Compressor Friction Losses due to Oil Viscosity and Asperity Contact Surfaces: a numerical study on crankshaft bearings lengths, clearances and roughness parameters

High energy efficiency refrigeration compressors have been increasingly demanded. This is achievable not only by the use of an efficient thermodynamic system and an efficient electric motor, but also by the design technologies applied to the compressor mechanism. In this work, a crankshaft bearing power losses optimization is presented regarding journal/shell surfaces run-in. The crankshaft bearings asperity friction power losses, combined with the viscous friction power losses, has been minimized for a reciprocating compressor running at ASHRAE condition. The core of the present approach was exploring a design space – computing asperity friction and viscous friction power losses – regarding journal/shell bearings clearances, lengths and surface roughness. The simulation takes into account the journal/shell ElastoHydroDynamic (EHD) behavior, surfaces topology and topography, material’s elastic properties, mechanism dynamics, refrigerant pressures, oil viscosity, electrical motor torques, mechanism speed etc. The main results are the quantification of the viscous and asperity crankshaft friction power losses that are input to the minimization problem solution. It is also presented the sensitivity analysis of surface roughness, bearings lengths and clearances to the asperity and viscous friction power losses