Conference Agenda

The transition to renewable energy sources poses various challenges. For instance, due to their volatility, there is a growing need for transporting and storing renewable energy. Hydrogen is often considered for this.

Compressor technology shows numerous applications that require oil-free compression to maintain high gas purity levels, including hydrogen in fuel cell applications. Reciprocating crosshead compressors can deliver and store hydrogen at high pressure. However, relevant sealing materials such as fluoropolymers and thermoplastic polymers for rider bands and piston rings yield significant wear and friction under high loads. Additionally, concerns have been raised about adverse effects of the bioaccumulation and persistence of per- and polyfluoroalkyl substances (PFAS) like many fluoropolymers once released into the environment. This has led to the proposal to ban these substances within the European Union. Therefore, it is necessary to investigate experimentally the tribological behavior of self-lubricating sealing materials under realistic compressor conditions to eventually find alternative PFAS-free sealing materials with suitable oil-free tribological properties.

The paper outlines a specialized tribometer designed to analyze friction and wear of sealing materials for reciprocating compressors. The tribological system components, including the forces, movements, and gas influence the frictional behavior of material pairings. The tribometer can provide a realistic compressor atmosphere while continuously monitoring friction and wear. The research will identify materials that endure high-pressure compression, exhibit low friction and wear, and comply with PFAS-free requirements.

A diaphragm pump is a reciprocating positive displacement pump. It works according to the principle that a volume (working chamber) is periodically increased and decreased by a diaphragm. Due to this, a medium is sucked in and pushed out of the working chamber. Valves are used to prescribe the direction of flow and prevent back flow. The valves open and close automatically depending on the flow values or existing pressure differences. The diaphragm and, in many cases, the valves are made of a material which is capable of large reversible deformations such as elastomers (i. e. rubber). Such a material is necessary due to the diaphragm being stretched and compressed during its reciprocating movement. In addition, these parts also seal off the flow domain from the environment (this does not mean the sealing of the working chamber, but the prevention of leakage from the pump) by squeezing defined sealing surfaces.

Numerical simulations with FEM are used to gain a deeper understanding of the movement, the strains and stresses that occur in the elastomeric part during operation. To achieve this, an adequate material model must first be created. A material model for elastomers differs substantially from a material model for steel, which in its simplest form consists only of a Young's modulus and a Poisson’s ratio. Elastomeric materials show a behavior that is nonlinear elastic (hyperelastic) and time dependent (viscoelastic).

The aim of this paper is to present two methods for measuring the nonlinear stress-strain relationship of EPDM with large strains, which is also affected by temperature and the strain rate at which the material is stressed. Firstly, a hyperelastic characterization method at low strain rates with dynamical mechanical analysis is introduced. Secondly, an advanced method is described that enables the examination of hyperelastic material properties at high strain rates. Furthermore, two viscoelastic material models are calibrated on the base of these measurements, the first is a Prony series approach and the second uses a Bergstrom-Boyce model.

Finally, simulation results are compared with measurements. Measured forces in the connecting rod when pumping air at different pressure levels are available for this purpose. This allows the determination of the best material model for the simulation of the elastomeric components.

The generation of relatively high oil-film pressure in the small radial gap between two scroll wraps in scroll compressors, due to the inscribed rolling and sliding motions, has long been hypothesized. However, neither the precise physical mechanism of this high oil-film pressure generation nor the significant characteristics of the oil-film pressure has been clearly identified. The motion between two scroll wraps is represented by the superposition of rolling and sliding. This study presents a development of theoretical analysis for the effects of oil viscosity on the oil-film pressure generated by the inscribed rolling and sliding motion between the scroll wraps, where the oil-film pressure and resultant oil film force are derived in a simplified form of the dimensionless expressions. Subsequently, the measurement of the oil-film pressure in a simplified equivalent physical model consisting of two circular cylinders undergoing inscribed rolling and sliding motions confirmed the theoretical results. Finally, the major characteristics of the oil-film pressure and resultant oil film force in a medium cooling capacity scroll compressor is calculated and demonstrates that the oil-film pressure acting on the outer periphery is sufficiently high so as to cause elastic deformation of scroll wrap.

The main causes of reduced performance efficiency and noise of compressors are mostly caused by mechanical friction and vibration between parts. Such friction and vibration can damage internal parts and cause them to seize, resulting in failure to the compressor and air conditioner. In addition, thermal deformation and heavy loads caused by compressing low-temperature and low-pressure refrigerant into high-temperature and high-pressure gas is also the cause of compressor damage.

To solve this problem, low-friction under heavy loads, superior heat wear-resistant solid lubricating coatings used in engineering applications such as air conditioning and refrigeration compressors are being applied through deposition through molybdenum disulfide, graphite and PTFE-based coatings.

Contain solid lubricants, such as molybdenum disulfide(MoS₂), graphite and PTFE-based coatings exhibited low friction properties and high anti-wear properties and, unlike DLC coatings, were not shown to be significantly affected by the environment. Although coating wear increases significantly at high contact pressures, it has been shown to play a beneficial role in the overall wear performance due to the wear particles generated. Due to their excellent tribological behavior under various experimental conditions, the coatings tested in this study can be used in compressor systems and other engineering applications.

Critical to compressor development is predicting friction and wear between surfaces in relative motion. In this study, the tribological properties of the sliding surface were investigated using various shapes of compressors. Friction tests were performed under various contact conditions including contact pressure and speed.

It was confirmed that friction and wear characteristics differ depending on the process conditions of solid lubricating coatings, and friction and wear tests were conducted depending on the coating according to curing temperature and time, and the presence or absence of post-treatment to find the optimal coating conditions.

The evaluation of the wear and lifespan of solid lubricants is derived in the components of rotary compressors operating in a refrigerant oil environment. Unlike conventional mechanical components that have established lifespan equations based on operating conditions, this research focuses on studying failure caused by mechanical wear. The objective is to derive a wear life equation according to various test conditions, and friction experiments were proceeded for this purpose. Considering the load application method of compressor, a pin-on-disc friction test method was employed, utilizing coated specimens to simulate real surface conditions. The friction tests were conducted, and the wear volume was measured at regular intervals during the test cycles. By employing lifespan calculation equations, the point at which the coating layer was delaminated could be determined. To ensure coating delamination, harsh conditions were implemented, surpassing conventional operating conditions. These harsh conditions were determined by conducting preliminary experiments, varying the parameters of load, speed, and temperature. The result is to derive the lifespan equation of coating delamination, comparing the acceleration life of compressor, lifespan of bearing in rotary compressor, and the lifespan with the experimentally obtained equation, and thereby assessing the differences. Additionally, the study aims to develop an evaluation method to investigate the effects of using different oil types. The findings will contribute to a better understanding of failure mechanisms and the development of evaluation techniques for rotary compressors operating in refrigerant oil environments.