Particle deposition in fully developed turbulent square duct flows is simulated using large eddy simulation for Reynolds numbers, based on the bulk velocity and duct width, equal to 250k, 83k and ...10,320. A particle equation of motion including Stokes drag, lift, buoyancy and gravitational forces is used for particle trajectory analysis. Results obtained for the fluid phase show good agreement with experimental data and the predictions of direct numerical simulations. Predictions for particles show that the secondary flow established in the duct cross-section plays an important role in the particle deposition process. Under the influence of this flow, high-inertia particles (particle Stokes number, St>12.38) tend to deposit close to the corners of the duct floor, while low-inertia particles (St<6.43) deposit near the floor centre. It is shown that the flow Reynolds number, particle size, drag force, shear-induced lift force and gravity all affect the particle deposition process. Particle deposition in the vertical direction increases with flow Reynolds number but simultaneously decreases in the horizontal direction. The particle deposition velocity is found to increase with both the particle size and the flow Reynolds number, with the tendency for deposition at the duct corners increasing with both variables. From a dynamic analysis, gravity most significantly affects particle deposition in the vertical direction, while in the horizontal direction the drag force dominates. The influence of the lift force increases with particle size, and its effect becomes significant as particles approach the duct floor; hence, it can act as another important factor causing particles to accumulate at the corners of the duct. Generally, and for all particle populations in the three flows considered, the particle deposition process can be described by the free-flight model.
▸ Particle deposition in fully developed turbulent square duct flows is simulated. ▸ The secondary flow plays an important role in the particle deposition process. ▸ High-inertia particles tend to deposit close to the corners of the duct floor. ▸ Low-inertia particles deposit near the floor centre. ▸ The particle deposition process can be described by the free-flight model.
The work described in this paper employs large eddy simulation and a discrete element method to study turbulent particle-laden channel flows at low concentrations (particle volume fraction ...10−4–10−5), including particle dispersion, collision and agglomeration. Conventional understanding of such flows is that particle interactions are negligible, this work however demonstrates that such interactions are common at large Stokes numbers in turbulent flow. The particle-particle interaction model is based on the Hertz-Mindlin approach with Johnson-Kendall-Roberts cohesion to allow the simulation of cohesive forces in a dry air flow. The influence of different flow Reynolds numbers, and therefore the impact of fluid turbulence, on agglomeration behaviour is investigated. The agglomeration rate is found to be strongly influenced by the flow Reynolds number, with most of the particle-particle interactions taking place at locations close to the channel walls, aided by the higher turbulence levels and concentration of particles in these regions.
Display omitted
•Turbulent structure of the flow dominates motion creating particle interactions•Agglomeration increase with Reynolds number at low surface energy•Process of particle agglomeration was seen to be enhanced in two separate regions
Methane and methane–hydrogen (10%, 20% and 50% hydrogen by volume) mixtures have been ignited in a fan stirred bomb in turbulence and filmed using high speed cine schlieren imaging. Measurements were ...performed at 0.1 MPa (absolute) and 360 K. A turbulent burning velocity was determined for a range of turbulence velocities and equivalence ratios. Experimental laminar burning velocities and Markstein numbers were also derived. For all fuels the turbulent burning velocity increased with turbulence velocity. The addition of hydrogen generally resulted in increased turbulent and laminar burning velocity and decreased Markstein number. Those flames that were less sensitive to stretch (lower Markstein number) burned faster under turbulent conditions, especially as the turbulence levels were increased, compared to stretch-sensitive (high Markstein number) flames.
•Turbulent structure dominates particle motion creating particle–particle interactions.•Positive relationship between particle surface energy and agglomeration observed.•Process of particle ...agglomeration enhanced in two separate regions in channel.•In near-wall region due to high particle concentration driven by turbophoresis.•In high turbulence regions close to walls caused by shearing effect of flow.
Coupled large eddy simulation and the discrete element method are applied to study turbulent particle–laden flows, including particle dispersion and agglomeration, in a channel. The particle–particle interaction model is based on the Hertz–Mindlin approach with Johnson–Kendall–Roberts cohesion to allow the simulation of van der Waals forces in a dry air flow. The influence of different particle surface energies, and the impact of fluid turbulence, on agglomeration behaviour are investigated. The agglomeration rate is found to be strongly influenced by the particle surface energy, with a positive relationship observed between the two. Particle agglomeration is found to be enhanced in two separate regions within the channel. First, in the near-wall region due to the high particle concentration there driven by turbophoresis, and secondly in the buffer region where the high turbulence intensity enhances particle–particle interactions.
•Subcooled boiling flows are predicted using a two-fluid Eulerian–Eulerian CFD model.•Model configuration is selected “a priori” and accuracy is evaluated over a large database.•At present, the model ...is not capable of a satisfactory accuracy over all flow conditions.•Void fraction, turbulence and liquid temperature are generally well predicted.•Further research required for bubble departure, population balance and near-wall modelling.
Boiling flows are frequently found in industry and engineering due to the large amount of heat that can be transferred within such flows with minimum temperature differences. In the nuclear industry, boiling affects in different ways the operation of almost all water-cooled nuclear reactors. Recently, the use of computational fluid dynamic (CFD) approaches to predict boiling flows is increasing and, in the nuclear area, CFD is being developed to solve thermal hydraulic safety issues such as establishing the critical heat flux, which is perhaps the major threat to the integrity of nuclear fuel rods. In this paper, the accuracy of an Eulerian–Eulerian, two-fluid CFD model is evaluated over a large database of subcooled boiling flows, avoiding the rather popular case-by-case tuning of descriptive models to a limited number of experiments. The model includes a Reynolds stress turbulence model, the method of moments-based Sγ population balance approach and a boiling model derived using the heat flux partitioning approach. The database covers a large range of conditions in subcooled boiling flows of water and refrigerants in vertical pipes and annular channels. Overall, a satisfactory predictive accuracy is achieved for some quantities of interest, such as the void fraction and the turbulence and liquid temperature fields, but results are less satisfactory in other areas, more specifically for the average bubble diameter and the mean velocity profiles close to the wall in annular channels. Agreement may be improved with advances in the treatment of large bubbles and bubble break-up and coalescence, as well as in improved modelling of the boiling region close to the wall, and more specifically the bubble departure diameter, the wall treatment and the contribution of bubbles to turbulence.
BackgroundNon-invasive ventilation (NIV), although effective in treating hypercapnic respiratory failure, has not demonstrated the same efficacy in treating acute hypoxaemic respiratory failure. We ...aimed to examine the effect of NIV use on ventilator-free days in patients with acute hypoxaemic respiratory failure admitted to the intensive care unit (ICU).MethodsWe conducted a retrospective study of patients admitted to the ICU with acute hypoxaemic respiratory failure at Waikato Hospital, New Zealand, from 1 January 2009 to 31 December 2018. Patients treated with NIV as the initial oxygenation strategy were compared with controls treated with early intubation. The two groups were matched using a propensity score based on baseline characteristics. The primary outcome was the number of ventilator-free days at day 28. The secondary outcomes were ICU and hospital length of stay and in-hospital mortality.ResultsOut of 175 eligible patients, 79 each out of the NIV and early intubation groups were matched using a propensity score. Early NIV was associated with significantly higher median ventilator-free days than early intubation (17 days vs 23 days, p=0.013). There was no significant difference in median ICU length of stay (112.5 hours vs 117.7 hours), hospital length of stay (14 days vs 14 days) or in-hospital mortality (31.6% vs 37.9%) between the NIV and the early intubation group.ConclusionCompared with early intubation, NIV use was associated with more ventilator-free days in patients with hypoxaemic respiratory failure. However, this did not translate into a shorter length of stay or reduced mortality based on our single-centre experience.
•A novel multi-phase model capable of predicting CO2 releases is presented.•Measurements of temperatures and concentrations of CO2 releases are presented.•Validation of mathematical models is ...undertaken against new experimental data.•Excellent level of agreement with measurements of jet characteristics obtained.•Tools presented to aid evaluation of hazard consequences of CO2 pipeline failure.
The deployment of a complete carbon capture and storage chain requires a focus upon the hazards posed by the operation of CO2 pipelines and intermediate storage vessels, and the consequences of accidental release. The aim of this work is the construction of a computational fluid dynamic model capable of accurately representing the complex physics observed in such a release, essential if dispersion phenomena are to be accurately predicted. The interacting thermo-physical processes observed include those associated with the rapid expansion of a highly under-expanded jet, leading to an associated sonic flow structure. In such a release, it is also possible for three phases to be present due to the expansion and subsequent Joule–Thomson cooling, and a suitable equation of state is required to elucidate a system's composition. The primary objective of this work is the consideration of these physical processes, and their integration into a suitable numerical framework which can be used as a tool for quantifying associated hazards. This also incorporates the validation of such a model using data available in the literature and also using that recently obtained, and presented here for the first time. Overall, the model has provided an excellent level of agreement with experimental data in terms of fluid and sonic structure and temperature measurements, and good agreement with respect to composition data.
Background
Although cytoreductive surgery has been shown to be beneficial in carefully selected patients with metastatic gastrointestinal stromal tumours (GISTs) treated with tyrosine kinase ...inhibitors (TKIs), factors predictive of postoperative morbidity have not been investigated previously.
Methods
A surgical complexity score for GIST metastasectomy (GM‐SCS) composed of patient‐related and surgical factors was assigned retrospectively to patients with metastatic GIST treated with TKI therapy and surgery at two institutions between 2002 and 2014. The ability of clinicopathological factors and GM‐SCS to predict postoperative morbidity was assessed by means of a multivariable logistic regression model. Postoperative complications were categorized using the Clavien–Dindo classification.
Results
Some 400 operations on 323 patients with metastatic GIST on TKIs were included. Complications were observed following 110 operations (27·5 per cent) including 70 major complications (grade III–V) (17·5 per cent of 400 operations). Patients were divided into low (5 points or less; 100 patients, 25·0 per cent), intermediate (6–9 points; 191, 47·8 per cent) and high (at least 10 points; 109, 27·3 per cent) complexity scoring groups based on the GM‐SCS. An intermediate (odds ratio (OR) 2·88; P = 0·008) and high (OR 5·40; P < 0·001) GM‐SCS were independent predictors of overall complications, whereas only a high GM‐SCS was independently predictive of a major complication (OR 3·65; P = 0·018). Metastatic mitotic index was also an independent predictor of overall complications (OR 2·55; P = 0·047). GM‐SCS did not predict progression‐free or overall survival.
Conclusion
A gastrointestinal stromal tumour metastastectomy surgical complexity score can predict morbidity, which may help in preoperative risk stratification and optimal treatment planning.
May help treatment planning
Background
Foam rolling (FR) has been shown to alleviate some symptoms of exercise-induced muscle damage and has been suggested to increase range of motion (ROM) without negatively impacting ...strength. However, it is unclear what neuromuscular effects, if any, mediate these changes.
Methods
In a randomized, crossover design, 16 healthy active males completed 2 min of rest or FR of the knee extensors on three consecutive days. Mechanical properties of vastus lateralis (VL) and rectus femoris (RF) were assessed via Tensiomyography. Knee extension maximal voluntary contraction (MVC) and knee flexion ROM were also assessed, and surface electromyography amplitude (RMS) was recorded during a submaximal isometric contraction (50% of MVC). Measures were performed before and after (0, 15, and 30 min) FR or rest.
Results
MVC was reduced on subsequent days in the rest condition compared to FR (
p
= 0.002,
p
η
2
= 0.04); ROM was not different across time or condition (
p
= 0.193,
p
η
2
= 0.01). Stiffness characteristics of the VL were different on the third day of FR (
p
= 0.002,
p
η
2
= 0.03). RMS was statistically reduced 0, 15, and 30 min after FR compared to rest (
p
= 0.006,
p
η
2
= 0.03;
p
= 0.003,
p
η
2
= 0.04;
p
= 0.002,
p
η
2
= 0.04).
Conclusions
Following FR, MVC was elevated compared to rest and RMS was transiently reduced during a submaximal task. Excitation efficiency of the involved muscles may have been enhanced by FR, which protected against the decline in MVC which was observed with rest.
Skeletal muscle operates as a near-constant volume system; as such muscle shortening during contraction is transversely linked to radial deformation. Therefore, to assess contractile properties of ...skeletal muscle, radial displacement can be evoked and measured. Mechanomyography measures muscle radial displacement and during the last 20 years, tensiomyography has become the most commonly used and widely reported technique among the various methodologies of mechanomyography. Tensiomyography has been demonstrated to reliably measure peak radial displacement during evoked muscle twitch, as well as muscle twitch speed. A number of parameters can be extracted from the tensiomyography displacement/time curve and the most commonly used and reliable appear to be peak radial displacement and contraction time. The latter has been described as a valid non-invasive means of characterising skeletal muscle, based on fibre-type composition. Over recent years, applications of tensiomyography measurement within sport and exercise have appeared, with applications relating to injury, recovery and performance. Within the present review, we evaluate the perceived strengths and weaknesses of tensiomyography with regard to its efficacy within applied sports medicine settings. We also highlight future tensiomyography areas that require further investigation. Therefore, the purpose of this review is to critically examine the existing evidence surrounding tensiomyography as a tool within the field of sports medicine.
PDF
