Experimental and numerical study on aerodynamic noise of outdoor unit of room air conditioner with different grilles

The aerodynamic and aeroacoustic performances of outdoor unit with two different types of grille have been investigated in present study. Experimental results indicate that the grille sharp will affect the flow rate and increase broadband noise level of outdoor unit. Based on noise generation mechanism and CFD simulation, vortex shedding noise model and inlet turbulence noise model are adopted to predict the broadband noise level of outdoor unit. When vortex shedding noise is concerned, the wake parameters should be calculated at 3 mm downstream of grille to achieve good accuracy. Inlet turbulence noise is generated from the interaction between blade wake and the grille, and plays less important role in present outdoor unit configuration. In comparison with experimental results, it is shown that the broadband noise prediction method could provide reasonable accuracy and the error between prediction and experiment is less than 1 dBA.     

选择性气体吸附剂的研究进展

具有高选择性的气体吸附剂是吸附领域的研究重点。对选择性气体吸附剂的最新研究概况进行了综述。重点阐述了选择性吸附机理、选择性吸附剂的进展及其有代表性的应用领域,并对选择性气体吸附剂的发展前景进行了展望。     

大理岩三轴压缩变形破坏与能量特征研究

利用伺服试验机对大理岩进行了常规三轴压缩试验,基于试验结果,研究了岩样三轴压缩变形破坏及其能量特征。结果表明,低围压时岩样内部材料并未均匀化,岩石表现为应变软化特性;而高围压时岩样内部材料强度由低到高逐渐屈服,变形趋于均匀,岩石出现塑性流动特性。岩石峰值应变与围压成正线性关系;岩石残余强度对围压的敏感性显著高于峰值强度。岩石破坏应变能随着围压的增大而增大,且两者成正线性关系;岩石全部断裂能随着围压的增加亦成正线性增加。     

Wear-corrosion mechanism of stainless steel in chloride media

A laboratory technique to study the combined effects of mechanical and electrochemical changes during a wear process in a corroding environment is presented. Cathodic protection is beneficial because it stops corrosion, and the wear is merely mechanical. At anodic potentials, chemical reactions lead to a wear rate almost twice the wear rate under cathodic protection. The difference between the two levels represents the rate of corrosive wear. A model is proposed for the corrosive wear based on the film growth rate and the rate of removal of the oxide layer. Experimental results verify this model.     

Computational analysis methods to quantify a.c. impedance data

For the interpretation of a.c. impedance data, two data analysis techniques are described and evaluated. The first method is a least squares analysis of a nonlinear model. Modifications to a previously published algorithm, CIRFIT, include a least squares estimate of the double layer capacitance. Also, two convergence techniques for CIRFIT were explored and evaluated. The second method is a nonlinear least squares analysis of an equivalent circuit consisting of three RC parallel combinations, the final circuit containing a diffusion limiting impedance. The method satisfactorily estimated the component values of the proposed equivalent circuit, even when two time constants were closely spaced. Both methods could be valuable in analyzing, modeling, and interpreting experimental a.c. impedance data.     

On the use of quantum chemical methods as an additional tool in studying corrosion inhibitor substances

A quantum chemical study of the efficiency of several aromatic organic compounds as corrosion inhibitors has been performed by means of the MNDO semi-empirical SCF molecular orbital method. The inclusion of metal atoms in the calculation and the corresponding formation of stable complexes between the inhibitor and the metallic surface allows a better realization of this kind of inhibition process. The agreement with the experimental data is quite good.     

Centrifugal pump for superfluid helium

This Paper summarizes and correlates the liquid helium pump data obtained previously in two separate test programs. In normal helium the second set of data shows a large performance improvement over the first set as a result of changes in measurement methods and in the pump itself. Peak pump efficiencies of 46% were measured. The pump appeared to perform approximately the same in He II as in He I; however, the He II data are not adequate for system design or analyses. Therefore, a new pump test program is planned to test the improved version of the pump in an apparatus designed specifically for He II.     

Disc cache for PCs: Speedier access to disc storage

Disc caching is a well-accepted technique designed to speed access to disc storage. For the first time, it is being applied to personal computers. The problem in the past has been designing and implementing caching algorithms. There are two types, prefetch and replacement. Both try to provide an optimum choice of what data to keep in cache memory and to predict future data accesses. A UK company has addressed the problem and claims to have radically improved access time.     

Charge-discharge characteristics of the lithium electrode in mixed ether electrolytes

Mixed ether solutions of 1,2-dialkoxyethanes with 1,3-dioxolane or tetrahydrofuran containing some lithium salts have been examined as electrolytes for ambient temperature, rechargeable lithium (Li) batteries. The electrolytic conductivity and the charge-discharge behaviour of the Li electrode were investigated in the alkoxyethane-based electrolytes. The solutions containing LiPF₆ showed high conductance. The polarization behavoiur and the charge-discharge efficiency of the Li electrode were markedly affected by the size of an alkoxy group of ether. The cycling efficiency also depended on the electrolytic salt and the blended co-solvent. The highest efficiency was observed in the mixed system of 1,2-dimethoxyethane-tetrahydrofuran containing LiPF₆.     

The effects of biaxial loading on the fracture characteristics of several engineering materials

A test system has been developed at The George Washington University for testing flat-sheet, center-cracked specimens over a wide range of applied biaxiality ratios. The test system provides independent control of the two perpendicular axes, with either phased static or cyclic loading (selectable phase angles) or completely independent loading functions possible. A photoelastic study was performed for several variations in specimen geometry, and the results showed good agreement with analytical predictions and other photoelastic results of similar specimen geometries. Two polymers, PMMA and PVC, and three aluminum alloys encompassing a wide range of ductility were tested.The fracture toughness values of both polymers decreased with increasing load biaxiality. The load biaxiality was found to have a strong influence on the crack growth direction in PMMA and a negligible influence on the PVC. The toughness values for 7075-T6 aluminum increased with increasing biaxiality, while for the more ductile 2024-T3 and 6061-T4 intermediate peak toughness values were observed at a biaxiality ratio of 0.5. The fracture toughnesses at the highest biaxiality ratios were approximately equal to the uniaxial results, which suggest the possibility that the tabs parallel to the cracks may have pulled off, thus releasing the biaxial constraint.