Heat Transfer Post-Processing

The main output is the predicted temperatures of bearings and solids for a particular load case. Figure 11 shows the predicted temperature with the deflector.

In reality, the temperature should be uniform on all bearing rollers due to their high rotational velocity. But considering that the film coefficients are averaged during just one simulated second, to keep calculation cost reasonable, and that the heat transfer analysis is steady state with fixed geometry, a temperature gradient can be observed on the bearing. To remain conservative, the maximum predicted temperature can be used. This misrepresentation of reality is explained by numerical reason, but the interpretation of the results remains acceptable and allows for design comparison and performance evaluation. According to the bearing spec sheet, the bearing could start to accumulate damage above 150°C. The analysis prediction of a maximum bearing temperature of 176°C correlated well with the manufacturer’s damage observations on the roller bearing. Figure 12 reveals the same prediction of temperature without the deflector. It clearly confirms the fact that the lubrication appeared to be better without the deflector, offering better cooling of the overheating bearing. Ironically, the manufacturer attempted to solve the anticipated overheating problem with the deflector actually exacerbated it.

The steady-state heat transfer analysis completes in a matter of minutes. Running the entire set of load cases is feasible within a few hours of computing time. If the thermal conductivities or thermal resistance values are not well known, these parameters can be quickly and easily varied to study their sensitivity on the predicted temperatures. Heat flux is another valuable output. Represented by symbols or arrows, it helps the user visualize how heat is being transferred within the gearbox. By focusing on specific surfaces to output the heat flux, the user can evaluate the amount of heat exchanged through solid contact (conduction) and the amount extracted by lubrication (convection).