|Title:||Experimental Investigation of Mobile Air Conditioning System Control for Improved Compressor Reliability
|Contributor(s):||Dunn, W.E.; Miller, N.R.
|Subject(s):||mobile air conditioning systems
|Abstract:||Mobile air conditioning circulating oil concentration and compressor start-up torque
were experimentally investigated to develop a control strategy to improve compressor
reliability. An installed electronic expansion valve provided the control actuation. Realtime
circulating oil concentration data were obtained for steady-state, quasi-steady, and
start-up operating regimes with an installed optical concentration sensor. A two-phase
refrigerant-oil model was developed for R134a and polyalkylene glycol (PAG) oil to
predict oil film thickness, average film velocity, and interfacial shear between the
refrigerant vapor and the refrigerant-oil liquid film.
Experimental and model results were analyzed and compared. Evaporator superheat
reduced the circulating oil concentration due to an increase in the oil film thickness on the
walls of the evaporator and suction line. The model predicted oil film thickness to increase
by a factor of four as refrigerant quality approaches one. Increasing the refrigerant-mass
flow rate only exhibited secondary effects due to slightly thinner oil films and a
correspondingly higher circulating oil concentration.
The influences of charge distribution, expansion valve position, compressor head
pressure, and refrigerant charge level on start-up torque and initial capacity were
investigated. Closing the expansion valve while the compressor clutch is disengaged was
found to reduce the start-up torque by retaining the refrigerant in the system high side and
preserving a pressure gradient across the expansion valve.
|Publisher:||Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
|Series/Report:||Air Conditioning and Refrigeration Center TR-128
|Sponsor:||Air Conditioning and Refrigeration Project 78
|Date Available in IDEALS:||2009-04-29
|Identifier in Online Catalog:||4170089