Real-Time Measurement of Flow Quality in CCOT Systems

Systematic design of mobile air-conditioning system components in R134a systems has been hampered by inaccurate knowledge of the flow quality, especially the amount of liquid returned to the compressor. The thermodynamic quality is typically used, but it is somewhat unreliable due to the large percentage of miscible compressor oil circulating with the refrigerant. A technique for measuring the flow quality in the refrigeration loop based on phase segregation and recombination has been developed and verified. The refrigerant quality has been deduced with the aid of standard sampling methods for measuring the percentage of oil in circulation. Hence, the relative contributions of all three components of the flow have been measured. The method is suitable for relative evaluation of component performance on a test stand. The method has been applied to measuring evaporator discharge quality at standard conditions and to quantifying accumulator liquid carryover. Measured flow quality at the accumulator outlet varied from 77-88%, corresponding to refrigerant quality of 83-93%. The flow quality measurement technique presented will be used to help determine the relative effects of different accumulator designs on system performance - improving accumulator design and speeding up the time to develop new products.