Design Contents |
JOURNAL BEARING WITH HYDRODYNAMIC LUBRICATION -
Effects of Variation of oil Viscosity with Temperature |
1. Introduction
This page shows the results of running two Scilab programmes, one of which assumes the
oil viscosity remains constant, results in column 2, and one which re-calculates the oil viscosity as the oil
temperature rises, results in columns 3 to 6.
The computation assumes that the oil at the line of maximum oil film thickness is at the
A difficulty has been to develop an equation that is a reasonable fit to published data of how absolute viscosity varies with temperature - consequently the only data included in the first version of the program for viscosity as a function of temperature is for SAE grade 30 (engine) oil. The equation used is based on one published by A S Seireg and S Dandage (1):
Viscosity = Viscosity_{o} exp[b/(T + 95)], b is a constant with units of ^{o}F and T is the temperature in ^{o}F. The viscosity_{o} was in reyn. The programme uses SI units so the constants in the original data have been converted, however accuracy is probably little better than 8%.
I plan on providing more data for other grades soon.
2. Notes About the table:
Column 2 calculation results are for constant viscosity.
Where 2 entries are shown in the Inputs of a single column (e.g: viscosity, number of iterations), there
will be 2 entries in all the Result cells affected.
The 'Load' input is the 'design specification', actual load carried is result: 'Resolved load'.
The 'Average projected pressure' is based on the design specification load, above.
Columns 3 - 4 are from the programme which adjusts the viscosity according to the temperature as part of
the iterative solution.
In Column 4, the eccentricity ratio has been increased from 0.59 (col. 3) to 0.62 which increases the resolved
load carrying to that of the value shown for the constant viscosity programme (r.h. entry in col. 1).
Inputs | 2. Const. Viscosity | 3. Var. Visc. | 4. | ||
Journal dia, mm | 40 | ||||
Journal legth, mm | 40 | ||||
Radial clearance, mm | 0.04 | ||||
Load, N | 2500 | ||||
Shaft RPM | 1800 | ||||
Oil viscosity initially, Pa.s | 0.0256 | ||||
No. circumferential intervals | 180 | ||||
No. longitudinal intervals | 16 | ||||
SoR factor | 0.9 | ||||
Number of iterations to be used | 2000, 5000 | 5000 | 5000 | ||
Initial oil temp. ^{o}C | 60 | ||||
Eccentricity ratio | 0.59 | 0.59 | 0.62 | ||
Oil density, kg/m^{3} | 850 | ||||
Specific heat of oil, J/kg.^{o}C | 1800 | ||||
Oil supply pressure, Pa | 100000 | ||||
Oil supply hole dia. mm | 4 | ||||
Calculated results | |||||
Sommerfeld no. | 0.1229 | 0.1229 | 0.1229 | ||
Av. Proj. Pressure, MPa | 1.56 | 1.56 | 1.56 | ||
Friction force, N | 15.02 | 15.02 | 15.457 | ||
Friction power, w | 56.6 | 56.6 | 58.27 | ||
Oil flow, l/s | 0.003578 | 0.003578 | 0.00376 | ||
Oil temp. rise, ^{o}C | 10.34 | 10.34 | 10.129 | ||
Load parallel to min oil film, N | 1467, 1484 | 1322 | 1551 | ||
Load perpendicular to min. oil film, N | 1870, 1903 | 1759 | 1930 | ||
Resolved load, N | 2377.2, 2413.959 | 2201.1 | 2476.37 | ||
Angle of attitude, ^{o} | 51.9, 52 | 53 | 51.2 | ||
Maximum pressure, MPa | 3.581, 3.6287 | 3.253 | 3.76 | ||
Angle of max. pressure past downward vertical, ^{o} | 19.9, 20.06 | 19.1 | 19.2 |
A Java Applet to assist with journal bearing design is given here
Listing of Scilab journal bearing programme - constant viscosity.
Listing of Scilab journal bearing programme - with viscosity varying as a function of temperature.
Comparison of Raimondi and Boyd chart result with Java applet (above) click here
I plan on updating the notes to give information about how the increase in temperature in reducing the oil viscosity effects the load carrying capability and the minimum oil film thickness.
Reference:
'Empirical Design Procedure for the Thermodynamic Behaviour of Journal Bearings', Lubrication Technology,
vol. 104, April 1982, pp. 135-148.
Back to notes on hydrodynamic lubrication
David J Grieve, Revised: 9th February 2015
Contact the Author:
Please contact me for comments and / or corrections or to purchase the book, at: davejgrieve@aol.com