Developing Mist-Annular Flow of R134a/PAG46 Oil in Inclined Tube at Compressor Discharge

摘要

This work reports on the droplet flow rate and film thickness of a mist-annular flow inside inclined tubes in a mobile air conditioning compressor discharge. A preliminary model of single droplet trajectories was used to evaluate the potential for droplet deposition enhancement and it was found that it would be able to collect droplets with diameters of 25μm or higher at the inclined tube wall. A test section with a 1m long, 6.35mm i.d., transparent PFA tube was placed immediately after the compressor discharge in a full system facility. Tests were performed varying mass flux, oil circulation ratio (OCR), and inclination angles. For several positions in the tube downstream of the compressor, high speed video analysis was used to determine droplet sizes and velocities, and film wavelength in addition to an indirect indication of film thickness. The experimental trends obtained for droplet flow and film thickness for high mass fluxes, were the opposite of what was expected. There was an indication that the transition from horizontal to inclined orientation introduced disturbances in the film at the wall which caused the film to shed bigger droplets that were entrained back into the flow, increasing the drop flow rate in the inclined section. A small inclination angle (approximately 5°) neither enhances nor diminishes droplet deposition. Higher inclination angles, 11° and above, have a negative effect on the droplet deposition in the inclined section. At low OCR (0.43%), the presence of an inclined section did not affect the droplet deposition rate. At higher OCR (2.5%), a negative effect was observed in drop deposition.