Oil-free Compressor Research Articles

A High-Temperature, High-Speed, Oil-Free Syngas Compressor for Small-Scale Combined Heat and Power

Abstract For low-emission, small-scale combined heat and power generation, integrating a biomass gasifier with a downstream solid oxide fuel cell system is very promising due to their similar operating conditions in terms of temperatures and pressures. This match avoids intermediate high-temperature heat exchangers and improves system efficiency. However, to couple both systems, a high-temperature and oil-free compressor is required to compress and push the low-density, high-temperature bio-syngas from the gasifier to the solid oxide fuel cell stack. The design and development of this high-temperature, high-speed, and gas-bearing supported compressor is presented in this work. An iterative process involving preliminary design, meanline analysis using commercial tools and in-house models is used for the design, which is then numerically analyzed using computational fluid dynamics. The goal is to achieve a design with a wide operating range and high robustness that withstands extreme working conditions. The 727 W machine is designed to run up to 210 krpm to compress 18.23kg/h of syngas at 350°C and 0.81bar. The centrifugal compressor has a tip diameter of 38 mm and consists of 9 backswept main and splitter blades. The impeller is made of Ti6Al4V and coated to prevent hydrogen embrittlement from the hot and highly reactive bio-syngas. The results obtained from the established models suggest a good concordance with the results from numerical analyses, despite the high temperatures and small scale of this design.

Experimental study on system characteristics of vapor compression refrigeration system using small-scale, gas-bearing, oil-free centrifugal compressor

Small-scale refrigeration centrifugal compressors hold the potential for superior efficiency compared to currently used positive displacement compressors. However, traditionally, centrifugal compressors have been employed in large refrigeration systems with cooling capacity of several hundred kilowatts or more. Conversely, the application of small-scale centrifugal compressors in smaller refrigeration systems, with cooling capacity in the tens of kilowatts, has largely remained theoretical, lacking practical experimental studies. For a better understanding of the operational characteristics of such systems, this study constructed a 45 kW R245fa refrigeration system test bench based on the small-scale oil-free centrifugal compressor utilizing gas foil bearings. The experimental investigation analyzed the impact of refrigerant charge amount, compressor speed, and coolant flow rate on system performance. Results indicate that the system achieves its peak cooling capacity of 49.73 kW with a system COP of 3.64 at 65,000 rpm. Moreover, at 50,000 rpm, the system demonstrates its highest system COP of 4.23 with a cooling capacity of 26.07 kW. In comparison to traditional positive displacement compressor refrigeration systems, it exhibits higher energy efficiency. Additional simulation studies were conducted to evaluate the effects of substituting R1233zd(E) for R245fa on the system performance and to assess the feasibility of such a substitution.

Rotordynamics of a rotor supported by foil bearings under various housing excitation

Proton Exchange Membrane (PEM) Fuel cell Systems(FCS) are rapid-growing technology in transportation systems. In such applications, a motor-driven oil-free air compressor is one of the critical auxiliary subsystems. Foil bearings are the perfect choice as oil-free bearings for the compressors due to high rotordynamics stability and shock-resistance. The platform of a motor-driven oil-free compressor can also be used as an electric turbocharger for traditional internal combustion engines. All electromechanical subsystems for electric vehicles must satisfy vibration endurance requirements following ISO 16750–3:2012, characterized by certain g-loading at specific frequencies. For the compressor to satisfy ISO 16750 requirement, detailed rotordynamics simulations with externally excited compressor housing under certain g-loading are essential to design the foil bearings considering the static and dynamic loads to the bearing and rotordynamics stability. The main objectives of the current research are 1) to develop a four degree of freedom (4-DOF) dynamic model of the rotor supported by foil bearings under external excitation to the compressor, 2) to simulate linear and non-linear rotordynamics of the compressor rotor supported by two radial foil bearings, and 3) to provide appropriate design guideline such as bump stiffness and axial length of the foil bearings. The simulations show that the rotor is stable for both under single frequency excitation and simultaneous excitations of all the frequencies in ISO 17650 standard. 4-DOF modal analyses were applied to identify natural mode of the system under the housing excitation.

Cooling power analysis of a small scale 4 K pulse tube cryocooler driven by an oil-free low input power Helium compressor

Here we report the performance of a small scale 4 K pulse tube cryocooler operating with a low input power reaching a minimum temperature of 2.2 K, as well as a cooling capacity of over 240 mW at 4.2 K. The compressor is air cooled and can be supplied by single phase power sockets. With an input power of about 1.3 kW the coefficient of performance reaches values of up to 185 mW/kW, which is among the highest currently reported values for small to medium power pulse tubes. The combination of an oil-free Helium compressor and low maintenance pulse tube cryocooler provides a unique miniaturized, energy efficient and mobile cooling tool for applications at 4 K and below.

Improving the tribological performance of CFRPTFE at elevated temperature by sliding against Ti-TiCx/DLC film

Polytetrafluoroethylene (PTFE) has been widely used in industrial field for sealing parts. However, it is well known that PTFE is always subject to serious wear at high temperature (over 150 °C), which has become the main drawback limiting serve life of important equipment such as compressors. In this paper, a new solution is proposed for improving the wear resistance of carbon fibers-reinforced PTFE (CFRPTFE). Multilayer Ti-TiCx/DLC film is prepared and used as the counterface of CFRPTFE. Friction and wear tests at high temperature (200 °C and 250 °C) are carried out. The uncoated 17-4PH steel disks precisely polished by abrasive papers with different grain sizes are used as the reference counterface (SS80 and SS7000). It is found that by sliding against Ti-TiCx/DLC film, the tribological behaviors of CFRPTFE at high temperature can be improved. The friction coefficient between CFRPTFE and DLC under different test conditions can be kept in stable state. The wear rates of CFRPTFE reduce by 50%–70% compared to SS80, and reduction of 20%–40% can be observed when compared to SS7000. It can be found that graphitization transition at high temperature promotes the transfer layer formation and contributes to lower friction and lower wear compared to traditional processed counterface at high temperature. These significant improvements can prolong the lifetime of CFRPTFE moving parts used in high-temperature and heavy-load applications. Finally, engineering verification of the proposed friction pair is carried out in miniature oil-free high-pressure compressor.

Design and testing of the fuel cell twin-screw air compressor

The oil-free dry air compressor plays a crucial role in the fuel cell system, particularly in commercial buses where twin-screw air compressors have proven effective. A novel rotor profile of the twin-screw dry air compressors has been developed, which simplifies the profile curve and yields excellent performance results with a volume flow of 11.99 m³/min and corrected specific power of 3.54 kW/(m³/min).

E-Support System for Identifying the Compressor

An E-Support system is an online system that provides users with support and assistance for various products or services. These systems are available 24/7, which means that customers can get the help they need at any time. The project is to implement and help people through online by developing the online website for compressor. This can be accessed online from any part of the world. It is a user - friendly website and was developed in visual studio code using java script, html and CSS. This website will assist to know more about the compressors like the details of pressure of the compressor, temperature of the compressor etc. It provides the details about the compressor. It is used to detect fault in the compressor and notify the customer about the fault. The developed website is used to know the customers online. For example, if the customer wants to buy an oil lubricated or oil free compressors then the website can be used. If any fault occurs in the air compressor the fault can be identified in troubleshooting. The customers can use this user-friendly website for checking compressors. The main objective is to provide better service and make the process easy for the customer to see the details about the compressors. The customer can make use of the website to explore about compressors

Design of Oil-Free Compressor in Compressed Air System PT Sanbe Farma Unit 1

This research is the development of a screw type compressor technology found in the utility system of PT. Sanbe Farma. This design aims to design a screw oil-free compressor focusing on solving problems that generally occur in a compressor, namely contamination between compressed air and oil. For this compressor, ISO Standard 8573-1: 2010 is used, and then the design results are compared with the simulation results that have been validated using the Aspen Hysys application. Several factors can affect the compressor's design, including the use of diameters in the pipe installation and the selection of the motor used to meet the demand for compressed air. The results of the theoretical design (simulation of Aspen Hysys software) show close values, so design is proven accurate and appropriate and can be applied. With a compressed air requirement of 0.0063 m3/s and a pressure of 8 bar, a compressor power of 72.7 kW and a motor power of 103 kW are required.

Benchmarking and Simulation of Solid-Oxide Steam Electrolysis for Propellant Production in a Vacuum Chamber-Simulated Lunar Environment

NASA and other space agencies have prioritized the development of in-situ resource utilization (ISRU) technology for producing critical materials such as propellants in space. Electrolysis to split water found in lunar, asteroid, and Martian environments provides a pathway for liquid H2 and O2 production, but the challenges of deploying such technology in extraterrestrial environments put an extreme emphasis on minimizing specific energy (measured in kWhelec/kgH2) and system specific mass (system kg/(kgH2/h)). High-temperature, solid oxide electrolysis cell (SOEC) systems have the potential to achieve lower specific energy than conventional liquid-phase alkaline and polymer electrolyte membrane (PEM) electrolysis systems, but this requires efficient thermal integration and minimization of balance of plant loads in order to take advantage of the lower electrolysis voltages for steam (vs. liquid H2O). The high operating temperatures of SOECs, however, require significant system mass for steam generators, heat exchangers for recuperation, and insulation of the electrolysis stack, particularly for space applications where ambient temperatures may be extremely low.This NASA-sponsored collaboration between OxEon Energy and Colorado School of Mines explored the feasibility of a lunar-based SOEC system, which was modeled and demonstrated at the lab-scale by operating a breadboard system, consisting of a SOEC stack and associated balance of plant BOP) in a cryogenic vacuum chamber in order to simulate a lunar environment. The combined »2.5-kWelec SOEC stack and BOP achieved a specific energy < 50 kWhelec/kgH2 at an H2 production rate of > 0.075 kgH2/h operating in the cryo-vacuum chamber.This study has benchmarked system-level models of the lab-scale SOEC stack based on doped-zirconia electrolytes fabricated at OxEon and designed to operate near thermoneutral voltage (1.28 V/cell) at 800°C. The stack BOP includes a steam generator, an oil-free scroll compressor, cathode and anode exhaust recuperators, and a H2 dryer, which uses cold incoming liquid water feeds to cool the cathode exhaust and condense most of the excess H2O in the H2 product stream out. Operation of this demonstration system provides a basis for designing scaled-up lunar fuel production systems of 40 kgH2/h. The success of the lab-scale tests in terms of thermal integration and the benchmarked models suggest a pathway to such a full-scale SOEC system that can achieve < 46 kWhelec/kgH2 with much lower specific mass.Both the modeling and the lab-scale demonstration tests revealed that system specific energy was most sensitive to stack steam utilization, and that achieving < 50 kWhelec/kgH2 required stack steam utilization > 75%. In addition, effective thermal integration that limited the electrical heating primarily to steam generation is critical to minimizing the SOEC-system BOP loads. The stack was shown to run reliably at steam utilizations > 90% with a single pass feed. Efforts will be presented on how to simulate such high utilization at larger scales for full lunar deployment. Additional testing of the lab-scale system in larger cryo-vacuum chambers at NASA during 2023 will allow for further confirmation of thermal management strategies to ensure reliable SOEC operation for lunar production of H2/O2 propellants.

Innovations in Refrigeration Compressor Technology: A Review of Recent Developments

This paper provides a panoptic overview of recent innovations in refrigeration compressor technology. The dynamic landscape of this field has witnessed transformative advancements driven by escalating demands for energy efficiency, environmental sustainability, and practical feasibility. Through an analysis of participant ratings, key innovations such as Variable Speed Compressors (VSC) and Intelligent Control Systems (ICS) have emerged as frontrunners, optimizing energy consumption and integrating data-driven decision-making. Furthermore, innovations like Oil-Free Compressors (OFC) and Alternative Refrigerants (AR) showcase notable contributions to reducing environmental impact. While challenges in practical implementation persist, these developments offer a promising trajectory for a greener and more advanced future, empowering industries to align with regulations and meet evolving global needs. This study underscores the significance of these innovations for researchers, engineers, policymakers, and stakeholders, serving as a compass to guide the refrigeration industry towards enhanced efficiency and sustainability

Design for a Heat Pump with Sink Temperatures of 200 °C Using a Radial Compressor

To reduce CO2 emissions in the industrial sector, high-temperature heat pumps are a key technology. This work presents an approach to design such an industrial heat pump system capable of supplying 200 °C sink temperature and a capacity of approximately 1 MW. Today’s market-available heat pumps using displacement compressors are not suitable for reaching that high sink temperatures as they need lubricating oil, which is not temperature resistant enough. As a consequence, in this study a transcritical heat pump cycle using a two-stage oil-free radial compressor is investigated. Based on preliminary studies, R1233zd(E) is chosen as a refrigerant. The procedure couples 1D thermodynamic cycle simulations with a radial compressor mean-line design model. A preliminary geometry for a compressor with and without inlet guide vanes is presented, and compressor maps including the compressors behaviour in off-design are calculated. The compressor design is then imported into a 1D simulation to analysis the performance of the heat pump in the whole operating range. In the analysis, the application of a fixed inlet is evaluated, and an improvement of approximately 21% and 16% of the isentropic efficiency is achieved. The thermodynamic simulations showed a maximum COP of approximately 2.8 and a possible operating range of 0.5 to 1.3 MW thermal power. Furthermore, a techno-economical analysis by means of a deep-fryer use case showed reasonable payback times of between 2 and 10 years, depending on the electricity to gas price ratio.

Multi-objective optimization of the oil-free centrifugal air compressor in hydrogen fuel cell vehicles based on grey relational analysis

Centrifugal air compressor is critical to hydrogen fuel cell vehicles due to it guarantees the air provided to the stack is higher pressure ratios and a larger flow rate. However, the compressor has low efficiency and high energy consumption. In this paper, the multi-objective optimization was performed based on experimental data, which considered both the maximum isentropic efficiency and minimum total power consumption. The effects of the factors on the performance of the compressor were obtained by mean S/N ratios. The contributions of the factors to the optimization objectives of the compressor were investigated by analysis of variance. The optimal parameters combination providing the larger isentropic efficiency and lower total power consumption was found by grey relational analysis. The isentropic efficiency increased by 34.5% and total power consumption decreased by 48.5% in comparison with the average value in all Taguchi cases for the optimal compressor.

Numerical investigation of an oil-free liquid-injected screw compressor with ammonia-water as refrigerant for high temperature heat pump applications

• Thermodynamic analysis of liquid injection with varying ammonia-water mixtures. • Model of an oil-free twin screw compressor with injection, leakage, and heat losses. • Injection of lean solution with low ammonia content is best for oil-free compressor. • Injection flow of 10% of compressor's suction flow is enough for full wet compression. • Two injection ports are advantageous to ensure sufficient lubrication and sealing. This study investigates a numerical model of an oil-free twin screw compressor with ammonia-water mixture as refrigerant and liquid injection. The compressor was identified as main constraint to increase the heat sink temperature of absorption-compression heat pump systems past 120 °C. liquid injection can reduce superheating of the vapor during compression, while an existing liquid film can provide lubrication and sealing, enabling oil-free operation. A quasi-one-dimensional numerical model was developed using the Modelica language. It considers the effects of liquid injection flows and injection positions, leakages, heat losses, and variation in ammonia mass fractions. The results revealed a strong influence of occurring internal leakages, varying ammonia mass fractions of the injected solution and changing injection flows and positions on the evolution of temperature, pressure, and compression power. The injection with lower ammonia mass fraction is beneficial for reducing the discharge temperature, discharge pressure and compression power. The increase in injection flow led to a further reduction in the values obtained. Continuous wet compression, which is required for sufficient sealing and lubrication of the compressor, was achieved with injection at 360° at the beginning of the compression phase and an injection rate of about 10% of the compressor’s suction mass flow. By distributing the injection to two injection ports, wet compression can be supported and occurring under-compression and backflow can be reduced.

Методика расчета толщины стенки лепестка манжетного цилиндропоршневого уплотнения

The presented article describes a method for calculating the wall thickness of the lip seal lobe in the ANSYS Workbench Mechanical software package. The main problem that designers face when choosing the wall thickness of the lobe of cuff seals for reciprocating compressor units operating without lubrication is described. As a result of the work, the maximum and minimum wall thickness are calculated for the materials most common in oil-free compressor units. Antifriction materials of the Flubon and Fluvis groups containing up to 20 % carbon fibers have the smallest wall thickness in all pressure ranges considered. At the same time, the results obtained allow us to speak about the low efficiency of cuff seals with a maximum wall thickness at pressures below 1 MPa.

Analysis of position response characteristics of magnetic driven oil-free scroll compressor

Traditional scroll compressors are difficult to achieve oil-free operation due to the presence of a high-friction anti-rotation mechanism. This paper proposes a magnetic drive oil-free scroll compressor to solve this problem. Firstly, the structure and principle of this scroll compressor are introduced. Then the finite element analysis of the electromagnetic system was conducted; the dynamics model of the magnetic scroll compressor operating in the uncompressed state was established. Finally, the PID control of the system is performed, and simulations and experiments are carried out. Experimental results: under the 0.05 mm step signal in the X direction, the position response time of the system is 0.1 s, and the angle response time of 0.001 rad is 0.2 s. The results show that the oil-free scroll compressor has good position control response characteristics.

Systematic engineering design approach for improvement of oil-free twin-screw compressors

Twin-screw compressors are widely used in industry, especially in compressed air, refrigeration, air-conditioning and process gas which consume a significant part of the world’s energy. Nowadays, oil-injected compressors represent the majority of twin-screw compressors in the market due to their high efficiency and reliability. The oil-free compressor is potentially a better solution in the context of the net-zero CO2 target in 2050. However, due to its high thermal deformation and small clearances, this technology still suffers from reliability issues. To remedy this problem disruptive innovative solutions are required. In this purpose, the present study uses a systematic engineering design process to develop new concepts for the improvement of the oil-free twin-screw compressor. The paper is focused on the first two phases of the design process which are the definition of problem and the conceptual design. In the problem definition, main objectives are expressed and are divided into sub-objectives and weighed using an objective tree decomposition. Moreover, a thorough functional model of the oil-free compressor is detailed with a focus on the leakage paths and heat transfers. For the conceptual design, engineering characteristics extracted from the functional analysis have been assessed against the most important objectives using Quality Function Deployment matrices (QFD). Based on the developed problem definition, new concepts have been generated and three distinct concept categories have been further explored: Secondary flow; Surface features; Clearance control and monitoring. The evaluation, embodiment and detailed designs of the concepts, using experimental and numerical analyses will follow.

Analysis of Trajectory Tracking Characteristics of a Magnetically Driven Oil-Free Scroll Compressor

The conventional scroll compressor cannot run oil-free because of wear and tear and lubrication problems during operation due to some parts, such as anti-rotation devices. The magnetic drive oil-free scroll compressor (MDOFSC) uses a contactless drive method to avoid this drawback. In order to solve the swing problem of the orbiting scroll during the operation of the MDOFSC, decentralized control and centralized control are used to study the trajectory tracking characteristics. Firstly, the structure and working principle of the MDOFSC are introduced, and the system’s magnetic circuit and differential control principle are analyzed. Then, the dynamic model of the MDOFSC under the condition of non-compressed gas is established, and the coordinate matrix decoupling method is used to analyze the relationship between the degree of freedom of the system and the measurement distance of the displacement sensor. Finally, the system is simulated and experimentally studied under centralized PID control, and the experimental comparison study between decentralized control and centralized control is conducted. The results show that centralized control dramatically improves the trajectory control ability of the system.

Design and development of an oil-free double-scroll air compressor used in a PEM fuel cell system

The purpose of this study is to arrive at an optimum design of a scroll compressor with requirements of a relative high volume flow rate and a compact structure, which is suitable for the use of hydrogen proton exchange membrane fuel cell (PEMFC) in the automotive application. An analytical model of multi-scroll compressors with arbitrary number of involute scrolls was established, and their working characteristics including the volume flow rate, built-in volume ratio, relative friction speed between the orbiting and fixed scrolls, and dimensions of scrolls were analyzed. An optimized double-scroll compressor, which can simultaneously meet the design requirements of the volume flow rate, structure size and oil-free lubrication, was designed, and a compressor prototype was developed and tested. Furthermore, numerical simulations of the working process of the double-scroll compressor were carried out and verified, and then p-V indicated diagram and the compressor performance were studied. Results show that the developed double-scroll compressor remarkably increases the volume flow rate, and reduces the relative friction speed between two scrolls simultaneously, compared with the conventional single-scroll structure; and therefore it shows very superior performance as an oil-free scroll air compressor used in the PEMFC of the automotive application.

A comprehensive review and analysis on CO2 heat pump water heaters

• Existing CO 2 HPWHs in industrial and residential sectors are reviewed. • Performance restricted by the pinch point effect is analyzed. • Limitations in CO 2 compressors and lubrication are revealed for the first time. • Current enhancements to overcome the limitations are summarized. In the context of the Montreal Protocol, CO 2 is considered as an appropriate natural refrigerant with an Ozone Depletion Potential (ODP) of zero and a Global Warming Potential (GWP) of one. A CO 2 heat pump water heater (HPWH) can provide hot water with a relatively high COP and consume significantly less energy than all electric or gas water heaters. This study reviews and analyses the existing CO 2 HPWHs both in industrial and residential sectors, where the low-temperature and high-temperature systems are classified by the heat delivery temperature of below and above 80 °C, respectively. The significance and features of existing CO 2 HPWHs are also summarised in this study. Moreover, the performance limitations of current CO 2 HPWHs are discussed considering the temperature gliding matching, and the technical constraints in both CO 2 compressors and heat exchangers. Due to the drastic variation of CO 2 heat capacity with temperature and pressure, the heat exchange process between sCO 2 and water is affected by the pinch point. The temperature gliding matching can be enhanced by optimising the parameters in both the CO 2 and water sides, using zeotropic refrigerant mixtures, or adding new devices or cycles to the existing CO 2 system. Another way to improve the system performance is increasing the discharge pressure or discharge temperature, while current CO 2 reciprocating compressors have an upper-temperature limit of 140 °C and upper-pressure limit of 140 bar, as well as some constraints in the heat exchangers. Due to the decomposition risk of lubricant in the compressor, two types of oil-free compressors (turbo and scroll) have been described. But it is found that the turbo-compressor is hard to provide a competitive efficiency when the pressure is high, and there is a significant leakage flow in a scroll compressor.

Trends in tribological behaviour of materials for compressors

This review accumulates information from various research works about the preferable manufacturing process, process parameters, parts of the compressor, working principle, material, and critical issues with some of the solutions that might be possible in the era of future industry. In addition, some work is also done on the tribological trends in the compressor. In this paper, detailed information has been gathered about the compressor parts and their working principle. A detailed analysis has been done on the material used to manufacture the compressor. Some details have been shared about preventing the loss to the compressor when it is in the application mode. As per this paper, PTFE/MoS2, FC, PEEK/Ceramic materials, mica-filled tetrafluoroethylene are advanced materials used for the compressor. Protective layers can be made on the parts to prevent some functional loss. Numerous studies have brought about great advancements in compressor performance, but many remain to be discovered. With n-TiO2 and n-MnO2, ZDDP (zinc disulfide) should be increased for antifriction properties. Some research has proven that CO2 can improve the tribological performance of two interacting surfaces by forming a lubricating carbonate layer that reduces friction and wears. New lubricating oils are showing promising results, but with the gradual depletion of natural oil resources, efforts have to be made to make various oils obtained from sources other than oil reserves or petroleum. A completely oil-free compressor with no lubrication in the crankcase and no lubrication in the other components dry oil-free air supply may be accomplished by employing various oil-less compressor technologies such as scroll water-injected screw, two-stage dry screw, and so on. In the 21st century, it aims to maximize energy savings from air compressors. It is critical to operating at a compression level that matches the amount of air consumption (optimal volume) and to avoid operating at a compression level that is greater than necessary. The conclusion can be obtained that understanding for the compressor will be established, and some tribological issues will be solved with new technology and material.