Valve, Compressor, Vibration, Impact fatigue, Frequency, Displacement, Flap-X, Martensitic stainless steel
During operation of a reciprocating compressor, its flapper valve opens to allow the passage of gases and closes by striking against the valve impact plate. This reed valve movement and impact is repeated billions of times. This cyclic movement has a significant influence on the impact fatigue life of the reed valve and, hence, the lifetime of a compressor. Inside a reciprocating compressor, a number of parameters including: the valve design, valve material, compressor operating frequency and suction/exhaust pressure, influence the reed valve movement. The valve movement can be defined in terms of valve frequency, valve lift, valve velocity and impact velocity. These response parameters heavily influence the compressor efficiency and impact fatigue life of reed valves. In this paper, we first studied the valve movement parameters for a reed valve design using an experimental test setup. In experimental testing, the valves were excited into movement using air pressure pulses at 100 Hz frequency (air pulse width of 5 milliseconds). The valve movement was recorded by a laser sensor at 10 000 frames per second. The operating conditions such as the operating frequency, air pulse width, applied pressure and airflow rate were measured. The valves were not tested to failure but only to collect the dynamic data of valve movement such as the valve movement curve (valve displacement vs time), average valve lift and reed velocity data. The experimental results were employed to validate a complex in-house 3D CFD finite-volume model aimed at studying in detail the valve and gas dynamics, whose interaction is solved by means of a Fluid-Structure Interaction (FSI) algorithm. The complete valve movement curve obtained from simulations – reed valve displacement vs time – correlated with that obtained from the experimental tests with small error. Similarly, the difference in experimental and numerically obtained average valve lift and impact velocity values were quite small for practical purposes. Finally, fluid-dynamic results for pressure and impact forces were employed to feed a finite-element based code aimed at studying the structural behavior of the reed vale. Bending fatigue and impact fatigue stresses induced in the reed valve during its movement cycle were calculated. The magnitude of stresses and their positioning was determined, which correlated with the commonly observed areas of fracture initiation in these valves. The numerical models, as well as the information obtained from this study will help the compressor manufacturers to design their compressors to enhance efficiency and reed valve’s reliability. This type of information is not readily available from a working compressor.