Tham khảo tài liệu 'bearing design in machinery episode 2 part 1', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | priate table of Raimondi and Boyd are substituted P 25 X 106 Pa 1 - ậ Q R C f DTm Cf 0 877 8- 3 25 77 106 C 1 - Qs Q 3 29 x 0 5195 b. Maximum and Average Oil Temperatures Maximum temperature Tmax Tin DT 20 106 123 C Average temperature Tav Tin DT 20 126 73 C Since the bearing material is subjected to the maximum temperature of 123 C the bearing material that is in contact with the lubricant should be resistant to this temperature. Bearing materials are selected to have a temperature limit well above the maximum temperature in the fluid film. For bearing design the Sommerfeld number S is determined based on lubricant viscosity at the average temperature of 73 C. Temperature Rise Based on the Tables of Raimondi and Boyd The specific heat and density of the lubricant affect the rate of heat transfer and the resulting temperature rise of the fluid film. However Eq. 8-5 does not consider the properties of the lubricant and it is an approximation for the properties of mineral oils. For other fluids such as synthetic lubricants the temperature rise can be determined more accurately from a table of Raimondi and Boyd. The advantage of the second method is that it can accommodate various fluid properties. The charts and tables include a temperature-rise variable as a function of the Sommerfeld number. The temperature-rise variable is a dimensionless ratio that includes the two properties of the fluid the specific heat c Joule kg- C and the density p kg m3 . Table 8-5 lists these properties for engine oil as a function of temperature. The following two problems illustrate the calculation of the temperature rise based on the charts or tables of Raimondi and Boyd. The two examples involve calculations in SI units and Imperial units. We have to keep in mind that The original charts of Raimondi and Boyd were prepared for use with Imperial units the conversion of energy from BTU to lbf-inch units is included in the temperature-rise variable . In this text
