Influence of shaped injection holes on turbine blade leading edge film cooling

To improve the film cooling performance by shaped injection holes for the turbine blade leading edge region, we have investigated the flow characteristics of the turbine blade leading edge film cooling using five different cylindrical body models with various injection holes, which are a baseline cylindrical hole, two laidback (spanwise-diffused) holes, and two tear-drop shaped (spanwise- and streamwise-diffused) holes, respectively. Mainstream Reynolds number based on the cylinder diameter was 7.1 × 10⁴ and the mainstream turbulence intensities were about 0.2%. The effect of injectant flow rates was studied for various blowing ratios of 0.7, 1.0, 1.3 and 1.7, respectively. The density ratio in the present study is nominally equal to one. Detailed temperature distributions of the cylindrical body surfaces are visualized by means of an infrared thermography (IRT). Results show that the conventional cylindrical holes have poor film cooling performance compared to the shaped holes. Particularly, it can be concluded that the laidback hole (Shape D) provides better film cooling performance than the other holes and the broader region of high effectiveness is formed with fairly uniform distribution.     

A Heuristic Method for Channel Allocation and Scheduling in an OFDMA System

In this letter, a heuristic channel allocation and scheduling scheme is proposed. By comparing the size of the alternative‐factor assessment, which is obtained by simple calculation, we can easily find the most appropriate channel for each user for overall throughput enhancement. Numerical results show that the downlink throughput of the proposed scheme is higher than that of proportional fairness and is almost the same as that of the maximum C/I scheme, while user fairness remains better than that of the maximum C/I scheme.     

Efficacy of various disinfectants in killing a resistant strain of Pseudomonas aeruginosa by comparing zones of inhibition: implications for endoscopic equipment reprocessing

OBJECTIVE: Previous studies have shown that high-level disinfection of GI endoscopes may not be reliably achieved using glutaraldehyde at room temperature. In our laboratory, we have isolated a strain of Pseudomonas aeruginosa that is resistant to disinfection with glutaraldehyde. We compared the bactericidal activity of various disinfectants against this organism. METHODS: One hundred microliters of an overnight culture of this organism was spread onto blood agar plates. Twenty microliters of a disinfectant was placed on a sterile 7-mm filter paper, placed on the blood agar plate, and incubated overnight at 37 degrees C to determine the zone of inhibition for each disinfectant tested. Disinfectants included Cidex, Dispatch, Virahol, OMNI II, Lysol, IodoFive, Lysol I.C. Spray, and Chlorox. The zone of inhibition (i.e., clearing) roughly correlates with the bactericidal strength of the disinfectant. RESULTS: Compared with the glutaraldehyde-containing solution Cidex, the alcohol-containing disinfectants Lysol I.C. Spray and Virahol had the largest mean zones of inhibition (11.33 vs 20.60 and 20.55 mm; p = 0.0001). The hypochlorite compounds Chlorox (1:10 dilution) and Dispatch had mean zones of inhibition similar to that of Cidex (11.08 and 11.25 mm vs 11.33 mm; p = not significant). The phenolic compounds OMNI II and Lysol had mean zones of inhibition smaller than that of Cidex (10.50 and 10.35 mm vs 11.33 mm; p < 0.006), and the phosphoric acid and iodine-containing IodoFive had the smallest mean zone of inhibition (9.70 vs 11.33 mm; p = 0.0001). CONCLUSIONS: The alcohol-containing disinfectants had the largest zones of inhibition against resistant P. aeruginosa. These compounds may be more effective than glutaraldehyde for endoscopic equipment reprocessing.     

Decoupled output voltage control of quantum series resonantconverter for improved buck-boost operation

A new output voltage control technique is proposed to obtain the improved buck-boost operation of the quantum series resonant power converter (QSRC). The new nonlinear dynamic model of QSRC is first derived and the cross-coupled nonlinear term existing in the output voltage dynamics is decoupled by using control methods such as the periodic control of the boosting switch (PCBS) and the resonant current control (RCC). By applying the state-space averaging concept to the decoupled dynamics, two linear large signal averaged models are obtained for PCBS and RCC schemes. Using the proposed technique, the flux imbalance problem of the isolation transformer and the robustness of the output voltage response can be easily considered. This technique can also be widely applicable to the cascade buck-boost power converter, which can be implemented by inserting a boosting switch between the output filter inductor and the ripple capacitor of the forward power converter. The validity of the proposed scheme is confirmed by the computer simulations and the experiments     

Determination of equivalent single crack based on coalescence criterion of collinear axial cracks

In a nuclear power plant the steam generator tubes cover a major portion of the primary pressure-retaining boundary. Thus, very conservative approaches have been taken in the light of steam generator tube integrity. According to the present criteria, tubes wall-thinned in excess of 40% should be plugged whatever the cause. However, many analytical and experimental results have shown that no safety problems exist even with thickness reductions greater than 40%. The present criterion was developed about 20 years ago when wear and pitting were dominant causes for steam generator tube degradation, and it is based on tubes with single cracks regardless of the fact that the appearance of multiple cracks is more common in general. The objective of this study is to review the conservatism of the present plugging criteria of steam generator tubes and to propose a new coalescence model for two adjacent through-wall cracks existing in steam generator tubes. Using the existing failure models and experimental results, we reviewed the conservatism of the present plugging criteria. In order to verify the usefulness of the proposed new coalescence model, we performed finite element analysis and some parametric studies. Then, we developed a coalescence evaluation diagram.