Large-eddy-simulation of buoyancy-induced mixing for water treatment applications

Large-Eddy Simulation is applied to investigate the turbulent mixing produced by aeration system in wastewater treatment. The solver uses an Eulerian-Lagrangian point-particle model to couple liquid and gas phases. Transport of a passive tracer is simulated to visualize the homogeneity of mixing. The accuracy of the solver predicting the mixing of the tracer time has been validated versus experimental data in a bubble reactor with different diffuser configurations. The mixing induced by bubble screens is simulated and compared - at different flow rates - with that produced by discrete plumes. The results show significant differences in the mixing times and energetic efficiency for different aerator setups

Initiation and early-stage growth of internal fatigue cracking under very-high-cycle fatigue regime at high temperature

The initiation and early-stage crack growth under very-high-cycle fatigue (VHCF) at room temperature, 750 degC and 850 degC on directionally-solidified Ni-base superalloy have been investigated. There was little frequency effect of 20 kHz on fatigue lives when compared with 100 Hz, nor did the deformation and fracture mechanisms. Dislocation tangles re-arranged themselves to form well-defined networks at interface of gamma/gamma-prime, accounting for the enhanced fatigue strength at 850 degC in VHCF regime when compared to that at 750 degC. In most cases, internal casting pore was the crack initiation site. Crack initiation and early-stage growth occurred on one of the {111} planes or their intersecting planes, a characteristic of Stage I cracking. With the use of optimized intermittent loading conditions, both the initiation and early-stage crack growth processes were successfully tracked on the basis of fine but visible beach marks within the Stage I cracking region. The first registered fatigue beach mark can be as close as only 86 um to the crack initiation site and the crack length increased steadily over the whole early-stage crack growth stage. The enhanced fatigue strength at 850 degC can be rationalized with the higher threshold for propagating the early-stage crack. The fraction of fatigue life consumed for early-stage crack growth reduces with the decreasing stress, eventually leading to the initiation-controlling VHCF fatigue failure. The implications of these results are discussed with respect to the model prediction of fatigue life and fatigue strength

Conversion of Residual Biomass into Liquid Transportation Fuel: An Energy Analysis

An energy balance, in broad outline, is presented for the production of a high-quality liquid transportation fuel from residual crop biomass. The particular process considered is comprised of (1) harvesting surplus biomass (such as crop residue); (2) locally pyrolyzing the biomass into pyrolysis oil (PO), char, and noncondensable gas (NCG); (3) transporting the PO to a remote central processing facility; (4) converting the PO at this facility by autothermal reforming (ATR) into synthesis gas (CO and H₂); followed by, at the same facility, (5) Fischer–Tropsch (FT) synthesis of the syngas into diesel fuel. In carrying out our calculations, we have made several assumptions about the values of the process parameters. These parameters, of course, can be modified as better input data become available. The material and energy balance has been incorporated into an Excel spreadsheet. The scope and our approach to the energy budget using a widely available spreadsheet hopefully provides greater transparency, as well as ease of scenario manipulation than has generally been found in the literature. The estimated energy efficiencies computed with the spreadsheet are comparable to those obtained with Aspen software. A spreadsheet is offered as a tool for further analysis of the energy budget of this and related processes. The Excel spreadsheet can be used as a nimble scouting tool to indicate promising avenues of study in advance of using a more comprehensive analysis such as that afforded by Aspen software. The process considered, in which a portion of the char and noncondensable gas are used to supply heat to the drying and pyrolysis steps and under the assumptions made, was found to have an energy efficiency to liquid fuel on the order of 40%. That is, 40% of the initial energy in the biomass will be found in the final liquid fuel after subtracting out external energy supplied for complete processing, including transportation as well as material losses. If the energy of the remaining char and NCG is added to that in the product diesel oil, the total recovered energy is estimated to be ∼50% of the initial energy content of the biomass. If char and NCG are not used as a heat source in the process, the energy efficiency of the produced diesel drops from 40% to 15%. It must be realized that the distribution of energy content among the fast pyrolysis products PO, char, and NCG is ∼69%, ∼27%, and ∼4%, respectively. Therefore, using char and NCG to provide fuel for the drying and pyrolysis steps is very critical in maintaining high energy efficiency of the product fuel. The weight of diesel fuel produced is estimated to be ∼13% of the initial weight of biomass, implying that 1 t of biomass (30% moisture) will produce 1.0 barrels of diesel oil. The pyrolysis of biomass to PO, char, and NCG is estimated to have an intrinsic energy efficiency of ∼90%. For the model considered, trucking biomass to a central facility without first converting it to PO is estimated to reduce energy efficiency by ∼1%

Association Between Telomere Length and Risk of Cancer and Non-Neoplastic Diseases: A Mendelian Randomization Study

Importance: The causal direction and magnitude of the association between telomere length and incidence of cancer and non-neoplastic diseases is uncertain owing to the susceptibility of observational studies to confounding and reverse causation. Objective: To conduct a Mendelian randomization study, using germline genetic variants as instrumental variables, to appraise the causal relevance of telomere length for risk of cancer and non-neoplastic diseases. Data Sources: Genomewide association studies (GWAS) published up to January 15, 2015. Study Selection: GWAS of noncommunicable diseases that assayed germline genetic variation and did not select cohort or control participants on the basis of preexisting diseases. Of 163 GWAS of noncommunicable diseases identified, summary data from 103 were available. Data Extraction and Synthesis: Summary association statistics for single nucleotide polymorphisms (SNPs) that are strongly associated with telomere length in the general population. Main Outcomes and Measures: Odds ratios (ORs) and 95% confidence intervals (CIs) for disease per standard deviation (SD) higher telomere length due to germline genetic variation. Results: Summary data were available for 35 cancers and 48 non-neoplastic diseases, corresponding to 420 081 cases (median cases, 2526 per disease) and 1 093 105 controls (median, 6789 per disease). Increased telomere length due to germline genetic variation was generally associated with increased risk for site-specific cancers. The strongest associations (ORs [95% CIs] per 1-SD change in genetically increased telomere length) were observed for glioma, 5.27 (3.15-8.81); serous low-malignant-potential ovarian cancer, 4.35 (2.39-7.94); lung adenocarcinoma, 3.19 (2.40-4.22); neuroblastoma, 2.98 (1.92-4.62); bladder cancer, 2.19 (1.32-3.66); melanoma, 1.87 (1.55-2.26); testicular cancer, 1.76 (1.02-3.04); kidney cancer, 1.55 (1.08-2.23); and endometrial cancer, 1.31 (1.07-1.61). Associations were stronger for rarer cancers and at tissue sites with lower rates of stem cell division. There was generally little evidence of association between genetically increased telomere length and risk of psychiatric, autoimmune, inflammatory, diabetic, and other non-neoplastic diseases, except for coronary heart disease (OR, 0.78 [95% CI, 0.67-0.90]), abdominal aortic aneurysm (OR, 0.63 [95% CI, 0.49-0.81]), celiac disease (OR, 0.42 [95% CI, 0.28-0.61]) and interstitial lung disease (OR, 0.09 [95% CI, 0.05-0.15]). Conclusions and Relevance: It is likely that longer telomeres increase risk for several cancers but reduce risk for some non-neoplastic diseases, including cardiovascular diseases