CORROSION BEHAVIOR OF POWDER METALLURGY ALUMINUM ALLOY 6061/AL2O3 METAL MATRIX COMPOSITES

The electrochemical behavior of aluminum alloy 6061/Al2O3 metal matrix composite was investigated in 3.5% NaCl aqueous solution. Two composite compositions were examined containing 10% and 30% (by volume) of sub-micron alumina particulates as the reinforcement phase. The composites were fabricated via powder metallurgy processing. Cyclic polarization tests were carried out to determine pitting potentials and repassivation potentials in deaerated 3.5% NaCl solution. The pitting potential was 50 mV more noble for the higher-content reinforcement composite, while the repassivation potentials were essentially identical. The scanning electron microscope was used to reveal pits morphologies generated potentiostatically at a potential 150 mV more noble than the open circuit potentials for two hours immersion in quiescent chloride solution. Excessive pitting of the matrix alloy was observed in both composites. Pits forming in the 6061/Al2O3/30p composite were more numerous and more uniformly dispersed compared to pits on the lower-content reinforcement composite which were deeper and more localized. Preliminary results suggest that pit initiation sites correlate with regions exhibiting agglomeration of the reinforcement particles

GT2004-53828 Instrumentation Selection and Uncertainty Analysis for Performance Test of Small Centrifugal Compressors

ABSTRACT In the design phase of centrifugal compressors, it is essential to have some experimental results on performance. The extent of usefulness of the experiments depends on quality and accuracy of the results. Part of proper experimental procedure is the correct selection of instrumentation leading to lower uncertainty in the final results. ASME PTC 10 (Performance Test Code on Compressors and Exhausters) requires fluctuation limits on the measured performance parameters. This does not guarantee limits for accuracy of performance parameters. Also, different experimental setup will affect uncertainty of the results, even with similar instrumentation accuracy. The present research deals with uncertainty analysis for performance evaluation of small-scale centrifugal compressor. The instrumentation errors are accommodated in the relation to ASME PTC 19.1 (test uncertainty). The analysis takes into consideration the correlated bias limits. Selection of proper type of instruments for measuring associated parameters is based on literature review. A case study is included as an example to illustrate the selection on instrumentation accuracy and preferred bias correlations. The analysis is a useful tool in designing experiments for testing compressor and optimizing accuracy of results

CORROSION BEHAVIOR OF POWDER METALLURGY ALUMINUM ALLOY 6061/AL2O3 METAL MATRIX COMPOSITES

The electrochemical behavior of aluminum alloy 6061/Al2O3 metal matrix composite was investigated in 3.5% NaCl aqueous solution. Two composite compositions were examined containing 10% and 30% (by volume) of sub-micron alumina particulates as the reinforcement phase. The composites were fabricated via powder metallurgy processing. Cyclic polarization tests were carried out to determine pitting potentials and repassivation potentials in deaerated 3.5% NaCl solution. The pitting potential was 50 mV more noble for the higher-content reinforcement composite, while the repassivation potentials were essentially identical. The scanning electron microscope was used to reveal pits morphologies generated potentiostatically at a potential 150 mV more noble than the open circuit potentials for two hours immersion in quiescent chloride solution. Excessive pitting of the matrix alloy was observed in both composites. Pits forming in the 6061/Al2O3/30p composite were more numerous and more uniformly dispersed compared to pits on the lower-content reinforcement composite which were deeper and more localized. Preliminary results suggest that pit initiation sites correlate with regions exhibiting agglomeration of the reinforcement particles

GT2004-53821 Design of Small Centrifugal Compressors Performance Test Facility

ABSTRACT Improper selection of the instrumentation for a single test rig may lead to inaccurate reading, increase cost or even failure in the system, such as the failure of the mass flow measurement at the venture nozzle, Colantuoni and Colella Actual performance testing is a key element in the design stage, development and troubleshooting of centrifugal compressors. The present work discusses the procedure for designing the experimental setup and the selection of drive unit for variable centrifugal compressors sizes. It starts with setting criteria of selection. A survey over different types of drive units and facility setup was conducted. It was found that the electric drive unit with the aid of transmission for stepping-up the speeds is the most suitable type. This is due mainly to the excellent control property of electric motors allowing for wide range of operational speed and power. A new methodology was developed for selecting operational power and speeds of the drive unit for different sizes of impellers. The code, used for the analysis, was developed by the authors. It calculates the range of input power, input torque, and rotational speeds, as well as, the mass flow rate, total pressure and temperature ratios for different sizes of impellers. This will aid in selecting the proper instrumentation for the experiments. The code used for design methodology is based on one dimensional through flow formulation and validated with experimental results in the literature. It is expected that the present methodology will enhance selection procedure for designing compressor test facility. Some commercial codes are available and designed to estimate the operating conditions of the centrifugal compressors. However, most of them are for industrial applications and used to evaluate conditions during operation and not for the designing purposes, such as, Centrifugal Compressor Tracking Program developed by Ronald, P. Lapina. On the other hand, there are limited codes that can calculate the operating conditions of the compressor for designing purposes. An example of that is the codes developed by PCA Engineering and Concepts Incs. However, these codes do not show on the same figure the effect of changing impeller size or configuration. The present work involves the development of a code that predicts centrifugal compressor performance at different sizes and configurations. Presentation of results is designed such as the selection of drive unit characteristics can be done in a very efficient manner. On the other hand, one of the main requirements in designing the test facility is selecting the proper type of driver unit. For instance, in the present study, the driver has to be flexible to test different types of compressors with good control system on the rotational speed, especially near the surge condition