Lubricating condition evaluation of the rotary compressor under high ambient temperature.

• Load on crank part doubles when ambient temperatures rises to 50°C. • Bottom viscosity drops to 1.59 mPa⋅s with increased temperature. • Proportion of squeeze and wedge effect changes at different rotation angle. • Contact force accounts for 35% supporting force in extreme condition. Propane has been suggested as one of the alternative working fluids for room air conditioners in hot climate areas because of its excellent environmental properties and lower discharge temperature though there still is concern about its flammability. The lubricating condition of rotor bearings system should also be emphasized because a heavier load and lower viscosity in the oil sump could impair the reliability of rotary compressor under high ambient temperature. In this study, in order to obtain the input of simulation, the dynamic pressures and viscosity of a R290 air conditioner are experimentally measured under several conditions. On these bases, lubricating characteristics are numerically simulated by coupling the dynamics equation of crank shaft and the modified Reynolds equation of oil film using finite element method. The results show that the load on crank under 50 °C is twice as large as that of 30 °C while the viscosity of bottom oil sump decreases from 1.89 to 1.59 mPa⋅s. Simulation results imply that the minimum oil film thickness decreased to 0.44 µm under 50 °C, in which asperity contact force peaks at 3 N when arithmetic mean roughness is 0.2 µm. Asperity contact force would significantly increase to 174 N if surface roughness is 0.6 µm and boundary lubrication regime is reached. Strategies to increase oil sump viscosity is recommended to avoid adhesive wear in this case. [ABSTRACT FROM AUTHOR]