Flow in the thin film created by a coherent turbulent water jet impinging on a vertical wall

When a liquid jet impinges on a vertical wall it forms a thin film which flows radially away from the point of impingement until a point where the outward momentum is balanced by surface tension and a film jump is formed. The model for the location for the film jump presented by Wilson et al. (Chem. Eng. Sci, 2012, Vol. 68, pp 449-460) is revised to include the development of laminar and turbulent boundary layers in the thin film. The criterion for film jump formation is also revisited, and the analysis explains why the location is insensitive to the nature of the wall material at high flow rates. The model is compared with published data for velocity profiles in the thin film, the transition to turbulence, and new experimental data where the average velocity in the thin film was estimated from the initial growth of the radial flow pattern for flow rates of 1.95 to 4.01 dm$^{3 }$s$^{-1}$, corresponding to jet Reynolds numbers of 15 500 to 32 000. Very good agreement with the published and measured data is obtained, with no adjustable parameters, for jets impinging perpendicularly as well as at an oblique angle. The model shows that the parabolic velocity profile assumed by Wilson et al. gives a reasonable estimate of the average velocity, but it is not able to predict phenomena such as the observed transition to turbulence.Commonwealth Scholarship CommissionThis is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.ces.2016.06.01

On the origin of the circular hydraulic jump in a thin liquid film

For more than a century, it has been believed that all hydraulic jumps are created due to gravity. However, we found that thin-film hydraulic jumps are not induced by gravity. This study explores the initiation of thin-film hydraulic jumps. For circular jumps produced by the normal impingement of a jet onto a solid surface, we found that the jump is formed when surface tension and viscous forces balance the momentum in the film and gravity plays no significant role. Experiments show no dependence on the orientation of the surface and a scaling relation balancing viscous forces and surface tension collapses the experimental data. Experiments on thin film planar jumps in a channel also show that the predominant balance is with surface tension, although for the thickness of the films we studied gravity also played a role in the jump formation. A theoretical analysis shows that the downstream transport of surface tension energy is the previously neglected, critical ingredient in these flows and that capillary waves play the role of gravity waves in a traditional jump in demarcating the transition from the supercritical to subcritical flow associated with these jumps.Commonwealth Scholarship Commission, EPSRC grant EP/K50375/

Cleaning of complex soil layers on vertical walls by fixed and moving impinging liquid jets

Cleaning by a horizontal water jet, impinging onto a soiled Perspex vertical plate, is described. The plate, the substrate, was coated with PVA or petroleum jelly, the soil. The substrate was either.(i) fixed, for batch tests in which the cleaned area, roughly circular, grew with time, or(ii) the substrate moved vertically up or down in its own plane, the water jet remaining fixed; this reproduced the effect of a jet moving across a surface for cleaning, as found in real tank cleaning operations.In the batch experiments, growth of the radius a of the cleaning area is well described, at early times t, by a5 – ao5 = K5 (t – to), ao being the initial radius of the cleaned area at time to; K is a constant. At later times with petroleum jelly, the cleaning front reached a maximum value, when the outward momentum of the radially flowing water film balanced the strength of the soil. This maximum value is modelled as a ramp of viscoplastic soil inclined at angle χ to the substrate surface, where χ was found to vary from 7° to 25°.In the tests of continuous cleaning of petroleum jelly, a lengthening cleaned area, of width wc, was observed on the moving substrate. Near the jet was a stationary clean front, whose shape looked like half an ellipse. This shape, and the width wc, are well described by theory (Wilson et al., 2015, 123, 450–459) using parameters from the above-mentioned batch experiments. This establishes a good link between batch and continuous cleaning experiments.Funding for RKB from the Commonwealth Scholarship Commission is gratefully acknowledged, as are helpful conversations with Michael Smith and Paul Hodgson. FDG measurements on the PVA layers were performed by Shiyao Wang.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.jfoodeng.2015.12.02

Impinging jet cleaning of tank walls: Effect of jet length, wall curvature and related phenomena

The effect of jet length and wall curvature on the flow patterns generated by an impinging water jet were quantified and the effect on cleaning investigated in a brief study. The length of time taken to establish steady flow was characterised. Jet impingement on a flat vertical wall was investigated for jets of diameter 2–4mm for lengths, L, up to 1m. The amount of liquid lost to splatter was measured and found to be insensitive to L for short L (1.5dm3min−1). The cleaning of two viscoplastic model food soils was studied briefly: a hydrophobic petroleum jelly and Carbopol®, a water-soluble gel. The splatter correction was not able to account for all the differences observed in cleaning at different jet lengths. There was no appreciable effect of curvature on cleaning behaviour. Soaking of the Carbopol® increased its cleaning rate.Funding for MWLC from Newnham College, Cambridge, and a Commonwealth Scholarship for RKB are gratefully acknowledged, as is travel funding for DIW to attend the FCFP2018 conference from Jesus College, Cambridge. Authors TVA, NT, SAW and RLW were all MEng research project students

Air flow experiments on a train carriage—Towards understanding the risk of airborne transmission

A series of experiments was undertaken on an intercity train carriage aimed at providing a “proof of concept” for three methods in improving our understanding of airflow behaviour and the accompanied dispersion of exhaled droplets. The methods used included the following: measuring CO2 concentrations as a proxy for exhaled breath, measuring the concentrations of different size fractions of aerosol particles released from a nebuliser, and visualising the flow patterns at cross-sections of the carriage by using a fog machine and lasers. Each experiment succeeded in providing practical insights into the risk of airborne transmission. For example, it was shown that the carriage is not well mixed over its length, however, it is likely to be well mixed along its height and width. A discussion of the suitability of the fresh air supply rates on UK train carriages is also provided, drawing on the CO2 concentrations measured during these experiments.</jats:p

The ventilation of buildings and other mitigating measures for COVID-19: a focus on wintertime.

The year 2020 has seen the emergence of a global pandemic as a result of the disease COVID-19. This report reviews knowledge of the transmission of COVID-19 indoors, examines the evidence for mitigating measures, and considers the implications for wintertime with a focus on ventilation.This work was undertaken as a contribution to the Rapid Assistance in Modelling the Pandemic (RAMP) initiative, coordinated by the Royal Society

Towards a Model of Corporate and Social Stakeholder Engagement: Analyzing the Relations Between a French Mutual Bank and Its Members

International audienceThe aim of this article is to develop a new classification of stakeholders based on the concept of corporate and social engagement. Engagement is analyzed as an organizational learning process between the managers of an organization and its stakeholders. It is a necessary condition to improve the organization's impact on its economic, social, and natural environment. Applied to the membership of a French mutual bank in order to identify the members' varying levels of engagement, this new mapping technique may help managers to adapt their practices to the degree of engagement of each identified group of members, and to modify their financial products and communications to foster engagement among as many of these groups as possible

The ventilation of buildings and other mitigating measures for COVID-19: a focus on wintertime.

The year 2020 has seen the emergence of a global pandemic as a result of the disease COVID-19. This report reviews knowledge of the transmission of COVID-19 indoors, examines the evidence for mitigating measures, and considers the implications for wintertime with a focus on ventilation

y Integrated analysis of 8-week glecaprevir/pibrentasvir in Japanese and overseas patients without cirrhosis and with hepatitis C virus genotype 1 or 2 infection

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