Effect Of Transition Region Research Articles

Experimental and numerical investigation on the tensile properties of a titanium alloy disc with dual microstructure

Titanium alloys are used extensively as compressor discs in aero engines. The operating condition of an engine demands better tensile strength and fatigue resistance at the center or bore region of a disc while better creep resistance, fracture toughness and lower crack growth rate are required at the rim. To meet the aforementioned location specific properties, a dual microstructure near α titanium alloy disc with an equiaxed microstructure at the center and fully transformed β microstructure at the rim has been produced using a differential heat treatment process. Varying the microstructures at bore and rim of an integral component results in a transition region where the microstructure varies drastically from one location to another. No systematic study has been reported so far either on the effect of transition region or on the effect of varying microstructural constituents on the mechanical properties. An attempt has been made here to provide this essential information which is required to decide the location of transition region or the proportion of varying microstructural constituents while producing dual microstructure discs for aero engine application. The room temperature tensile property of dual microstructure disc has been evaluated experimentally by varying the microstructural proportion across the tensile sample cross-section or gauge length. Further, to gain better insight on the tensile behaviour of dual microstructure samples, three different numerical approaches were investigated to identify a suitable one. Using the identified numerical procedure, the strength of dual microstructure samples with varying microstructural constituents across the sample gauge length were predicted and compared with the experimental results. The results obtained are presented and discussed here.

Experimental investigations on adiabatic frictional pressure drops of R134a during flow in 5 mm diameter channel

The article presents detailed two-phase adiabatic pressure drops data for refrigerant R134a at a saturation pressure of 5.5bar corresponding to the saturation temperature of 19.4°C. Study cases have been set for a mass flux varying from 100 to 500kg/m2s. The frictional pressure drop was characterized for the refrigerant R134a, for vapor qualities ranging from 0 to 1. Long-time thermal stability of test facility allowed to gather a comprehensive experimental database for two-phase frictional pressure drop including multiple data points in transition and dryout flow regions. The effect of transition region on the peak value of two-phase frictional pressure drop, for literature models and experiment, is recognized.A systematic assessment of predictive techniques for two-phase frictional pressure drop in adiabatic flows for varying vapor quality was conducted. Both qualitative and quantitative analysis of gathered data vs. literature models was presented. Verification of the pressure drop for two-phase adiabatic flow showed that for Zhang and Webb correlation 93% of experimental data fits in the range of ±30%. The model proposed by Thome et al. in other hand predicts almost 33% of data within 10% error, but only 80% of the data is predicted within 30% error. Additional prediction of the peak value of two-phase frictional pressure drop with literature models and the experiment was made.

The effect of transition region on the direct tunneling current and Fowler–Nordheim tunneling current oscillations in ultrathin MOS structures

The effects of transition region on direct tunneling and Fowler–Nordheim (FN) tunneling in ultrathin metal–oxide–semiconductor field transistors are investigated by numerical analysis. Direct tunneling current in ultrathin gate oxide is shown to increase with the width of transition region. The applied voltage across the oxide at the maximum and minimum of FN tunneling current oscillations is observed to increase with the width of the transition region, and its relative increase also strongly depends on the width. Furthermore, the amplitude of FN tunneling current oscillations descends with the width of transition region, however, its attenuation factor trends to increase with the width. Usually the amplitude and its attenuation factor decrease with the ordinal number of current oscillation increasing. So the effect of the transition region on FN tunneling current oscillations may be used to extract the information about the transition region.

Disturbance Phenomena in Probe Measurement of Ionized Gases

This paper is concerned with disturbance phenomena occuring when a probe is immersed in plasma. There are two types of disturbance, i.e., one independent of probe potential and one which depends upon it. The former (inherent) disturbance has three effects which are classified: Asymmetrical effect, formation effect of transition region, and the scattering effect. The latter (incidental) depends on either the negative probe or the positive probe. In the negative probe, penetration of ion sheath into surrounding plasma is characteristic. In the positive probe, there is an unexpected change of electron current, as a result of drainage of electron, which is observed with rise of positive probe voltage. The mechanism of collection of ion and electron on probe is also explained in terms of these disturbance effects.