Stall Margin Improvement in a Centrifugal Compressor through Inducer Casing Treatment

The increasing trend of high stage pressure ratio with increased aerodynamic loading has led to reduction in stable operating range of centrifugal compressors with stall and surge initiating at relatively higher mass flow rates. The casing treatment technique of stall control is found to be effective in axial compressors, but very limited research work is published on the application of this technique in centrifugal compressors. Present research was aimed to investigate the effect of casing treatment on the performance and stall margin of a high speed, 4 : 1 pressure ratio centrifugal compressor through numerical simulations using ANSYS CFX software. Three casing treatment configurations were developed and incorporated in the shroud over the inducer of the impeller. The predicted performance of baseline compressor (without casing treatment) was in good agreement with published experimental data. The compressor with different inducer casing treatment geometries showed varying levels of stall margin improvement, up to a maximum of 18%. While the peak efficiency of the compressor with casing treatment dropped by 0.8%–1% compared to the baseline compressor, the choke mass flow rate was improved by 9.5%, thus enhancing the total stable operating range. The inlet configuration of the casing treatment was found to play an important role in stall margin improvement

Self-reported musculoskeletal pain among dentists in Visakhapatnam: A 12-month prevalence study

Background: Of the occupational hazards experienced by dental professional worldwide, work-related musculoskeletal disorders (WRMSDs) are quite common. Research in the past has recognized that musculoskeletal disorders in dentistry contribute considerably to sick leave, reduced productivity, and dentist attrition. Considering the magnitude of these disorders, an attempt has been made to determine the prevalence and associated factors of various WRMSD. Aim: The aim of this study was to investigate the prevalence of self-reported, work-related musculoskeletal problems regarding the perception of pain, over the preceding 12 months and also to identify associated factors which might influence pain among dentists. Subjects and Methods: A self-administered questionnaire was personally handed over to a select sample of practicing dentists in Visakhapatnam, Andhra Pradesh. The survey was performed using the Nordic Musculoskeletal Questionnaire. Results: This study revealed musculoskeletal pain with a frequency of 56% in the neck, 39% in the hand, 32% in the lower back, and 18% in the shoulder regions. Chi-square test showed a significant association between pain in the neck and gender, age, height, and weight (P < 0.05). Pain in lower back was associated with gender, body mass index (BMI), height, and experience (P < 0.05). Pain in the hand was only related to the experience of the dentist (P < 0.05). Conclusion: Within the limits of the study, the prevalence of WRMSD among dentists in Visakhapatnam, especially involving the neck, hand, lower back, and shoulders, is high. Gender, age, height, and weight, BMI and experience were found to be related with musculoskeletal pain