Initial objectives of on-site empirical modelling of thermal plumes: A preliminary evaluation of a river-site and a lake-site thermal plume

Abstract In this study, the dispersion and deposition of particles in the respiratory system attached to a mannequin lying down inside a room were investigated numerically. The respiratory system model was prepared by processing the CT scan images of a volunteer and was attached to a mannequin lying in the middle of a room. The flow field around the mannequin and effects of the thermal plume on the particle aspiration by the mannequin model was simulated using the Ansys-Fluent software. The aspiration efficiency of spherical particles in the airway was studied with the Lagrangian particle trajectory analysis, including the turbulence dispersion effects. For validation of numerical simulations, the aspiration efficiency of the particles obtained from the numerical solution was compared with the case of a standing mannequin. The results are presented for two different modes with upward and downward thermal plumes. For the first mode, due to the strong effect of the thermal plume in the upward direction, the aspiration efficiency of midrange particles increases. However, the aspiration efficiency of large micro-particles decreases for the first mode. For the second mode, with the downward thermal plume, the aspiration efficiency of small micro-particles increases significantly.

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Numerical simulation of urban thermal plume merging

10.5194/ems2021-5 ◽

2021 ◽

Author(s):

Shuojun Mei ◽

Chao Yuan ◽

Wenhui He ◽

Tanya Talwar

Keyword(s):

Air Quality ◽

Thermal Comfort ◽

Urban Areas ◽

Turbulence Models ◽

Wave Radiation ◽

Thermal Plume ◽

Water Tank ◽

Surface Cooling ◽

Thermal Plumes ◽

The Impact

<p>Densely packed urban buildings trap outgoing long-wave radiation, leading to reduced surface cooling and increased building surface temperature. In calm conditions, poor natural ventilation causes both thermal comfort and air quality issue. The buoyancy flow generated by heated urban surfaces is the main driving of the urban flow and pollutant dispersion. A 3D numerical modelling is conducted to investigate the thermal plumes merging and buoyancy-driven airflow in urban areas. The performances of four different turbulence models, i.e., two URANS (Unsteady Reynolds-averaged Navier&#8211;Stokes equations) models and two LES (Large-Eddy Simulation) models are evaluated by comparing the velocity field with previous water tank measurements. Validation results show that all four turbulence models can capture the bending of thermal plumes toward the centre, and LES models provide a better prediction on the vertical velocity profiles, while both URANS models show underestimation. The plume merging mechanism is analysed with the high accuracy LES results. Both pressure difference and swaying motion caused by mean flow and turbulence are important for plume merging. The turbulence coherent structure of plume merging is analysed by a quadrant analysis, which shows ejection and sweep events could significantly change with the building density. A case study with complex urban geometry is conducted to show the impact of thermal plumes merging in the real high-density urban areas. The convergence airflow at the pedestrian level is estimated to 2 m/s under a surface-air temperature difference of 5 &#176;C, which is comparable to wind-driven ventilation and beneficial to thermal comfort and air quality.</p>

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CFD Model of Thermal Plume Occuring above Hot Surface of Kitchen Appliance

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.861.433 ◽

2016 ◽

Vol 861 ◽

pp. 433-437

Author(s):

Petra Vojkůvková ◽

Ondřej Šikula ◽

Jan Weyr

Keyword(s):

Flow Rate ◽

Volume Flow Rate ◽

Ambient Air ◽

Volume Flow ◽

Thermal Plume ◽

Ansys Fluent ◽

Thermal Plumes ◽

Cooking Process ◽

German Standard ◽

Hot Surface

During the cooking process, pollutant fumes are released into the ambient air by the convection plumes. These convective plumes - thermal plumes – are generated above hot surfaces and they need to be efficiently and ecologically ventilated in order to achieve appropriate internal climate. Calculation method for determination of volume flow rate of rising convective plumes is described in German standard DIN 18869 [1]. This article focuses on study of thermal plumes using numerical model in software Ansys Fluent, determinates volume flow rate of rising air and compares the simulation results with the results from known computational relations.

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Experimental and numerical investigation on the convective thermal plume around the head of the standing and lying hu-man body

E3S Web of Conferences ◽

10.1051/e3sconf/20198502016 ◽

2019 ◽

Vol 85 ◽

pp. 02016 ◽

Cited By ~ 1

Author(s):

Laurenţiu Tăcutu ◽

Ilinca Năstase ◽

Florin Bode ◽

Cristiana Verona Croitoru ◽

Angel Dogeanu ◽

...

Keyword(s):

Distribution System ◽

Particle Image ◽

Numerical Models ◽

Experimental Studies ◽

Air Distribution ◽

Thermal Plume ◽

Thermal Plumes ◽

Image Velocimetry ◽

Convective Thermal ◽

Made In

This paper presents a study for two thermal plumes generated by two humanoid thermal manikins, one standing and one lying down. The research was approached from a numerical and experimental perspective. The numerical model represents an operating room (OR) with two surgeons, a patient and a unidirectional air flow (UAF) diffuser. The experimental study was made in a climatic chamber, having a similar air distribution system, using particle image velocimetry (PIV) and infrared thermography (IR) measurements. The purpose of the study was to characterize the thermal plumes of the two manikins by numerical and experimental studies. The results obtained from these different approaches were compared with each other and with the ones from the literature in order to validate our numerical models.

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Three-Dimensional Characterization of a Pure Thermal Plume

Journal of Heat Transfer ◽

10.1115/1.1863275 ◽

2005 ◽

Vol 127 (6) ◽

pp. 624-636 ◽

Cited By ~ 31

Author(s):

Minh Vuong Pham ◽

Fre´de´ric Plourde ◽

Son Doan Kim

Keyword(s):

Direct Method ◽

Three Dimensional ◽

Momentum Equation ◽

Thermal Plume ◽

Thermal Plumes ◽

Heating Source ◽

Entrainment Coefficient ◽

Particle Imaging ◽

First Time

Pure thermal plumes have been investigated by two-dimensional (2D) and three-dimensional (3D) particle imaging velocimetry (PIV) techniques. While classical plume features have been checked out, time-dependent analysis allows one to clearly detect contraction and expulsion phases which are mainly driven by turbulent structure behavior. Balance of momentum equation demonstrates the link between stronger structures and expulsion-contraction motion mainly dominated by plume engulfment during contraction phases. A ratio of 3 between entrained mass flow rate during contraction and expulsion phases has been estimated. A new method, never previously applied to pure thermal plume, allows one to accurately characterize entrainment mechanism and for the first time, the latter renders it possible to estimate the entrainment coefficient all along the plume height, even close to the heating source. Moreover, entrainment coefficient is found to be 20% higher with direct method as opposed to the classical differential one widely used in the literature. Such a huge gap is found to be due to the fluctuating density and velocity part. Even through it markedly contributes to an enhanced entrainment mechanism, the role of fluctuation was generally overlooked in the previous works devoted to entrainment coefficient estimate.

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Direct Numerical Simulation of Unstably Stratified Turbulent Channel Flow

Journal of Heat Transfer ◽

10.1115/1.2824100 ◽

1997 ◽

Vol 119 (1) ◽

pp. 53-61 ◽

Cited By ~ 35

Author(s):

O. Iida ◽

N. Kasagi

Keyword(s):

Channel Flow ◽

Transport Mechanism ◽

Large Scale ◽

Reynolds Shear Stress ◽

Wall Turbulence ◽

Thermal Plume ◽

Streamwise Vortices ◽

Mean Velocity ◽

Thermal Plumes ◽

Turbulent Friction

Direct numerical simulations of the fully developed horizontal channel flow under unstable density stratification were carried out to investigate interactive shear and buoyancy effects on the turbulent momentum and heat transport. As the Grashof number is increased, buoyant thermal plumes are generated. The large-scale thermal convection involving the thermal plumes diminishes the quasi-coherent streamwise vortices, which are known to play a major role in the transport mechanism of near-wall turbulence. The destruction of the streamwise vortices result in the increased bulk mean velocity and the decreased turbulent friction coefficient. The vertical fluid motion of thermal plumes drastically changes the transport mechanism of the Reynolds shear stress. The thermal plumes are spatially aligned in the streamwise direction, and the low-speed streaks and vortical structures are concentrated in the region where the thermal plume starts to rise. The Prandtl number effects on the turbulent kinetic energy are also studied when the thermal plumes emerge.

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Widespread detection of antibiotic-resistant bacteria from natural aquatic environments in southern Ontario

Canadian Journal of Microbiology ◽

10.1139/cjm-2018-0286 ◽

2019 ◽

Vol 65 (4) ◽

pp. 322-331 ◽

Cited By ~ 1

Author(s):

Rosha Pashang ◽

Farhan Yusuf ◽

Simon Zhao ◽

Shadi Deljoomanesh ◽

Kimberley A. Gilbride

Keyword(s):

Antibiotic Resistance ◽

Agricultural Land ◽

Water Environment ◽

Resistance Index ◽

Resistant Bacteria ◽

Antibiotic Resistant ◽

Southern Ontario ◽

The City ◽

River Site ◽

Lake Site

To elucidate how widespread antibiotic resistance is in the surface water environment, we studied the prevalence of antibiotic resistance bacteria at four locations in southern Ontario. We found that the percentage of bacteria resistant to the antibiotic tetracycline was higher at the river site, which flows through agricultural land, and lower at the lake sites. A total of 225 colonies were selected for further testing of antibiotic disc susceptibility to eight different antibiotics to calculate the multiple antibiotic resistance (MAR) score and the antibiotic resistance index for each site. Although the isolates from the lake site outside the city displayed resistance to fewer antibiotics, their MAR scores were not significantly different from that of the lake sites adjacent to urban beaches, showing that MAR was widespread in the natural water environments tested. Isolation of colonies under selection pressure to tetracycline was found to have a significant effect on the likelihood that the isolates would contain multiple resistance traits for other antibiotics. Identification of isolates selected on tetracycline was compared with that of isolates that were sensitive to tetracycline, and the community composition was found to be distinctly different, although isolates from the genera Chryseobacterium, Pseudomonas, and Stenotrophomonas were found in both communities.

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Investigation of transportation of nanofluid within non-equilibrium porous media

International Journal of Modern Physics C ◽

10.1142/s0129183122500103 ◽

2021 ◽

pp. 2250010

Author(s):

Yahya Ali Rothan

Keyword(s):

Numerical Modeling ◽

Porous Media ◽

Homogeneous Model ◽

Working Fluid ◽

Thermal Plume ◽

Temperature Model ◽

Thermal Plumes ◽

Solid Region ◽

Porous Zone ◽

Two Temperature

In this investigation, numerical modeling for the behavior of nanomaterial inside a porous zone with imposing Lorentz force has been illustrated. The working fluid is a mixture of H2O and CuO and due to concentration of 0.04, it is reasonable to use the homogeneous model. Two-temperature model for porous zone was employed in which new scalar for calculating temperature of solid region was defined. CVFEM has been applied to model this complex physics. Radiation terms were considered and their influence on Nu has also been considered. Verification with benchmark proves greater accuracy. Dispersing nanopowders helps the fluid to increase velocity and reduce the temperature of inner wall. Rise of Ra results in three strong eddies inside the zone which creates two thermal plumes and it reduces the temperature of square surface about 68%. With rise of Nhs, the power of counter-clockwise vortex reduces about 61.6% and inner wall becomes warmer about 33.3%. Raising the Ha makes thermal plume to vanish and cooling rate decreases about 46.6%. Augment of Nhs makes Nu to reduce about 5.08% while augment of Ra makes it to augment about 35.64%. Also, augmenting Ha makes Nu to decline about 56.45%.

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Preliminary Evaluation of a Weibull Function for Fitting Slow-Component Eye Velocity over the Time Course of Caloric-Induced Nystagmus

Journal of Speech Language and Hearing Research ◽

10.1044/jshr.3203.681 ◽

1989 ◽

Vol 32 (3) ◽

pp. 681-687 ◽

Cited By ~ 1

Author(s):

C. Formby ◽

B. Albritton ◽

I. M. Rivera

Keyword(s):

Time Course ◽

Slow Component ◽

Weibull Function ◽

Preliminary Evaluation ◽

Mathematical Function ◽

Before And After ◽

Best Fitting ◽

Eye Velocity ◽

Fitting Parameters ◽

Weibull Equation

We describe preliminary attempts to fit a mathematical function to the slow-component eye velocity (SCV) over the time course of caloric-induced nystagmus. Initially, we consider a Weibull equation with three parameters. These parameters are estimated by a least-squares procedure to fit digitized SCV data. We present examples of SCV data and fitted curves to show how adjustments in the parameters of the model affect the fitted curve. The best fitting parameters are presented for curves fit to 120 warm caloric responses. The fitting parameters and the efficacy of the fitted curves are compared before and after the SCV data were smoothed to reduce response variability. We also consider a more flexible four-parameter Weibull equation that, for 98% of the smoothed caloric responses, yields fits that describe the data more precisely than a line through the mean. Finally, we consider advantages and problems in fitting the Weibull function to caloric data.

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