CFD Based Prediction of Rotordynamic Coefficients and Stability Analysis for Centrifugal Pump/Compressor

Fluid forces acting on the shrouded centrifugal pump/compressor impellers are evaluated using the computational fluid dynamics (CFD) approach. A face-seal impeller is selected to study for predicting the rotordynamic coefficients of the whirling impeller. The resultant impedances of the face-seal impeller can be modeled as a quadratic polynomial of whirling frequency to calculate the rotordynamic coefficients. However, the impedances of a conventional wear-ring seal impeller have some inflection points in the curves. Some possible sources that can affect the fluctuating impedance curves are investigated by varying design parameters such as shape of leakage path, inlet tangential velocity, flow rate of primary passage, and seal clearance. Effects of the peaks in the impedance curves of the wear-ring seal impeller are evaluated by performing stability analysis of a rotordynamic finite element (FE) model with the unconventional impedances. A linear curve-fit algorithm is developed to identify the complex shape of impedance curves of the wear-ring seal impeller. A Jeffcott rotor model with the impeller forces is modeled to apply and validate the developed curve-fit algorithm and the stability analysis has been performed. The analysis results indicate that the bump and dip in the impedance curves destabilize the Jeffcott rotor. Precessing motion of the shrouded centrifugal impeller is also an important vibration source that can cause the rotordynamic instability problem. By considering the tilted impeller, the reaction force and moment coefficients of the face-seal impeller are predicted utilizing CFD technique, and a full set of the rotordynamic coefficient matrices (4x4) is calculated. In order to evaluate the coupled motion of whirling and precessing for the face-seal impeller, a 3D impeller model with the dynamic eccentricity and the tilting angle is generated and the corresponding rotordynamic coefficients are obtained. The calculated results indicate that the precessing motion increases the tendency towards destabilization of the rotor. Lastly, influence of static eccentricity on the face-seal impeller is investigated. In actual operation of the rotor, misalignment may be destabilizing and cause serious vibration problems. A CFD modeling approach is developed to evaluate the forces for the statically eccentric face-seal impeller, and it has been found that the presence of static eccentricity on the face-seal impeller has an adverse effect on rotordynamic stability

Stability Analysis of a Multi-stage Gas Compressor With Swirl-brakes Using Three Dimensional Transient CFD Model

LectureMinimizing fluid induced forces through the secondary leakage flow paths in shrouded centrifugal impellers is crucial to improve the rotordynamic stability of high-pressure centrifugal gas compressors. Swirl brakes (SBs) are widely used in turbomachinery to reduce the fluid induced forces and enhance the system rotordynamic behavior. Prior to the present study, swirl-brakes of a high-pressure multistage compressor were designed using 3D steady-state computational fluid dynamics (CFD) analysis and verified through multiple fullscale closed loop tests for a compressor, operating with and without the SBs. In the present study, a 3D transient CFD analysis is conducted to calculate the fluid induced rotordynamic coefficients of a Teethon- Rotor (TOR) seal and the impeller shroud cavity. Full 360o fluid domains including the impeller, the shroud cavity, and TOR seals with either a swirl-brake or without it are numerically modeled. A mesh deformation technique is employed to follow the whirling rotor motion of the impeller. To evaluate the capability of the transient CFD model, comparisons are made between the prior test results and predictions from the current numerical study. The cross-coupled destabilizing forces as calculated from CFD are then compared with the methodologies recommended by API 617 and a few other researchers in the literature. In addition, the destabilizing forces calculated through the CFD methodology are used in rotordynamic simulations of the rotor, with and without SBs. Comparisons of simulation results to test results and field performance show good qualitative correlation. CFD predicts forces in the secondary flow path (without SBs) that cause early signs of instability observed in the compressor. The same methodology with SBs predicts cross-coupling forces that are benign, which is also confirmed by stable operation of the same compressor when rebuilt with SBs. These results are included in the paper

Novel water filtration of saline water in the outermost layer of mangrove roots

The scarcity of fresh water is a global challenge faced at present. Several desalination methods have been suggested to secure fresh water from sea water. However, conventional methods suffer from technical limitations, such as high power consumption, expensive operating costs, and limited system durability. In this study, we examined the feasibility of using halophytes as a novel technology of desalinating high-concentration saline water for long periods. This study investigated the biophysical characteristics of sea water filtration in the roots of the mangrove Rhizophora stylosa from a plant hydrodynamic point of view. R. stylosa can grow even in saline water, and the salt level in its roots is regulated within a certain threshold value through filtration. The root possesses a hierarchical, triple layered pore structure in the epidermis, and most Na+ ions are filtered at the first sublayer of the outermost layer. The high blockage of Na+ ions is attributed to the high surface zeta potential of the first layer. The second layer, which is composed of macroporous structures, also facilitates Na+ ion filtration. This study provides insights into the mechanism underlying water filtration through halophyte roots and serves as a basis for the development of a novel bio-inspired desalination method.Creative Research Initiative (Diagnosis of Biofluid Flow Phenomena and Biomimic Research) of the Ministry of Science, ICT and Future Planning (MSIP) , National Research Foundation (NRF) of Korea , ICT R&D program of MSIP/IITP (Korea

In vivo two-photon fluorescent imaging of fluoride with a desilylation-based reactive probe

A two-photon excitable molecular probe for fluoride, developed based on a fluoride-specific desilylation reaction, is demonstrated to be useful for fluorescent imaging of fluoride ions in live zebrafish by one-photon as well as two-photon microscopy for the first time.X117778Nsciescopu

Understanding Cultural Issues in the Diabetes Self-Management Behaviors of Korean Immigrants

PURPOSE: The purpose of this study was to explore potential factors affecting self-management behaviors in Korean immigrants with type 2 diabetes mellitus (KIT2Ds). METHODS: A qualitative descriptive design guided this study. Semi-structured interviews lasting 45-60 minutes were conducted with 20 KIT2Ds in the participant’s preferred language; in all cases this was Korean. Each interview was audio-taped, transcribed, and analyzed using conventional content analysis. Data analysis was performed in two steps. The data written in Korean were initially analyzed by three bilingual researchers. A qualitative researcher then participated in the analysis to refine the findings for presentation to an English speaking audience while staying true to the data and preserving the nuanced Korean meanings. RESULTS: The mean age of the sample was 64. 5 ± 11.6 years (9 men and 11 women). The mean years of staying in the U. S. and age at diabetes mellitus diagnosis were 23.6 ± 9.7 years and 52.5 ± 12.3 years, respectively. Three major ideas were identified: (a) issues on treatment regimen related to both medications and diet, (b) resources that helped or hindered their ability to manage diabetes, and (c) the physician/patient relationship. CONCLUSIONS: There were important cultural nuances that need to be addressed to better prepare KIT2Ds to manage their diabetes more effectively. A culture specific program should extend beyond a diabetes self-management education delivered in Korean language. Rather, content and education methods need to consider acculturation effects on diabetes management behaviors

Lifestyle habits and obesity progression in overweight and obese American young adults: Lessons for promoting cardiometabolic health: Lifestyle habits and obesity progression

Obesity among young adults is a growing problem in the United States and is related to unhealthy lifestyle habits such as high caloric intake and inadequate exercise. Accurate assessment of lifestyle habits across obesity stages is important for informing age-specific intervention strategies to prevent and reduce obesity progression. Using a modified version of the Edmonton Obesity Staging System (mEOSS), a new scale for defining obesity risk and predicting obesity morbidity and mortality, this cross sectional study assessed prevalence of mEOSS in 105 overweight/obese young adults and compared young adults’ lifestyle habits across the mEOSS stages. Descriptive statistics, chi-square tests, and one-way analyses of variance (ANOVA) were performed. About 80% of participants (n=83) fell into the mEOSS-2 group and had obesity-related chronic disorders such as diabetes, hypertension and/or dyslipidemia. There were significant differences in dietary quality and dietary patterns across the mEOSS stages. Findings highlighted the significance of obesity prevention and early treatment for overweight and obese young adults to prevent/stop obesity progression

Anti-Biofouling Features of Eco-Friendly Oleamide-PDMS Copolymers

The biofouling of marine organisms on a surface induces serious economic damage. One of the conventional anti-biofouling strategies is the use of toxic chemicals. In this study, a new eco-friendly oleamide-PDMS copolymer (OPC) is proposed for sustainable anti-biofouling and effective drag reduction. The anti-biofouling characteristics of the OPC are investigated using algal spores and mussels. The proposed OPC is found to inhibit the adhesion of algal spores and mussels. The slippery features of the fabricated OPC surfaces are examined by direct measurement of pressure drops in channel flows. The proposed OPC surface would be utilized in various industrial applications including marine vehicles and biomedical devices. © Copyright © 2020 American Chemical Society.1