Mathematical modeling of mixing phenomena in a gas stirred liquid bath

A macroscopic, steady state energy balance model has been formulated to describe mixing phenom-ena in a liquid bath stirred by injecting gas through a straight nozzle fitted axially at the bottom of the vessel. This, along with experimental data on a water model previously reported, was employed to make predictions. Input energy terms considered in the model consist of buoyancy energy and empirically determined fraction of gas kinetic energy. Dissipation of energy was attributed to liquid circulation and bubble slip. The two-phase plume was assumed to be a truncated cone whose dimen-sions depended upon operating conditions. Numerical solution of model equations gave liquid velocity and gas hold-up inside the plume as well as liquid circulation rate and liquid velocity in the region outside the plume. Influence of process variables, e.g., gas flow rate, bath height, and nozzle diameter, have been predicted. Validity of the model has been established by comparing some pre-dicted entrainment ratios with those experimentally measured by other investigators. Empirical cor-relations to predict circulation time and circulation number have been proposed. Circulation number was found to vary between 2 and 12 in contrast to the existing assumption in the literature of a con-stant value of 3. Usefulness of these correlations in predicting mixing time for industrial vessels has been demonstrated. Formerly a Graduate Student in the De-partment of Metallurgical Engineering at the Indian Institute of Technol-ogy, Kanpur     

Toward targets for initiation of chronic dialysis

OBJECTIVES: To better define the targets for initiation of chronic dialysis, we compared the relationship between the normalized protein equivalent of nitrogen appearance (nPNA, g/kg standard weight/day) and weekly urea clearance (Kt) normalized to total body water (V) in predialysis chronic renal failure (CRF) patients and in patients on continuous ambulatory peritoneal dialysis (CAPD) and hemodialysis (HD). We also studied the relationships of other nutritional parameters to weekly Kt/Vurea in CRF patients. DESIGN: This cross-sectional study was a prospective observational design meant to study each patient once. SETTING: The University Hospital and Clinics and Harry S. Truman VA Medical Center, Columbia, Missouri. PATIENTS: Forty-five consecutive predialysis CRF patients were enrolled and the results compared with patients on CAPD and HD. RESULTS: In CRF, the nPNA calculated from urea appearance correlated with the weekly Kt/Vurea (r = 0.57, p < 0.0001) and, using exponential best-fit, nPNA = 1.217 x (1-e-0.769Kt/V). This exponential relationship was similar to that for CAPD and both were different from that in patients on HD. Likewise, nPNAs, calculated from Kjeldahl nitrogen output, and weekly Kt/Vurea were correlated (r = 0.37, p = 0.014) and, using exponential best-fit, nPNA = 1.102(1-e-0.867Kt/V), similar to the relationship in patients on CAPD. Evidence is presented that these relationships are not explained only by mathematical coupling. There was a significant correlation between the weekly Kt/Vurea and 24-hour urinary creatinine excretion. CONCLUSIONS: The findings suggest that in CRF, as in CAPD, a weekly Kt/Vurea less than 2.0 is likely to be associated with a nPNA less than 0.9 g/kg standard weight. In CRF patients, initiation of chronic dialysis should be considered if weekly renal Kt/Vurea falls below 2.0 and a nPNA greater than 0.8 is desired.     

Biodegradation of Phenol with Wastewater as a Cosubstrate in Upflow Anaerobic Sludge Blanket

Anaerobic degradation of phenol mixed with a readily degradable synthetic wastewater (DSWW) as a cosubstrate was studied in a 12?L upflow anaerobic sludge blanket reactor at 30±2°C over a period of 632?days. DSWW was prepared by diluting sugar cane based molasses. The biomass was acclimatized to high phenol concentration by gradually decreasing the DSWW chemical oxygen demand (COD) of 4,000?mg/L. Feed made up of phenol COD and DSWW COD in the ratio of 7:3 (phenol concentration = 1,176?mg/L) was successfully treated at a hydraulic retention time (HRT) of 12?h and organic loading rate (OLR) of 8?g?COD/L?day. Phenol removal ranged from 99.9 to 84% at phenol COD varying from 10 to 70% in the feed. During the entire operation, COD removal varied from about 74 to 91.3%. The influent COD was distributed into CH4–COD ( ～ 72%), effluent COD ( ～ 17%), and sludge and unaccounted COD ( ～ 11%). The process failure occurred at 4:1 phenol COD: DSWW COD. Specific methanogenic activity of granular sludge exhibited uniform activity up to phenol COD of 70%. The performance of the reactor could not be maintained beyond 70% phenol COD even by reducing the sludge loading rate, increasing HRT, or decreasing OLR.     

Anaerobic Degradability: Effect of Particulate COD

Batch bioassay tests were conducted to evaluate the effect of particulate chemical oxygen demand (COD) (CODP) on anaerobic digestion of wastewater at different ratio of food to microorganism (F/M). Synthetically prepared soluble and complex wastewaters were used. Experiments were conducted in seven sets of serum bottles maintained at F/M ranging from 0.18 to 2.0. Each set contained six bottles having a total COD (CODT) of 500 mg and CODP from 0 to 100%. Methane generation conforms to the first order rate kinetics. At all F/M, k?(day?1) decreased linearly with increase in fraction of CODP?(CODPF = CODP/CODT). Biomethane potential (BMP), and substrate and sludge activities also exhibited declining trend with increasing CODPF. The optimum value of F/M ranged from 0.57 to 0.68. The two variables, CODPF and F/M, were compounded to yield the ratio of CODP to microorganisms [M, measured as volatile suspended solids (VSS)]. On increasing the CODP/VSS from 0 to 0.9, the rate constant for methane generation is reduced by 81%. BMP30, percent sludge activity, and substrate utilization rate are lowered by 52–55%. These correlations could serve as useful guidelines to quantitatively assess the impact of particulate COD on biodegradability parameters.     

Thermodynamics of iron-aluminum alloys at 1573 K

The activities of iron (Fe) and aluminum (Al) were measured in Fe-Al alloys at 1573 K using the ion-current-ratio technique in a high-temperature Knudsen cell mass spectrometer. The Fe-Al solutions exhibited negative deviations from ideality over the entire composition range. The activity coefficientsγ _Fe, andγ _A1 are given by the following equations as a function of mole fraction (x _Fe,x _Al): 1 $$\begin{gathered} 0< \chi _{A1}< 0.4 \hfill \\ ln \gamma _{Fe} = - 4.511 ( \pm 0.008)\chi _{A1}^2 \hfill \\ ln \gamma _{A1} = - 4.462 ( \pm 0.029)\chi _{Fe}^2 + 0.325( \pm 0.013) \hfill \\ 0.6< \chi _{A1}< 1.0 \hfill \\ ln \gamma _{Fe} = - 4.065 ( \pm 0.006)\chi _{A1}^2 + 0.099( \pm 0.003) \hfill \\ ln \gamma _{A1} = - 4.092 ( \pm 0.026)\chi _{Fe}^2 + 0.002( \pm 0.001) \hfill \\ \end{gathered} $$ The results showed good agreement with those obtained from previous investigations at other temperatures by extrapolation of the activity data to 1573 K.     

Manufactured Housing Production Layout Design

This paper presents exploratory research work in facility layout design of a manufactured housing production plant. Manufactured homes are built in a factory on an assembly line that consists of activity stations, subactivity stations, feeder stations, and storage areas. This research developed systematic process steps for the layout design of manufactured housing production plants with a qualitative approach. The qualitative approach takes into account space requirements and proximity parameters. For this purpose, the tools and techniques available in industrial and manufacturing engineering were investigated. Data related to the space and proximity requirements in the two case study production plants were collected, and alternative layouts were developed. These layouts were analyzed to suggest the best possible layout. Finally, layout design steps for the qualitative analysis of the facility design were presented in the form of a process flowchart.     

Sex Differences and Individual Differences in Cognitive Performance and Their Relationship to Endogenous Gonadal Hormones and Gonadotropins.

Sexually dimorphic cognitive performance in men (n=42) and women (n=42) was related to testosterone, estradiol, progesterone, luteinizing hormone, follicle-stimulating hormone, and sex hormone binding globulin, measured in 10-ml blood samples collected between 0900 and 1030 and, among women, during the follicular phase of the menstrual cycle. Significant sex differences favored men on spatial tasks (Mental Rotation and Judgment of Line Orientation) and on an inhibition task and favored women on a verbal task (category fluency). However, there were no significant relationships between any of the hormones and cognitive performance, suggesting that there are few, if any, consistent, substantial relationships between endogenous, nonfluctuating levels of gonadal hormones or gonadotropins and these cognitive abilities in men or women. (PsycINFO Database Record (c) 2010 APA, all rights reserved)