What is Petroff's equation?

Q.  Which of the following parameters in Petroff's equation f = 2π2 (μns/p) (r/c) is/are dimensionless?
- Published on 23 Sep 15

a. r/c
b. μns/p
c. Both a. and b.
d. None of the above

ANSWER: Both a. and b.

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    Discussion

  • Sravanthi   -Posted on 05 Oct 15
    • Petroff was the first to explain phenomenon of hydrodynamic journal bearing and assumed that the journal and bearing are concentric and there is no eccentricity between journal and bearing. This assumption is satisfied only if rotation speed, viscosity of lubricant is high and projected area of bearing is large.

    • 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.

    • Petroff's equation estimates co-efficient of friction for light loaded bearings.

    • Now-a-days Reynold's equation based on fully developed hydrodynamic theory is available, hence Petroff's equation hardly used.

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