Thermal Plume Research Articles

Unsteady Flow Oscillations in a 3-D Ventilated Model Room with Convective Heat Transfer

Improving indoor air quality and energy consumption is one of the high demands in the building sector. In this study, unsteady flow oscillations in a 3-D ventilated model room with convective heat transfer have been studied for three configurations of an empty room (case 1), a room with an unheated box (case 2) and a room with a heated box (case 3). Computational results are validated against experimental data of airflow velocity, temperature and turbulence kinetic energy. For each case, flow unsteadiness is presented by the time history of airflow velocity and temperature at prescribed monitor points and further analyzed using the Fast Fourier Transform technique. For case 1, the flow oscillation is irregular and less dependent on the monitor points. For case 2, the flow oscillation is still irregular but with increased frequency, possibly due to enhanced flow recirculation around the corners of the unheated box. For case 3, a dominant frequency exists, and thermal energy oscillating is higher than flow kinetic energy. Among the three cases, case 3 has the highest dominant frequency in a range of 4.3–4.6 Hz, but the kinetic energy is the lowest at 1.25 m2⁄s. The unsteady flow oscillation is likely due to a high Grashof number and corner flow recirculation for cases 1 and 2, and a combination effect of a high Grashof number, corner flow recirculation and thermal instability (induced by the formation and movement of the thermal plume) for case 3.

Natural convection heat transfer with anisotropic thermal diffusion for tilted two-dimensional cavities

The effects of a domain tilt (counterclockwise, γ=00,300and600) and an anisotropic thermal diffusion on the natural convection heat transfer inside a square or rectangular cavity are investigated. The multiple relaxation time Lattice Boltzmann method with a double distribution function is used. The simulations are performed for a range of Rayleigh number (Ra=104to108). It is observed that the number of eddies is reduced due to the counterclockwise inclination of the cavity for a given Rayleigh number. The flow reversal is observed with a change in γ and anisotropic thermal diffusion ratio (β). Further, the stretching and merging of the inner core eddy with changes in γ and β are discussed. The spatially averaged Nusselt number along the hot wall (Nu¯h) is calculated to study the heat transfer rate and characteristics. It shows that the rate of heat transfer increases with an increase in the inclination and the thermal diffusivity ratio. For Ra=107and108 the observed flow structures are unsteady. The heat transfer in this type of unsteady flow and corresponding thermal plume dynamics are studied by computing Nu¯h at each non-dimensional timestep.

Study of turbulence behavior above two different crops

Turbulence structures are studied for momentum and sensible heat fluxes above different crops, maize and soybean, under neutral and unstable regimes through quadrant analysis. Micrometeorological sensors were installed at the same height (5 m) over productive plots in Buenos Aires province, Argentina. The effect of variations in crop height (in relation to sensor height) throughout the growing season is studied. In the maize experiment, canopy mixing-layer conditions prevail, with strong unstable situations, where a more efficient sensible heat transport relative to that of momentum follows a pattern explained by thermal plume type structures. Ejections are more intense but sweeps dominate in time for sensible heat transport. In addition, sweeps dominate both in intensity and time for momentum flux, due to the closeness of measurements to the canopy top. Above soybean, surface layer behavior is identified with near-neutral conditions, and there is a flux transport pattern associated with hairpin vortex type structures. Sensible heat and momentum fluxes are driven by the same motions, with no clear differences in transport efficiency. In soybean, ejections are more important because of a higher distance of measurement height to the canopy top. For each experiment, turbulence vary mainly due to atmospheric stability, while the effect of variation in the distance between the sensor and the top of the canopy due to plant growth is negligible. In this work, turbulence interactions in the surface layer are identified at heights that are not studied by works based on LES simulations.

Three-dimensional features of the lateral thermal plume discharge in the deep cross-flow using dynamic adaptive mesh refinement

Three-dimensional features of the lateral thermal plume discharge in the deep cross-flow using dynamic adaptive mesh refinement

Effects of vertical ship exhaust plume distributions on urban pollutant concentration – a sensitivity study with MITRAS v2.0 and EPISODE-CityChem v1.4

Abstract. The modeling of ship emissions in port areas involves several uncertainties and approximations. In Eulerian grid models, the vertical distribution of emissions plays a decisive role for the ground-level pollutant concentration. In this study, model results of a microscale model, which takes thermal plume rise and turbulence into account, are derived for the parameterization of vertical ship exhaust plume distributions. This is done considering various meteorological and ship-technical conditions. The influence of three different approximated parameterizations (Gaussian distribution, single-cell emission and exponential Gaussian distribution) on the ground-level concentration are then evaluated in a city-scale model. Choosing a Gaussian distribution is particularly suitable for high wind speeds (>5 m s−1) and a stable atmosphere, while at low wind speeds or unstable atmospheric conditions the plume rise can be more closely approximated by an exponential Gaussian distribution. While Gaussian and exponential Gaussian distributions lead to ground-level concentration maxima close to the source, with single-cell emission assumptions the maxima ground-level concentration occurs at a distance of about 1500 m from the source. Particularly high-resolution city-scale studies should therefore consider ship emissions with a suitable Gaussian or exponential Gaussian distribution. From a distance of around 4 km, the selected initial distribution no longer shows significant differences for the pollutant concentration near the ground; therefore, model studies with lower resolution can reasonably approximate ship plumes with a single-cell emission.

Numerical analysis of thermal comfort and air freshness generated by a multi-cone diffuser with and without lobed inserts

In this work, a numerical investigation using Ansys Fluent software is performed to study the flow pattern, the indoor thermal comfort, and the air freshness generated in a full-scale ventilated office room occupied by a sitting occupant. The performance of a multi-cone ceiling diffuser equipped with lobed inserts is assessed and compared with a traditional multi-cone ceiling diffuser. The indoor thermal comfort is evaluated using the predicted percentage of dissatisfaction (PPD) and the draft rate (DR) indicators. To assess the air freshness inside the office room, the mean age of air (MAA) is evaluated. After validating the simulation, the effect of the supply flow rate on the airflow pattern, the thermal comfort, and the air freshness, are investigated. Velocity contours show that recirculation zones in the domain result from the interaction between the supplied air and the thermal plume above the occupant's head. The statistical analysis of PPD and DR reveals that - depending on the supply flow rate - lobed inserts reduce the thermal dissatisfaction and the draft effect in the occupied zone. However, in terms of MAA, the lobed inserts reduce the air freshness slightly in the vicinity of the occupant's head.

Hybrid forced-buoyancy convection in a channel with a backward facing step

The present work integrates and expands the line of inquiry started in Inam and Lappa (2021), Int. J. of Heat and Mass Transfer, 173, 121267 for unsteady mixed forced-buoyancy convection in a channel with a forward facing step by addressing the mirror case where the fluid flowing in a duct undergoes a sudden expansion (i.e., a channel with a backward facing step). By alternatively setting some portions of the lower boundary of the system as isothermal (heated) or adiabatic surfaces, the interplay of forced and buoyancy convection is investigated numerically for a fixed expansion ratio (ER = 2) and a variety of conditions corresponding to extended intervals of the Rayleigh number Ra and several values of the Richardson number Ri (Ra≥O(104) and Ri≥O(1)). It is shown that the emerging dynamics involve a variety of concurrent mechanisms, which range from the standard hydrodynamic phenomena typical of isothermal fluids, to specific effects of buoyant nature (driven by the instability of thermal boundary layers and the ensuing emergence of thermal plumes in various parts of the domain). Comparison with the equivalent forward facing step configuration indicates that, besides the differences, these two systems display interesting analogies.

Assessment of airborne transmission from coughing processes with thermal plume adjacent to body and radiators on effectiveness of social distancing.

The new coronavirus disease COVID-19 has caused a worldwide pandemic to be declared in a very short period of time. The complexity of the infection lies in asymptomatic carriers that can inadvertently transmit the virus through airborne droplets. This kind of viral disease can infect the human body with tiny particles that carry various bacteria that are generated by the respiratory system of infected patients. In this study, numerical results are proposed that demonstrate the effect of human body temperature and temperature from radiators in a room on the spread of the smallest droplets and particles in an enclosed space. The numerical model proposed in this work takes into account the sedimentation of particles and droplets under the action of gravitational sedimentation and transport in a closed room during the processes of breathing, sneezing or coughing. Various cases were considered, taking into account normal human breathing, coughing or sneezing, as well as three different values of the rate of emission of particles from the human mouth. The heat plume, which affects the concentration of particles in the breathing zone, spreads the particle up to a distance of 4.29m in the direction of the air flow. It can also be seen from the results obtained that the presence of radiators strongly affects the propagation of particles of various sizes in a closed room. From the obtained results, it should be noted that in order to recommend the optimal social distance, it is necessary to take into account many factors, especially momentum, gravity, human body temperature, as well as the process of natural convection, which greatly affect the propagation of particles in a closed room. The conclusions drawn from the results of this work show that, given the environmental conditions, the social distance of 2m may not be enough.

Numerical analysis of a counter-flow wet cooling tower and its plume

A one-dimensional model to study the heat and mass transfer inside and immediately above a wet counter-flow cooling tower is described. The wet cooling tower thermodynamic model assigns zone-specific Merkel numbers to each of the rain, fill, and spray zones, and it includes an atmospheric plume model. Using the present formulation, zone-by-zone rates of heat rejection and water evaporation can be estimated, as can the visible plume height. The model is validated against the well-established Poppe and Merkel methods as well as select field data. Cooling tower performance and plume visibility are evaluated under a variety of climatic conditions (hot-dry, hot-humid, cool-dry and cool-humid), cooling tower designs (e.g. fill zone height, H f z ), and operating conditions (e.g. water-to-air mass flow rate ratio, L / G ). The parametric study in question highlights the ability of the proposed model to predict the impact of ambient conditions, cooling tower design parameters, and operating conditions on overall performance and patterns of atmospheric dispersion. The proposed model is ideal for numerical optimization of cooling towers that need to meet stringent thermal performance and plume visibility requirements. • A coupled one-dimensional cooling tower and plume model is developed. • Heat transfer in each zone of the tower analyzed at varying ambient conditions. • Plume visibility at different air flow rates studied at varying ambient conditions.

Turbulent vertical convection under vertical vibration

Vertical convection (VC) under the action of vertical vibration in a square cavity has been investigated using direct numerical simulation. The simulations are conducted with Prandtl number Pr fixed at 4.38 and Rayleigh number Ra ranging from 108 to 1010. To examine the influence of vertical vibration, the dimensionless vibration frequency is varied in the range of 0≤ω≤1000 and a small dimensionless amplitude is fixed at a=1.52×10−3. First, for low vibration frequency, trivial results are obtained where flow structures and the scalings of Nu and Re resemble that of the standard VC cases. In contrast, when the vibration frequency ω increases beyond a critical value ω*, a strong shearing effect from vibration leads to abundant eruptions of thermal plumes from sidewalls, and thus a laminar-turbulent transition of the bulk flow. As a result, heat-transport is greatly enhanced and the scaling exponent β of Nu∼Raβ substantially increases in such the vibration-dominated regime. In specific, the scaling relations obtained transit from Nu∼Ra0.25 and Re∼Ra0.37 at ω = 0 in the laminar regime to Nu∼Ra0.42 and Re∼Ra0.52 at ω≳300 in the turbulent regime. Analysis of the mean flow field shows that the vibration thins the thermal boundary layer and enhances the thermal dissipation rate in the bulk region. Furthermore, we found that the trend of Nu and Re can be well described by the vibrational Rayleigh number Ravib. In particular, Nu is insensitive to Ravib for Ravib≤Ravib*, whereas Nu(ω)/Nu(0)∼(Ravib/Ravib*)0.42 for Ravib>Ravib*, where the critical vibrational Rayleigh number exhibits a scaling relation Ravib*∼Ra0.68 obtained from numerical results.

Steady thermal convection representing the ultimate scaling.

Nonlinear simple invariant solutions representing the ultimate scaling have been discovered to the Navier-Stokes equations for thermal convection between horizontal no-slip permeable walls with a distance [Formula: see text] and a constant temperature difference [Formula: see text]. On the permeable walls, the vertical transpiration velocity is assumed to be proportional to the local pressure fluctuations, i.e. [Formula: see text] (Jiménez et al. 2001 J. Fluid Mech., 442, 89-117. (doi:10.1017/S0022112001004888)). Two-dimensional steady solutions bifurcating from a conduction state have been obtained using a Newton-Krylov iteration up to the Rayleigh number [Formula: see text] for the Prandtl number [Formula: see text], the horizontal period [Formula: see text] and the permeability parameter [Formula: see text]-[Formula: see text], [Formula: see text] being the buoyancy-induced terminal velocity. The wall permeability has a significant impact on the onset and the scaling properties of the found steady 'wall-bounded' thermal convection. The ultimate scaling [Formula: see text] has been observed for [Formula: see text] at high [Formula: see text], where [Formula: see text] is the Nusselt number. In the steady ultimate state, large-scale thermal plumes fully extend from one wall to the other, inducing the strong vertical velocity comparable with the terminal velocity [Formula: see text] as well as intense temperature variation of [Formula: see text] even in the bulk region. As a consequence, the wall-to-wall heat flux scales with [Formula: see text] independent of thermal diffusivity, although the heat transfer on the walls is dominated by thermal conduction. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 1)'.

Immersed boundary method and virtual physical model for onset turbulence flow around complex geometry / Método de fronteira imersa e modelo físico virtual para fluxo de turbulência de início em torno de geometria complexa

An immersed boundary method is development for the fluid-body interaction, being consider the heat-transfer for the onset turbulence in two-dimensional (2D) thermofluid dynamics around isothermal complex geometries immersed in incompressible Newtonian flows. The fluid motion and temperature are defined on a fixed Eulerian grid, while the immersed body is defined on a Lagrangian grid. A virtual physical model is used for the diffusion of interfacial forces within the flow, guarantees the imposition of the no-slip boundary condition. This model dynamically evaluates not only the force that the fluid exerts on the solid surface, but the heat exchange between them. Therefore, this work presents the Navier-Stokes equations, together with the energy equation, under physically appropriate boundary conditions. To calculate the turbulence viscosity, was used the Smagorinsky model, implemented in the context of the Large Eddy Simulation (LES) model. This work confirms that, downstream of the immersed body, the recirculation: 1) increases with the increase in the number of Reynolds, keeping the numbers of Richardson constant, and 2) decrease with the increase in the number of Richardson, preserving the number of Reynolds constant. It also confirms the generation of the thermal plumes moving upwards. The results are compared with previous numerical results, considering different Reynolds numbers.

Experimental study on the exposure level of surgical staff to SARS-CoV-2 in operating rooms with mixing ventilation under negative pressure

The purpose of this study was to reveal the exposure level of surgical staff to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from the patient's nose and wound during operations on COVID-19 patients. The tracer gas N2O is used to simulate SARS-CoV-2 from the patient's nose and wound. In this study, concentration levels of tracer gas were measured in the breathing zones of these surgical staff in the operating room under three pressure difference conditions: −5 pa–15 pa and −25 pa compared to the adjunction room. These influencing factors on exposure level are analyzed in terms of ventilation efficiency and the thermal plume distribution characteristics of the patient. The results show that the assistant surgeon faces 4 to 12 times higher levels of exposure to SARS-CoV-2 than other surgical staff. Increasing the pressure difference between the OR lab and adjunction room can reduce the level of exposure for the main surgeon and assistant surgeon. Turning on the cooling fan of the endoscope imager may result in a higher exposure level for the assistant surgeon. Surgical nurses outside of the surgical microenvironment are exposed to similar contaminant concentration levels in the breathing zone as in the exhaust. However, the ventilation efficiency is not constant near the surgical patient or in the rest of the room and will vary with a change in pressure difference. This may suggest that the air may not be fully mixed in the surgical microenvironment.

Synthesis of Nanoparticles of Aluminium–Boron complex for Radiation Sensor

Radiation sensors based on thermo luminescence from nanoparticles of aluminium-boron complex for gamma radiation have been reported. Crystal chemistry of aluminium boride is quite complicated and is derived from complex tetragonal modification of boron. The crystal structure varies with the method of preparation and energy band gap contains defect states governed by the temperature during synthesis. There are various methods of preparing nanoparticles like boll milling, sol-gel and RF-thermal plasma. In the present studies Aluminum boron complex nanoparticles were synthesized by DC- transferred arc thermal plasma method. The DC-transferred arc thermal plasma has been received great attention as a useful method to synthesize nanoparticles. Since a substance is easily evaporated in large volume of thermal plasma. A pure aluminium and boron powders were mixed together and made to evaporate from water cooled graphite after impinging thermal plasma plume. Argon with flow rate of 3L/min was used as a plasma forming gas for the evaporation of raw powder mixture in Ar ambient in the plasma reactor. The obtained nanoparticles of aluminum –boron complex were characterized using X-ray diffraction technique for structural analysis, Transmission electron microscopy (TEM) for morphological analysis and energy dispersive analysis by X-ray (EDAX) for elemental analysis. The aluminum boron complex so obtained was investigated for thermoluminscence properties.

Consistent time-step optimization in the lattice Boltzmann method

Owing to its efficiency and aptitude for a massive parallelization, the lattice Boltzmann method generally outperforms conventional solvers in terms of execution time in weakly-compressible flows. However, the authorized time-step (being inversely proportional to the speed of sound) becomes prohibitively small in the incompressible limit, so that the performance advantage over continuum-based solvers vanishes. A remedy to increase the time-step is provided by artificially tailoring the speed of sound throughout the simulation, so as to reach a fixed target Mach number much larger than the actual one. While achieving considerable speed-ups in certain flow configurations, such adaptive time-stepping comes with the flaw that the continuities of mass density and pressure cannot be fulfilled conjointly when the speed of sound is varied. Therefore, a trade-off is needed. By leaving the mass density unchanged, the conservation of mass is preserved but the pressure presents a discontinuity in the momentum equation. In contrast, a power-law rescaling of the mass density allows us to ensure the continuity of the pressure term in the momentum equation (per unit mass) but leaves the mass density locally discontinuous. This algorithm, which requires a rescaling operation of the mass density, will be called “adaptive time-stepping with correction” in the article. Interestingly, we found that this second trade-off is generally preferable.In the case of a thermal plume, whose movement is governed by the balance of buoyancy and drag forces, the correction of the mass density (to ensure the continuity of the pressure force) has a beneficial impact on the resolved velocity field. In a pulsatile channel flow (Womersley's flow) driven by an external body force, no difference was observed between the two versions of adaptive time-stepping. On the other hand, if the pulsatile flow is established by inlet and outlet pressure conditions, the results obtained with a continuous pressure force agree much better with the analytical solution. Finally, by using adaptive time-stepping in a channel entrance flow, it was shown that the correction is compulsory for the Poiseuille flow to develop. The expected compressibility error due to the discontinuity in the mass density remains small to negligible, and the convergence rate is not notably affected compared to a simulation with a constant time step.

Heat flow and 2D multichannel seismic reflection survey of the Devil's Hole geothermal reservoir in the Wagner basin, northern Gulf of California

The Wagner basin, located in the northernmost Gulf of California, hosts a large reservoir with geothermal potential documented in recent heat flow surveys. Although there is evidence of heat generation above the average value for an oceanic crust in the Wagner basin, it is unclear what the heat source is. To better understand the thermal structure in the northern Gulf of California, we acquired four 2D multichannel seismic reflection profiles and two systematic heat flow profiles across the Wagner basin. The survey targeted a geothermal anomaly, which we denominated “Devil's Hole” in a clear reference to pockmarks on the seafloor, and very high heat flow values. The heat flow profiles are ∼12 and ∼9 km long, are sub perpendicular to each other, have a nominal measurement spacing of ∼1 km, and were located along the transects of two of the four seismic reflection profiles. The two remaining seismic profiles are ∼34 and ∼40 km long, respectively, and are oriented SWW-NEE. To obtain seismic images, we used a conventional seismic processing workflow. After heat flow data correction, the minimum, maximum, and standard deviation of heat flow values for the Wagner basin are 295±42 and 10,894±114 mW/m2. We interpret the relatively high heat flow and large variability in the central part of the acquired profiles is caused by upward fluid flow at the Wagner fault zone. In contrast, the lower heat flow in the western flank of the basin suggest conductive heat transfer given the absence of faults. Based on these observations, we develop a geological model in which venting is not the product of a nascent spreading center as other authors have suggested. Instead, hydrothermal activity appears to result from isolated thermal plumes, rising from the base of the sedimentary column, captured by permeable fracture systems.

The effect of body position while coughing on the airborne transmission of pathogens

Given the recent acceptance of the central role of airborne transmission for SARS-CoV-2, increased attention has been paid to the dispersion of respiratory droplets in different scenarios. Studies including numerical simulations have been conducted on methods for breaking the chains of transmission. Here, we present the first such study on the impact of body position while coughing on the dispersion of respiratory droplets. Four scenarios are examined, including normal standing, bending the head at different angles, coughing into the elbow in still air, and a gentle breeze from the front and behind. The model showed that an uncovered cough is dangerous and causes many droplets to enter the environment, posing a cross-contamination threat to the others. Droplets with an initial diameter smaller than 62.5 μm remain suspended in windless air for more than 3 min. In the presence of wind, these droplets move with the wind flow and may travel long distances greater than 3.5 m. The model showed that covering the mouth with the elbow while coughing is clearly the best strategy for reducing airborne transmission of exhaled pathogens. About 62% of the initial number of droplets deposit on the cougher's elbow immediately after the cough and have no chance of spreading through the air in both windless and windy conditions. Covering the cough in windless or light breeze conditions also causes the upward thermal plume around the body to expel many small droplets.

Transport modes of inertial particles and their effects on flow structures and heat transfer in Rayleigh–Bénard convection

We investigate the flow characteristics and kinetic behaviors of particles in turbulent Rayleigh–Bénard convection particulate flows. Direct numerical simulations combined with a Lagrangian point-particle strategy were carried out in the range of Stokes numbers 2×10−4≤StL≤7.3×10−2 for Rayleigh numbers from 2×106 to 108 at the Prandtl number Pr=0.678. A two-way coupling model is employed in which the momentum exchange between the dispersed particles and the carrier fluid is taken fully into account. Based on various patterns of particle motion, we find three transport modes of inertial particles which are labeled as the circling transport (CCT) mode, the channel transport (CNT) mode, and the downpour transport (DPT) mode, respectively. These modes can switch to each other when Stokes numbers and Rayleigh numbers vary and exhibit different effects of particle motions on the flow field and heat transfer. For the CCT and DPT modes, compared with the CNT, a weakening alteration of flow structures and thermal plumes leads to no significant effect on the transport of momentum and heat. For the CNT mode, a pronounced effect of particles on enhancements of the turbulent momentum transport and heat transfer relates to the strong interaction between the particle clusters and the chaotic structures of eddies. What is more, the particles tend to homogeneously distribute for the CCT and DPT modes, although the particles exhibit different transport states. As for the CNT mode, under both preferential sweeping and centrifugal effects, particles accumulate into clusters that hover toward the region of high strain rate and the edges of eddies. We found that the averaged particle settling speeds are almost proportional to the Stokes number. The particle settling speeds are larger than the terminal velocity of Stokesian particles for the CCT and CNT modes as particles tend to settle in the downward fluid. In contrast, it becomes smaller than the terminal velocity for the DPT mode due to the drag of the upward fluid.

Numerical investigation of airborne transmission of respiratory infections on the subway platform

Underground subway platforms are among the world’s busiest public transportation systems, but the airborne transmission mechanism of respiratory infections on these platforms has been rarely studied. Here, computational fluid dynamics (CFD) modeling is used to investigate the airflow patterns and infection risks in an island platform under two common ventilation modes: Mode 1- both sides have air inlets and outlets; Mode 2- air inlets are present at the two sides and outlets are present in the middle. Under the investigated scenario, airflow structure is characterized by the ventilation jet and human thermal plumes. Their interaction with the infector’s breathing jet imposes the front passenger under the highest exposure risk by short-range airborne route, with intake fractions up to 2.57% (oral breathing) or 0.63% (nasal breathing) under Mode 1; oral breathing of the infector may impose higher risks for the front passenger compared with nasal breathing. Pathogen are efficiently diluted as they travel further, in particular to adjacent crowds. The maximum and median value of intake fractions of passengers in adjacent crowds are respectively 0.093% and 0.016% (oral breathing), and 0.073% and 0.014% (nasal breathing) under Mode 1. Compared with Mode 1, the 2nd mode minimizes the interaction of ventilation jet and breathing jet, where the maximum intake fraction is only 0.34%, and the median value in the same crowd and other crowds are reduced by 23–63%. Combining published quanta generation rate data of COVID-19 and influenza infectors, the predicted maximum and median infection risks for passengers in the same crowds are respectively 1.46%–40.23% and 0.038%–1.67% during the 3–10 min waiting period, which are more sensitive to ventilation rate and exposure time compared with return air. This study can provide practical guidance for the prevention of respiratory infections in subway platforms.

Spiral Thermal Plumes in Water under Conventional Heating: Numerical Results on the Effect of Rotation

In this paper, we study numerically the effect of rotation within a sample of water in a cylindrical container subject to rotation which is heated with a constant temperature at the bottom and lateral wall. We analyze the temporal behavior of temperature and flow velocity of the solvent. The thermal plumes developed at lower levels, already observed in the case without rotation, begin to spiral spreading outwards by the effect of rotation, increasing the azimuthal velocity of the fluid. No significant increases in the radial and vertical velocity components are observed which do not favor the mixture of hotter and colder flows in the sample and a faster heating of the solvent. In the rotation range studied, the state loses the axisymmetry and becomes fully 3D earlier in time as the rotation rate increases. To perform simulations, we use a 3D temporal model that couples momentum and heat equations and is based on spectral element methods.