Mechanism of discharge backflow in reciprocating refrigeration compressors and its reduction using carbon fiber composite valve reeds

Abstract This study investigates the mechanism of discharge backflow in reciprocating refrigeration compressors and its reduction using carbon fiber composite valve reeds. A one-dimensional dynamic model is developed to capture the coupled behavior of piston motion, thermodynamic processes, valve dynamics, and transient gas flow. The model is validated through experimental measurements of valve reed motion under no-load conditions. The results show that discharge backflow is a transient reverse flow phenomenon caused by the delayed closure of the discharge valve after pressure reversal. This delay originates from valve inertia, leading to a mismatch between the valve response time and the pressure variation time scale. When the valve response is insufficiently fast, reverse flow occurs and increases in magnitude. Parametric analysis indicates that increasing the valve natural frequency and appropriately enhancing stiffness can significantly improve the dynamic response, thereby reducing both the duration and magnitude of backflow. However, higher motor rotation operating frequencies accelerate pressure variations and may intensify backflow. Furthermore, a comparative study between steel and carbon fiber composite valve reeds demonstrates that carbon fiber reeds, due to their lower mass and higher stiffness-to-mass ratio, exhibit a faster dynamic response. As a result, discharge backflow is significantly reduced, leading to improved cooling capacity and higher coefficient of performance (COP). The findings reveal that discharge backflow is fundamentally governed by a time-scale mismatch mechanism. Matching the valve dynamic response with the pressure variation time scale, together with optimized material selection, provides an effective strategy for suppressing backflow and enhancing compressor performance.