Conference Agenda

The reliability of compressor valves is a significant challenge in extending the operational speed range of compressors due to the risk of impact fatigue failure. Valve raw material suppliers have adopted the velocity of valve impact against the seat as a criterion to assess the reliability of impact fatigue. This article analyzes the capabilities of a low-cost numerical model developed with GT-SUITE in predicting the suction valve impact velocity, while analyzing the influence of each model parameter and operational condition on the prediction of velocity impact. The numerical investigation was validated through measurements of valve velocity carried out with a laser doppler vibrometer. The study shows that valve contact modeling significantly affects the prediction of valve dynamics due to the rebound effect following valve impact. Furthermore, oil stiction has substantial influence on the prediction of valve velocity impact under high-speed operations. Overall, the model was able to predict the impact velocity in good agreement with the measurements. Compressor speed was found to significantly increase the valve impact velocity up to a certain point, after which it shows little variation between the two highest speeds tested. On the other hand, the pressure ratio showed an insignificant influence on valve impact velocity. The findings of this study improve the valve dynamics predictions, especially under high-speed operations.

This study focuses on a 3-D transient Computational Fluid Dynamics (CFD) model for a rolling piston compressor with a dynamic reed valve, a crucial element in refrigeration and air-conditioning systems known for its energy-intensive operation. The growing popularity of rolling piston compressors stems from their favorable characteristics, including silent and smooth operation, as well as high reliability and efficiency. Efficient CFD modeling of such compressors necessitates a thorough understanding of the flow dynamics within the suction chamber, compression chamber, and the thin leakage volume. This modeling must be coupled with considerations for the rotating piston and the dynamic behavior of the reed valve, which plays a pivotal role in discharging compressed fluid at prescribed pressures. Analyzing the discharge valve system is crucial for addressing over-compression loss and reliability issues.The presented work employs a detailed 3D transient CFD model, utilizing the Simerics-MP+ internal rolling piston template to generate a mesh for the entire system. The template incorporates a rotational dynamics module to accurately capture the movement and deformation of the mesh. Additionally, a rotational ordinary differential equation, based on cantilever beam theory, is formulated to account for the bending motion of the valve reed near the discharge port. A test simulation of a generic rolling compressor, incorporating a discharger reed valve, demonstrates the robustness, speed, and user-friendly nature of the algorithms and implementations. The findings suggest the potential applicability of these methods to rolling piston compressor systems, effectively capturing various physical phenomena.

A reciprocating compressor comprises a reed valve which is a critical component that contributes to a compressor’s structural reliability, efficiency, and noise emission. Thinner the reed valve, the higher the efficiency and the lower the noise emission. Thinner reed valves are, however, more susceptible to premature failure at compressor load levels because the size of crack initiating inclusions makes major fraction of the reed valve cross-section. However, it is critical for a reed valve to operate reliably without failure.

Flap-X is a high strength martensitic stainless steel grade that is developed as a reed valve steel whose higher impact fatigue and fatigue strength, in general, allow using thinner gauges for reed valves. By testing Flap-X reed valves in the ultra-thin gauge of 0.08 mm, we are looking to gain advantages like higher valve efficiency that can translate to higher compressor efficiency and reduced noise while ensuring reliability of valve operation. Tests were conducted in a custom-built impact fatigue test system (iFTS) that uses compressed air pulses to induce reed valve movement and striking against the valve plate. Reliability tests were conducted by testing multiple reed valve samples to millions of load cycles that helped estimate their impact fatigue strength/life. Reed valve efficiency and noise emission tests were also conducted.

From our tests, the ultra-thin Flap-X reed valves demonstrated efficiency gains as well as noise reduction. Moreover, the Flap-X reed valves showed reasonable impact fatigue life at compressor load levels. This is believed to be due to the higher cleanness and smaller size of crack initiating inclusions in Flap-X.

Since its most original formulations, the Finite Volume Method (FVM) is usually associated with fluid and heat transfer problems. Unlike other numerical methods, such as the Finite Element Method (FEM) and the Finite Difference Method, which were first devised to solve problems in solid mechanics, the FVM began to be used in this field only in the last few years.
The FVM has always excelled in Computational Fluid Dynamics (CFD) by solving equations that come from conservative laws. FVM has a more straightforward mathematical formulation than FEM, and fluxes only need to be evaluated on the faces of the elements, making the method simpler and cheaper from a computational point of view. On the other hand, and unlike FVM methods, FEM has always stood out for its ability to increase, in a straightforward way, the order of interpolation of the main variable of the problem, which is an advantage in stress concentration problems or when the shear locking effect appears.
The shear locking occurs in bending-dominant problems due to the inability of the element edges to bend, which causes the appearance of an artificial shear deformation, making the element stiffer. This problem happens when using FEM or FVM with linear interpolation. Refining the mesh makes it possible to obtain a sufficiently accurate solution to these problems. However, the computational cost is usually unacceptable, and the best way to address the problem is to increase the interpolation order.
A common real example where the effect of shear locking appears is in compressor reed valves. Due to its small thickness, the solution of the simulation may be affected by this phenomenon and could require a high computational effort if linear interpolation is used. The correct simulation of a compressor valve is of great industrial interest since it would allow predicting the failure of the piece, usually caused by fatigue. This problem was traditionally addressed by means of FEM models, but, recently a fully 3D high-order FVM model
for solid mechanics was presented by the authors to solve shear dominant problems, opening the way to fully couple Fluid-Structure Interaction simulations with a common finite volume discretization framework for both turbulent fluid dynamics and solid mechanics.
The problem analyzed in the current work consists in the simulation of a compressor reed valve considering the interaction between fluid and structure and the impact of the valve on the seat, replicating an analogous laboratory experiment. The high-order method presented in past works is used to obtain the displacement, velocity, and stress tensor of the reed valve. This work focuses on the deep analysis of the results and in the comparison of the results with those obtained when using FEM to solve the same problem.

In fluid machinery, especially compressors, suction and discharge valves are key components that greatly affect performance, noise, and reliability. The use of flapper valves, manufactured through sheet material punching, is prevalent in these applications. While flapper valves are often chosen over other types like poppet valves for their cost advantages, they demand high fatigue strength and impact resistance, necessitating a high level of quality and reliability.

One of the challenges in using flapper valves is evaluating their durability in real-world conditions due to their robust fatigue strength and impact resistance. This report introduces a novel approach to impact resistance testing that closely simulates the operational conditions of compressors. The study focuses on constructing and implementing a methodology for this form of testing, ensuring a more realistic evaluation of the valves in conditions similar to actual use.

A specific aspect of compressor flapper valves is that the fluid forces acting on them primarily consist of gaseous refrigerants in refrigerant compressors. When the load is gaseous, its low density presents challenges in conducting tests under sufficiently high loads. To address this, the report details the development of an impact resistance tester using refrigeration oil as the working fluid. By controlling the load on the flapper valve through variations in the flow rate of the refrigeration oil, and intermittently flowing a denser fluid through the valve, the report successfully replicates the valve's operational behavior for impact resistance testing. The tests revealed that different materials exhibit varying impact resistance performances. This finding is crucial for selecting suitable materials for compressor flapper valves and provides valuable data for material selection.