On the limits of industrial premixed combustion simulation

This work analyses the simulation potential of two premixed turbulent combustion models based on different combustion mechanism concepts: the Eddy Dissipation Concept based on the volume combustion mechanism, and the Turbulent Flame-speed Closure based on the thickened-wrinkled amelets combustion mechanism. Ability of simulating numerically a standard experimental test case (premixed methane-air combustion in a plane channel at high flow velocity) and the influence of flow parameters variation on the combustion process have been tested. The paper shows that the flamelets model describes the standard experimental data more accurately. Furthermore, comparisons of the two models results obtained varying combustion flow parameters show the presence of quantitatively, and in one case even qualitatively different trends. These results are explained, and potentialities and limits of these models are discussed from an industrial premixed burner applications standpoint

Numerical simulation of premixed combustion flows: a comparative study

In this work four different commercial and research CFD codes have been compared for the simulation of two combustion test cases. The aim was to get an overview of the capabilities of these different tools to simulate combustion flows in premixed regimes. Codes tested were Fluent, CFX, StarCD and Tanit. Three combustion models have been applied, namely the Eddy Break Up, the Eddy Dissipation Model and the Turbulent Flame Closure, the turbulence model used being the standard k-epsilon. Numerical results have been found to fairly fit experiments and helped to show some drawbacks of combustion models. In its theoretically correct range of applicability the TFC model has been found to give the better agreement with experiments

Model for heterogeneous catalysis on metal surfaces with application to hypersonic flows

A model for heterogeneous catalysis for Copper, Nickel, and Platinum has been devised. The model simulates the heterogeneous chemical kinetics of dissociated air flow impinging metal surfaces. Elementary phenomena such as, atomic and molecular adsorption, Eley-Rideal and Langmuir-Hinshelwood recombinations, and thermal desorptions have been accounted for. Comparisons with experimental results for Nitrogen and Oxygen recombination show good agreement. In the second part of this work, the finite rate catalysis model has been used to analyzed numerically the problems of the heterogeneous catalysis similarity between hypersonic ground testing and reentry flight. Therefore the flow around a blunt cone under these conditions has been calculated and results for heat fluxes and for a suggested similarity parameter have been compared and discussed

Skeletal Anomalies and Normal Variants in Patients with Palatally Displaced Canines

Objective: To test the null hypothesis that there is no increased prevalence of skeletal anomalies and/or normal variants as evidenced by the cephalometric radiographs of patients with palatally displaced canines (PDC). Materials and Methods: The treatment records of 38 white subjects between 14 and 20 years old with PDC were collected and evaluated retrospectively. Inclusion criteria for the study required that the case records include good-quality panoramic radiographs and lateral cephalometric radiographs with the first four cervical vertebrae clearly visible. The anomalies recorded for each case included sella bridge, atlanto-occipital ligament calcification or ponticulus posticus, and posterior arch atlas deficiency. A control group consisted of 70 consecutively treated subjects who had no other dental anomalies and whose maxillary canines had erupted normally. Fisher's exact test and Pearson's chi-square test were used to determine possible statistically significant differences in the incidence of skeletal anomalies and/or normal variants between the group of patients with PDC and the control group. Results: The prevalence of skull anomalies and normal variants seen in cephalometric radiographs was increased in patients with PDC. Because of the presence of ponticulus posticus (Pearson's chi-square, P < .050; Fisher's exact test, P < .052), sella bridge (Pearson's chi-square, P < .042; Fisher's exact test, P < .042), and posterior arch deficiency (Pearson's chi-square, P < .047; Fisher's exact test, P < .039), statistically significant differences were observed between subjects with PDC and the control group. Conclusions: The null hypothesis was rejected. There is an increased prevalence of skull skeletal anomalies and/or normal variants in patients with PDC. (Angle Orthod. 2009;79:727-732.

effect of contact stiffness and machine calibration in nano indentation testing

Abstract Instrumented indentation tests enable evaluation of several material parameters. Preliminary investigations underlined the influence of contact stiffness in the nano-range. ISO 14577-1 recommends two methods for contact stiffness evaluation, which, however, present shortcomings mainly related to the disregard of actual shape of unloading indentation curve. Given the relevance not only at the extent of material characterization, but also at testing machine calibration, alternative evaluation procedures have been developed, showing better agreement with experimental data and lower uncertainty in the evaluation of contact stiffness. In this work, shortcomings of standard and alternative methods in the evaluation of material parameters are highlighted, and innovative procedures are proposed to overcome them

Experimental and Numerical Investigation of Combined Sensible/Latent Thermal Energy Storage for High-Temperature Applications

Combined sensible/latent heat storage allows the heat-transfer fluid outflow temperature during discharging to be stabilized. A lab-scale combined storage consisting of a packed bed of rocks and steel-encapsulated AlSi12 was investigated experimentally and numerically. Due to the small tank-to-particle diameter ratio of the lab-scale storage, void-fraction variations were not negligible, leading to channeling effects that cannot be resolved in 1D heat-transfer models. The void-fraction variations and channeling effects can be resolved in 2D models of the flow and heat transfer in the storage. The resulting so-called bypass fraction extracted from the 2D model was used in the 1D model and led to good agreement with experimental measurements

Impacted maxillary canines and root resorption of adjacent teeth : a retrospective observational study

The prevalence of impacted maxillary canine is reported to be between 1% and 3%. The lack of monitoring and the delay in the treatment of the impacted canine can cause different complications such as: displacement of adjacent teeth, loss of vitality of neighbouring teeth, shortening of the dental arch, follicular cysts, canine ankylosis, recurrent infections, recurrent pain, internal resorption of the canine and the adjacent teeth, external resorption of the canine and the adjacent teeth, combination of these factors. An appropriate diagnosis, accurate predictive analysis and early intervention are likely to prevent such undesirable effects. The objective is to evaluate, by means of a retrospective observational study, the possibility of carrying out a predictive analysis of root resorption adjacent to the impacted canines by means of orthopantomographs, so as to limit the prescription of additional 3D radiography. 120 subjects with unilateral or bilateral maxillary impacted canine were examined and 50 patients with 69 impacted maxillary canine (22 male, 28 female; mean age: 11.7 years) satisfied the inclusion criteria of the study. These patients were subjected to a basic clinical and radiographic investigation (orthopantomographs and computerized tomography). All panoramic films were viewed under standardized conditions for the evaluation of two main variables: maxillary canine angulations (a, b, g angles) and the overlapping between the impacted teeth and the lateral incisor (Analysis of Lindauer). Binary logistic regression was used to estimate the likelihood of resorbed lateral incisors depending on sector location and angle measurements. Results indicated that b angle has the greatest influence on the prediction of root resorption (predictive value of b angle = 76%). If ? angle <18° and Lindauer = I, the probability of resorption is 0.06. Evaluation of b angle and superimposition lateral incisor/impacted canine analysed on orthopantomographs could be one of the evaluation criteria for prescribing second level examination (CT and CTCB) and for detecting root resorption of impacted maxillary canine adjacent teeth

FBR for Polyolefin Production in Gas Phase: Validation of a Two-phase Compartmentalized Model by Comparison with CFD

Two different modeling approaches are applied in this work to the simulation of fluidized bed reactors containing solid particles of Geldart A-B type and operated at conditions typically used for polyolefins production. On one side, a fully detailed computational fluid dynamics (CFD) model is developed, considering a 2D planar geometry and a multi-fluid description with kinetic theory of granular flows. On the other, a conventional three-phase, 1D compartmentalized model (SCM) is also developed, implementing the fluid dynamic description based on popular, semi-empirical relationships available in the literature. Given the huge difference of computational effort associated with the corresponding numerical solutions, our aim is to confirm the reliability of the simplified model by comparison with the results of the detailed CFD model. The comparison is carried out considering the fluidization of a bed of solid particles without reaction and solid injection or withdrawal, thus focusing on the steady-state fluid dynamic behavior of the expanded bed. Three different gas velocities and different monodisperse and polydisperse particle populations are analyzed. The results show that the oversimplified compartmentalized approach is capable to predict the solid mixing features established inside the reactor operated in bubbling fluidization regime with good reliability for non-reactive polyethylene particles. Average solid volume fractions are particularly close to the values predicted by the CFD model when monodisperse particles are considered inside the examined range of gas velocity values. A generally good agreement is also found when solids with broad size distribution are analyzed. Overall, these comparisons provide a meaningful validation of the simplified compartmentalized models: given their negligible computational demand and general versatility (complex kinetic schemes and single particle models are easily accounted for), they still represent an effective tool of industrial process design

Comparison between detailed (CFD) and simplified models for the prediction of solid particle size distribution in fluidized bed reactors

This work is aimed at developing a simplified model suitable to effectively describe the fluidization behavior within fluidized beds with minimal computational efforts. The simplified model was validated through detailed CFD Euler-Euler simulations showing a good agreement in the case of large particles (about 450 micron) at all the gas velocities considered (20, 40, 61 cm/s). Slightly less accurate outcomes were observed for smaller particles (about 220 micron). This was due to the underestimation of the particle size effect on the fluidization behavior by the simplified approach

Aesthetic- And patient- related outcomes following root coverage procedures: A systematic review and network meta- analysis

BackgroundAim of this systematic review (SR) of randomized controlled trials (RCTs) was to evaluate effect of different flap designs and graft materials for root coverage, in terms of aesthetics, patient satisfaction and self- reported morbidity (post- operative pain/discomfort).Material and MethodsA comprehensive literature search was performed. A mixed- modelling approach to network meta- analysis was utilized to formulate direct and indirect comparisons among treatments for Root Coverage Esthetic Score (RES), with its individual components, and for subjective patient- reported satisfaction and post- operative pain/discomfort (visual analogue scale (VAS) of 100).ResultsTwenty- six RCTs with a total of 867 treated patients (1708 recessions) were included. Coronally Advanced Flap (CAF) + Connective Tissue Graft (CTG) (0.74 (95% CI [0.24, 1.26], p = .005)), Tunnel (TUN) + CTG (0.84 (95% CI [0.15, 1.53]), p = .01) and CAF + Graft substitutes (GS) (0.55 (95% CI [0.006, 1.094], p = .04)) were significantly associated with higher RES than CAF. No significant difference between CAF + CTG and TUN + CTG was detected (0.09 (95% CI [- 0.54, 0.72], p = .77)). Addition of CTG resulted in less natural tissue texture (- 0.21 (95% CI [- 0.34, - 0.08]), p = .003) and gingival colour (- 0.06 (95% CI [- 0.12, - 0.03], p = .03)) than CAF. CTG techniques were associated with increased morbidity.ConclusionsConnective tissue graft procedures showed highest overall aesthetic performance for root coverage, although graft integration might impair soft tissue colour and appearance. Additionally, CTG- based techniques were also correlated with a greater patient satisfaction and morbidity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163404/2/jcpe13346.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163404/1/jcpe13346_am.pd