We find changes in conductance that are caused by this run-in process. Bearing thermal conductance  decreases in magnitude after run-in in both cases, as expected due to the smaller lubricant area.However, the thermal conductance in the larger bearing decreases significantly more than the smaller bearing, possibly due to a combined initial larger amount of lubricant and higher centrifugal force actingon the bearing during run-in, throwing out more lubricant. The final lubricant contact area is slightly  greater in the larger bearing and likewise, the thermal conductance is slightly higher for the larger bearing. In both cases, the final thermal conductance is still higher than the dry condition as would be expected. The dry case represents the lowest possible bearing thermal conductance value for a given bearing, geometry, materials, and load condition. The total amount of lubricant in the bearing was measured before and after run-in for three different  bearing sizes. The results are shown in Table 3.4.2, with additional initial weight data from a fourth bearing.   Table 3.4.2 Lubricant Loss as a Function of Run-In Speed Bearing Details Lubricant Weight Bearing Size OD (mm)Dry  Bearing  Weight (g)Initial  Lubricant  Weight (mg)After  6krpm  Run-in (mg)After  10 krpm  Run-in (mg) Large bearing, steel 62 228.54 130 100 not weighed Large bearing, hybrid 62 188.05 130 90 70 Medium bearing, steel 42 63.4076 96.9 not operated not weighed Small bearing, steel 28 19.8058 49.9 39.2 not operated In each case, we find that the conductance reached a steady state after prolonged operation at its run-in  speed. The measured amount of lubricant loss can be attributed to the initial quantity and maximum runin speed. In the case of the large hybrid bearing the weight fell further after additional testing at 10 krpm,  showing that as run-in speeds increase, the amount of lubricant left in the bearing decrease. In section 4.4 below, we will show how this decrease affects conductance. Even though most of this lubricant weight is not distributed in the ball to race pathway, there is a corresponding drop in lubricant in the critical areas,resulting in lower bearing thermal conductance with increase run-in speeds. 3.5 Oil Lubricated Dynamic Run-In Bearing Next, dynamic (constant speed motion at 6000 rpm) thermal conductance measurements were taken at  various thrust loads for the small and large sized bearings. While the bearing is in motion at high speed,the heat transfer mechanism changes. For a static bearing, the mechanism of heat transfer wasconduction through the contact pathway, through the ball, and finally through the outer contact pathway.However, once the bearing rotates at a significant speed (such as 6000 rpm), our data suggests that the mechanism of heat transfer changes to mass transport, as warm lubricant picks up heat at the hotter raceway and gets transported with the ball. It then deposits heat at the cooler raceway. Thus, the  lubricant film thickness on the ball becomes important, and the Yovanovich analysis no longer holds. Comparisons of the conductance during both dynamic and static states as well as oiled and dry  conditions were made for both bearing sizes in Figures 3.5.1 and 3.5.2. For all of the dynamic test cases, bearing thermal conductance was stable for a given set of conditions once the bearing had fully run-in. To produce the test data shown below, the test fixture thermal  conditions were adjusted and the data set was interpolated for a constant average bearing temperature of  20°C throughout. Despite the differences in bearing sizes, the behavioral /g87/g85/g72/g81/g71/g86 were similar between the  28mm OD and 62mm OD bearing sizes. Conductance /g80/g68/g74/g81/g76/g87/g88/g71/g72/g86 , however, were very different, with the  122