flat Plate Couple Stress Fluid Model, Camputers Structures, Vol. 75,2000, pp. 73-80. 

Pandey, A. K. and Pratap, R., Coupled Nonlinear Effects of Surface Roughness and Rarefaction on Squeeze Film Damping in MEMS Structures," 7. Micromech. Microeng., Vol. 14, 2004, pp. 1430-1437. 

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