Fluid films

The film pressure is defined as the difference between the surface tension of the pure fluid and that of the film-covered surface. While any method of surface tension measurement can be used, most of the methods of capillarity are, for one reason or another, ill-suited for work with film-covered surfaces with the principal exceptions of the Wilhelmy slide method (Section II-6) and the pendant drop experiment (Section II-7). Both approaches work very well with fluid films and are capable of measuring low values of pressure with similar precision of 0.01 dyn/cm. In addition, the film balance, considerably updated since Langmuir s design (see Section III-7) is a popular approach to measurement of V. 

Fluse D A and Leibler S 1988 Phase behavior of an ensemble of noninterseoting random fluid films J. Physique 49 605... 

The tenn tribology translates literally into the study of nibbing . In modem parlance this field is held to include four phenomena adhesion, friction, lubrication and wear. For the most part these are phenomena that occur between pairs of solid surfaces in contact with one another or separated by a thin fluid film. Adhesion describes the resistance to separation of two surfaces in contact to while friction describes their tendency to resist shearing. Lubrication is the phenomenon of friction reduction by the presence of a fluid (or solid) film between two surfaces. Finally, w>ear describes the irreversible damage or defonnation that occurs as a result of shearing or separation. 

External Fluid Film Resistance. A particle immersed ia a fluid is always surrounded by a laminar fluid film or boundary layer through which an adsorbiag or desorbiag molecule must diffuse. The thickness of this layer, and therefore the mass transfer resistance, depends on the hydrodynamic conditions. Mass transfer ia packed beds and other common contacting devices has been widely studied. The rate data are normally expressed ia terms of a simple linear rate expression of the form... 

Table 2. Typical Design Limits for Fluid-Film Hydrodynamic Bearings...

W. A. Gross, ed.. Fluid Film Eubrication, John Wiley Sons, Inc., New York, 1980. 

B. J. Hamrock, Fundamentals of Fluid Film Eubrication, NASA Reference Pubhcation 1255, U.S. Government Printing Office, Washiagton, D.C., 1991. 

When significant continuous loads have to be taken on a thrust washer, it is necessary to machine into the bearing surface a profile to generate a fluid film. This profile can be either a tapered wedge or occasionally a small step. 

The resistance to transfer of mass between a gas and a hquid is assumed confined to that of fluid films between the phases. Let... 

Figure 6-28. First forward mode on fluid film tilt pad bearings.

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... 

Gears, Fluid Film Bearings, Couplings, and Clutehes... 

Hydrodynamic whirl N > 2Nt Nf =, 5N Nf <, 5N built-up parts Fluid film bearings... 

Lund, J.W., Stability and Damped Critical Speeds of a Flexible Rotor in Fluid-Film Bearings, ASME No. 73-DET-103. 

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

Abramovitz, S., Fluid Film Bearings, Fundamentals and Design Criteria, and Pitfalls, Proceedings of the 6th Turbomachinery Symposium, December 1977, pp. 189-204. 

Garner, D.R., and Leopard, A.J., Temperature Measurements in Fluid Film Bearings, Proceedings of the 13th Turbomachinery Symposium, Texas A M University p. 133 1984. 

Herbage, B., High Efficiency Fluid Film Thrust Bearings for Turbomachinery, 6th Proceedings of the Turbomachinery Symposium, Texas A M University, December 1977, pp. 33-38. 

Modal balaneing is one of the proven methods for flexible rotor balan-eing. Modal balaneing has also been applied to problems of dissimilar lateral stiffness, hysteretie whirl, and to eomplex shaft-bearing problems. In many diseussions on modal balaneing fluid-film damping is not ineluded. In other... 

The liquid film seal uses metallic sealing rings and is liquid buffered to maintain a fluid film in the clearance area and thereby preclude gas leakage. It is not unusual in the screw compressor to find the radial bearing and seal combined. 

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