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LINN, IRONS—POWER LOSSES IN HIGH-SPEED JOURNAL BEARINGS 627C. D. W i l s o n . 28 In their paper, the authors take into accountthe quantity of oil flowing through the bearing. This is animportant factor which has been long neglected in calculatingbearing power losses. Over 2 years ago, the writer conductedmany power-loss tests on high-speed bearings. One of thefirst things noticed was the considerable effect that the oil flowhad upon the power loss. When the test data were plotted inthe conventional manner (i.e., coefficient of friction as a functionof ZN/p), it was found that a separate and distinct curve wasobtained for each rate of oil flow to the bearing.In large high-speed turbine bearings, more oil is usually circulatedthan the minimum required for stable operation. Thisis done in order to provide a large factor of safety and to keepthe operating temperatures within the limits of current practice.Much of the excess oil supplied to the bearing spills out the endswithout passing through the load-carrying portion of the bearing.When the oil flow to the bearing is changed, a greater or lesspercentage of the oil is by-passed in this way. This undoubtedlytest results obtained with different oil flows were found to beconsistent for the same bearing.In order to check test data obtained with bearings of differentdiameters and loads, however, it was found necessary to modifyfurther the ZN/p relation by multiplying it by the diameter dand by omitting the unit load p. This resulted in the empiricalrelationTest data showing this relation for two different types ofbearings are shown in Fig. 17 of this discussion. One curveF ig . 17R e s u l t s o f A l l i s - C h a l m e b s T e s t s o n 23 D i f f e r e n tB e a r i n g sresults in a different temperature distribution inside the bearingfor each rate of oil flow and makes the determination of themean viscosity of the oil film extremely difficult. The authorsin their paper have taken this into account by modifying theviscosity value of the oil at the average bearing temperature bythe actual oil flow in gallons per minute. The writer, in correlatinghis own test data, found that the relation / = {ZN/p)agreed well with the test results when the viscosity Z was expressedas the ratio of the oil-outlet viscosity Zi divided by thesquare root of the oil-inlet viscosity Z2. By expressing the viscosityterm as a function of both the inlet and outlet viscosities,the temperature rise in the bearing is taken into account, and28 Steam Turbine Engineering D epartm ent, Allis-Chalmers M anufacturingCompany, Milwaukee, Wis. Mem. A.S.M.E.shows the relation for bearings with a groove cut in the top halfof the bearing and the other curve shows the relation for similarbearings without the groove. The test data represent tests ontwenty-three different bearings, ranging in size from 2V2 in.diam X 3V2 in. long, to 17 in. diam X 18 in. long, running atspeeds between 1500 rpm and 8000 rpm. Oil flows were variedfrom 1.2 gpm in the smaller bearings to over 100 gpm in thelarger bearings. One series of tests was made on a 12-in-diambearing running at 3600 rpm with various oil flows, ranging from16 gpm up to 100 gpm, so as to study the effect of oil flow on thepower losses. Four different oils having Saybolt Universal viscositiesof 150, 210, 350, and 560 at 100 F were used.All of the tests were made on commercial bearings operatingin standard pedestals as set up for regular shop tests. Powerlosses were determined by the heat-balance method. Inlet andoutlet temperatures were measured by test thermometers andoil flows were measured with positive-displacement oil meters.Bearing loads were limited by commercial practice to between60 psi and 175 psi. Referring to Fig. 17 of this discussion, it isinteresting to note the reduction in the coefficient of friction fora constant temperature rise and constant speed when a grooveis cut in the top half of the bearing. For a constant oil flow,tests showed that the power loss in a 12 X 12 in. bearing runningat 3600 rpm was reduced by more than 20 per cent whena groove was cut in the top half of the bearing and the bearingwas retested under otherwise identical conditions.The power-loss formula for bearings with a groove cut in the