What is Petroff equation?
• Petroff’s equation is given as f = 2π2 (μns/p) (r/c) • (μns/p) & (r/c) are dimensionless parameters. • (μns/p) denotes the bearing modulus & (r/c) denotes clearance ratio.
What is Sommerfeld number in bearing?
In the design of fluid bearings, the Sommerfeld number (S) is a dimensionless quantity used extensively in hydrodynamic lubrication analysis. The Sommerfeld number is very important in lubrication analysis because it contains all the variables normally specified by the designer.
How does a journal bearing work?
In a journal bearing, the shaft rotates inside a loose-fitting bearing shell of softer, often porous, bearing material. Lubricant, such as oil, grease or a low-friction compound like PTFE or graphite is used between the surfaces. The shell is sometimes split into two halves.
How does a hydrodynamic bearing work?
Hydrodynamic bearings rely on bearing motion to suck fluid into the bearing, and may have high friction and short life at speeds lower than design, or during starts and stops. An external pump or secondary bearing may be used for startup and shutdown to prevent damage to the hydrodynamic bearing.
What are the difference between hydrodynamic and hydrostatic bearings?
Hydrostatic bearings are externally pressurized with a lubricant and do not rely on rotating of the shaft to develop a fluid film. Conversely, hydrodynamic bearings rely on the speed of the shaft to pressurize the fluid in the bearing and lift the shaft off the bearing.
Which of the following parameters are in the Petroff equation?
Petroff’s equation indicates that there are two important dimensionless parameters, rc and μnsp that govern the coefficient of friction and other frictional properties like frictional torque, frictional power loss and temperature rise in the bearing.
What is Raimondi and Boyd method?
Raimondi and Boyd (1958) gave a methodology for computer–aided solution of Reynolds equation using an iterative technique. For L/d ratios of 1, 1:2 and 1:4 and for bearing angles of 3600 to 600 extensive design data are available.
What is the difference between journal bearing and ball bearing?
Journal bearings require less radial space than rolling-element bearings but need more length axially. Journal bearings are more capable of managing shock and overload compared with ball and roller bearings. They can run quieter than rolling-element bearings, especially when the rolling-element bearings begin to wear.
Where is hydrodynamic bearing used?
Hydrodynamic bearings are commonly used in large turbines, generators, compressors, gearboxes and pumps in the power generation and oil, gas and chemical processing industries.
What was Petroff’s method of lubrication analysis?
Petroff’s method of lubrication analysis, which assumes a concentric shaft and bearing, was the first to explain the phenomenon of bearing friction.
How is Petroff’s law used to predict friction?
This method, which ultimately produces the equation known as Petroff’s Law, is useful because it defines groups of relevant dimensionless parameters, and predicts a fairly accurate coefficient of friction, even when the shaft is not concentric.
What causes lubricant build up on a bearing?
Insufficient surface area, a drop in the velocity of the moving surface, a lessening in the quantity of lubricant delivered to a bearing, an increase in the bearing load, or an increase in lubricant temperature resulting in a decrease in viscosity—any one of these—may prevent the buildup of a film thick enough for full-film lubrication.
Why do you need lubrication for a journal bearing?
Introduction •Lubrication reduces friction, wear and heating of mating parts • A shaft (or Journal) rotates within a sleeve (or bushing) and the relative motion is sliding. •Journal bearings are more applicable for extreme operational conditions (high loads and rotational speeds)