Pressure Drop and Void Fraction in Microchannels Using Carbon Dioxide, Ammonia, and R245fa as Refrigerants

摘要

Aluminum multi-port microchannels are currently utilized in automotive air conditioners for refrigerantcondensation. In general, research activities are directed towards developing other air conditioning and refrigerationsystems with microchannel condensers and evaporators by analyzing heat exchanger performance parameters of heattransfer, pressure drop, and void fraction.The purpose of this particular study is the experimental investigation of frictional pressure drop and voidfraction in microchannels. Experiments are performed using 6-port and 14-port microchannels with hydraulicdiameters of 1.54 mm and 1.02 mm, respectively. Fluids and saturation temperatures used in this experimentationinclude carbon dioxide at 15??C, ammonia at 35??C, and R245fa at 40??C. Two-phase flow conditions include massfluxes from 50 to 440 kg/s.m2 and qualities varying from 0 to 1.Experiments indicate that two-phase pressure drop and void fraction are dependent upon hydraulicdiameter, mass flux, quality, and vapor density. Two-phase pressure drop is most significantly influenced by inertialforce of the flow. Void fraction is strongly influenced by flow regime, which can be related to the vapor density ofthe refrigerant. In general, models exist to predict the experimental two-phase flow pressure drop and void fractionsatisfactorily for specific conditions, but no comprehensive model has been formulated that encompasses thephysical properties defining two-phase flow.