Investigation On Premature Failure Of the Self-lubricated Piston Rings in Oil-free Compressor

Abstract: This paper presents the numerical simulation and experimental investigation on impact factors on premature failure of the self-lubricated piston rings in oil-free compressor. In this paper, the finite element method (FEM) was applied to study the non-uniform pressure distributions among the piston rings and the friction process between the self-lubricating piston rings and the cylinder wall, which influence the failure of the self-lubricated piston rings most. In order to verify the mathematic model, a test rig was built to measure the dynamic pressure distributions and temperature field between the piston rings. Both the theoretical and experimental results showed that the first piston ring afford more than 75% of the total pressure difference which was the main reason for the non-uniform wear and thus lead to early invalidation. The friction heat produced between the first piston ring and the cylinder was far more than the rest, which cannot be diffused rapidly through the low conductivity self-lubricating plastics and led to thermal failure of the self-lubricating piston rings. The results provide the theoretical basis to determine the design parameters and the thermal performance of piston rings reasonably

Study on the Effects of Vane Parameters on Separation Performance in an Axial Flow Cyclone Separator

The oil-gas cyclone separator is a key component to an oil injection compressor system for its advantages of small volume, simple structure, high separation efficiency and low pressure loss. This paper presents the investigation on new type axial flow cyclone separator performance under different structural parameters, including the angle of vanes, the number of vanes, the rotation angle of single vane, by numerical simulation and verification experiments. A numerical model of two-phase flow in the cyclone separator was established and the separation efficiency and pressure loss of cyclone separators were simulated. A test rig was built and the diameter distributions of droplets at the inlet and outlet of separator were measured by a Malvern laser particle size analyzer to verify the simulation model. The results showed that the separation efficiency and pressure loss can be improved with the increase of the rotation angle of vanes. With the decrease of the outlet angle of the first stage vane and the increase of the number of vanes, the critical separated droplet diameter of separator can be lowered effectively. The results showed that the optimum outlet angle of vanes is 22°~25° considering the separation efficiency and the pressure loss of separators

Analysis And Control Of Severe Vibration Of A Screw Compressor Outlet Piping System

The severe vibration of a screw compressor outlet piping system caused the fatigue failure of some thermowells and the unscheduled shut down of the system. The main reasons of the abnormal vibration in the outlet piping system were investigated by developing an acoustic model to simulate the gas pulsation and establishing two finite element models to conduct the mechanical vibration analyses. The acoustic analysis results showed that the pulsation amplitudes of most nodes in the outlet piping system exceeded the allowable values. The results of mechanical vibration analyses indicated that the insufficient stiffness of the outlet piping system and the first-order structure resonance occurred on thermowells were also the key factors inducing vibration. Several methods were put forward to attenuate vibration amplitude of the outlet piping system as well as the thermowells. A new pulsation attenuator was installed and the piping layout was rearranged to reduce pulsation amplitudes and shaking forces of all nodes in the outlet piping system. Several reasonable supports were added to improve the stiffness of the outlet piping system. After reinforcing the thermowells, the first-order natural frequency of the thermowells increased from 207.4Hz to 280.7Hz, away from the excitation frequency of 196.67Hz. The field measurement results showed that vibration amplitude and the vibration velocity decreased significantly after modifications

Different response to 1-methylcyclopropene in two cultivars of Chinese pear fruit with contrasting softening characteristics

In this study, the change in softening and its related genes expression under influence of 500 nl L-1 1-methylcyclopropene (1-MCP) was assessed in the two Chinese pear fruit, ‘Jingbaili’ (Pyrus ussuriensis Maxim) and ‘Yali’ (Pyrus bretschneideri Rehd), which exhibit different softening characteristics. ‘Jingbaili’ pear fruit softened rapidly after harvest, and was strongly inhibited by 1-MCP. In contrast, there was no obvious change of firmness compared to the control after 1-MCP treatment in ‘Yali’ pear fruit. The respiration and ethylene production rates were reduced by 1-MCP at early storage in both two cultivars. ‘Jingbaili’ pear fruit exhibited dramatically increased expression levels of the softening-related genes, i.e., polygalacturonase1 (PG1), polygalacturonase2 (PG2), β-Galactosidase4 (GAL4), α-arabinofuranosidase1 (ARF1) and α-arabinofuranosidase2 (ARF2), and these genes’ expression levels were significantly decreased by 1-MCP treatment. In contrast, ‘Yali’ pear fruit showed lower expression levels of the above-mentioned genes, as well as a relatively smaller inhibition effect by 1-MCP treatment before day 27. These results suggest that ‘Jingbaili’ pear fruit are more sensitive to 1-MCP/ethylene than ‘Yali’ pear fruit during ripening

Global analysis of data on the spin-orbit coupled A1Σu+A^{1}\Sigma_{u}^{+} and b3Πub^{3}\Pi_{u} states of Cs2

We present experimentally derived potential curves and spin-orbit interaction functions for the strongly perturbed $A^{1}\Sigma_{u}^{+}$ and $b^{3}\Pi_{u}$ states of the cesium dimer. The results are based on data from several sources. Laser-induced fluorescence Fourier transform spectroscopy (LIF FTS) was used some time ago in the Laboratoire Aim\'{e} Cotton primarily to study the $X ^{1}\Sigma_{g}^{+}$ state. More recent work at Tsinghua University provides information from moderate resolution spectroscopy on the lowest levels of the $b^{3}\Pi_{0u}^{\pm}$ states as well as additional high resolution data. From Innsbruck University, we have precision data obtained with cold Cs$_{2}$ molecules. Recent data from Temple University was obtained using the optical-optical double resonance polarization spectroscopy technique, and finally, a group at the University of Latvia has added additional LIF FTS data. In the Hamiltonian matrix, we have used analytic potentials (the Expanded Morse Oscillator form) with both finite-difference (FD) coupled-channels and discrete variable representation (DVR) calculations of the term values. Fitted diagonal and off-diagonal spin-orbit functions are obtained and compared with {\it ab initio} results from Temple and Moscow State universities

Complete genome sequence of the extremely acidophilic methanotroph isolate V4, Methylacidiphilum infernorum, a representative of the bacterial phylum Verrucomicrobia

<p>Abstract</p> <p>Background</p> <p>The phylum <it>Verrucomicrobia </it>is a widespread but poorly characterized bacterial clade. Although cultivation-independent approaches detect representatives of this phylum in a wide range of environments, including soils, seawater, hot springs and human gastrointestinal tract, only few have been isolated in pure culture. We have recently reported cultivation and initial characterization of an extremely acidophilic methanotrophic member of the <it>Verrucomicrobia</it>, strain V4, isolated from the Hell's Gate geothermal area in New Zealand. Similar organisms were independently isolated from geothermal systems in Italy and Russia.</p> <p>Results</p> <p>We report the complete genome sequence of strain V4, the first one from a representative of the <it>Verrucomicrobia</it>. Isolate V4, initially named "<it>Methylokorus infernorum</it>" (and recently renamed <it>Methylacidiphilum infernorum</it>) is an autotrophic bacterium with a streamlined genome of ~2.3 Mbp that encodes simple signal transduction pathways and has a limited potential for regulation of gene expression. Central metabolism of <it>M. infernorum </it>was reconstructed almost completely and revealed highly interconnected pathways of autotrophic central metabolism and modifications of C₁-utilization pathways compared to other known methylotrophs. The <it>M. infernorum </it>genome does not encode tubulin, which was previously discovered in bacteria of the genus <it>Prosthecobacter</it>, or close homologs of any other signature eukaryotic proteins. Phylogenetic analysis of ribosomal proteins and RNA polymerase subunits unequivocally supports grouping <it>Planctomycetes</it>, <it>Verrucomicrobia </it>and <it>Chlamydiae </it>into a single clade, the PVC superphylum, despite dramatically different gene content in members of these three groups. Comparative-genomic analysis suggests that evolution of the <it>M. infernorum </it>lineage involved extensive horizontal gene exchange with a variety of bacteria. The genome of <it>M. infernorum </it>shows apparent adaptations for existence under extremely acidic conditions including a major upward shift in the isoelectric points of proteins.</p> <p>Conclusion</p> <p>The results of genome analysis of <it>M. infernorum </it>support the monophyly of the PVC superphylum. <it>M. infernorum </it>possesses a streamlined genome but seems to have acquired numerous genes including those for enzymes of methylotrophic pathways <it>via </it>horizontal gene transfer, in particular, from <it>Proteobacteria</it>.</p> <p>Reviewers</p> <p>This article was reviewed by John A. Fuerst, Ludmila Chistoserdova, and Radhey S. Gupta.</p

Microstructural alterations of the hypothalamus in Parkinson's disease and probable REM sleep behavior disorder

Whether there is hypothalamic degeneration in Parkinson's disease (PD) and its association with clinical symptoms and pathophysiological changes remains controversial. We aimed to quantify microstructural changes in hypothalamus using a novel deep learning-based tool in patients with PD and those with probable rapid-eye-movement sleep behavior disorder (pRBD). We further assessed whether these microstructural changes associated with clinical symptoms and free thyroxine (FT4) levels. This study included 186 PD, 67 pRBD, and 179 healthy controls. Multi-shell diffusion MRI were scanned and mean kurtosis (MK) in hypothalamic subunits were calculated. Participants were assessed using Unified Parkinson's Disease Rating Scale (UPDRS), RBD Questionnaire-Hong Kong (RBDQ-HK), Hamilton Depression Rating Scale (HAMD), and Activity of Daily Living (ADL) Scale. Additionally, a subgroup of PD (n = 31) underwent assessment of FT4. PD showed significant decreases of MK in anterior-superior (a-sHyp), anterior-inferior (a-iHyp), superior tubular (supTub), and inferior tubular hypothalamus when compared with healthy controls. Similarly, pRBD exhibited decreases of MK in a-iHyp and supTub. In PD group, MK in above four subunits were significantly correlated with UPDRS-I, HAMD, and ADL. Moreover, MK in a-iHyp and a-sHyp were significantly correlated with FT4 level. In pRBD group, correlations were observed between MK in a-iHyp and UPDRS-I. Our study reveals that microstructural changes in the hypothalamus are already significant at the early neurodegenerative stage. These changes are associated with emotional alterations, daily activity levels, and thyroid hormone levels. [Abstract copyright: Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.